EP3866136B1 - Method and system to assist with navigation for an aircraft by detecting maritime objects in order to implement an approach flight, hovering or landing - Google Patents

Description

The present invention relates to the field of navigation aids for aircraft and in particular aircraft.

The present invention relates to a method and a system for aiding navigation for an aircraft by detecting maritime objects for the purpose of an approach flight, hovering or landing as well as a aircraft equipped with such a system.

The present invention is particularly intended for rotary wing aircraft, also referred to as “rotorcraft”.

A rotary wing aircraft has the advantage of being able to perform stationary flights and land on landing areas of reduced dimensions designated for example "heliport" when they are located on land and more generally "helipad". A helipad can in particular be a landing area located for example on a ship or on a fixed or floating maritime platform such as an offshore oil platform.

A helipad can possibly also be used by other types of aircraft capable of performing substantially stationary flights and substantially vertical landings.

A helipad at sea, or more generally on a water surface, can then be mobile on the one hand following the movements of the water surface and the waves and on the other hand following the movements of the ship or the platform. -oil form on which the helipad is located.

An aircraft can thus land on a static or mobile helipad, or hover above a ship or maritime platform. For this purpose, a pilot of the aircraft can use visual information to make an approach and position itself in relation to the vessel, maritime platform or helipad.

This visual information includes in particular the position and movements of the ship or the maritime platform as well as the potentially dangerous elements of this ship or the maritime platform and likely to constitute an obstacle, such as a mast, a crane. , an upper part of drilling or even a wind turbine for example. This visual information may also relate to the position and movements of other ships or other maritime platforms located near the target. This visual information allows the pilot to guide the aircraft to the helipad or to the hover position while avoiding collisions with potentially dangerous elements.

However, ships and/or maritime platforms may be more or less visible depending on climatic conditions, the presence of clouds or smoke for example or even at night. Likewise, the movements of the ship or the maritime platform due to water movements can be amplified in the event of bad weather conditions generating, for example, violent wind and strong waves.

Visual information can be acquired and taken into account only by the pilot of the aircraft without assistance. The aircraft is then piloted visually. The specific movements of the moving elements due to water movements can be difficult to take into account and anticipate by the pilot of the aircraft and as such constitute potential dangers for the maneuvers of the aircraft.

Certain aircraft include a pilot assistance device equipped with one or more obstacle detection devices and/or one or more image acquisition systems combined with an image processing system in order to detect obstacles. fixed and/or mobile elements present in the environment of the aircraft, and in particular ships, maritime platforms and helipads.

For example, the document EP 3125213 describes an on-board system for identifying moving helipads. This system allows the display of the position of the helipads present in the environment of an aircraft as well as information relating in particular to its movements and its attitude, namely its roll and pitch angles. All of this information can be extracted from a field database, extracted from images captured via detection devices, such as a camera, a radar type or LIDAR type device for designation in English “Light Detection And Ranging”, for example, or be retrieved via a communication device.

We also know the document EP 3082121 which describes a system and a method allowing the display of symbologies relating to helipads in the environment of an aircraft as well as information relating to the helipads such as their dimensions, their speed, their direction of movement and their attitude for example. This information can be provided on the one hand by a field database and on the other hand by the helipad carrier via a communication device. A helipad can be fixed or mobile, and located on a land, sea or air carrier.

In addition, the document EP 3270365 describes a device for assisting the piloting of an aircraft for carrying out an approach phase in view of a landing on a landing zone. This device comprises at least one camera capturing images of the environment and a system for processing these images making it possible to identify at least one landing zone. According to this document, an approach flight instruction towards an identified landing zone is determined. The approach flight can then be carried out automatically by the aircraft.

Finally, the document EP 2515285A1 describes a method of assisting the piloting of an aircraft for landing on a helipad, in particular located on a platform at sea. This assistance method allows the display on a display screen of the platforms and helipads captured by an acquisition means, for example a digital camera or a LIDAR type device. This assistance method suggests identifying, by a system for processing the captured images, the known platforms using a database and attributes specific to each platform, for example means of support of a supporting structure of the platform, elements extending in elevation from the supporting structure and/or the position of one or more flames directly above the supporting structure...

However, these assistance devices and methods do not allow the detection of potentially dangerous obstacles, nor the automatic completion of a flight phase towards the helipad.

The prior art still includes the document US 2016/0284222 describes a radio navigation receiver for an aircraft capable of establishing a trajectory of the aircraft towards a platform or a point of interest. This receiver can use an instrument landing system and/or a VOR system for “VHR Omni-Ranging”. This receiver can also use an AIS type system possibly combined with a meteorological radar to detect obstacles, such as ships, platforms or lighthouses and determine their positions and possible speeds. The navigation receiver may also include a satellite location receiver to determine the position and speed of the aircraft. A pilot of the aircraft may select an object of interest toward which a trajectory may be established.

We also know the document US 2014/0365044 which describes a method of approaching a platform developing an approach trajectory towards a theoretical position of the platform. For this purpose, this method comprises a step of consolidating the trajectory of the aircraft by determining in particular the current position of the platform and a securing step determining the position and speed of the objects located in a surveillance zone. A representation of the trajectory and the detected objects is displayed on a screen.

Finally, the document FR 3061343 describes a system for assisting the landing of a rotary-wing aircraft on a maritime platform. The landing assistance system suggests, based on a representation of the area flown over, to continue the flight, interrupt it or modify the approach parameters of the aircraft, in particular the axis of flight. approach and/or approach distance.

Furthermore, the technological background of the invention includes in particular the documents WO 2018/182814 , EP 2824529 And US 2018/0211549 .

The document WO 2018/182814 describes a system for protecting a flight envelope of an aircraft by checking the conformity of the trajectories envisaged for the aircraft with respect to the flight envelope of the aircraft.

The document EP 2824529 describes a method and a device for issuing alerts for terrain avoidance for a rotary wing aircraft by generating an alert in the event of potential collisions between potential trajectories of an aircraft with the ground and/or obstacles outside ground. The positions of the ground and above-ground obstacles are extracted from a database.

The document US 2018/0211549 describes an air traffic management method comprising determining the position of an aircraft and receiving the positions of other aircraft. Then, a risk of collision between this aircraft and one or more other aircraft can be detected and an avoidance action instruction for the aircraft can be generated to avoid the collision. A risk of collision between two aircraft can be proven for example when there is a risk of collision between two cylindrical safety envelopes defined respectively around each aircraft.

The present invention, set out in the attached set of claims, then relates to a method and a navigation aid system for an aircraft by detection of fixed and mobile maritime objects with a view to an approach flight in the direction of a maritime object, a landing on a helipad at sea or the achievement of a hovering flight above a ship or a maritime platform making it possible to overcome the limitations mentioned above.

The present invention also relates to an aircraft equipped with such a system.

The present invention is particularly intended for rotary wing aircraft. The present invention may also be intended for any type of aircraft capable of performing substantially stationary flights and substantially vertical landings.

In the context of the invention, and for the sake of simplification, the term "object" is subsequently used to designate a construction or a maritime vehicle located at sea or on any surface of water, for example a lake or a river, A maritime vehicle can in particular be a ship, and a maritime construction can be a maritime platform or even a wind turbine for example. Likewise, the term “sea” is used generally to designate a surface of water and can as such be replaced by any surface of water, in particular a lake or a river.

The present invention therefore aims, on the one hand, to detect fixed and mobile maritime objects, such as ships or maritime platforms as well as possibly a helipad, in the environment of the aircraft and, on the other hand, on the other hand, to carry out a particular flight phase of the aircraft in relation to such an object, for example an approach flight towards an objective point, a hovering flight above an object or a landing on a helipad at sea, taking into account these objects and their possible movements.

• au moins un dispositif de localisation fournissant une position et/ou une vitesse absolue de l'aéronef,
• au moins une centrale inertielle fournissant une attitude de l'aéronef, l'attitude comportant au moins un angle de roulis et un angle de tangage de l'aéronef,
• un dispositif de pilotage automatique,
• au moins un dispositif de visualisation,
• au moins un système de détection configuré pour la détection d'objets maritimes fixes et mobiles, et
• au moins un calculateur.

The presence of the invention thus aims at a method of aiding navigation for an aircraft by detecting fixed and mobile maritime objects. This aircraft includes for example:

• at least one location device providing a position and/or an absolute speed of the aircraft,
• at least one inertial unit providing an attitude of the aircraft, the attitude comprising at least one roll angle and a pitch angle of the aircraft,
• an automatic piloting device,
• at least one display device,
• at least one detection system configured for the detection of fixed and mobile maritime objects, and
• at least one calculator.

The location device includes for example a GNSS satellite location device for the English language designation “Global Navigation Satellite System”. The inertial unit includes, for example, an AHRS type device for the English language designation “Attitude and Heading Reference System”.

The computer can for example be dedicated to carrying out this method according to the invention or shared with other functions of the aircraft and integrated as such into an avionics system of the aircraft. The calculator may include for example at least one processor and at least one memory, at least one integrated circuit, at least one programmable system or at least one logic circuit, these examples not limiting the scope given to the expression "computer" . The memory can for example store one or more segments of codes or algorithms in order to carry out the method according to the invention as well as one or more databases.

• surveillance d'une zone de surveillance sur la mer par l'intermédiaire dudit au moins un système de détection,
• détection d'au moins un objet dans la zone de surveillance et estimation de sa position relativement à l'aéronef par l'intermédiaire dudit au moins un système de détection,
• sélection d'au moins un objet à suivre et d'un point objectif sur un objet à suivre,
• détermination d'une position et d'une attitude de l'aéronef dans un repère terrestre,
• détermination des positions et des mouvements dudit au moins un objet à suivre ainsi que des positions et des mouvements du point objectif relativement à l'aéronef sur une durée glissante,
• transfert des positions et des mouvements dudit au moins un objet à suivre ainsi que des positions et des mouvements du point objectif d'un repère lié à l'aéronef vers le repère terrestre,
• estimation d'une enveloppe de sécurité attachée à chaque objet à suivre à partir des positions et des mouvements de cet objet à suivre dans le repère terrestre, ladite enveloppe de sécurité se situant autour de chaque objet à suivre et prenant en compte les mouvements de chaque objet à suivre sur la durée glissante (Δt_1-2 ), et
• réalisation d'une phase de vol particulière de l'aéronef par rapport au point objectif en respectant une distance de sécurité vis-à-vis de l'enveloppe de sécurité attachée à chaque objet à suivre.

The process according to the invention is remarkable in that it comprises the following steps:

• surveillance of a surveillance zone on the sea via said at least one detection system,
• detection of at least one object in the surveillance zone and estimation of its position relative to the aircraft via said at least one detection system,
• selection of at least one object to be tracked and an objective point on an object to be tracked,
• determining a position and an attitude of the aircraft in a terrestrial reference frame,
• determination of the positions and movements of said at least one object to be followed as well as the positions and movements of the objective point relative to the aircraft over a sliding period,
• transfer of the positions and movements of said at least one object to be tracked as well as the positions and movements of the objective point of a reference point linked to the aircraft towards the terrestrial reference point,
• estimation of a security envelope attached to each object to be tracked based on the positions and movements of this object to be tracked in the terrestrial reference frame, said security envelope being located around each object to be tracked and taking into account the movements of each object to follow over the sliding duration ( Δt _1-2 ), and
• carrying out a particular flight phase of the aircraft relative to the objective point while respecting a safety distance with respect to the safety envelope attached to each object to be followed.

In this way, the method according to the invention makes it possible to detect and identify, in a surveillance zone at sea towards which the aircraft is likely to be heading, any fixed or moving object and to follow the movements of at minus some of these objects after their selection. These objects may include a ship at anchor or in progress, a platform, for example fixed or floating, or any object likely to be located at sea and may in particular constitute a danger to the flight of the aircraft.

Thus, knowledge of the position of the objects located in the area as well as their movements due both to their movements and to the movement of the surface of the sea and the waves advantageously allows these objects to be taken into account in order, on the one hand, to carry out the particular flight phase of the aircraft relative to the objective point and, on the other hand, to avoid any collision between the aircraft and these fixed or mobile objects during the final flight phase of the aircraft.

The step of monitoring the surveillance zone at sea is carried out via at least one detection system. This step is carried out during the flight of the aircraft.

Likewise, the step of detecting at least one object in the surveillance zone and estimating its position relative to the aircraft is carried out via said at least one detection system.

The step of detecting at least one object in the monitoring zone and estimating its position can be carried out simultaneously with the monitoring step or after this monitoring step. A detection system allows both the surveillance of the surveillance zone at sea, the detection of at least one fixed or mobile object and the estimation of the position of each detected object relative to the aircraft.

A detection system may include at least one electromagnetic, optical or even acoustic detector. A detection system may for example comprise a radar type detection device, at least one ultrasonic type detection device, at least one LIDAR type detection device or at least one LEDDAR type detection device for the English language designation “LED Detection And Ranging” and/or at least one infrared detection device. A radar or ultrasonic type detection device uses, for example, waves, while a LIDAR , LEEDAR or infrared type detection device uses a beam of light.

A detection system can also include a camera and a computer. Such a camera may for example be a camera providing two-dimensional images or a three-dimensional camera. A detection system can also include several cameras and a computer in order to construct, via the computer and from the two-dimensional images provided by each camera, a three-dimensional image of the environment of the aircraft and the maritime objects.

The calculator makes it possible to analyze the images provided by the camera(s), by known processes of image analysis and shape recognition for example, in order, on the one hand, to detect objects and, on the other hand , to determine the position, movements and speed of each detected object. In this way, one or more cameras associated with a computer can be considered as a detection device in their own right.

This computer can be dedicated to the detection system or be shared for example for the implementation of the method according to the invention or even with other functions of the aircraft.

A radar, ultrasound, LEDDAR or LIDAR type detection device generally integrates a calculation unit making it possible to directly and quickly process the information captured and can detect an object and provide almost instantly and precisely its position, or even its movements and its speed.

The dimensions of the surveillance zone are defined by the installation of said at least one detection system on the aircraft as well as by and its range. In this way, a surveillance zone can for example be formed for the entire area located around the aircraft over a predetermined distance equal to the range of each detection system used, for example of the order of several hundred meters to several kilometers. A surveillance zone can also be limited to a sector located for example at the front of the aircraft, having a predetermined sector angle and length.

A detection device can have long detection ranges, typically greater than one kilometer. A radar-type detection device as well as certain optical cameras make it possible to cover such long ranges.

A detection device can have medium or short detection ranges, typically less than one kilometer. A LEDDAR or LIDAR type detection device, as well as certain optical cameras, make it possible to cover such medium or short ranges.

In general, a calculator integrated into the detection system can analyze the information provided to one or more detection devices and/or by one or more cameras using, for example, known methods of information processing and/or data analysis. images in order to detect the presence of one or more objects and to estimate their respective positions relative to the aircraft, namely in a local landmark linked to the aircraft subsequently designated “aircraft landmark”.

In this way, independently of the detection device(s) used, the presence of an object is detected and its position relative to the aircraft is estimated by at least one detection device. detection possibly aided by a computer, each detection device being arranged on the aircraft. The position of an object can be estimated from the information provided by a single detection device or by combining the information provided by several detection devices of the same type or of different types.

Then, a step of selecting at least one object to be tracked and an objective point on an object to be tracked is carried out. This selection can in particular be carried out manually by an occupant of the aircraft, for example a pilot or a co-pilot, or automatically. This selection of at least one object to follow makes it possible, for example, to select objects potentially dangerous for the flight of the aircraft and/or located near the objective point towards which the aircraft is going to head, or even a helipad on which is the objective point and on which the aircraft can consider landing. The objective point is a specific point of an object towards which the aircraft will head according to a particular flight phase by carrying out, for example, an approach flight towards the objective point, a landing on this objective point or else a hover above this objective point.

The step of determining the position and attitude of the aircraft is then carried out via the location device making it possible in particular to provide the position and/or speed of the aircraft and via the inertial unit providing the attitude of the aircraft. The tracking device can simultaneously provide the position and speed of the aircraft in a terrestrial reference frame. The location device can also provide only the position of the aircraft in the terrestrial reference frame, its speed being able to be calculated from successive positions of the aircraft, for example over the sliding duration or any other duration.

Likewise, the location device can only provide the speed of the aircraft 1 in the terrestrial reference frame, the position of the aircraft 1 then being calculated by integration of this speed.

The attitude of an aircraft includes in particular a roll angle and a pitch angle of the aircraft. An inertial unit can measure, for example, the accelerations of the aircraft in three dimensions and deduce from this by a double derivation the roll and pitch angles of the aircraft. The position and attitude of the aircraft are determined in a terrestrial reference frame. The positions and attitude of the aircraft determined successively are stored for example in a computer memory.

The terrestrial reference can for example be a local geographical reference or an absolute reference (L, G, Z).

The location device includes for example a GNSS satellite location device for the English language designation “Global Navigation Satellite System”. The inertial unit includes, for example, an AHRS type device for the English language designation “Attitude and Heading Reference System”.

The location device may also include a device for measuring a _radio height Z of the aircraft relative to the surface of the water overflown by the aircraft, making it possible on the one hand to detect the surface of the water and on the other hand to measure a generally vertical distance, namely a height, between the aircraft and said surface of the water. Such a device for measuring a _radio height Z is for example a radio altimeter or an altimeter radar.

The step of determining the positions and movements of each object and the objective point relative to the aircraft is carried out only for the objects to be followed and the objective point via said at least one detection system. These movements include in particular variations in the roll and pitch angles as well as a variation in the height of each object due in particular to movements of the sea surface and waves. In addition, this step is carried out over a generally predetermined sliding duration, for example a duration of 2 to 4 seconds. The positions and movements of each object to be followed and of the objective point are determined during this sliding duration in the terrestrial reference frame and are stored in a computer memory for example.

The variation in height of an object is constituted by the variation, over the sliding duration, of the position of a point of the object in a substantially vertical direction or in elevation of a reference, for example the terrestrial reference or the aircraft marker. This variation in height can also be equal to an average value of several measurements of such a variation in the position of several points of the same object.

Likewise, the variations in the roll and pitch angles of each object are constituted by the angular variations, over the sliding duration, of a point of the object around respectively the roll and pitch axes of the object. These variations in roll and pitch angles are equal to average values of several measurements of angular variations of several points of the same object.

The expression “sliding duration” means that the determination step is sequenced according to a frequency of execution independently of this sliding duration and without waiting for the end of a sliding duration. For example, every 0.5 seconds, a determination step is carried out for a sliding duration of 2 to 4 seconds.

The step of determining the positions and movements of each object to be tracked and of the objective point can be carried out identically whatever the particular flight phase, using information provided by the detection system and applying the same algorithm. independently of the particular flight phase in order to determine positions and movements of each object relative to the aircraft.

Furthermore, independently of the detection device used that the detection system includes, the step of determining the positions and movements of each object to be followed and of the objective point can apply a specific algorithm depending on the particular flight phase envisaged in order to in particular that the precision of these positions and these movements of each object to be followed and of the objective point is adapted to this particular phase of flight. For example, when the particular flight phase is a landing phase or a hovering flight, this determination step can use one or more Hough transforms to obtain precise positions and movements. In this way, the estimation step can include a reconstruction of the rectilinear high points characteristic of each identified object using one or more Hough transforms with threshold logic in order to ensure the validity of the information. provided by said at least one detection device.

In addition, independently of the algorithm used, the step of determining the positions and movements of each object to be tracked and of the objective point can use one or more different detection devices that the detection system includes depending on the phase of detection. particular to achieve. For example, one or more cameras associated with an image analysis process and/or a radar-type detection device, constituting long-range detection devices, can be used. when the particular flight phase is an approach flight. According to another example, at least one LIDAR type detection device, possibly combined with one or more cameras, constituting short or medium range detection devices, can be used when the particular flight phase is a landing phase or a hover.

Then, the step of transferring the positions and movements of each object to be followed as well as the position and movements of the objective point previously determined during the sliding duration relative to the aircraft, namely in an aircraft reference frame, is carried out this aircraft reference to the local land reference. This transfer uses the successive positions and attitude of the aircraft stored in the memory. Such a transfer is carried out in a known manner.

Therefore, the step of estimating a security envelope attached to each object to be tracked is carried out from the positions and movements of each object to be tracked in the local terrestrial reference frame. Each security envelope is thus estimated by taking into account the positions and movements of each object to be followed previously determined during the sliding duration and transferred to the local terrestrial reference frame. Each safety envelope includes all the characteristic elements of the maritime object, in particular potentially dangerous elements likely to constitute an obstacle to the flight of the aircraft, such as a mast, a crane, an upper drilling part or a wind turbine for example.

The step of estimating a security envelope around each object to be tracked is carried out by constructing a three-dimensional security envelope. The security envelope is built around a profile of the object and therefore takes into account variations in height and attitude of the object over the sliding period.

The object profile is constructed for average values of height and attitude of the object over the sliding time using the measured heights induced by the observed movements of the sea as well as by the movement of the object himself. The safety envelope is for example constructed by a three-dimensional extrapolation taking into account the translations of the object, namely variations in heights and horizontal positions, and the rotations of the object, namely variations in roll angles. and pitching, detected during the sliding duration.

Finally, the step of carrying out a particular flight phase of the aircraft relative to the objective point is carried out while respecting a safety distance with respect to the safety envelopes of each object to be followed. In this way, the particular flight phase of the aircraft can be carried out in safety with respect to maritime objects located on the trajectory of the aircraft, in particular with respect to objects likely to be dangerous for the aircraft during the particular flight phase. This security is ensured through security envelopes which advantageously take into account the movements of each object to be tracked.

The particular flight phase of the aircraft relative to the objective point may for example be an approach flight in the direction of the objective point making it possible to approach the objective point at a preestablished distance of less than one kilometer, for example between 100 and 200 meters.

The particular flight phase of the aircraft relative to the objective point can also be a landing phase on the objective point then formed by a helipad for example or a stationary flight phase above the objective point formed by a helipad or any point of an object in order to carry out, for example, a helicopter hoist, a rescue or resupply operation, etc.

The particular flight phase may also combine two distinct flight phases. For example, the particular flight phase may initially include an approach flight towards the objective point up to a pre-established distance from the objective point, then secondly a landing phase on the objective point or else a hovering phase above the objective point.

The choice of the particular flight phase can be defined via an input interface, for example before takeoff of the aircraft or in flight, for example during the step of selecting at least one object to follow. and the objective point. Likewise, during a hover, the height of the hover above the objective point is variable depending on the type of operation to be carried out. This height can therefore be defined for example when choosing the particular flight phase.

The method of aiding navigation for an aircraft by detecting fixed and mobile maritime objects may further include one or more of the following characteristics, taken alone or in combination.

• affichage des enveloppes de sécurité de chaque objet à suivre et du point objectif sur le dispositif de visualisation, et
• pilotage manuel de l'aéronef par un pilote de l'aéronef de sorte à réaliser la phase de vol particulière.

According to one aspect, the step of carrying out a particular flight phase of the aircraft relative to the objective point may include the following sub-steps:

• displaying the security envelopes of each object to be tracked and the objective point on the display device, and
• manual piloting of the aircraft by a pilot of the aircraft so as to carry out the particular flight phase.

The display of the security envelopes attached respectively to the objects to be tracked and of the objective point is carried out on at least one display device of the aircraft. A device of visualization is for example a screen arranged on the dashboard of the aircraft and can display only the safety envelopes and the objective point. Such a display device can also display an image of the objects to be tracked, captured for example by a camera of the detection system or a camera independent of the detection system. The security envelopes and the objective point are then displayed superimposed on this image, in particular superimposed in relation to the objects to be followed.

A display device can also be a head-up display, for example a visor of a helmet or even a part of the windshield of the aircraft. In this case, the pilot of the aircraft has direct vision of the objects to be followed. The display of the security envelopes and the objective point are then displayed superimposed on this view of the pilot, in particular superimposed in relation to the objects to be followed.

The display step thus allows an occupant of the aircraft, and the pilot or co-pilot in particular, to advantageously visualize the objective point and each object to be followed with the safety envelope attached to this object, taking into account the positions and possible movements of the objects to be tracked as well as their movements due to movements of the sea surface and waves. The pilot can then manually pilot the aircraft relative to the objective point while taking into account these safety envelopes so as to achieve the particular flight phase of the aircraft in safety.

In addition, a speed vector corresponding to the possible movement of each object to be followed can be displayed in order to indicate to the pilot of the aircraft the direction of possible movement of this object.

The display positions of the safety envelopes, the objective point and possibly the speed vector on a display device are determined by the computer based on the information provided by at least one location device, at least one inertial unit and at least the detection system.

• détermination d'une trajectoire de vol par rapport au point objectif en respectant une distance de sécurité vis-à-vis de l'enveloppe de sécurité attachée à chaque objet à suivre, et
• suivi automatique de trajectoire de vol par le dispositif de pilotage automatique de l'aéronef de sorte à réaliser la phase de vol particulière selon la trajectoire de vol.

According to one aspect, the step of carrying out a particular flight phase of the aircraft relative to the objective point may include the following sub-steps:

• determination of a flight trajectory relative to the objective point while respecting a safety distance with respect to the safety envelope attached to each object to be followed, and
• automatic flight path tracking by the automatic piloting device of the aircraft so as to achieve the particular flight phase according to the flight path.

This flight trajectory is intended for the achievement of the particular flight phase relative to the objective point and is determined for example by the computer using known algorithms for establishing a flight trajectory taking into account the envelope of security attached to each object to be followed located near the aircraft and on the route leading to the objective point as well as a safety distance between this flight path and each safety envelope. The automatic piloting device of the aircraft then uses this flight trajectory as instructions in order to follow this flight trajectory so as to automatically carry out the particular flight phase relative to the objective point while remaining at least at a distance equal to the safety distance from each safety envelope thus advantageously avoiding any collision with an object to be followed.

The safety distance can be predetermined and constant for each object to be tracked.

The safety distance can also vary from one object to be followed to another, depending on the dimensions of the safety envelope of this object, and in particular variations in height and roll and pitch angles on the sliding duration. Indeed, the greater the dimensions of a safety envelope of an object to be tracked, the more this object is subject to significant variations in its roll angle, its pitch angle and/or its height. Consequently, in order to secure the particular flight phase of the aircraft, the safety distance can be increased when the dimensions of a safety envelope of an object to be followed are large.

An exclusion envelope for each object to be followed into which the aircraft must not penetrate in order to ensure the safety of the flight of the aircraft can thus be formed for each object by the safety envelope attached to this object increased by the safety distance in all directions.

When applying this flight trajectory, the automatic piloting device of the aircraft will thus advantageously adapt the speed, attitude and altitude of the aircraft according to the dimensions of the safety envelopes and therefore the positions and of the specific movements of each maritime object detected and selected as well as the position and movements of the objective point.

In addition, each security envelope being determined over a sliding period, and therefore updated in a substantially continuous manner, at a sampling frequency, changes in course, speed of objects as well as movements due to the sea and to waves are taken into account in real time in order to guarantee maximum security of the determined flight path. The flight trajectory thus makes it possible to ensure fully controlled guidance during the particular flight phase with the movements and movements of each object to be followed.

In particular, when the particular flight phase is a hovering flight above the objective point, the use of these safety envelopes makes it possible to control the relative position of the aircraft with respect to the objective point as much as possible in order to to maintain a substantially constant height between the aircraft and the objective point.

Of course, the pilot of the aircraft can at any time take over the controls of the aircraft in order to direct the flight of the aircraft himself relative to the objective point or in the event of a change of objective point for example.

In addition, a step of displaying the security envelopes of each object to be followed and the objective point on a display device can be carried out even when the particular flight phase is carried out automatically. In this way, the pilot of the aircraft can visualize the safety envelopes and the objective point, particularly in the case where the pilot needs to regain control of the controls of the aircraft.

Furthermore, two particular flight phases can be linked together automatically without the method according to the invention being stopped, namely by retaining in particular the selection previously made of at least one object to be followed and of an objective point on a object to follow. In this way, an approach flight can initially be carried out in the direction of the objective point up to the pre-established distance, then a phase of hovering above the objective point or a landing phase on the objective point is carried out.

• détermination d'un mouvement propre caractérisé par un vecteur vitesse pour chaque objet à suivre sur la durée glissante,
• estimation de variations des angles de roulis δϕ et de tangage δθ et d'une variation de hauteur δh de chaque objet à suivre sur la durée glissante,
• détermination d'un centre de mouvement de chaque objet à suivre par rapport aux variations des angles de roulis δϕ et de tangage δθ sur la durée glissante, et
• estimation d'une enveloppe de sécurité autour de chaque objet à suivre et en prenant en compte le du centre de mouvement pour chaque objet à suivre en fonction de la variation de hauteur δh et des variations des angles de roulis δϕ et de tangage δθ de chaque objet à suivre sur la durée glissante.

According to one aspect, the step of estimating a security envelope may include the following substeps:

• determination of a proper movement characterized by a speed vector for each object to follow over the sliding duration,
• estimation of variations of the roll angles δϕ and pitch angles δθ and of a variation in height δh of each object to be followed over the sliding duration,
• determination of a center of movement of each object to be followed in relation to the variations of the roll angles δϕ and pitch angles δθ over the sliding duration, and
• estimation of a safety envelope around each object to be followed and taking into account the center of movement for each object to be followed as a function of the variation in height δh and variations in the roll angles δϕ and pitch angles δθ of each object to follow over the sliding duration.

The sub-step of determining a proper movement is carried out from the information provided by said at least one detection system over the sliding duration, by analysis and use of this information. For example, the application to this information of a differential method averaged with a Kalman filter on a “rolling” sequence corresponding to the sliding duration is carried out during this sub-step of determining a proper movement. Other methods can be used such as methods using optical flows for example.

Likewise, the sub-step of estimating the variations of the roll angles δϕ and pitch angles δθ and the height variation δh of each object is carried out from the information provided by said at least one detection system over the sliding duration , by analyzing and using this information.

Then, during the sub-step of determining a center of movement of each object to be followed, knowledge of the values of the variations of the roll angles δϕ and pitch angles δθ for each object to be followed over the sliding duration makes it possible to determine the center of movement for each object to be tracked. A center of movement can correspond, for example, to the center of instantaneous rotation of an object. This center of movement can be determined for example from an average roll angle ϕ _avg and a hub pitch angle θ _avg over the sliding duration.

Finally, the sub-step of estimating a security envelope around each object to be tracked and taking into account the center of movement for each object to be tracked allows the construction of a three-dimensional security envelope for each object. to be continued. Each safety envelope is positioned at the position of the object to be followed at the end of the sliding duration and around an average position of the object to be followed, namely with an average roll angle ϕ _avg , an angle of hub pitch θ _avg and an average height h _avg . Each safety envelope covers the amplitude of the height variation δh and the variations in the roll angles δϕ and pitch angles δθ of the object to be followed over the sliding duration. Each security envelope thus makes it possible to take into account the movements undergone by the object to be tracked during the sliding duration.

In addition, the sub-step of estimating said safety envelope can also take into account a vertical variation of water δm of the water surface, corresponding in particular to the height of the swell or waves over the sliding duration in order to anticipate the effect of this vertical variation of water δm on each object to be followed and in particular on the variation of height δh of each object to follow. Indeed, by knowing the vertical variation of water δm of the water surface upstream of an object, it is advantageously possible to anticipate the variation in height δh of each object to follow which will be caused by this vertical variation of water δm from the water surface. This vertical variation of water δm of the water surface can be measured over the sliding duration by said at least one detection system. This vertical variation of the water is preferably defined in a vertical direction or in elevation of a terrestrial landmark.

According to one aspect, the method according to the invention may comprise at least one additional step relating to an anticipation of the positions of each object to be followed over an anticipation period.

In particular, an additional step of determining by anticipation of the movements of each object to be followed over the anticipation duration as a function of its speed vector determined during the sub-step of determining an own movement for each object to be followed. This anticipation duration can be predetermined and is for example equal to 5 seconds. In this way, the successive forecast positions of the security envelopes of each object to be tracked over the anticipation period can be calculated, for example via the calculator, using the last known speed vector for each object to be tracked.

These successive forecast positions can then be taken into account during the sub-step of determining a trajectory of flight for the achievement of the particular flight phase relative to the objective point.

Then, an additional step of displaying the successive forecast positions of the security envelope of each object on the display device for the anticipation duration can also be carried out by exploiting the successive forecast positions of the security envelopes of each object to be follow. In this way, the pilot can visualize these successive forecast positions and choose a trajectory taking into account these successive forecast positions to come from the safety envelopes of each object to be followed and the objective point. Such anticipation can in particular be very useful in the event of visual loss of an object to be followed during manual piloting of the aircraft, for example in the presence of fog or smoke masking this object.

• affichage de chaque objet détecté sur un dispositif de visualisation de l'aéronef, et
• sélection manuelle sur le dispositif de visualisation de chaque objet à suivre et d'un point objectif sur un objet à suivre.

According to one aspect, the step of selecting at least one object to follow can be carried out manually by an occupant of the aircraft and can include the following sub-steps:

• displaying each object detected on a display device of the aircraft, and
• manual selection on the display device of each object to be tracked and of an objective point on an object to be tracked.

In this way, an occupant of the aircraft, in particular the pilot or co-pilot, can view on the display device the objects which have been detected in the surveillance zone. An occupant of the aircraft can then select directly on the display device, for example via a touch screen or a pointer directed via a mouse or others, the objects to follow likely to be on the flight path. and he wishes to watch. Likewise, this occupant of the aircraft can also select identically on one of these maritime objects to follow the objective point with respect to which the particular flight phase is carried out.

• application d'un processus de reconnaissance de forme de chaque objet détecté aux informations fournies par ledit au moins un dispositif de détection,
• identification d'au moins un objet détecté par comparaison de la forme attribuée à chaque objet (50) détecté avec au moins une base d'une base de données contenant des formes d'objets maritimes connus, et
• sélection automatique d'au moins un objet à suivre dont la forme est identifiée dans ladite au moins une base de données et d'un point objectif sur un objet à suivre.

According to one aspect, the step of selecting at least one object to follow and an objective point can be carried out automatically and can include the following sub-steps:

• application of a shape recognition process of each detected object to the information provided by said at least one detection device,
• identification of at least one object detected by comparison of the shape assigned to each object (50) detected with at least one base of a database containing shapes of known maritime objects, and
• automatic selection of at least one object to be tracked whose shape is identified in said at least one database and of an objective point on an object to be tracked.

The application by the computer of a shape recognition process to the information provided by at least one detection device makes it possible in a known manner to associate a shape with each detected object. This shape recognition process can be associated with an image processing process carried out on the images captured by at least one detection device. These image processing and shape recognition processes can for example implement methods known to those skilled in the art, for example a method of mathematical morphology, a method of simultaneous localization and mapping known in English under the name designation “Simultaneous Localization And Mapping” or any other comparable method...

Then, the comparison of each of these shapes of each detected object with shapes contained in at least one database containing characteristics of known maritime objects via the calculator makes it possible to identify certain detected objects corresponding to known objects . In this way, a type of ship or a type of maritime platforms known and present in at least one database stored for example in a memory of the computer or in a memory connected to the computer can for example be identified. Each identified object is then automatically selected to be an object to track.

In addition, the application by the computer of a shape recognition process to the information provided by at least one detection device also makes it possible to identify in a similar manner a helipad present on a detected object. A helipad is, for example, identifiable by the presence of a letter “H” or a circle represented on the helipad. When a single helipad is identified, the center of it is automatically selected as the objective point by the calculator. In the case where several helipads are identified, an objective point is also automatically selected at the center of one of these helipads by the computer using additional information provided for example by the pilot or co-pilot of the aircraft. This additional information can be provided, via an input interface, for example before takeoff of the aircraft when choosing the particular flight phase envisaged or when selecting this objective point.

For example, the latitude and longitude coordinates of a desired objective point are entered and the center of the helipad located closest to these coordinates is automatically selected as the objective point by the calculator. According to another example, a characteristic of an AIS system, for the English language designation “Automatic Identification System”, of an object on which the desired objective point is located is entered and the center of the helipad located on this object, is it is among the objects detected, is then automatically selected as an objective point by the computer. In this case, the aircraft includes an AIS receiver connected to the computer in order to exploit such AIS characteristics.

• sélection automatique d'au moins un objet à suivre telle que précédemment décrit,
• affichage d'au moins un objet détecté et/ou identifié sur un dispositif de visualisation de l'aéronef, et
• sélection manuelle d'un point objectif sur un objet détectés et/ou identifiés sur le dispositif de visualisation, par exemple par l'intermédiaire d'un écran tactile ou par l'intermédiaire d'un pointeur dirigé via une souris.

However, if no automatic selection of an objective point is possible or upon choice of the aircraft crew, manual selection of an objective point can be carried out. In this case, the sub-step of automatic selection of at least one object to follow and of an objective point can be replaced by the following three sub-steps:

• automatic selection of at least one object to follow as previously described,
• display of at least one object detected and/or identified on a display device of the aircraft, and
• manual selection of an objective point on an object detected and/or identified on the display device, for example via a touch screen or via a pointer directed via a mouse.

Under these conditions, the method according to the invention can be applied in order to manually select the objective point, for example when this objective point is not a helipad, but a point of an object with a view, for example, to achieving a hovering flight. above this objective point.

• application d'un processus de reconnaissance de forme de chaque objet détecté aux informations fournies par ledit au moins un système de détection,
• identification d'au moins un objet détecté par comparaison par comparaison de la forme attribuée à chaque objet détecté avec au moins une base d'une base de données contenant des objets maritimes connus
• présélection automatique d'au moins un objet dont la forme est identifiée dans ladite au moins une base de données,
• affichage d'au moins un objet présélectionné sur un dispositif de visualisation de l'aéronef, et
• sélection manuelle sur le dispositif de visualisation d'au moins un objet à suivre et/ou d'un point objectif sur un objet à suivre par un occupant de l'aéronef.

According to one aspect, the step of selecting at least one object to follow and an objective point can be carried out semi-automatically and can include the following sub-steps:

• application of a shape recognition process of each detected object to the information provided by said at least one detection system,
• identification of at least one detected object by comparison by comparison of the shape assigned to each detected object with at least one base of a database containing known maritime objects
• automatic preselection of at least one object whose shape is identified in said at least one database,
• displaying at least one preselected object on a display device of the aircraft, and
• manual selection on the display device of at least one object to be followed and/or of an objective point on an object to be followed by an occupant of the aircraft.

In this way, the calculator preselects each known object after identification among each detected object, then displays each known and preselected object on the display device. Then, an occupant of the aircraft selects manually, as previously mentioned, on the display device each object to be tracked and the objective point on an object to be tracked.

According to one aspect, during the step of selecting at least one object to track and an objective point, all the detected objects and an objective point among these detected objects can be selected automatically.

• au moins un dispositif de localisation fournissant une position et/ou une vitesse absolue de l'aéronef,
• au moins une centrale inertielle fournissant une attitude de l'aéronef,
• un dispositif de pilotage automatique de l'aéronef,
• au moins un dispositif de visualisation,
• au moins un système de détection destiné à la détection d'objets maritimes fixes et mobiles, et
• au moins un calculateur.

The present invention also relates to a navigation aid system for an aircraft by detecting fixed and mobile maritime objects configured to implement the method previously described. The navigation aid system for an aircraft comprises in particular:

• at least one location device providing a position and/or an absolute speed of the aircraft,
• at least one inertial unit providing an attitude of the aircraft,
• an automatic piloting device for the aircraft,
• at least one display device,
• at least one detection system intended for the detection of fixed and mobile maritime objects, and
• at least one calculator.

The present invention also relates to an aircraft comprising such a navigation aid system.

• la figure 1, un aéronef selon l'invention,
• la figure 2, un objet maritime détecté sur une durée glissante,
• la figure 3, un schéma synoptique d'un procédé selon l'invention,
• la figure 4, une enveloppe de sécurité d'un objet maritime détecté, et
• la figure 5, un schéma synoptique d'un procédé selon l'invention.

The invention and its advantages will appear in more detail in the context of the description which follows with examples given by way of illustration with reference to the appended figures which represent:

• there figure 1 , an aircraft according to the invention,
• there figure 2 , a maritime object detected over a sliding period,
• there Figure 3 , a synoptic diagram of a process according to the invention,
• there Figure 4 , a security envelope of a detected maritime object, and
• there Figure 5 , a block diagram of a process according to the invention.

Elements present in several distinct figures are assigned a single and same reference.

The aircraft 1 shown on the figure 1 comprises a fuselage 4, a main rotor 2 arranged above the fuselage 4 and a rear rotor 3 arranged on a tail boom 7 of the aircraft 1. The aircraft 1 also comprises a landing gear 8 with skids and a power plant 6 rotating the two rotors 2,3.

An aircraft marker (X _A , Y _A , Z _A ) is attached to the aircraft 1 and formed by three orthogonal axes. A longitudinal axis X _A extends from the rear of the aircraft 1 towards the front of the aircraft 1, that is to say from the rear end of the tail boom 7 of the aircraft 1 to the front tip of the fuselage 4 of the aircraft 1. An elevation axis Z _A extends from top to bottom perpendicular to the longitudinal axis X _A. Finally, a transverse axis Y _A extends from left to right perpendicular to the longitudinal axes X _A and elevation Z _A. The longitudinal axis X _A is the roll axis of the aircraft 1, the transverse axis Y _A is its pitch axis and the elevation axis Z _A is its yaw axis.

The aircraft 1 also includes a system 10 for aiding navigation by detecting fixed and mobile maritime objects. This system 10 is dedicated, when the aircraft 1 is located near the sea or above the sea, to the detection of maritime objects with a view to carrying out a particular maneuver, for example, a flight of approach or a hovering flight phase in relation to one of these objects or even a landing phase on one of these objects. Such a navigation aid system 10 can equip such a rotary wing aircraft as well as any type of aircraft.

• un dispositif de localisation 15 fournissant une position et/ou une vitesse absolue de l'aéronef 1,
• une centrale inertielle 16 fournissant une attitude de l'aéronef 1,
• un dispositif de pilotage automatique 13 de l'aéronef 1,
• un dispositif de visualisation 11,
• un système de détection 20 destiné à la détection d'objets maritimes fixes et mobiles, et
• un calculateur 14.

This navigation aid system 10 includes:

• a location device 15 providing a position and/or an absolute speed of the aircraft 1,
• an inertial unit 16 providing an attitude of the aircraft 1,
• an automatic piloting device 13 of the aircraft 1,
• a display device 11,
• a detection system 20 intended for the detection of fixed and mobile maritime objects, and
• a calculator 14.

The locating device 15 can directly provide the position of the aircraft 1 in a local terrestrial reference or else the locating device 15 can provide the speed of the aircraft 1 in the local terrestrial reference, the position of the aircraft 1 being then calculated by integration of this speed of the aircraft 1 via for example a calculator. The location device 15 may include, for example, a GNSS satellite location device.

Likewise, the inertial unit 16 can directly provide a roll angle ϕ and a pitch angle θ of the aircraft 1 in a local terrestrial reference frame. The inertial unit 16 can also provide angular velocities or angular accelerations of the aircraft 1 around the roll and pitch axes of the aircraft 1 in the local terrestrial reference frame, the roll angles ϕ and pitch angles θ of the aircraft 1 in this local terrestrial reference then being calculated by a single or double integration respectively of these speeds or these angular accelerations of the aircraft 1 via for example a calculator. The inertial unit 16 may include, for example, an AHRS type device.

The automatic pilot device 13 is configured to automatically pilot the aircraft 1, namely without intervention from a pilot on board the aircraft 1, when an automatic pilot mode is engaged. This automatic piloting can follow, for example in a known manner, a pre-established trajectory between two points or until the aircraft 1 lands on a helipad. The automatic pilot device 13 may include, for example, an automatic pilot computer and various actuators acting on the control elements of the aircraft 1.

The display device 11 makes it possible to display information of any type, for example information superimposed on an image of the environment of the aircraft 1 captured by a camera for example. The display device 11 may include for example a screen, and in particular a touch screen, arranged on a dashboard 9 of the aircraft 1.

The computer 14 can for example be dedicated to the system 10 or can also fulfill other functions of the aircraft 1. The computer 14 can in particular carry out the integrations possibly necessary for the calculations of the position and/or the roll angles ϕ and pitch θ of the aircraft 1 if necessary.

The detection system 20 intended for the detection of fixed and mobile maritime objects makes it possible to detect objects, fixed or mobile, in the surveillance field of this detection system 20 as well as to determine their positions relative to the aircraft 1, namely in the aircraft reference (X _A , Y _A , Z _A ). The detection system 20 can also estimate the movements of each detected object, for example in the form of a speed vector, in the aircraft reference frame (X _A , Y _A , Z _A ).

The detection system 20 may comprise at least one electromagnetic detector, for example a radar type detection device 21, a LIDAR type detection device 22, an LEDDAR type detection device or even an infrared detection device.

The detection system 20 may include at least one acoustic detector, for example an ultrasound type detection device.

The detection system 20 may include at least one optical detector, for example a camera 25.

The detection system 20 of the aircraft 1 shown on the figure 1 comprises three detection devices 21,22,25 intended for the detection of fixed and mobile maritime objects as well as an imaging computer 26. A radar type detection device 21 is installed on a front area of the fuselage 4 and allows to detect an object in a surveillance zone corresponding for example to a conical sector located at the front of the aircraft 1 and over a long range of the order of one to several kilometers.

A LIDAR type detection device 22 is installed under the fuselage 4 and makes it possible to detect an object in a surveillance zone located all around the aircraft 1, namely at 360 degrees (360°), with a short to medium range. , less than one kilometer.

A detection device 25 is a camera installed on an upper front zone of the fuselage 4, below the main rotor 2, and makes it possible to capture images in two dimensions or in three dimensions and to detect an object in a corresponding surveillance zone for example to a conical sector located at the front of the aircraft 1. Advantageously, the surveillance zone of the camera 25 can cover a short, medium and long range, but with different levels of precision, the precision being optimal for short ranges.

A detection device 21,22 can directly provide information concerning a detected object, namely its presence as well as its position and its speed vector in the aircraft reference frame (X _A , Y _A , Z _A ). This is for example the case for the radar type detection device 21 and the LIDAR type detection device 22 which each include an integrated computer. For the camera 25, analysis and processing of the captured images are necessary, via the imaging calculator 26 of the detection system 20, in order to detect objects located in the detection zone. surveillance and estimate their positions and their speed vectors in the aircraft reference frame (X _A , Y _A , Z _A ).

The information provided by each detection device 21,22,25 can be used alone and independently of the other detection devices 21,22,25. The information provided by these detection devices 21,22,25 can be used in a combined manner in order to compare them so as to verify their reliability and/or to merge them so as to improve their precision.

There figure 2 represents a view of a part of the surveillance zone monitored by the detection system 20 and located on the surface of the sea 100 as well as the information relating to an object 50 provided over a sliding duration Δt _1-2 by the monitoring system detection 20. The object 50 represented on the figure 2 is a ship, but could also be any object 50 located on the surface of the sea 100 such as a maritime platform or a wind turbine for example. This ship comprises a hull 51 and two elongated elements 52,53, arranged substantially vertically and elevated, such as two masts or two cranes for example. This ship also includes a helipad 59 intended for landing an aircraft.

There figure 2 comprises two representations of the object 50 at two distinct instants t ₁ , t ₂ , namely at the beginning and at the end of this sliding duration Δt _1-2 . The center of gravity G of this object 50 is also represented.

• une distance D1,D2 entre l'aéronef 1 et l'objet 50 parallèlement à l'axe longitudinale X_T du repère terrestre local (X_T,Y_T,Z_T),
• une distance ha1,ha2 entre l'aéronef 1 et un point arrière de l'objet 50 parallèlement à l'axe en élévation Z_T,
• une distance hb1,hb2 entre l'aéronef 1 et un point avant de l'objet 50 parallèlement à l'axe en élévation Z_T,
• une distance hc1,hc2 entre l'aéronef 1 et un élément allongé 52 de l'objet 50 parallèlement à l'axe en élévation Z_T,
• une distance hd1,hd2 entre l'aéronef 1 et l'autre élément allongé 53 de l'objet 50 parallèlement à l'axe en élévation Z_T,
• un angle θ1,θ2 autour de l'axe de tangage de l'aéronef 1, à savoir l'axe transversal Y_A du repère aéronef (X_A,Y_A,Z_A), entre l'axe en élévation Z_T du repère terrestre local (X_T,Y_T,Z_T) et un élément allongé 53 de l'objet 50, et
• un vecteur vitesse V de l'objet 50.

Characteristics of the detected object 50 are represented on the figure 2 respectively for these two instants t ₁ , t ₂ , namely:

• a distance D1 , D2 between the aircraft 1 and the object 50 parallel to the longitudinal axis X _T of the local terrestrial reference (X _T , Y _T , Z _T ),
• a distance ha1 , ha2 between the aircraft 1 and a rear point of the object 50 parallel to the elevation axis Z _T ,
• a distance hb1 , hb2 between the aircraft 1 and a front point of the object 50 parallel to the elevation axis Z _T ,
• a distance hc1 , hc2 between the aircraft 1 and an elongated element 52 of the object 50 parallel to the elevation axis Z _T ,
• a distance hd1 , hd2 between the aircraft 1 and the other elongated element 53 of the object 50 parallel to the elevation axis Z _T ,
• an angle θ1 , θ2 around the pitch axis of the aircraft 1, namely the transverse axis Y _A of the aircraft reference (X _A , Y _A , Z _A ), between the elevation axis Z _T of the reference local terrestrial (X _T , Y _T , Z _T ) and an elongated element 53 of the object 50, and
• a speed vector V of the object 50.

In addition, an additional characteristic of the object 50 detected is an angle ϕ1 , ϕ2 around the roll axis of the aircraft 1, namely the longitudinal axis X _A of the aircraft mark (X _A , Y _A , Z _A ), between the elevation axis Z _T of the local terrestrial reference (X _T , Y _T , Z _T ) and an elongated element 53 of the object 50, this angle not being visible on the figure 2 .

These distance and angle characteristics of the detected object 50 are obtained from information provided by the detection system 20 in the aircraft reference frame (X _A , Y _A , Z _A ) and location information of the aircraft 1 provided by the localization device 15 respectively for these two instants t ₁ , t ₂ so as to obtain these characteristics in the local terrestrial reference frame (X _T , Y _T , Z _T ).

• une distance entre l'aéronef 1 et l'objet 50 parallèlement à l'axe longitudinale X_A,
• une distance entre l'aéronef 1 et un point arrière de l'objet 50 parallèlement à l'axe en élévation Z_A,
• une distance entre l'aéronef 1 et un point avant de l'objet 50 parallèlement à l'axe en élévation Z_A,
• une distance entre l'aéronef 1 et un élément allongé 52 de l'objet 50 parallèlement à l'axe en élévation Z_A,
• une distance entre l'aéronef 1 et l'autre élément allongé 53 de l'objet 50 parallèlement à l'axe en élévation Z_A, et
• un angle autour de l'axe de tangage de l'aéronef 1, à savoir l'axe transversal Y_A entre l'axe en élévation Z_A de ce repère aéronef (X_A,Y_A,Z_A) et un élément allongé 53 de l'objet 50, et
• un angle autour de l'axe de roulis de l'aéronef 1, à savoir l'axe transversal Y_A, entre l'axe en élévation Z_A de ce repère aéronef (X_A,Y_A,Z_A) et un élément allongé 53 de l'objet 50, et
• un vecteur vitesse V de l'objet 50.

The characteristics of the detected object 50 are obtained from information provided by the detection system 20 in the aircraft reference frame (X _A , Y _A , Z _A ) are:

• a distance between the aircraft 1 and the object 50 parallel to the longitudinal axis X _A ,
• a distance between the aircraft 1 and a rear point of the object 50 parallel to the elevation axis Z _A ,
• a distance between the aircraft 1 and a front point of the object 50 parallel to the elevation axis Z _A ,
• a distance between the aircraft 1 and an elongated element 52 of the object 50 parallel to the elevation axis Z _A ,
• a distance between the aircraft 1 and the other elongated element 53 of the object 50 parallel to the elevation axis Z _A , and
• an angle around the pitch axis of the aircraft 1, namely the transverse axis Y _A between the elevation axis Z _A of this aircraft reference (X _A , Y _A , Z _A ) and an elongated element 53 of object 50, and
• an angle around the roll axis of the aircraft 1, namely the transverse axis Y _A , between the elevation axis Z _A of this aircraft reference (X _A , Y _A , Z _A ) and an elongated element 53 of object 50, and
• a speed vector V of the object 50.

On the figure 2 , a vertical _radio height Z between the aircraft 1 and the surface of the sea 100 flown over by the aircraft 1 is also measured. This information is provided by a device 18 for measuring a _radio height Z included in the aircraft 1.

In addition, at two complementary instants t ₃ , t ₄ , the height m ₃ , m ₄ of the surface of the sea 100 is measured via at least one of the detection devices 21,22,25 in the reference frame aircraft (X _A , Y _A , Z _A ), parallel to the elevation axis Z _A. Then, the heights m ₃ , m ₄ of the sea surface 100 respectively for these two complementary instants t ₃ , t ₄ can be estimated in the local terrestrial reference frame (X _T , Y _T , Z _T ) parallel to the elevation axis Z _T as shown on the figure 2 . A variation δm of this height of the sea surface 100 can then be determined parallel to the elevation axis Z _T of the local terrestrial reference (X _T , Y _T , Z _T ), this variation being equal to the difference in heights m ₃ , m ₄ of the surface of the sea 100 respectively for these two complementary moments t ₃ , t ₄ . The two complementary moments t ₃ , t ₄ are posterior to the two moments t ₁ , t ₂ .

The system 10 is configured to implement a navigation aid method for an aircraft 1, two synoptic diagrams of which are represented on the figures 3 And 5 . A memory integrated into the computer 14 or connected to the computer 14 can store instructions relating to these synoptic diagrams and allowing in particular to execute such a process.

According to the synoptic diagram shown on the Figure 3 , the navigation assistance method for an aircraft 1 by detection of fixed and mobile maritime objects 50 comprises the following steps.

First of all, a monitoring step 110 of a monitoring zone on the water surface 100 is carried out via the detection system 20.

In the presence of at least one object, a step 120 of detecting at least one object 50 in the surveillance zone and estimating its position relative to the aircraft 1 is carried out via the detection system 20 .

These steps of monitoring 110 and detection 120 of at least one object 50 and estimation of its position can be implemented using all the detection devices 21,22,25 of the detection system 20 or only part of these devices detection 21,22,25 depending on the detection range and/or the precision sought.

A step of selection 130 of at least one object 50 to follow and of an objective point 55 on an object 50 to follow, as illustrated in the figure 2 , is then carried out. This selection step 130 can be carried out manually, automatically or semi-automatically. As such, this selection step 130 may include the following sub-steps.

• une étape d'affichage 131 d'au moins un objet 50 détecté sur le dispositif de visualisation 11 de l'aéronef 1, et
• une étape de sélection manuelle 132 sur le dispositif de visualisation 11 d'au moins un objet 50 à suivre et d'un point objectif 55 sur un objet 50 à suivre.

For manual selection, the step 130 of selecting at least one object 50 to follow and an objective point 55 comprises the following sub-steps:

• a step 131 of displaying at least one object 50 detected on the display device 11 of the aircraft 1, and
• a step of manual selection 132 on the display device 11 of at least one object 50 to be followed and of an objective point 55 on an object 50 to be followed.

This manual selection can be carried out directly on the display device 11 when it is a touch screen or via a selection device 17, such as a mouse for example.

• une étape d'application 133 d'un processus de reconnaissance de forme d'au moins un objet 50 détecté aux informations fournies par le système de détection 20,
• une étape d'identification 134 d'au moins un objet 50 détecté par comparaison de la forme attribuée à chaque objet 50 détecté avec au moins une base de données contenant des objets maritimes connus, et
• une étape de sélection automatique 138 d'au moins un objet 50 à suivre dont la forme est identifiée dans au moins une base de données et d'un point objectif 55 sur un objet 50 à suivre.

For automatic selection, the step 130 of selecting at least one object 50 to follow and an objective point 55 comprises the following sub-steps:

• a step 133 of applying a shape recognition process of at least one object 50 detected to the information provided by the detection system 20,
• a step of identifying at least one object 50 detected by comparison of the shape assigned to each object 50 detected with at least one database containing known maritime objects, and
• a step of automatic selection 138 of at least one object 50 to be followed whose shape is identified in at least one database and of an objective point 55 on an object 50 to be followed.

• une étape d'application 133 d'un processus de reconnaissance de forme d'au moins un objet 50 détecté aux informations fournies par le système de détection 20,
• une étape d'identification 134 d'au moins un objet 50 détecté par comparaison de la forme attribuée à chaque objet 50 détecté avec au moins une base de données contenant des objets maritimes connus
• une étape de présélection automatique 135 d'au moins un objet 50 à suivre dont la forme est identifiée dans au moins une base de données,
• une étape d'affichage 136 d'au moins un objet 50 présélectionné sur le dispositif de visualisation 11 de l'aéronef 1, et
• une étape de sélection manuelle 137 sur le dispositif de visualisation 11 d'au moins un objet 50 à suivre supplémentaire et/ou d'un point objectif 55 sur un objet 50 à suivre.

For a semi-automatic selection, the step of selecting at least one object 50 to follow and an objective point 55 comprises the following sub-steps:

• a step 133 of applying a shape recognition process of at least one detected object 50 to the information provided by the detection system 20,
• a step of identifying at least one object 50 detected by comparing the shape assigned to each object 50 detected with at least one database containing known maritime objects
• a step of automatic preselection 135 of at least one object 50 to follow whose shape is identified in at least one database,
• a step 136 of displaying at least one preselected object 50 on the display device 11 of the aircraft 1, and
• a step of manual selection 137 on the display device 11 of at least one additional object 50 to be followed and/or an objective point 55 on an object 50 to be followed.

As before, the manual selection can be carried out directly on the display device 11 when it is a touch screen or via a selection device 17, such as a mouse for example.

Once one or more detected objects 50 have been selected, a step 140 of determining a position and an attitude of the aircraft 1 is carried out via the locating device 15 and the inertial unit 16 of the aircraft 1.

A step 150 of determining the positions and movements of each object 50 to be followed as well as the position and movements of the objective point 55 relative to the aircraft 1 over the sliding duration Δt _1-2 is also carried out via the detection system 20. The sliding duration Δt _1-2 is preferably predetermined. In addition, this sliding duration Δt _1-2 can be fixed or variable. In particular, the sliding duration Δt _1-2 can be variable as a function of the speed of the aircraft 1 and/or the distance separating the aircraft 1 from the objective point 55.

The step of determining 140 of the position and the attitude of the aircraft 1 and the step of determining 150 of the positions and movements of each object 50 and of the objective point 55 relative to the aircraft 1 can be carried out in parallel, i.e. simultaneously, as shown in the Figure 3 . However, these two steps 140,150 can be carried out sequentially.

During the determination step 150, the positions and movements of each object 50 to be followed and of the objective point 55 are determined in the aircraft reference frame (X _A , Y _A , Z _A ). For example, distances are estimated parallel to the axes of the aircraft reference frame (X _A , Y _A , Z _A ) between the aircraft 1, for example its center of gravity, and several points of each object 50 to follow. Angles are also estimated around the roll and pitch axis of the aircraft 1, namely the longitudinal axes X _A and transverse axes Y _A , between the elevation axis Z _A of the aircraft reference frame (X _A , Y _A ,Z _A ) and an elongated element 53 of the object 50.

These positions of each object 50 to be followed and of the objective point 55 are determined over a sliding duration Δt _1-2 , for example of the order of 2 to 4 seconds, and are stored in a memory of the calculator 14 or in a connected memory to the computer 14. In this way, variations in the positions relative to the axes of the aircraft reference point (X _A , Y _A , Z _A ) and variations in the angles around these axes of each object 50 to be followed and of the objective point 55 can be calculated over the sliding duration Δt _1-2 .

The positions and movements of each object 50 to be followed and of the objective point 55 are determined by using the information provided by the detection system 20. Different known algorithms can be used to determine the positions and movements from this information. of each object 50 to follow and of the objective point 55.

In addition, a specific algorithm can be used when significant precision is required, in particular in the case of carrying out a landing phase or a hovering phase on or above an object to be followed. For example, the determination step 150 can perform a reconstruction of rectilinear high points characteristic of each object 50 to be followed, and of the elongated elements 52,53 in particular, using one or more Hough transforms.

Then, a step 160 of transferring the positions and movements of each object 50 to be followed as well as the position and movements of the objective point 55 of the aircraft reference point (X _A , Y _A , Z _A ) to the local terrestrial reference point (X _T ,Y _T ,Z _T ). This transfer step 160 is carried out by the computer 14 and uses on the one hand the positions and movements of each object 50 and of the objective point 55 determined in the aircraft reference frame (X _A , Y _A , Z _A ) by the system of detection 20 as well as the position and attitude of the aircraft 1 in the local terrestrial reference frame (X _T , Y _T , Z _T ) determined by the detection device location 15 and the inertial unit 16. In this way, the positions and movements of each object 50 to be followed are known in the local terrestrial reference frame (X _T , Y _T , Z _T ) as represented on the figure 2 .

At least one variation in height δh parallel to the elevation axis Z _T of the local terrestrial reference frame (X _T , Y _T , Z _T ) for each object 50 to be followed can then be calculated over the sliding duration Δt _1-2 . For example, several variations in height δh can thus be determined by subtraction of the two distances measured for the different points of an object 50 at the two distinct instants t ₁ , t ₂ , as represented on the figure 2 . A single variation in height δh can also be determined by calculating an average value of the results of these subtractions for these different points of an object 50.

Likewise, variations of the angles δϕ and δθ around the longitudinal axes X _T and transverse axes Y _T of each object 50 to be followed and of the objective point 55 can be calculated over the sliding duration Δt _1-2 .

A step 170 of estimating a security envelope 60 attached to each object 50 to be followed is then carried out from the positions and movements of each object 50 to be followed in the local terrestrial reference frame (X _T , Y _T , Z _T ). The security envelope 60 attached to an object to be tracked is located around this object 50 to be tracked and takes into account the movements of this object to be tracked.

• détermination 171 d'un mouvement propre caractérisé par un vecteur vitesse pour chaque objet 50 à suivre sur la durée glissante Δt_1-2 ,
• estimation 172 des variations des angles de roulis et de tangage δϕ, δθ et de la variation de hauteur δh de chaque objet 50 à suivre sur la durée glissante Δt_1-2 ,
• détermination 173 d'un centre de mouvement de chaque objet 50 à suivre par rapport aux variations des angles de roulis et de tangage δϕ, δθ sur la durée glissante Δt_1-2 , et
• estimation 174 d'une enveloppe de sécurité 60 attachée à chaque objet 50 à suivre se situant autour de chaque objet 50 à suivre et en prenant en compte le centre de mouvement pour chaque objet 50 à suivre en fonction de la variation de hauteur δh, des variations des angles de roulis et de tangage δϕ,δθ sur la durée glissante Δt_1-2.

This estimation step 170 of a security envelope 60 is made by constructing a security envelope 60 in three dimensions of each object 50 to follow and can include the following sub-steps:

• determination 171 of a proper movement characterized by a speed vector for each object 50 to follow over the sliding duration Δt _1-2 ,
• estimation 172 of the variations of the roll and pitch angles δϕ , δθ and of the variation in height δh of each object 50 to be followed over the sliding duration Δt _1-2 ,
• determination 173 of a center of movement of each object 50 to be followed in relation to variations in the roll and pitch angles δϕ , δθ over the sliding duration Δt _1-2 , and
• estimation 174 of a safety envelope 60 attached to each object 50 to be followed located around each object 50 to be followed and taking into account the center of movement for each object 50 to be followed as a function of the variation in height δh, of variations of the roll and pitch angles δϕ , δθ over the sliding duration Δt _1-2 .

Such a security envelope 60 attached to an object 50 is shown on the Figure 4 . In this way, the security envelope 60 represents at a time t ₂ an object 50 detected and selected by taking into account these movements over the sliding duration Δt _1-2 . This security envelope 60 is represented at the position where this object 50 is located at time t ₂ . In particular, after a calculation of the height variations δh and the roll and pitch angles δϕ , δθ of the object 50 in the local terrestrial reference frame (X _T ,Y _T ,Z _T ) over the sliding duration Δt _1-2 , a center of movement C of this object 50 around which the variations in roll and pitch angles δϕ , δθ are carried out over the sliding duration Δt _1-2 is estimated. Then, the shape of the object 50 is constructed by applying an average height variation value and average variation values of the average roll and pitch angles over the sliding duration Δt _1-2 .

Then, the safety envelope 60 is constructed in three dimensions around this shape of the object 50, by applying the variations δh and the roll and pitch angles δϕ , δθ over the sliding duration Δt _1-2 .

In addition, the estimation sub-step 174 of a safety envelope 60 can also take into account a vertical variation of water δm of the surface 100 of the water in front of each object 50 to be followed. Indeed, a vertical variation of water δm of the surface 100 of the water generally represents a wave of a height equal to this vertical variation of water δm and located in front of the object 50 to be followed. This wave will then probably generate a movement at least parallel to the elevation axis Z _T of the local terrestrial reference (X _T , Y _T , Z _T ) of the object 50 when it comes into contact with the object 50. Taking it into account in the estimation sub-step 174 of a safety envelope 60 thus advantageously makes it possible to anticipate the effect of the vertical variation of water δm on each object 50 to be followed.

Finally, following the estimation of the security envelope 60 attached to each object 50 to be followed, a step 180 of carrying out a particular flight phase of the aircraft relative to the objective point 55, while respecting a distance of security with respect to the security envelopes 60 is achieved. A particular flight phase relative to the objective point 55 may be an approach flight towards the objective point 55, namely remaining at a pre-established distance from the objective point 55, generally less than one kilometer, and for example between 100 and 200 meters. A particular flight phase relative to the objective point 55 can also be a landing phase on the objective point 55 or a hovering flight phase above the objective point 55.

This step of carrying out 180 a particular flight phase can be carried out manually or automatically. As such, this step 180 of carrying out a particular flight phase may include sub-steps.

• détermination 181 d'une trajectoire de vol par rapport au point objectif 55 en respectant la distance de sécurité vis-à-vis de l'enveloppe de sécurité 60 attachée à chaque objet 50 à suivre, et
• suivi automatique 182 de la trajectoire de vol par le dispositif de pilotage automatique de l'aéronef 1 de sorte à réaliser la phase de vol particulière selon la trajectoire de vol.

For automatic realization of the particular flight phase, the realization step 180 comprises for example the following sub-steps:

• determination 181 of a flight trajectory relative to the objective point 55 while respecting the safety distance with respect to the safety envelope 60 attached to each object 50 to follow, and
• automatic tracking 182 of the flight trajectory by the automatic piloting device of the aircraft 1 so as to carry out the particular flight phase according to the flight trajectory.

• affichage 138 de l'enveloppes de sécurité 60 attachée à chaque objet 50 à suivre et du point objectif 55 sur le dispositif de visualisation 11, et
• pilotage manuelle 184 de l'aéronef 1 par un pilote de l'aéronef 1 de sorte à réaliser la phase de vol particulière par rapport au point objectif 55.

For manual production of the particular flight phase, production step 180 comprises the following sub-steps:

• display 138 of the security envelope 60 attached to each object 50 to be followed and of the objective point 55 on the display device 11, and
• manual piloting 184 of the aircraft 1 by a pilot of the aircraft 1 so as to carry out the particular flight phase relative to the objective point 55.

Furthermore, the safety distance can be constant or variable. In particular, the safety distance can be variable for each object 50 to be followed depending on the dimensions of the safety envelope 60 attached to the object 50 and possibly depending on variations in the height δh and the roll angles and pitching δϕ , δθ over the sliding duration Δt _1-2 . For example, for a large tonnage ship, typically around 200 meters in length, and with a sea inducing angle variations of 20 degrees, the safety distance can be 75 meters. For a vessel of smaller dimensions, for example of the order of 50 meters in length, and always with seas causing variations in angles of 20 degrees, the safety distance can be 20 meters. In the two previous cases, if the effect of the sea is halved, namely that the sea induces angle variations of 10 degrees, the safety distance is also halved.

The safety distance can also be variable depending on the distance between the aircraft 1 and the objective point 55.

Furthermore, during a landing phase, the method according to the invention is carried out until reaching a particular point designated "height decision" also designated by the acronym DH for the English designation "Decision Height". Indeed, when the aircraft 1 reaches this particular point designated "height decision", the final part of the landing phase is engaged and the method according to the invention is inhibited to allow the aircraft 1 to land on the helipad 59 corresponding to the objective point 55.

Furthermore, according to a variant shown on the figure 5 , two particular flight phases can advantageously be chained together while retaining in particular the selection of at least one object 50 to follow and of an objective point 55. In this case, the method comprises the steps 110-180 previously described, the phase of particular flight carried out during the realization step 180 being an approach flight in the direction of the objective point 55 up to the preestablished distance from the objective point 55.

Once this approach flight is completed, a step of determining 240 the position and attitude of the aircraft 1 as well as a step of determining 250 of the positions and movements of each object 50 and the objective point 55 relative to the aircraft 1 are carried out in an identical manner to the determination steps 140,150 previously described. Then, a transfer step 260 and an estimation step 270 of a security envelope 60 attached to each object 50 to follow, identical to the transfer 160 and estimation 170 steps previously described, are carried out.

Finally, a step 280 of carrying out a particular flight phase is carried out, manually or automatically, the particular flight phase being a hovering flight above the objective point 55 or a landing phase on the objective point 55.

• une étape de détermination 155,255 par anticipation des mouvements de chaque objet 50 à suivre sur une durée d'anticipation, de sorte à estimer les positions prévisionnelles successives de chaque objet 50 à suivre sur cette durée d'anticipation et
• une étape d'affichage 156,256 des positions prévisionnelles successives de l'enveloppe de sécurité 60 attachée à chaque objet 50 sur le dispositif de visualisation 11 pour la durée d'anticipation.

In addition, according to this variant, the process may include optional steps:

• a step of determining 155,255 by anticipation of the movements of each object 50 to be followed over an anticipation period, so as to estimate the successive forecast positions of each object 50 to be followed over this anticipation period and
• a step 156,256 of displaying the successive forecast positions of the safety envelope 60 attached to each object 50 on the display device 11 for the anticipation period.

These optional steps can be carried out between the step of determining 150,250 of the positions and movements of each object 50 to be followed and of the objective point 55 and the step of transferring 160,260 of the positions and movements of each object 50 to be followed and of the point objective 55 in the local terrestrial reference (X _T , Y _T , Z _T ).

The steps of estimating 170,270 of a security envelope 60 attached to each object 50 to be followed and of producing 180,280 of a particular flight phase of the aircraft 1 can thus take into account these movements determined by anticipation of each object 50 to be followed and the successive forecast positions of each object 50 to be followed over this anticipation duration.

Naturally, the present invention is subject to numerous variations as to its implementation. Although several embodiments have been described, it is clearly understood that it is not conceivable to exhaustively identify all the possible modes. It is of course possible to replace a means described by an equivalent means without departing from the scope of the present invention.

Claims (16)

1. Method to assist with navigation for a rotary wing aircraft (1) by detecting fixed and moving maritime objects (50), said aircraft (1) comprising:

   - at least one tracking device (15) providing a position and/or an absolute speed of said aircraft (1),

   - at least one inertial unit (16) providing an attitude of the aircraft (1),

   - an automatic pilot device (13) of said aircraft (1),

   - at least one display unit (11),

   - at least one detection system (20) intended to detect fixed and moving maritime objects (50), and

   - at least one computer (14),

   said method comprising the following steps:

   - surveillance (110) of a surveillance region on an area of water (100) by means of said at least one detection system (20),

   - detection (120) of at least one object (50) in said surveillance region and estimation of its position relative to said aircraft (1) by means of said at least one detection system (20),

   - selection (130) of at least one object (50) to be tracked and of a target point (55) on an object (50) to be tracked,

   - determination (140) of a position and an attitude of said aircraft (1) in a terrestrial reference mark,

   - determination (150) of the positions and movements of said at least one object (50) to be tracked and also the positions and movements of said target point (55) relative to said aircraft (1) over a sliding period (Δt_1-2),

   - transfer (160) of said positions and said movements of said at least one object (50) to be tracked and also said positions and said movements of said target point (55) from a mark related to said aircraft (1) to said terrestrial reference mark,

   - performance (180) of a particular flight phase of said aircraft with respect to said target point (55), keeping a safe distance around each object (50),

   characterised in that said method comprises the following steps:

   - estimation (170) of a safety envelope (60) attached to each object (50) to be tracked based on said positions and said movements of said objects (50) to be tracked in said terrestrial reference mark, said safety envelope (60) being located around each object (50) and taking account of the movements of said object (50) to be tracked over said sliding period (Δt_1-2),

   said step (170) for estimating said safety envelope (60) comprising the following substeps:

   - determination (171) of a specific movement characterised by a speed vector for each object (50) to be tracked over said sliding period (Δt_1-2),

   - estimation (172) of variations of the roll and pitch angles (δ_ϕ, δθ) and of a variation of height (δh) of each object (50) to be tracked over said sliding period (Δt_1-2) by analysing said positions and said movements of said at least one object (50) to be tracked over said sliding period (Δt_1-2), these variations of the roll and pitch angles being equal to mean values of several measurements of angular variations of several points of one object (50),

   - determination (173) of a centre of movement of each object (50) to be tracked with respect to said variations of said roll and pitch angles (δ_ϕ, δθ) over said sliding period (Δt_1-2), said centre of movement being an instantaneous centre of rotation of said object (50) over said sliding period (Δt_1-2), and

   - estimation (174) of a safety envelope (60) attached to each object (50) to be tracked located around each object (50) to be tracked and taking account of said specific movement and said centre of movement for each object (50) to be tracked according to said variation of height (δh) and said variations of said roll and pitch angles (δ_ϕ, δθ) of each object (50) to be tracked over said sliding period (Δt_1-2),

   said step (180) of performing a particular flight phase of said aircraft with respect to said target point (55) being executed while keeping a safe distance in respect of said safety envelope (60) around each object (50).
2. Method according to claim 1,
   characterised in that said step (130) for selecting at least one object (50) to be tracked and a target point (55) comprises the following substeps:

   - display (131) of at least one object (50) detected on said display device (11) of said aircraft (1), and

   - manual selection (132) on said display device (11) of at least one object (50) to be tracked and of a target point (55) on an object (50) to be tracked.
3. Method according to claim 1,
   characterised in that said step (130) for selecting at least one object (50) to be tracked and a target point (55) comprises the following substeps:

   - application (133) of a process for recognising the shape of at least one object (50) detected in information provided by said at least one detection system (20),

   - identification (134) of at least one object (50) detected by comparing the shape attributed to each object (50) detected with at least one database containing shapes of known maritime objects, and

   - automatic selection (138) of at least one object (50) to be tracked whose shape is identified in said at least one database and of a target point (55) on an object (50) to be tracked.
4. Method according to claim 1,
   characterised in that said step (130) for selecting at least one object (50) to be tracked and a target point (55) comprises the following substeps:

   - application (133) of a process for recognising the shape of at least one object (50) detected in information provided by said at least one detection system (20),

   - identification (134) of at least one object (50) detected by comparing the shape attributed to each object (50) detected with at least one database containing known maritime objects,

   - automatic preselection (135) of at least one object (50) whose shape is identified in said at least one database,

   - display (136) of at least one preselected object (50) on said display device (11) of said aircraft (1), and

   - manual selection (137) on said display device (11) of at least one object (50) to be tracked and/or of a target point (55) on an object (50) to be tracked.
5. Method according to any one of claims 1 to 4,
   characterised in that said step (180) for performing a particular flight phase of said aircraft (1) in relation to said target point (55) comprises the following substeps:

   - determination (181) of a flight path in relation to said target point (55) while keeping said safe distance in respect of said safety envelope (60) attached to each object (50) to be tracked, and

   - automatic tracking (182) of said flight path by said automatic pilot device of said aircraft (1) so as to perform said particular flight phase according to said flight path.
6. Method according to any one of claims 1 to 4,
   characterised in that said step (180) for performing a particular flight phase of said aircraft (1) in relation to said target point (55) comprises the following substeps:

   - display (183) of said safety envelope (60) attached to each object (50) to be tracked and of said target point (55) on said display device (11), and

   - manual flying (184) of said aircraft (1) by a pilot of said aircraft (1) so as to perform said particular flight phase.
7. Method according to any one of claims 1 to 6,
   characterised in that said particular flight phase in relation to the target point (55) comprises an approach flight in the direction of said target point (55), a landing phase on said target point (55) and/or a hover flight phase above said target point (55).
8. Method according to any one of claims 1 to 7,
   characterised in that said safe distance is variable for each object (50) to be tracked according to the dimensions of said safety envelope (60) attached to each object (50) to be tracked.
9. Method according to any one of claims 1 to 8,
   characterised in that said at least one detection system (20) intended for detecting fixed and moving maritime objects (50) comprises at least one electromagnetic detector, optical and/or acoustic.
10. Method according to any one of claims 1 to 9,
    characterised in that said step (170) for estimating a safety envelope (60) is achieved by constructing said safety envelope (60) in three dimensions around each object (50) to be tracked.
11. Method according to any one of claims 1 to 10,
    characterised in that said substep (174) for estimating a safety envelope (60) takes into account a vertical variation of water (δm) of said surface (100) of the water in order to anticipate the effect of said vertical variation of water (δm) on each object (50) to be tracked.
12. Method according to any one of claims 1 to 11,
    characterised in that because said particular flight phase in relation to the target point (55) performed during said performance phase (180) is an approach flight in the direction of said target point (55), said method comprises the following substeps:

    - determination (240) of a position and an attitude of the aircraft (1) within said terrestrial reference mark,

    - determination (250) of the positions and movements of said at least one object (50) to be tracked and also the positions and movements of said target point (55) relative to said aircraft (1) over said sliding period (Δt_1-2),

    - transfer (260) of said positions and said movements of said at least one object (50) to be tracked and also said positions and said movements of said target point (55) from a mark related to said aircraft (1) to said terrestrial reference mark,

    - estimation (270) of a safety envelope (60) attached to each object (50) to be tracked based on said positions and said movements of said objects (50) to be tracked within said terrestrial reference mark, said safety envelope (60) being located around each object (50) to be tracked and taking account of the movements of said object (50) to be tracked over said sliding period (Δt_1-2), and

    - performance (280) of a landing phase on said target point (55) or of a hover flight phase above said target point (55), while keeping a safe distance in respect of said safety envelope (60) attached to each object (50).
13. Method according to any one of claims 1 to 12,
    characterised in that said method comprises two supplementary steps:

    - determination (190) by anticipation of the movements of each object (50) to be tracked over an anticipation period, and

    - display (200) on said display device (11) for said anticipation period of successive expected positions of said safety envelope (60) attached to each object (50) to be tracked.
14. Method according to any one of claims 1 to 13,
    characterised in that said step (150) for determining said positions and said movements of each object (50) to be tracked and of the target point (55) comprises a reconstruction of characteristic rectilinear high points of each object (50) to be tracked and of said target point (55) by means of one or more Hough transforms.
15. System (10) to assist with navigation for a rotary wing aircraft (1) by detecting fixed and moving maritime objects (50), said system (10) comprising:

    - at least one tracking device (15) providing a position and/or an absolute speed of said aircraft (1),

    - at least one inertial unit (16) providing an attitude of the aircraft (1),

    - an automatic pilot device (13) of said aircraft (1),

    - at least one display unit (11),

    - at least one detection system (20) intended to detect fixed and moving maritime objects (50), and

    - at least one computer (14),

    characterised in that said system (10) is configured to implement the method according to any one of claims 1 to 14.
16. Aircraft (1) comprising a system (10) to assist with navigation for an aircraft (1), characterised in that said system is according to claim 15.

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