FR2785993A1 - System for locating submerged objects towed by a line, used e.g. for ship navigation, includes beacons and GPS system to enable a precise fix of the submerged object - Google Patents

Abstract

The system includes a course correction unit (39) and acoustic signal beacons (2) located in geographic co-ordinates, situated on the surface or under the surface of the water but not connected to the object to be located. There is a receiving equipment (5) compatible with these emitted acoustic signals located at the side of the submerged object (4). Radio waves (6) are transmitted between the emitters and the receivers using GPS system (3) to update the course correction unit.

Description

Method and device for locating underwater objects having a wire link with the surface
The present invention relates to a method and a device for locating in geographic coordinates and immersion, one or more underwater objects having a wire connection with the surface.

 It applies in many fields, in particular to the location of towed sonars, radio-controlled devices, objects deposited on the seabed, etc., ..

 The technical field of the invention is that of localization systems using ultrasonic waves.

 Various systems for locating an underwater object are already known, which in particular use acoustic signals. These systems fall into two main families: those called "Long Base" and those called "Short Base".

 Long Base navigation systems are characterized by the measurement of the time interval elapsing between the emission, by a mobile, of an acoustic signal and the responses to this signal of "n" responding beacons located at the bottom of the sea.

 Knowledge of the celerity of sound in water makes it possible to deduce the distances from this mobile to beacons. The coordinates of the beacons being known, it is easy, by a triangulation technique, to deduce therefrom the geographic position of the mobile.

 These systems, although precise, are cumbersome to implement (wetting and recovery of beacons). They require prior calibration and offer a low refresh rate (of the order of 5 to 10 seconds).

 "Base Courte" systems appeared in the 1975s with dynamically positioned drilling vessels. These materials make it possible to measure the position of a submerged acoustic transmitter in relation to a reference frame linked to the ship's axes.

 The physical principle consists in measuring the phase difference of the acoustic signals received by a group of hydrophones secured to the hull of the ship.

Knowing the distances separating the hydrophones, the measurement of the phase differences makes it possible to locate, with respect to the ship reference frame, the direction of the acoustic source. The intersection of this line with the horizontal plane corresponding to the immersion of the transmitter makes it possible to determine the coordinates. Alternatively, the source-ship distance can be obtained by an interrogation-response type cycle.

The position is then known in polar coordinates.

The transition from the local benchmark to the absolute geographic benchmark is done by knowing the course, roll, pitch, latitude and longitude of the ship delivered by a radiolocation device or a satellite positioner of the type
D-GPS.

 Short Bases require delicate installation on board ships and are not very suitable for operations with a strong lateral offset of the object relative to the ship (case encountered by very shallow water, case of sonar towed by deep sea, ...) .

 Acoustic devices are also known for locating wire antennas (flutes) used in petroleum seismic, such as that presented in document US Pat. No. 5,031,159A. In the device described in this document, the acoustic transmitters integral with the flutes are not located in geographic coordinates. The main objective of the device is to locate a flute in relative coordinates with respect to another flute. In addition, this device requires to measure the distances between the transmitters and the receivers a return journey of an acoustic wave or, in the hypothesis of a simple journey, synchronization of the transmitter by a second wired link. It is precisely these return journeys and this second wired link that we have sought to overcome by implementing the method and the device of the invention. In addition, the method described in document US Pat. No. 5,031,195A is limited to use for flutes pulled under the surface. It does not allow a precise location of the flute in geographical coordinates if it is towed deep or deposited on the bottom of the sea.

 In recent years, there has been a growing interest in techniques using buoys located by satellites. These techniques are described in particular in documents US-5,579,285A and US-5,331,602A, as well as in an article which appeared in the American review "SEA TECHNOLOGY" in April 1998.

 In general, the problem posed consists in allowing the location in three-dimensional geographical coordinates of one or more objects, or even one or more points of the same object, with metric precision, in some cases submetric. The present invention relates to objects connected to the surface by a wire link (metal conductors, optical fiber, ...).

According to the invention, a solution to the problem of locating one or more submerged objects, whether placed on the bottom or not, is obtained by means of a method and a device using a processing station and one or more emission equipment for acoustic signals located on the surface or subsurface (such as one or more fixed, towed or self-propelled buoys), and one or more equipment for receiving acoustic signals located on the object or objects to be located and characterized in that: - each transmission equipment comprises means enabling its location in
geographic coordinates, an acoustic signal transmitter, a reference
a time scale and a means of tetetransmission by radio waves; - each underwater equipment for receiving acoustic signals is associated
a time scale reference synchronous with the time scale reference
said transmitters allowing precise dating of the signal arrival time
acoustic on the hydrophone of said receiver; - each underwater acoustic signal reception equipment has a
means of remote transmission of said instants of arrival of the acoustic signals to a
treatment station; -It has a processing station where the information of
position from the transmitting equipment (s) and the information from the or
underwater reception equipment, said processing means uses said information in order to allow the
location of said submerged objects in geographic coordinates
three-dimensional.

The solution to the problem also consists in using a device according to the invention by a method of locating one or more underwater objects, characterized in that it comprises the following operations: -a device is provided according to the invention including one or more pieces of equipment
transmitting and receiving acoustic signals and a processing station, -one or more transmitting equipment is deployed in the work area from a
air or naval means. They can be drifting, anchored, towed or self-propelled, the position of the signals is transmitted by radio waves to a processing station.
acoustic transmitters, - it is detected using acoustic receivers located on the objects to be located and
measures the instants of arrival of the acoustic signals with respect to a scale of
time reference common with that of the transmitters, -it is transmitted by a wired link to a processing station, at least the instants of
reception of the acoustic signals, -on the processing station collects position information from the
acoustic transmitters and the timing information of the times of reception of
acoustic signals, the information thus acquired is processed in order to determine the position or positions of the
acoustic receivers.

 The conversion of the propagation times into distances is carried out by calculating the product of the propagation times by the speed of the acoustic waves in the medium considered.

 The mathematical resolution of the problem posed, namely, the calculation of the coordinates in latitude and longitude and immersion of the reception points is carried out according to a well-known method of triangulation (intersection of spheres centered on the emission points and of radii equal to the distances separating the transmitters from the receiver such as those calculated previously) or by any other numerical method, such as the so-called "least squares" method after taking into account the immersion of objects such that they can be deduced from measurements originating from pressure implanted on the underwater object near the receiving hydrophone.

The result is a new method and a new device for locating one or more submerged objects using one or more equipment for transmitting and receiving acoustic signals and a processing station. The main configuration features of the invention relate to: -The architecture of the system composed of a processing station, equipment
for transmitting and receiving acoustic signals and means for
radio and wired teletransmission as defined above, as well as its
implementation process, the choice and the nature of the electronic modules installed in each of the
transmission or reception equipment, -the choice of information acquired there, transmitted or possibly
stored, -the type of information transmitted between the various devices, -the direction of transmission of the acoustic signals, i.e. from the surface to the
background, the direction of the transmission of position information by waves
, namely, equipment for transmitting acoustic signals to
the processing station, - the direction of the transmission of information of dating of the moments of reception of
acoustic signals, namely, reception equipment located on board
objects submerged towards the treatment station, -the conditions for implementing the device.

 The device according to the invention differs from location equipment of the "Long Base" type by the fact that the positions of the emission points, which could be assimilated to the underwater beacons placed on the bottom, are constantly evolving and transmitted by a radio channel at the treatment center.

 It is also distinguished from certain families of equipment known by the fact that the measurements of distances are not carried out by interrogation-response cycles requiring a round trip of the acoustic waves; but by the use of synchronous time reference scales between the transmitters and the receiver (s).

 It differs from known systems using relay buoys, in particular that described in document US-5,119,341A, by the fact that the processing center is located on the surface and receives your coordinates of the buoys by a radio channel and not on board the vessel. object to be located and receiving the coordinates of the buoys through an acoustic channel.

 It differs from the device described in document US-5,031,159A, in that its acoustic transmitters are completely dissociated from the objects to be located. It is thanks to this characteristic that the new method and device according to the invention make it possible to locate objects located in open water or at the bottom of the sea and are not imitated to objects located in the immediate vicinity of the surface.

 It differs from the device described in document FR-2,643,463A by the direction of the acoustic transmissions. In this document, the acoustic receivers are located on the surface, on board the buoys, and the transmitter is on board the object to be located. In the new device according to the invention, the acoustic waves propagate from the surface to the underwater object; or the opposite of the meaning retained by the patented device.

These characteristics show the following advantages provided by the device of the invention, compared with known systems: it allows the simultaneous localization of an unlimited number of underwater objects equipped
a wire link to the surface, -it locates the object or objects in absolute geographic coordinates with a
high precision, in particular by eliminating errors linked to misunderstanding of
the speed of the acoustic waves by pre-positioning the transmitters so
symmetrical with respect to the object to be located, -it allows very high rates of refreshment of the position data, -the position is known on the surface with a very small delay which makes it possible to enslave
the position of the underwater object by active means in a very short time
thus allowing tracking with great finesse, -it does not require any prior calibration, -it is easy to implement.

 In addition, the device can be rapidly deployed in the work area by any airborne or naval means.

 Another interest of the device and of the method of the invention is linked to the fact that the acoustic signals coming from transmitters extinguished from the localized object, the possible other acoustic means which would be carried by the object, such as a lateral sonar, are only slightly or not at all disturbed by emissions from the locating device.

 According to a preferred embodiment of the device and method for locating underwater objects of the invention as presented in FIG. 1, the device comprises a vessel 1. towing a submerged object 4 to which it is connected by a wire connection 7, such as a sonar, said object is equipped with an acoustic signal receiver 5. The device also includes one or more pieces of equipment for transmitting acoustic signals 2, which may be drifting, towed from the ship or self-propelled. Satellites 3 emit radio signals which allow precise positioning in geographic coordinates of the equipment 2 and of the ship 1. a. A local radio network 6 allows data exchanges between a processing station 1. b installed on the ship 1. a and the transmission equipment 2.

 Figure 2 shows the block diagram of an equipment for transmitting acoustic signals 2; it can be drifting, towed or self-propelled. A satellite location receiver 12 transmits its position every second to the processing unit 8. A radio transceiver 14 serves to receive and apply to the receiver 12 any differential corrections received by the equipment 28 (FIG. 4) , located on board ship 1. a. The same transceiver is used to transmit, at each acoustic emission cycle, the position of the acoustic signal transmission equipment to the remote processing station 1. b on board the ship 1. a. Acoustic signal transmission electronics 9 are activated at regular time intervals using the time scale reference 10 from the satellite positioning receiver 12.

 In a self-propelled version, the vessel determines at each treatment cycle the ideal position of each float in relation to the objects to be located.

Knowing the current position of the float, optimal setpoint and speed setpoints are then generated and transmitted by the radio transmitter 36 of the processing station (Figure 4). These instructions 11. a are transmitted via the processing unit 8 of the acoustic signal transmission equipment to the control-command computer 13. a. The latter compares the measured heading value as delivered by the heading sensor 13. c and generates on the servo unit 13. b a rudder angle correction. The same goes for speed control. The speed being known by deriving the position information delivered by the receiver 12. The input-output module 13. b takes information on the state of the self-propelled mobile with a view to their retransmission to the processing station of the ship by the radio transmitter 14 via link 11. b.

 Figure 3 shows the block diagram of the equipment for receiving acoustic signals located on board the object to be located. 11 includes in particular a hydrophone 17, an acoustic signal preamplifier 18 provided with a variable gain control as a function of time controlled by the link 21 so that the level of signal received is constant whatever its distance from the equipment. emission of acoustic signals. This is only made possible by the use of a common time scale reference. After filtering 19, the signal undergoes an analog-to-digital conversion 20. A digital signal processing processor 25 performs the operations of detecting and dating the time of reception of the received signal with respect to the common timescale reference received of the surface via the wired link 15. This information can be temporarily stored in a memory 22, then transmitted to the surface, at the processing station using an interface circuit 23 and an upward wired link 24. Immersion sensors , course, speed and attitude 26 optional, complete the device.

 Figure 4 shows a block diagram of the treatment center. It comprises a central unit 31 serving as an interface circuit between the various materials and a processing and display unit 39. A time scale receiver 29 is used in order to transmit to the submerged equipment for receiving acoustic signals the common timescale reference using the downlink wired link 30. The radio modem 36 and its link 38 are used to receive position information from the acoustic signal transmission equipment 2 and possibly to transmit it via the link 37 differential corrections from an optional receiver 28 received via link 34.

 The interface circuit 35 is used to receive from the submerged equipment for receiving the acoustic signals the dating information of the instants of reception of the acoustic signals and their identification.

 The position of the vessel 1.a can be known at the processing station 1.b by processing the information received from the satellite positioning receiver 29 via the link 33 after possible application of differential corrections received via the link 32.

 According to a first particular embodiment, the equipment for receiving acoustic signals comprises a submerged part which includes a hydrophone located at the point to be located, signal conditioning and interface circuits as well as a wire connection to the area. The detection and dating of the times of arrival of the acoustic signals on the hydrophone is then carried out by specific circuits located on the surface, at the other end of the wire connection.

 According to a second particular embodiment, the equipment on board the object comprises specific sensors 26 such as a pressure, heading, speed, attitude sensor, the measurements of which are transmitted to the surface by the wire link in order to be treated jointly with the datings in order to improve the location accuracy.

 According to another particular embodiment, the wire connection between the submerged object and the treatment station can comprise a radio device located between a relay buoy located on the surface and the treatment station which can thus be remote (case in particular of the use of a helicopter).

Advantageously, the method according to the invention comprises the implementation of the equipment of the device described above and the operations: -on install on board the ship the materials of the treatment station, -on deploys buoys on the emission of acoustic signals,
anchored, drifting, towed or self-propelled, - one or more underwater objects or objects are deployed from a ship with a wired connection
and one or more pieces of equipment for receiving acoustic signals, - the radioelectric and acoustic emissions of said pieces of equipment are activated, - the position or positions of the said object (s) are calculated at the processing station, - possibly new orders are transmitted to active control devices
of the position of the underwater mobile located on board the latter.

 In the event that the acoustic signal transmission equipment is self-propelled, the heading and speed instructions to be followed are transmitted at regular time intervals.

 The object to be located and provided with a wired link can be connected to a center on land, to an aerial means such as a helicopter or to a submerged means such as a submarine then receiving position information from the acoustic transmitters via a relay surface, either by a wire connection, or by an optronic channel (modulated laser beam for example).

 According to another particular mode of use, the equipment for transmitting acoustic signals could be deployed from the underwater environment, in an upward movement towards the surface.

The present device for locating underwater objects relied on the surface is more particularly applicable advantageously to the following interventions: -Operations for reconnaissance and surveying of the seabed by sonars
towed, - Oil seismic operations using hydrophone chains
posed on the bottom of the sea, - Operations of neutralization of underwater mines by self-propelled charge
wire-guided, -Anti-torpedo fight operations.

Claims (10)

 positions of the transmitters towards the processing station (39).  (2) and receivers (5), transmission by radio waves (6) of  submerged (4), a common time scale reference between the transmitters  compatible with the acoustic signals emitted on board the object (s)  sub-surface and not linked to the object to be located, reception equipment (5)  acoustic (2) located in geographic coordinates, located on the surface or  remote processing (39), one or more signal transmission equipment  wired connection (7), characterized in that it comprises at least one  CLAIMS 1.-Device for locating one or more underwater objects (4) provided with a 2.- Device according to claim 1, characterized in that it comprises circuits  preamp) ification (18), filtering (19), scanning (20), detection (25) and  interface (23) located on board the submerged object (2) and connected to the  processing (39) by a wired link (7), these circuits being configured for  detect and date the signal arrival times  acoustics within the submerged object and to transmit them to the  processing, via said wired link. 3.- Device according to claim 1, characterized in that it comprises circuits  interface (35) and detection on board the ship (1. a), these circuits being  configured to perform, on the surface, the detection and dating of instants  arrival of acoustic signals. 4.- Device according to any one of claims 1 to 3, characterized in that  the acoustic signal transmission equipment (2) is drifting, anchored.  towed or self-propelled. 5.- Device according to any one of claims 1 to 4, characterized in that  the equipment on board the submerged object (2) includes one or more  immersion, heading, speed and attitude sensors (26). 6.- Device according to any one of claims 1 to 5, characterized in that it  includes a radio channel for relaying the wire link between the  treatment station and the submerged object, in the aerial part of the course. 7.- Device according to any one of claims 1 to 6, characterized in that it  includes a downlink or optical channel such as a beam  modulated laser, to relay the transmission of position information  acoustic transmitters, from the surface to a submerged treatment station.  active control of the position of the acoustic emission equipment (2).  -We possibly transmit new orders to  active control of the position of the underwater mobile (4),  -We possibly transmit new orders to  acoustic receivers (5),  -We process the information thus acquired in order to determine the position (s)  receiving acoustic signals,  from acoustic transmitters and timing information  -We collect position information at the processing station (39)  the moments of reception of the acoustic signals,  -We transmit by a wire link (7) to a processing station (1.b), at least  transmitters,  compared to a common time reference scale with that of  locate and measure the instants of arrival of the acoustic signals by  -We detect using acoustic receivers (5) located on the objects to  position of the acoustic transmitters,  -We transmit by radio waves (6) to a processing station  drifting, anchored, towed or self-propelled,  from air or naval means (1. a). This or these equipment can be  -We deploy one or more transmission equipment (2) in the work area  acoustic signals (5) and a treatment station (39),  comprising one or more transmission (2) and reception equipment for  -We provide a device according to any one of claims 1 to 7,  acoustic characterized in that it comprises the following operations:  submerged using signal transmission and reception equipment  8.-Method of localization in geographical coordinates of one or more objects 9.- Method according to claim 8, characterized in that the ship (1.a) is  replaced by a center on land, an air or underwater means and in that,  in the latter case, the acoustic signal transmission equipment (2)  are deployed from the underwater environment, in an upward movement towards  the surface. 10.- Method according to one of claims 8 to 9, characterized in that the connection  wired between the treatment station (1.b) and the submerged object (4) is relayed in the  aerial part of the route by a radio channel.