WO2017002092A1

WO2017002092A1 - Moving device for a radar system

Info

Publication number: WO2017002092A1
Application number: PCT/IB2016/053978
Authority: WO
Inventors: Pier Paolo RICCI; Francesco Coppi
Original assignee: Ids Georadar S.R.L.
Priority date: 2015-07-01
Filing date: 2016-07-01
Publication date: 2017-01-05
Also published as: EP3317694A1; ZA201800049B; ITUB20151776A1; AU2016285494A1

Abstract

An apparatus for interferometric SAR (100) comprises at least a radar antenna (110) arranged to emit and receive a signal with frequency in the microwaves range and a moving means arranged to actuate each radar antenna (110) along a trajectory s in such a way that each antenna implement interferometric SAR. In particular, the means for moving comprises a support base (120) and a kinematic chain (130) arranged to provide to each radar antenna (110) at least 3 rotational degrees of freedom with respect to the support base (120). The kinematic chain (130) comprises a proximal stiff link (132) having a first end (132a) and a second end (132b), a first pivotal constraint (131) arranged to pivotally connect the first end (132a) of the proximal stiff link (132) to the support base (120), a distal stiff link (134) having a first end (134a) and a second end (134b), said distal stiff link (134) being pivotally connected to the proximal stiff link (132), a second pivotal constraint (135) arranged to pivotally connect the second end (134b) of the distal stiff link (134) to each radar antenna (110), and a third pivotal constraint (133) arranged to pivotally connect the second end (132b) of the proximal stiff link (132) to the first end (134a) of the distal stiff link (134). This way, the trajectory s lies on a plane n orthogonal to the emitted signal by said or each radar antenna (110), for implementing linear interferometric SAR, and/or lies on a circular arc, for implementing curvilinear interferometric SAR.

Description

TITLE

MOVING DEVICE FOR A RADAR SYSTEM

DESCRIPTION

Field of the invention

The present invention relates to the field of remote radar sensing for environmental monitoring.

In particular, the invention relates to the field of interferometry by means of technique SAR {Synthetic Aperture

Radar) .

Description of the prior art

As well known, the interferometry by means of technique SAR provides the handling along a linear or curvilinear trajectory of at least one radar antenna, in order to obtain additional information about the objects present in the image thanks to the information contained in the phase of the return signal. In particular, it is possible to obtain information from the phase difference of the signal obtained from measurements of the same pixel made from different positions.

This technology is very useful for monitoring mountainsides, building facades, dam faces, bridges and other, to obtain measures with sub-millimeter precision of displacements of the ground or of the structures, in order to foresee in advance possible collapses or damages and allowing to activate methods of prevention and restoration or, in the worst cases, at least to ensure sufficient time to evacuate the area potentially interested by the collapse and then ensure the safety of who works or lives in the area itself .

To implement the technique SAR, devices are known that comprise motorized rectilinear guide on whose slides are located radar antennas that are moved by steps or continuously .

Devices are also known that move radar antennas on curvilinear trajectories, in order to carry out acquisitions by means of technology so called "arcSAR". In particular, these systems use a single rotating arm, at the end of which is mounted the radar system.

The operating principles of the interferometry by means of technologies SAR or arcSAR are described, for example, in:

— "Remote monitoring buildings using to ground based SAR: application to cultural heritage survey", D. Tarchi (2000);

— "Terrain Mapping by Ground-Based Interferometric Radar", Masthe likeano Pieraccini (2001);

— "Landslide monitoring by using ground-based SAR interferometry : an example of application to the Tessina landslide in Italy" Dario Tarchi (2003) ; — "A ground-based Arc-scanning synthetic apertures radar (ArcSAR) system and focusing algorithms", Hoonyol (2010);

— CH699249 "One-dimensional imaging radar measurements implementing method for acquiring, surveying and monitoring groundin and object movements, involves determining geometric resolution by radar delay or distance resolution procedure" (2010);

— EP2392943 "Synthetic-aperture radar system and operating method for monitoring ground and structure displacements arranged to emergency conditions" (2011) .

However, all the prior art systems that perform this type of interferometry have the drawback of not being convertible, i.e. of not having the ability to move the radar both on a linear trajectory (SAR) both on a curvilinear trajectory (arcSAR) , and therefore the two techniques cannot be to each other combined by the same instrument.

Furthermore, the prior art tools that perform this technology have normally a high encumbrance, since they require rails of at least 2-3 meters for handling the radar. This aspect makes very complex the handling of these apparatus in order to place them in the location from which performing the remote sensing. Another drawback of the above described devices lies in the exposition of the rails to weather and dirt. In particular, in case of snow on the rails an ice layer is formed that in the long run creates a resistance higher than the couple available to the motor.

In US2014/285375A1 an apparatus for non-interferometric technique SAR is described, where a mechanical arm is provided capable of moving the radar antenna according to 2 rotational degrees freedom. However, this solution, not performing interferometric SAR, does not allow to move the radar antenna along a trajectory arranged in a plane orthogonal to the signal emitted by the radar, but only along a curvilinear trajectory. Such apparatus can therefore being used in field of the interferometry only for performing the interferometric technique arcSAR, but not to pass between SAR and arcSAR.

Summary of the invention

It is therefore a feature of the present invention to provide an apparatus for interferometric SAR which allows to move the radar antennas both on a rectilinear trajectory, for performing linear interferometric SAR, both on a curvilinear trajectory, for performing curvilinear interferometric SAR, or arcSAR.

It is also an object of the above described invention to provide an apparatus that has smaller overall dimensions than prior art apparatus, especially when the apparatus is not in use and has to be transported.

It is still an object of the above described invention to provide an apparatus that is usable also in severe climates without that ice and snow block the movement of the radar.

These and other objects are achieved by a apparatus for interferometric SAR comprising:

— at least a radar antenna arranged to emit and receive a signal with frequency in the microwaves range;

— a moving means that is arranged to actuate said or each radar antenna along a trajectory s in such a way that said or each antenna implements the technique SAR;

said moving means comprising:

— a support base;

— a kinematic chain arranged to provide to said or each radar antenna at least 3 rotational degrees of freedom with respect to the support base;

whose main feature is that the kinematic chain comprises :

— a proximal stiff link having a first end and a second end;

— a first pivotal constraint arranged to pivotally connect the first end of the proximal stiff link to the support base;

— a distal stiff link having a first end and a second end, said distal stiff link being pivotally connected to the proximal stiff link;

— a second pivotal constraint arranged to pivotally connect the second end of the distal stiff link to said or each radar antenna (110) ;

— a third pivotal constraint arranged to pivotally connect the second end of the proximal stiff link to the first end of the distal stiff link;

in such a way that the trajectory s lies on a plane n orthogonal to the emitted signal by the or each radar antenna, for implementing linear interferometric SAR, and/or lies on a circular arc, for implementing curvilinear interferometric SAR.

The apparatus provided by the present invention is then much easier than prior art apparatus, since it allows actuating the antennas radar according to a wide variety of possible trajectories.

Furthermore, the present invention overcomes the difficulties of the prior art above described due to the block of the rails owing to debris or ice. Advantageously, antennas can be moved along the trajectory s in a continuous manner or in a discrete manner, according to consecutive steps.

In particular, the antennas are connected to the second end of the distal stiff link by a support plate.

Advantageously, on the support plate can be located a demodulator .

Advantageously between the proximal link and the distal link intermediate links can be located arranged to increase the degrees of freedom of the kinematic chain.

Advantageously, the first and the second pivotal constraint are operated by means of electric motors.

In particular, the first and the second pivotal constraint are cylindrical constraints with 1 rotational degree of freedom.

Advantageously, such cylindrical constraints with 1 rotational degree of freedom have vertical rotation axis and the proximal stiff link is configured to vertically translate with respect to the support base, said or each radar antenna configured to be moved on a trajectory s having a plurality of parallel horizontal lines arranged in the plane π , in order to implement linear interferometric SAR on a plurality of parallel horizontal lines.

This way, in addition to the ability to perform rectilinear or circular trajectories s in a plane parallel to the ground, is also possible to move the antennas in a vertical direction. Such solution is particularly useful to allow to provide trajectories s on a plurality of planes parallel to the ground, i.e. on more "baselines". Such solution provides to implement the technique of three- dimensional reconstruction of the scenario.

In particular, the proximal stiff link has length a and the distal stiff link has length b > a , and the plane n is located at a distance d by the first pivotal constraint, with d set between values b— a and b + a. Furthermore, the first pivotal constraint, the second pivotal constraint and the third pivotal constraint are adapted to rotate contemporaneously, respectively, of a first angle 6_lr of a second angle θ₂ and of a third angle θ₃, for moving the radar antenna along a first horizontal line having length L and having center 0 at the projection of the first pivotal constraint in the plane π .

More in particular, the angles 6_lr θ₂ and θ₃ are interrelated by the following relations:

Alternatively, the first and the second pivotal constraint are cylindrical constraints with 2 rotational degrees of freedom. Alternatively, a plurality of radar antennas is provided located at different heights, in order to implement, with a single rectilinear handling, the technique SAR at the different heights for three-dimensional reconstruction of the scenario. Such solution is particularly useful in case that, for simplicity of production, it is not possible to have the degree of freedom of the vertical translation and the cylindrical constraints have a single degree of freedom.

Alternatively, an actuator is provided arranged to adjust the height of the support base with respect to the ground, in order to provide the technique SAR at different heights. Even this exemplary embodiment is particularly advantageous in case of cylindrical constraints with 1 rotational degree of freedom without vertical translational degree of freedom.

Advantageously, the proximal stiff link and the distal stiff link are arranged, when the apparatus is not in use, to overlap one another for reducing the encumbrance of the kinematic chain. Such aspect is a further advantage with respect to the prior art, since it makes the apparatus more portable and then much easier in the different modes of use.

In particular, the proximal stiff link and the distal stiff link are adapted to increase and reduce telescopically its own length. This way, it is reduced further the encumbrance of the apparatus during transport . Advantageously, the support base comprises a carriage arranged to actuate the support base itself. Furthermore, the carriage allows to implement linear SAR in case of damage of the articulated arm.

In particular, an electric generator is provided arranged to feed the apparatus, in order to make it energetically independent.

Advantageously, a presence sensor is also provided configured to notice the presence of a user near said or each radar antenna, in such a way that the motion of said or each radar antenna is stopped in case of presence of a user. Such aspect increases the safety of the apparatus, preventing a user from being accidentally hit whereas the apparatus is actuating the kinematic chain.

According to another aspect of the invention, a method is claimed for implementing linear interferometric SAR along a trajectory s having a plurality of parallel horizontal lines for three-dimensional reconstruction of the scenario, said method using an apparatus for interferometric SAR according to the present invention, said method comprising the steps of:

— moving the radar antenna along a first horizontal line of the trajectory s by means of contemporaneous rotation of the first pivotal constraint of a first angle 6_{l r} of the second pivotal constraint of a second angle θ₂ and of the third pivotal constraint of a third angle θ₃;

— moving the radar antenna along a first vertical line by translating the proximal stiff link with respect to the support base;

— repeating the steps of moving the radar antenna for a number n of times, where n is the number of baselines predetermined for implementing the linear interferometric SAR for three-dimensional reconstruction of the scenario.

Brief description of the drawings

Further characteristic and/or advantages of the present invention are more bright with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings in which:

— Fig. 1 shows a top plan view of a first exemplary embodiment of the apparatus for interferometric SAR according to the present invention;

— Fig. 2 shows, in side view, an exemplary embodiment of Fig. 1;

— Fig. 3 shows a top plan view of a second exemplary embodiment of the apparatus for interferometric SAR according to the present invention; — Fig. 4 shows, side view, an exemplary embodiment of Fig. 3;

— Fig. 5 shows, in side view, a third exemplary embodiment of the apparatus for interferometric

SAR according to the present invention;

— Fig. 6 shows in a schematic view the rotation of the cylindrical constraints during the handling of the radar antenna along a linear trajectory .

Description of a preferred exemplary embodiment

With reference to Figs. 1 and 2, a first exemplary embodiment of the apparatus for interferometric SAR 100, according to the present invention, comprises a support base 120 to which is connected the first end 132a of a proximal stiff link 132 through a first pivotal constraint 131. At the second end 132b of the proximal stiff link 132 the first end 134a of a distal stiff link 134 is pivotally connected, by means of a pivotal constraint 133. At the second end 134b of the distal stiff link 134 a couple of antennas 110 is then connected, by means of a second pivotal constraint 135.

In this exemplary embodiment, all three rotational constraints 131,133,135 allow a rotation about vertical axes. In particular, such constraints are motorized and then the rotation of the links and/or of the antennas can be automated. This way, it is possible to actuate the antennas 110 according to a plurality of trajectories s , and in particular according to a linear trajectory and a curvilinear trajectory, in order to provide both the technique SAR that the technique arcSAR.

In particular, it is possible to implement interferometric SAR moving the radar antenna 110 along a linear trajectory s lying on a plane π orthogonal to the signal emitted by the antenna.

With reference to Figs. 3 and 4, in an exemplary embodiment of the present invention, the pivotal constraint 131 allows the proximal stiff link 132 both to rotate about a vertical axis both to rotate about a horizontal axis. The rotational constraints 133 and 135, instead, allow only the rotation about horizontal axes.

In Fig. 5, embodiment variant of the exemplary embodiment of Fig. 1 and 2 is shown, wherein is provided the possibility of vertical translation of the proximal stiff link 132 with respect to the support base 120. This way, the radar antenna 110 can be moved along a s-shaped trajectory s having a plurality of parallel horizontal lines placed in the plane π , in order to implement linear interferometric SAR on more baselines allowing the three-dimensional reconstruction of the scenario. In Fig. 6 is shown in a schematic view the rotation of the cylindrical constraints during the handling of the radar antenna along a linear trajectory having length L and having centre 0 at the projection of the first pivotal constraint 131 in the plane π . In the case of Fig., it is supposed that the proximal stiff link 132 has length a and the distal stiff link 134 has length b > a , and that the plane n is located at a distance d = b— a by the first pivotal constraint 131.

this case, to move along the line of length L the first pivotal constraint 131, the second pivotal constraint 135 and the third pivotal constraint 133 are adapted to rotate contemporaneously, respectively, of a first angle 6_lr of a second angle θ₂ and of a third angle θ₃, following the relations :

The foregoing description some exemplary specific embodiments will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt in various applications the specific exemplary embodiments without further research and without parting from the invention, and, accordingly, it is meant that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention, it is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation .

Claims

1. An apparatus for interferometric SAR (100) comprising:

— at least a radar antenna (110) arranged to emit and receive a signal with frequency in the microwaves range;

— a moving means arranged to actuate said or each radar antenna (110) along a trajectory s in such a way that said or each antenna implements the technique SAR;

said moving means comprising:

— a support base (120);

— a kinematic chain (130) arranged to provide to said or each radar antenna (110) at least 3 rotational degrees of freedom with respect to said support base (120);

said apparatus (100) characterized in that said kinematic chain (130) comprises:

— a proximal stiff link (132) having a first end (132a) and a second end (132b) ;

— a first pivotal constraint (131) arranged to pivotally connect said first end (132a) of said proximal stiff link (132) to said support base (120) ;

— a distal stiff link (134) having a first end (134a) and a second end (134b), said distal stiff link (134) being pivotally connected to said proximal stiff link (132);

— a second pivotal constraint (135) arranged to pivotally connect said second end (134b) of said distal stiff link (134) to said or each radar antenna (110) ;

— a third pivotal constraint (133) arranged to pivotally connect said second end (132b) of said proximal stiff link (132) to said first end (134a) of said distal stiff link (134) ;

in such a way that said trajectory s lies on a plane n orthogonal to said emitted signal by said or each radar antenna (110), for implementing linear interferometric SAR, and/or lies on a circular arc, for implementing curvilinear interferometric SAR.

2. Apparatus for interferometric SAR (100), according to claim 1, wherein said first pivotal constraint (131), said second pivotal constraint (135) and said third pivotal constraint (133) are cylindrical constraints with 1 rotational degree of freedom.

3. Apparatus for interferometric SAR (100), according to claim 2, wherein said cylindrical constraints with 1 rotational degree of freedom have vertical rotation axis and said proximal stiff link (132) is arranged to vertically translate with respect to said support base (120), said or each radar antenna (110) configured to be moved on a trajectory s having a plurality of parallel horizontal lines arranged in said plane π, in order to implement linear interferometric SAR on a plurality of parallel horizontal lines.

4. Apparatus for interferometric SAR (100), according to claim 3, wherein said proximal stiff link (132) has length a and said distal stiff link (134) has length b > a, wherein said plane n is located at a distance d from said first pivotal constraint (131) with b— a<d<b + a, and wherein said first pivotal constraint (131), said second pivotal constraint (135) and said third pivotal constraint (133) are arranged to rotate contemporaneously, respectively, of a first angle 6_lr of a second angle θ₂ and of a third angle θ₃, for moving said radar antenna (110) along a first horizontal line having length L and having center 0 at the projection of said first pivotal constraint (131) on said plane π, said angles 6_lr θ₂ and θ₃ being interrelated by the following relations:

5. Apparatus for interferometric SAR (100), according to claim 1, wherein said first pivotal constraint (131) and said second pivotal constraint (135) are spherical constraints with 2 rotational degrees of freedom.

6. Apparatus for interferometric SAR (100), according to claim 1, wherein said first pivotal constraint (131) and said second pivotal constraint (135) are operated by means of electric motors.

7. Apparatus for interferometric SAR (100), according to claim 1, wherein a plurality of radar antennas (110) is provided located at different heights, in order to implement the technique SAR at different heights for three-dimensional reconstruction of the scenario.

8. Apparatus for interferometric SAR (100), according to claim 1, wherein said proximal stiff link (132) and said distal stiff link (134) are arranged to telescopically increase and reduce its own length.

9. Apparatus for interferometric SAR (100), according to claim 1, wherein a presence sensor (140) is also provided configured to notice the presence of a user near said or each radar antenna (110) , in such a way that the motion of said or each radar antenna (110) is stopped in case of presence of a user.

10. A method for implementing linear interferometric SAR along a trajectory s having a plurality of parallel horizontal lines for three-dimensional reconstruction of the scenario, said method using an apparatus for interferometric SAR (100) according to claim 3, said method comprising the steps of:

— moving said radar antenna (110) along a first horizontal line of said trajectory s by means of contemporaneous rotation of said first pivotal constraint (131) of a first angle 6_lr of said second pivotal constraint (135) of a second angle θ₂ and of said third pivotal constraint (133) of a third angle θ₃ ;

— moving said radar antenna (110) along a first vertical line by translating said proximal stiff link (132) with respect to said support base (120) ;

— repeating said steps of moving said radar antenna (110) for a number n of times, where n is the number of baselines predetermined for implementing said linear interferometric SAR for three-dimensional reconstruction of the scenario.