Radar system for locating pipes buried in the ground and for detecting underground leaks of liquid, in particular water, with a square waveguide antenna for emitting orthogonally polarised signals of the same frequency

Abstract

The invention relates to a radar system for locating pipes buried in the ground and for detecting underground leaks of liquid, in particular water, with a square waveguide antenna for emitting orthogonally polarised signals of the same frequency. The invention essentially consists of a radar system (1) with an antenna (4) that can emit waves at a nominal frequency towards the ground in two polarisations that are distinct and orthogonal to one another, and that incorporates a measuring element (5) configured to measure the polarimetric ratio of the signals received in the two polarisations, in order to deduce from the imbalance between the two received signals the presence of a pipe buried in the ground, and, where appropriate, the presence of leaks of liquid, in particular water.

Description

[0001] Description

[0002] Title: Radar system for locating pipes buried in the ground and detecting underground leaks of liquid, particularly water, with a square waveguide antenna to emit orthogonally polarized signals of the same frequency.

[0003] technical field

[0004] The present invention relates to the field of detecting liquid leaks, particularly water leaks in the ground, and more particularly those originating from buried distribution and / or transport pipes.

[0005] Previous technique

[0006] The shortage of drinking water is a serious global problem. Part of this shortage is due to significant leaks of drinking water from water supply systems. Water leaks can typically cause more than 20 to 30%, and even more than 50%, of the drinking water losses for an urban water network.

[0007] Most water leaks occur underground and are difficult to detect. Unfortunately, such underground leaks are usually only detected after they have caused flooding above ground or massive damage to buildings, infrastructure, etc.

[0008] Currently, there is no reliable and automatable solution for detecting buried pipes and / or underground water leaks.

[0009] The methods and devices that have already been implemented can be classified into several categories, with an operator placing a device above a location where they suspect the existence of an underground leak and attempting to identify the water leaks.

[0010] A first category concerns noise / ultrasound measurements. We can cite patent application WO2011 / 157685 which describes a method for detecting and locating a leak in a drinking water supply network, by analyzing the amplitude and frequency of leak-noise spectra detected at a plurality of points in the network, which have different distances from a presumed location, the recording being carried out by geophones.

[0011] A second category involves taking measurements using electromagnetic waves. GB2362529 describes an antenna for detecting water leaks by detecting the Doppler effect caused by a flow in a water leak room, the antenna comprising a planar dipole antenna element with specific dimensions depending on the electromagnetic wave emitted in the ground and a frame housing covering one face of the dipole to form a resonant cavity.

[0012] A third category concerns microwave measurements. US945942B2 discloses a remote detection of underground liquid content including a microwave radiation reflection scan in an area of ​​a finite length band.

[0013] A fourth category concerns ground-penetrating radar (GPR), more commonly known as geological radar or georadar, which uses the principle of a radar pointed at the ground to study its composition and structure. To the inventors' knowledge, these GPR devices are those systematically used, at least in France, for over thirty years for detecting pipelines. These devices essentially operate by emitting a broadband frequency range and receiving these frequencies to locate buried pipelines. The formation of the emission range requires a 3-octave transmission frequency band.Another example is KR10-2478882, which discloses a detection system comprising a ground-penetrating radar (GPR) module. This module measures the pipe's reflectance index, the time it takes for waves transmitted through the underground medium to reach the receiving antenna, and determines the characteristics of the pipe section to identify water leaks. These GPR devices have major drawbacks: their performance is limited to soil moisture levels above 15%, propagation losses restrict penetration at high frequencies, and in the presence of a significant leak, it cannot be accurately detected because the echo of the wave emitted by the device is reflected across a highly reflective area.

[0014] Furthermore, estimation methods have already been proposed, such as the one described in GB2555535, which provides an estimate of the location of water leaks in a drinking water network by implementing flow measurements from sensors distributed throughout the network. These estimates are highly empirical and their reliability is very uncertain.

[0015] A final method involves conducting a local excavation in an area of ​​land considered suspect. However, each local excavation is costly and time-consuming, requiring the use of complex and lengthy algorithms. Therefore, there is a need to improve methods and equipment for locating buried pipes and detecting groundwater leaks to overcome the aforementioned drawbacks.

[0016] The aim of the invention is to meet at least part of this need.

[0017] Description of the invention

[0018] To this end, the invention relates to a radar system for locating a pipeline buried in the ground and detecting underground leaks of liquid, particularly water, the radar system comprising:

[0019] - a narrowband radio wave transmitter, comprising a main port and, where applicable, at least two auxiliary ports;

[0020] - a hybrid coupler, called 3dB, whose input port is connected to the main port of the transmitter, and two output ports adapted to output signals of equal amplitude with a negligible phase shift between them;

[0021] - a waveguide antenna with a square cross-section or an antenna with crossed dipoles in the same plane, comprising two radiating transitions arranged at 90° to each other and adapted, one to transmit and receive signals with vertical polarization (V) and the other to transmit and receive signals with horizontal polarization (H);

[0022] - a comparative measurement element for the signals received by the antenna on the two vertical and horizontal polarizations (V and H);

[0023] - two electromagnetic wave circulators, each circulator comprising three ports, the input port being connected to one of the two output ports of the hybrid coupler, the intermediate port being connected to one of the radiating transitions (H or V) of the antenna, and the output port being connected to the measuring element;the system being configured to, when above a ground area, continuously send waves from the transmitter at a single nominal frequency (f), and continuously measure, by the measuring element, the difference in amplitude and phase of the signals received by each of the two radiating transitions (H and V) of the antenna via their respective circulator, each signal corresponding to a radar cross-section (RCS) of the ground area, according to a polarization, and establish, when the difference between the two RCSs is greater than a predetermined threshold value, the presence of a detectable pipe in the ground, or, when the difference between the two RCSs is less than the predetermined threshold value, the absence of a pipe in the ground and / or the presence of leak(s) of liquid masking the pipe.;

[0024] Preferably, the signals emitted by the coupler are UHF signals.

[0025] By "narrowband transmitter", we mean here and within the framework of the invention, the usual meaning, namely a transmitter which emits a signal whose Fourier transform is zero outside a determined frequency band but of small width compared to the nominal center frequency (f).

[0026] The term "3dB hybrid coupler" is used here and within the context of the invention in its usual sense, namely a type of hybrid coupler with a power division ratio of 3 dB. This means that the two output signals have the same amplitude and half the power of the input signal.

[0027] By "hybrid coupler" we mean here and within the scope of the invention, the usual meaning, namely an electronic component also known as a directional coupler or hybrid splitter, commonly used in RF and microwave communication systems, which is a device that separates a signal into two parts of distinct amplitudes.

[0028] For the purposes of this invention, a "radiating transition" is understood in its usual sense as a passive electronic component that allows a signal to be transmitted from one propagation medium to another and transmits electromagnetic radiation. A transition may include a radiating element for propagating a signal from a coaxial connector to a waveguide. The current flowing in the radiating element produces an electromagnetic wave in its vicinity.

[0029] The term "radar cross section" (RCS) refers, in the context of this invention, to the physical property inherent in the area of ​​the ground affected by the system according to the invention, which indicates the relative importance of the surface area reflecting an electromagnetic beam that the area produces. For further information on the concept of Radar Cross Section (RCS) of targets, and in particular of cylinders, see [1] and [2].

[0030] Thus, by considering the model described in [1] and adapting it to pipes, typically 10 cm to 100 cm in diameter, buried in wet soils (soil epsilon, loss tangent dependent on humidity), the inventors highlighted that the UHF frequency band, around 0.4 GHz, is the most relevant for detecting leaks, with a contrast of up to 2.7 dB: the signal on one polarization is almost twice as strong as on the other polarization of the antenna according to the invention.

[0031] According to an advantageous embodiment, the system is further configured to emit by the transmitter at least two distinct frequencies (fl, f2) on either side of the nominal frequency and to measure by the detector at least two phases (PHI, PH2) of received signals, so as to measure the burial distance of the pipeline.

[0032] Preferably, the value of the two frequencies (fl, f2) is equal to that of the nominal frequency (f) to + / - 10% maximum, preferably + / - 5%.

[0033] Preferably, the transmitter is configured so that the antenna emits signals at a nominal frequency (f) of 420 MHz.

[0034] Three advantageous alternatives for implementing the measuring element can be considered.

[0035] Thus, the measuring element can be:

[0036] - an Amplitude and Phase Detector (APD) comprising two input ports each connected to one of the two radiating transitions (H and V) of the antenna via their respective circulator, the APD being configured to determine respectively the differences in amplitude and phase of the signals received by its two input ports;

[0037] - a magic T comprising two input ports each connected to one of the two radiating transitions (H and V) of the antenna via their respective circulator, and two output ports from which respectively exit the sum and the difference of the signals received by its two input ports;

[0038] - a magic T associated with two Amplitude and Phase Detectors (APDs), the two input ports of the magic T being connected each to one of the two radiating transitions (H and V) of the antenna via their respective circulators, one of the two output ports of the magic T from which comes out the sum of the signals received by its two input ports being connected to an input port of a first DAP whose other input port is connected to a first auxiliary port of the single-frequency transmitter, and the other of the two output ports of the magic T from which comes out the difference of the signals received by its two input ports being connected to an input port of a second DAP whose other input port is connected to a second auxiliary port of the single-frequency transmitter, each of the first and second DAPs configured to measure the differences in amplitude and phase of the signals of the magic T.

[0039] In an advantageous embodiment, the radar system comprises two identical variable phase shifters, each connected to a circulator and a radiating transition, adapted for continuous adjustment during continuous measurement by the measuring element. If a pipeline is buried too deep, the received signals may interfere with residual leakage from the circulators, thus limiting the dynamic range of the radar system. The phase shifters overcome this drawback.

[0040] The invention also relates to a vehicle comprising a support on which the antenna of the radar system as described above is mounted so that the waveguide can be oriented towards the ground.

[0041] Advantageously, the antenna is mounted pivotally on the support, and possibly motorized, so as to be able to modify the angle of orientation of the two vertical and horizontal polarizations (V and H), with respect to the possible pipe buried in the ground.

[0042] Thus the invention essentially consists of a radar system with an antenna, in particular a waveguide, which can emit waves at a nominal frequency towards the ground, in particular in the UHE band, according to two distinct polarizations orthogonal to each other, and which integrates a measuring element capable of measuring the polarimetric ratio of the signals received according to the two polarizations, in order to deduce from the imbalance between the two signals received, the presence of a pipe buried in the ground, and where applicable the presence of leaks of liquid, in particular water.

[0043] In other words, the radar system according to the invention is configured to function as an electromagnetic balance which, when it measures an imbalance of received signals above a predetermined threshold value, characterizes the presence of a buried pipeline and below this value characterizes the absence of a pipeline in the ground and / or the presence of leak(s) of liquid masking the pipeline.

[0044] In other words, the electromagnetic balance works as follows:

[0045] - In the absence of a channel, the signals received on both polarizations are equal. The balance is therefore balanced;

[0046] - In the presence of a pipe, the balance is unbalanced; - In the presence of at least one leak, the contrast is greatly reduced, the balance rebalances.

[0047] Furthermore, with the same system components but emitting at least two other frequencies close around the nominal frequency, the burial distance of a pipe in the ground can be established.

[0048] The advantages of a radar-forming system are numerous, including:

[0049] - Reliable and rapid detection of buried pipes and liquid leaks from those pipes, even with low humidity levels;

[0050] - a system that is easy to implement and can be easily transported on-site;

[0051] - the ability to measure the burial distance of a pipe in the ground.

[0052] Other advantages and features will become clearer upon reading the detailed description, which is provided for illustrative purposes only and is not exhaustive, with reference to the following figures.

[0053] Brief description of the drawings

[0054] [Fig 1] Figure 1 is a schematic view illustrating a radar system according to the invention with all of its main components.

[0055] [Fig 2] Figure 2 shows a concrete way of implementing a waveguide antenna of the radar system which supports and integrates components.

[0056] [Fig 3], [Fig 4], [Fig 5] Figures 3, 4 and 5 are synoptic diagrams of the operation of a first, second and third alternative embodiment of the measuring element of the radar system according to the invention.

[0057] Detailed description

[0058] Figure 1 shows a radar system 1 according to the invention.

[0059] This system 1 includes first of all a narrowband radio wave transmitter 2, comprising a main port 20 and at least two auxiliary ports 21, 22.

[0060] The input port 30 of a 3-to-3dB hybrid coupler is connected to the main port 20 of the transmitter.

[0061] The coupler 3 also includes two output ports 31, 32 adapted for outputting UHF signals of equal amplitude with negligible phase difference between them. The system 1 also includes a square cross-section waveguide antenna 4, comprising two radiating transitions 41, 42, each of which may comprise one element, arranged at 90° to each other and adapted, one for transmitting and receiving signals with vertical (V) polarization and the other for transmitting and receiving signals with horizontal (H) polarization.

[0062] A measuring element 5 allows a comparative measurement of the signals received by the antenna 4 on the two polarizations vertical and horizontal (V and H).

[0063] To direct the electromagnetic wave flows in transmission and reception, the radar system 1 includes two electromagnetic wave circulators 6, each comprising three ports 60, 61, 62. The input port 60 of a circulator 6 is connected to one of the two output ports of the hybrid coupler 3, the intermediate port 61 is connected to one of the radiating transitions 41, 42 (H or V) of the antenna 4, and the output port 62 is connected to the measuring element 5.

[0064] Figure 2 shows a concrete example of the realization of a waveguide antenna with a square cross-section 4 which also integrates directly on its walls the circulators 6 and the hybrid coupler 3.

[0065] The waveguide antenna 4 can incorporate a horn 43.

[0066] The operation of such a radar system 1 which has just been described is as follows.

[0067] First, the radar system 1 is positioned above a ground area, with the antenna 4 oriented so that it emits its signals at a nominal single frequency (f) towards said area.

[0068] In the absence of underground conduits in the area, the signals received by the radiating elements 41 and 42 on each polarization (H or V) are of low power and substantially similar, because the radar cross-section (RCS) of the subsoil in the area is small and insensitive to polarization. In other words, the signals received by the two elements are balanced, and the electromagnetic balance of the system is not unbalanced.

[0069] When a pipe is oriented at a different angle than 45° relative to the horizontal and vertical polarizations, the strand oriented at the smallest angle to the pipe receives a much stronger signal than the other, because the subsurface RCF (Resonant Frequency Enrichment) will be significantly increased due to the pipe. In other words, the signals received by the two strands are unbalanced.

[0070] In particular, to determine the threshold value beyond which the difference in SER can be considered as indicating the presence of a pipeline, a calibration of the system is carried out prior to operation.

[0071] This calibration is performed by considering the H and V signals received by strands 41 and 42 in an area where the subsoil is known to be free of pipes. Measuring element 5 signals low power and small phase shift.

[0072] System 1 is then moved transversely until a SER (Sequence of Reference) is established, revealing the presence of a pipe. To avoid a 45° axis, the direction of the pipe can be visualized, or several passes can be made at different angles.

[0073] During system movement, the presence of a pipe disrupts the balance between the two signals H and V, which are therefore different, as the planimetric ratio is different due to the SER differential. Refer to the reference work [1] which explains this correlation.

[0074] Once the pipeline is located, its longitudinal monitoring allows for the continuous measurement of the planimetric ratio.

[0075] In the event of a liquid leak, particularly water, the amount of liquid spilled around the pipe will both attenuate the soil asymmetry and absorb the emitted waves. Thus, the amplitude of the measured signals decreases.

[0076] Measurement element 5 can be implemented according to different alternatives.

[0077] Figure 3 shows a measurement element consisting of a 50-degree magic tee. Its two input ports are each connected to one of the two radiating transitions (H and V) of the antenna, and its two output ports respectively output the sum and difference of the signals received by its two input ports. Thus, it is possible to measure the power of the sum and difference signals from the magic tee. When the soil area is homogeneous, the difference signal is zero. In the presence of buried pipes, the difference signal reflects the difference in the pipe's RCF (Resistance Factor Enhanced) level. In the presence of a leak, the RCF asymmetry is significantly reduced.

[0078] Figure 4 shows another alternative with an Amplitude and Phase Detector (APD) 51 comprising two input ports each connected to one of the two radiating transitions (H and V) of the antenna, the APD being configured to determine respectively the amplitude and phase differences of the signals received by its two input ports.

[0079] Figure 5 shows another alternative with a Magic Tee 50 associated with two Amplitude and Phase Detectors (APDs) 51, the two input ports of the Magic Tee being connected each to one of the two radiating transitions (H and V) of the antenna via their respective circulators, one of the two output ports of the Magic Tee from which comes the sum of the signals received by its two input ports being connected to an input port of a first DPD whose other input port is connected to a first auxiliary port of the single-frequency transmitter, and the other of the two output ports of the Magic Tee from which comes the difference of the signals received by its two input ports being connected to an input port of a second DPD whose other input port is connected to a second auxiliary port of the single-frequency transmitter, each of the first and second DPDs being configured to determine the differences in amplitude and phase of the signals of the Magic Tee.

[0080] The radar system 1 can advantageously measure the burial depth of a pipeline. Indeed, independently of pipeline detection, the analysis of burial depths can be performed using at least two frequencies separated by + / - 5% to 10% of the nominal transmission frequency. The measurements of the transmission and reception phases and the grouping of ambiguous frequencies allow for localization with an accuracy of R / 2, where R is the radius of the pipeline.

[0081] Theoretically, the polarimetry ratio of the radar system 1 is constant regardless of the burial depth of a pipeline.

[0082] However, the signals are attenuated with depth.

[0083] Thus, if the depth is too great, the signals will be too weak compared to the differential leakage of the circulators, which will therefore overpower the useful signals. In other words, the received planimetric signals H and V interfere with the residual leakage of the circulators. The system's dynamics are then limited.

[0084] To overcome this drawback, as illustrated in Figure 1, identical phase shifters 7 can advantageously be arranged between the circulators 6 and the radiating transitions 41, 42. The simultaneous control of the phases of these phase shifters 7 allows the planimetric signal and the electromagnetic leakage of the circulators to resonate constructively, and the detection of the maximum enables the increase in the dynamics of the radar system 1. The invention is not limited to the examples just described; in particular, features of the illustrated examples can be combined in unillustrated variants.

[0085] Other variations and improvements can be envisaged without departing from the scope of the invention.

[0086] For example, instead of a waveguide antenna with a square cross-section, one can implement an antenna with crossed dipoles in the same plane.

[0087] List of cited references

[0088] [1]: David K. BARTON “Radar System Analysis and Modeling” Artech House Publishers; Revised ed. edition (November 30, 2004).

[0089] [2]: “Methods of Radar Cross-Section Analysis”, Edited by JW CRISPIN, jr. and KM SIEGEL (Academie Press New York - London)

Claims

Demands 1. Radar system (1) for locating a pipeline buried in the ground and detecting underground leaks of liquid, in particular water, the radar system comprising: - a narrowband radio wave transmitter (2), comprising a main port (20) and optionally at least two auxiliary ports (21); - a hybrid coupler (3), said to be 3dB, whose input port (30) is connected to the main port of the transmitter, and two output ports (31, 32) adapted to output signals of equal amplitude with a negligible phase shift between them; - an antenna (4) with a waveguide of square cross-section or an antenna with crossed dipoles in the same plane, comprising two radiating transitions (41, 42) arranged at 90° to each other and adapted, one to emit and receive signals with vertical polarization (V) and the other to emit and receive signals with horizontal polarization (H); - a comparative measurement element (5) of the signals received by the antenna on the two vertical and horizontal polarizations (V and H), - two electromagnetic wave circulators, each circulator comprising three ports, the input port being connected to one of the two output ports of the hybrid coupler, the intermediate port being connected to one of the radiating transitions (H or V) of the antenna, and the output port being connected to the measuring element;the system being configured to, when above a ground area, continuously send waves from the transmitter at a single nominal frequency (f), and continuously measure, by the measuring element, the difference in amplitude and phase of the signals received by each of the two radiating transitions (H and V) of the antenna via their respective circulator, each signal corresponding to a radar cross-section (RCS) of the ground area, according to a polarization, and establish, when the difference between the two RCSs is greater than a predetermined threshold value, the presence of a detectable pipe in the ground, or, when the difference between the two RCSs is less than the predetermined threshold value, the absence of a pipe in the ground and / or the presence of leak(s) of liquid masking the pipe.; 2. Radar system according to claim 1, the system further configured to emit from the transmitter at least two distinct frequencies (fl, f2) on either side of the frequency nominal and to measure by the detector at least two phases (PHI, PH2) of received signals so as to measure the burial distance of the pipeline.

3. Radar system according to claim 2, the value of the two frequencies (fl, f2) being equal to that of the nominal frequency (f) to + / - 10% maximum, preferably + / - 5%.

4. Radar system according to any one of the preceding claims, the transmitter being configured so that the antenna emits signals at a nominal frequency (f) of 420 MHz.

5. Radar system according to any one of the preceding claims, the measuring element being an Amplitude and Phase Detector (APD) comprising two input ports each connected to one of the two radiating transitions (H and V) of the antenna via their respective circulators, the APD being configured to determine respectively the amplitude and phase differences of the signals received by its two input ports.

6. Radar system according to any one of claims 1 to 4, the measuring element being a magic T comprising two input ports each connected to one of the two radiating transitions (H and V) of the antenna via their respective circulators, and two output ports from which respectively exit the sum and the difference of the signals received by its two input ports.

7. Radar system according to any one of claims 1 to 4, the measuring element being a magic tee associated with two Amplitude and Phase Detectors (APDs), the two input ports of the magic tee being connected each to one of the two radiating transitions (H and V) of the antenna via their respective circulators, one of the two output ports of the magic tee from which the sum of the signals received by its two input ports is connected to an input port of a first APD whose other input port is connected to a first auxiliary port of the single-frequency transmitter, and the other of the two output ports of the magic tee from which the difference of the signals received by its two input ports is connected to an input port of a second APD whose other input port is connected to a second auxiliary port of the single-frequency transmitter, each of the first and second APDs being configured to measure the differences in amplitude and phase of the signals from the magic tee.

8. Radar system according to any one of the preceding claims, comprising two identical variable phase shifters, each connected to a circulator and a radiating transition, adapted to be continuously adjusted during continuous measurement by the measuring element.

9. Vehicle comprising a support on which the antenna of the radar system according to one of the preceding claims is mounted so that the waveguide can be oriented towards the ground.

10. Vehicle according to claim 9, the antenna being pivotally mounted on the support, and optionally motorized, so as to be able to modify the angle of orientation of the two vertical and horizontal polarizations (V and H), with respect to the possible pipeline buried in the ground.

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