Method and apparatus for monitoring surface deformations of a scenario

Abstract

A method for monitoring surface deformations of a scenario by means of differential interferometry technique, including the steps of prearranging a radar sensor having a transmitting antenna and a receiving antenna arranged to transmit and acquire radar signals, the radar sensor arranged to move along a planar trajectory γ having centre O; defining a reference system S having origin in the centre O; acquiring by SAR technique the scenario by means of handling the radar sensor along the planar trajectory γ, the radar sensor being configured so that the radiation pattern of the antennas is oriented radially with respect to the centre O, the acquisition occurring at points of acquisition s.sub.i arranged on the trajectory γ, the three-dimensional position of each target point t.sub.i being definable by means of spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i).

Claims

1. A method for monitoring surface deformations of a scenario by means of differential interferometry technique, said method comprising the steps of: prearranging a radar sensor comprising at least one transmitting antenna and a receiving antenna arranged to transmission and acquisition of radar signals, said radar sensor arranged to move along a planar trajectory γ having centre O; defining a reference system S having origin in said centre O; acquiring by SAR technique said scenario by means of handling said radar sensor along said planar trajectory γ, said radar sensor being configured in such a way that the radiation pattern of said antennas is oriented radially with respect to said centre O, said acquisition occurring at points of acquisition s.sub.i arranged on said trajectory γ, obtaining a plurality of data for each point of acquisition s.sub.i; defining a plurality of target points t.sub.i of said scenario, the three-dimensional position of each target point t.sub.i being definable by means of spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i) referring to said reference system S, being known the values of said coordinates ρ.sub.i and θ.sub.i; three-dimensional determining of said target points t.sub.i by the steps of: focusing at a first height of acquisition h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; focusing at a second height of acquisition h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; controlling, by means of interferometric technique, said focusings at the height of acquisition h.sub.α1 and h.sub.α2 obtaining a value of said coordinate β.sub.i for each target point; and by that a step is further provided of global focusing each target point t.sub.i with respect to its own three-dimensional position definable by said spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i), obtaining a first focused radar datum, said step of focusing being obtained, for each target point t.sub.i, by analyzing data obtained at each point of acquisition s.sub.i wherein said target point t.sub.i is detectable.

2. The method according to claim 1, wherein downstream of said step of global focusing, is provided a reiteration of said steps of: acquiring by means of SAR technique said scenario; global focusing each target point t.sub.i, obtaining a second focused radar datum; and where a step is then provided of comparing said first and second focused datum by means of differential interferometry technique, in order to monitor the variation of said scenario and to measure its deformation.

3. The method according to claim 1, wherein downstream of said step of three-dimensional determining of said target points t.sub.i a step is provided of simplifying said plurality of target points t.sub.i of said scenario, said step of simplifying providing the steps of: selecting, in said plurality of target points t.sub.i, target points t.sub.i having identical values of θ.sub.i, obtaining a subgroup of said target points t.sub.i; arranging target points t.sub.i in said subgroup for increasing values of ρ.sub.i, obtaining an ordered succession of target points t.sub.i of said subgroup; attributing a same value of β.sub.i to target points t.sub.i of said subgroup selected by means of isotonic regression technique according to said ordered succession.

4. The method according to claim 1, wherein said step of three-dimensional determining of said target points t.sub.i is made by said radar sensor.

5. The method according to claim 4, wherein said step of three-dimensional determining of said target points t.sub.i is made by at least one transmitting antenna and at least two receiving antennas having heights of location, respectively, h.sub.t1, h.sub.r1, h.sub.r2, with h.sub.r1≠h.sub.r2, said first height of acquisition h.sub.α1 and said second height of acquisition h.sub.α2≠h.sub.α1 being a function of said heights of location h.sub.t1, h.sub.r1, h.sub.r2 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}.$

6. The method according to claim 4, wherein said step of three-dimensional determining of said target points t.sub.i is made by at least two transmitting antennas and a receiving antenna having heights of location, respectively, h.sub.t1, h.sub.t2, h.sub.r1, with h.sub.t1≠h.sub.t2, said first height of acquisition h.sub.α1 and said second height of acquisition h.sub.α2≠h.sub.α1 being a function of said heights of location h.sub.t1, h.sub.t2, h.sub.r1 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t2}+h_{r1}}{2}.$

7. The method according to claim 4, wherein said radar sensor comprises two transmitting antennas and two receiving antennas having heights of location, respectively, h.sub.t1, h.sub.t2, h.sub.r1, h.sub.r2, and wherein said step of three-dimensional tracking of said target points t.sub.i furthermore comprises the steps of: focusing at a third height of acquisition h.sub.α3≠h.sub.α2≠h.sub.αt each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; focusing at a fourth height of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; said heights of acquisition being a function of said heights of location h.sub.t1, h.sub.t2, h.sub.r1, h.sub.r2 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}{h}_{a3}=\frac{h_{t2}+h_{r1}}{2}{h}_{a4}=\frac{h_{t2}+h_{r2}}{2}.$

8. The method according to claim 4, wherein said radar sensor comprises a transmitting antenna and four receiving antennas having heights of location, respectively, h.sub.t1, h.sub.r1, h.sub.r2, h.sub.r3, h.sub.r4, with h.sub.r1≠h.sub.r2≠h.sub.r3≠h.sub.r4, and wherein said step of three-dimensional determining of said target points t.sub.i also comprises the steps of: focusing at a third height of acquisition h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; focusing at a fourth height of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal β.sub.0; said heights of acquisition being a function of said heights of location h.sub.t1, h.sub.r1, h.sub.r2, h.sub.r3, h.sub.r4 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}{h}_{a3}=\frac{h_{t1}+h_{r3}}{2}{h}_{a4}=\frac{h_{t1}+h_{r4}}{2}$

9. A method for monitoring surface deformations of a scenario by means of differential interferometry technique, said method comprising the steps of: prearranging a radar sensor comprising at least one transmitting antenna and one receiving antenna arranged to acquire of radar signals, said radar sensor arranged to move along a planar trajectory γ having centre O; defining a reference system S having origin in said centre O; acquiring by SAR technique said scenario by means of handling said radar sensor along said planar trajectory γ, said radar sensor being configured in such a way that the radiation pattern of said antennas is oriented radially with respect to said centre O, said acquisition occurring at points of acquisition s.sub.i arranged on said trajectory γ, obtaining a plurality of data for each point of acquisition s.sub.i; defining a plurality of target points t.sub.i of said scenario, the three-dimensional position of each target point t.sub.i being definable by means of spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i) referring to said reference system S, being known the values of said coordinates ρ.sub.i and θ.sub.i; acquiring a three-dimensional mapping of said scenario, said mapping comprising a cloud of highlights ρ.sub.i arranged to define a three-dimensional surface Σ superimposable to said scenario, each highlight ρ.sub.i definable by means of spherical coordinates (ρ.sub.k,θ.sub.k,β.sub.k) referring to said reference system S; three-dimensional determining said target points t.sub.i by means of intersection, for each target point t.sub.i, between said three-dimensional surface Σ and the locus of points having the coordinates ρ.sub.i and θ.sub.i of said target point t.sub.i, obtaining a value of β.sub.i for each target point t.sub.i; global focusing each target point t.sub.i with respect to its own three-dimensional position definable by said spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i), said step of focusing being obtained, for each target point t.sub.i, by analyzing data obtained at each point of acquisition s.sub.i wherein said target point t.sub.i is detectable.

10. An apparatus for monitoring surface deformations of a scenario by means of differential interferometry technique, said apparatus comprising: a radar sensor comprising at least one transmitting antenna and one receiving antenna arranged to acquire radar signals; a kinematical chain arranged to actuate said radar sensor along a planar trajectory γ having centre O for carrying out an acquisition by means of SAR technique of said scenario, said radar sensor being configured in such a way that the radiation pattern of said antennas is oriented radially with respect to said centre O, said acquisition occurring at points of acquisition s.sub.i arranged on said trajectory γ, obtaining a plurality of data for each point of acquisition s.sub.i; a control unit arranged to provide the steps of: defining a plurality of target points t.sub.i of said scenario, the three-dimensional position of each target point t.sub.i being definable by means of spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i) referring to said reference system S, being known the values of said coordinates ρ.sub.i and θ.sub.i, said focusing comprising the steps of: three-dimensional determining said target points t.sub.i by the steps of: focusing at a first height of acquisition h.sub.α1 each target point t.sub.i with respect to its own position considering a value of A predetermined and equal to β.sub.0; focusing at a second height of acquisition h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; controlling said focusings at the heights of acquisition h.sub.α1 and h.sub.α2 obtaining a value of said coordinate β.sub.i for each target point; wherein said control unit is also arranged for carrying out a step of global focusing each target point t.sub.i with respect to its own three-dimensional position definable by said spherical coordinates (ρ.sub.i,θ.sub.i,β.sub.i), said step of focusing being obtained, for each target point t.sub.i, by analyzing data obtained at each point of acquisition s.sub.i wherein said target point t.sub.i is detectable.

11. The apparatus according to claim 10, wherein said radar sensor comprises at least one transmitting antenna and at least two receiving antennas having heights of location, respectively, h.sub.t1, h.sub.r1, h.sub.r2, with h.sub.r1≠h.sub.r2, said first height of acquisition h.sub.α1 and said second height of acquisition h.sub.α2≠h.sub.α1 being a function of said heights of location h.sub.t1, h.sub.r1, h.sub.r2 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}$ wherein $\frac{\lambda }{10}<.Math.h_{a1}-h_{a2}.Math.<40\lambda ,$ where γ is the wavelength of the radiofrequency signal emitted by said radar sensor.

12. The apparatus according to claim 10, wherein said radar sensor comprises at least two transmitting antennas and a receiving antenna having heights of location, respectively, h.sub.t1, h.sub.t2, h.sub.r1, with h.sub.t1≠h.sub.t2, said first height of acquisition h.sub.α1 and said second height of acquisition h.sub.α2≠h.sub.α1 being a function of said heights of location h.sub.t1, h.sub.t2, h.sub.r1 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t2}+h_{r1}}{2}$ wherein $\frac{\lambda }{10}<.Math.h_{a1}-h_{a2}.Math.<40\lambda ,$ where γ is the wavelength of the radiofrequency signal emitted by said radar sensor.

13. The apparatus according to claim 10, wherein said radar sensor comprises two transmitting antennas and two receiving antennas having heights of location, respectively, h.sub.t1, h.sub.t2, h.sub.r1, h.sub.r2 and wherein said step of three-dimensional determining of said target points t.sub.i furthermore comprises the steps of: focusing at a third height of acquisition h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; focusing at a fourth height of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; said heights of acquisition being a function of said heights of location h.sub.t1, h.sub.t2, h.sub.r1, h.sub.r2 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}{h}_{a3}=\frac{h_{t2}+h_{r1}}{2}{h}_{a4}=\frac{h_{t2}+h_{r2}}{2}$ wherein |h.sub.α−h.sub.α4|>|h.sub.α2−h.sub.α3|.

14. The apparatus according to claim 13, wherein h.sub.t1=h.sub.r1 and h.sub.t2≠h.sub.t1 and h.sub.r2≠h.sub.t2.

15. The apparatus according to claim 10, wherein said radar sensor comprises a transmitting antenna and four receiving antennas having heights of location, respectively, h.sub.t1, h.sub.r1, h.sub.r2, h.sub.r3, h.sub.r4, with h.sub.r1 ≠h.sub.r2≠h.sub.r3≠h.sub.r4, and wherein said step of three-dimensional determining of said target points t.sub.i also comprises the steps of: focusing at a third height of acquisition h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; focusing at a fourth height of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0; said heights of acquisition being a function of said heights of location h.sub.t1h.sub.r1, h.sub.r2, h.sub.r3, h.sub.r4 according to the equations: $h_{a1}=\frac{h_{t1}+h_{r1}}{2}{h}_{a2}=\frac{h_{t1}+h_{r2}}{2}{h}_{a3}=\frac{h_{t1}+h_{r3}}{2}{h}_{a4}=\frac{h_{t1}+h_{r4}}{2}.$

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 shows a flowchart of a first method for monitoring surface deformations of a scenario, according to the present invention;

(3) FIG. 2 shows a flowchart of a second method for monitoring surface deformations of a scenario, according to the present invention, wherein an external acquisition of a three-dimensional mapping of the scenario is provided;

(4) FIG. 3 diagrammatically shows an apparatus for implementing the method according to the present invention, comprising a radar sensor having two transmitting antennas and two receiving antennas;

(5) FIG. 3A diagrammatically shows the radar sensor, according to the present invention, during the inclination step;

(6) FIG. 4 diagrammatically shows a first exemplary embodiment of the radar sensor according to the present invention comprising two transmitting antennas connected alternatively to a transmission chain and two receiving antennas connected alternatively to a receiving chain;

(7) FIG. 5 diagrammatically shows a second exemplary embodiment of the radar sensor according to the present invention comprising two transmitting antennas connected alternatively to a transmission chain and two receiving antennas connected to two receiving chains arranged in parallel to each other;

(8) FIG. 6 diagrammatically shows a generic antenna arrangement geometry and the resulting acquisition heights in a radar sensor having two transmission antennas and two receiving antennas;

(9) FIG. 7 diagrammatically shows a second exemplary embodiment of the radar sensor according to the present invention comprising a transmitting antenna connected to a transmission chain and four receiving antennas connected to respective four receiving chains arranged in parallel to each other;

(10) FIG. 8 diagrammatically shows a generic antenna arrangement geometry and the resulting acquisition heights in a radar sensor having a transmission antenna and four receiving antennas.

DESCRIPTION OF SOME PREFERRED EXEMPLARY EMBODIMENTS

(11) FIG. 1 shows a flowchart 300 where it is diagrammatically shown a method for monitoring surface deformations of a scenario by means of differential interferometry technique, according to the present invention, wherein a first step is provided of prearranging a radar sensor 110 comprising at least one transmitting antenna 111 and one receiving antenna 112 arranged to the transmission and to the acquisition of a signal modulated by means of linear frequency modulation technique, said radar sensor 110 arranged to move along a planar trajectory γ having centre O [301].

(12) The method comprise furthermore a step of defining a reference system S having origin in said centre O [302] and a step of acquiring, by SAR technique, the scenario by means of handling the radar sensor 110 along the planar trajectory γ. In particular, the acquisition is carried out at points of acquisition s.sub.i arranged on the trajectory γ, obtaining a plurality of data for each point of acquisition s.sub.i [303].

(13) A step is then provided of defining a plurality of target points t.sub.i of the scenario. The three-dimensional position of each target point t.sub.i is definable by means of spherical coordinates ρ.sub.i,θ.sub.b,β.sub.i referring to the reference system S, wherein are known the values of the coordinates ρ.sub.i and θ.sub.i [304].

(14) The method then provides a step of three-dimensional determining the target points t.sub.i, by means of: focusing at a first height of acquisition h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0 [305]; focusing at a second height of acquisition h.sub.α2≠h.sub.α1 each target point t.sub.i with respect to its own position considering a value of β.sub.i predetermined and equal to β.sub.0 [306]; controlling the above described focusings at the height of acquisition h.sub.α1 and h.sub.α2 obtaining a value of the coordinate β.sub.i for each target point [307].

(15) A step is furthermore provided of global focusing each target point t.sub.i with respect to its own three-dimensional position definable by the spherical coordinates ρ.sub.i,θ.sub.i,β.sub.i. In particular, this step of focusing is obtained, for each target point t.sub.i, by analyzing data obtained at each point of acquisition s.sub.i where the target point t.sub.i is detectable [308].

(16) In FIG. 2 is present a flowchart 400 where it is diagrammatically shown a method alternative for monitoring surface deformations of a scenario by means of differential interferometry technique, according to the present invention, where the steps [305], [306], [307] of the method shown in the diagram 300 are replaced by the steps [401] and [402].

(17) In particular, the step [401] provides the acquisition of a three-dimensional mapping of the scenario from the outside. The mapping comprises a cloud of highlights p.sub.i arranged to define a three-dimensional surface Σ superimposable to the scenario, each highlight p.sub.i definable by means of spherical coordinates ρ.sub.k,θ.sub.k,β.sub.k referring to the reference system S.

(18) The step [402] provides instead the three-dimensional determining of the target points t.sub.i by means of intersection, for each target point t.sub.i, between the three-dimensional surface Σ and the locus of points having the coordinates ρ.sub.i and θ.sub.i of the target point t.sub.i itself, obtaining a value of β.sub.i for each target point t.sub.i.

(19) This way, the step of three-dimensional determining the target points t.sub.i is simplified, but at a same time, is dependent to an external acquisition, that is not always available. The exemplary embodiment of FIG. 1, instead, carries out the whole method without the need of an external acquisition, using only the radar sensor 110.

(20) In FIG. 3 is diagrammatically shown an apparatus 100, designed for implementing the method according to the present invention, comprising a radar sensor 110 having two transmitting antennas 111 and two receiving antennas 112.

(21) FIG. 3A shows schematically the radar sensor 110, highlighting the possibility of making a rotation around an axis parallel to the ground, so as to vary the inclination of the antennas.

(22) In general, the difference between two acquisition heights h.sub.α1 e h.sub.α2, also called baselines (B=|h.sub.α1−h.sub.α2|) is chosen so as to avoid phase ambiguity in determining the height of the target with respect to the rotation plane by means of the use of the interferometric technique between acquisitions made at different heights. The condition to be respected to avoid phase ambiguity is the following:

(23) $B=\frac{\lambda }{4}.Math.\frac{R_{\min }}{\Delta Z_{\max }}$

(24) where λ is the wavelength of the radar signal, R.sub.min is the minimum distance between radar and the target/measurement area and ΔZ.sub.max the maximum elevation in the measurement area.

(25) On the other hand, with the same accuracy σ.sub.φ in the measurement of the interferometric phase φ the greater the baseline the better the accuracy σ.sub.z n the measure of the height Z, since:

(26) ${\sigma }_z=R.Math.\frac{\lambda }{4\pi B}.Math.{\sigma }_{\phi }$

(27) where R is the distance from the radar.

(28) FIG. 4 diagrammatically shows a first exemplary embodiment of the radar sensor 110, according to the present invention, comprising two transmitting antennas 111 and two receiving antennas 112, all located at different heights h.sub.t1, h.sub.t2 h.sub.r1 h.sub.r2. The transmitting antennas 111 are connected alternatively to a single transmission chain and, similarly, the receiving antennas 112 are connected alternatively to a receiving chain. This means that both the transmitting antennas 111 and the receiving antennas 112 operate in a non-contemporary manner. This way, it is possible to adjust the height of acquisition h.sub.α1 of the signal according which antennas are activated, but it is not possible to provide a further height of acquisition h.sub.α2≠h.sub.α1 at the same time.

(29) FIG. 5 diagrammatically shows a second exemplary embodiment of the radar sensor 110, alternative to that one of FIG. 4, where the transmitting antennas 111 are connected alternatively to a single transmission chain whereas the receiving antennas 112 are connected to two independent chains of receiving arranged in parallel to each other. This way, it is possible to provide two different heights of acquisition h.sub.α1 and h.sub.α2 at the same time. In particular, both can be raised or lowered, depending, respectively, on whether the first or second transmitting antenna is selected.

(30) For the sake of clarity, in FIG. 6 is diagrammatically shown a possible geometry, applicable both to the first exemplary embodiment of FIG. 4 and to the second exemplary embodiment of FIG. 5, of the arrangement of the antennas and the resulting acquisition heights, in a radar sensor 110 having two transmitting antennas 111 and two receiving antennas 112.

(31) As can be seen, by appropriately differentiating the positioning heights of the antennas, it is possible to provide up to four different heights of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1, and such heights of acquisition may vary in value both changing the values of the positioning heights of the antennas both changing the dependence of each height of acquisition by the positioning heights. Even maintaining constant the positioning heights, it is therefore possible to change the height of acquisition combining differently the positioning heights itself.

(32) FIG. 7 diagrammatically shows a third exemplary embodiment of the radar sensor 110, according to the present invention, comprising a transmitting antenna 111 connected to a transmission chain and four receiving antennas 112 connected to four independent receiving chains arranged in parallel to each other.

(33) Also in this case, as shown by way of example in FIG. 8, it is possible to obtain contemporaneously up to four different heights of acquisition h.sub.α4≠h.sub.α3≠h.sub.α2≠h.sub.α1.

(34) 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.