Method of estimating target height by a detection device

Abstract

The present disclosure relates to a method for estimating a target height by a detection device. The detection device has a transmitter unit for transmitting a wave signal and two receiver units (11A, 11B) vertically aligned and spaced apart by a given distance (d) for receiving the wave signal. The method comprises: at the transmitter unit, transmitting a wave signal to be reflected by the target (2); at each receiver unit, receiving the wave signal (S r1 , S r2 ) reflected by the target (2), which is propagated via a plurality of paths generated by the reflecting surface (3); while the target distance (D) changes over time, measuring a phase difference (Δφ) between the reflected wave signals (S r1 , S r2 ) received by the two receiver units; determining a physical quantity fluctuation related to the target distance (D) from the measured phase difference; obtaining information about the target height (h) from the physical quantity fluctuation.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for estimating the height of a target by processing a wave signal sent from a detection device to the target and reflected by the target in the case of multipath propagation of the wave by reflection on a reflecting surface. Such a method can be used for example in a vehicle having a radar device to estimate the height of a target object above the road surface. BACKGROUND

[0002] In the field of motor vehicles, radar devices are used to provide reliable accurate information about the driving environment to advanced driver assistance systems even in adverse weather and poor lighting conditions. Radar devices are considered as a key technology for motor vehicle safety systems and highly automated driving systems. Radar devices can provide a measure of the target distance, i.e. the distance between the radar device and the target, and the relative speed of the target.

[0003] The road surface is a good reflecting surface for radar waves. As a result, there are two propagation paths in each of the two propagation directions between the radar device and the target: a direct propagation path and an indirect propagation path via the road surface. Both propagation paths are taken by the radar waves sent from the radar device to the target and by the radar waves reflected by the target towards the radar device. Due to the reflection on the road surface, the radar device seems to see two targets: the real target and an artificial target corresponding to the mirror image of the target below the road surface. The two targets, the real target and the artificial target, are known to cause an interference phenomenon which leads to peaks and dips in the intensity modulation of the reflected radar signal received by the radar device over the range of target distances. In other words, when the distance between the radar device and the target varies, the intensity of the reflected radar signal received by the radar device varies and presents peaks and dips at specific target distances due to the interference phenomenon.

[0004] US 6266005 B1 discloses a radar signal processing method for estimating the height of a target above a reflecting surface such as a road surface which exploits the interference phenomenon to estimate the target height above the reflecting surface. Specifically, the modulation of the intensity of the reflected radar signal received by the radar device is measured when the target distance varies. Then, the height of the target is derived from the intensity modulation process over the range of target distances.

[0005] In US 6266005 B1, the estimation of the target height is based on the measurement of the intensity of the received radar signal reflected by the target. A drawback of this method is that it relies on the target reflectivity. Indeed, the target reflectivity depends on the target material and affects the measured intensity of the received radar signal. This can deteriorate the estimation of the target height.

[0006] Therefore, there is a need for a more robust estimation of the height of a target above a reflecting surface. SUMMARY

[0007] The present invention relates to a method for determining information on the height of a target above a reflecting surface, the method being performed by a detection device having a transmitter unit for transmitting a wave signal and two receiver units vertically aligned and spaced apart by a given distance for receiving the wave signal, the method comprising the steps of:

[0008] at the transmitter unit, transmitting a wave signal, which is to be reflected by the target;

[0009] at each receiver unit, receiving a reflected wave signal reflected by the target, which is propagated via a plurality of paths resulting from the reflecting surface;

[0010] measuring S3 a phase difference Δφ between the reflected wave signals received by the two receiver units, while the target distance between the detection device and the target varies over time;

[0011] determining from the measured phase difference a fluctuation of a physical quantity as a function of the target distance; deriving from the fluctuation of the physical quantity information on the height of the target.

[0012] In the present disclosure, the information on the target height is derived from the phase difference measured between the two receiver units. The estimation of the target height is thus based on a differential method. Since the unwanted correlation affecting both channels is eliminated by the two receiver elements, the estimation is allowed to be more robust. For example, the method is less dependent on the target reflectivity.

[0013] Since the fluctuation of the physical quantity is derived from the phase difference measurement, a sharper valley is allowed to be obtained, so that the valley is more easily detected. In addition, in the curve representing the fluctuation of the physical quantity as a function of the target distance, the region where no valley appears is almost flat. As a result, the valley is more easily and robustly detected compared to the detection of the valley in the modulation of the intensity of the reflected radar signal disclosed in the prior art.

[0014] In some embodiments, the fluctuation of the estimated elevation angle as a function of the target distance is determined from the measured phase difference and in accordance with a calculated relationship between the distance between the receiver units and the phase difference, the elevation angle being formed between a horizontal plane comprising the detection device and a line from the detection device to the target.

[0015] Advantageously, the method further comprises a valley search step of searching for at least one valley in the fluctuation of the physical quantity, and wherein the information on the height of the target is determined (derived) from the result of the valley search.

[0016] In a particular embodiment, when no valley is found in the fluctuation of the physical quantity as the target distance decreases, the height of the target is determined to be less than one or more predetermined reference heights.

[0017] In case a first valley is detected in the fluctuations of the physical quantity as the target distance decreases from a long-range target distance, the height of the target can be calculated from the target distance of the first valley in dependence of a calculated relationship between the target distance of the first valley and the height of the target.

[0018] In case a second valley is detected in the fluctuations of the physical quantity as the target distance continues to decrease, the height of the target can be calculated again from the target distance of the second valley in dependence of a calculated relationship between the target distance of the second valley and the height of the target, and the heights of the target calculated both times can be compared to check if the heights are consistent.

[0019] In some embodiments, the method comprises the steps of: detecting a plurality of valleys in the fluctuations of the physical quantity; estimating the height of the target from the respective target distances of the detected plurality of valleys.

[0020] The detected valleys can be compared to a plurality of pre-stored models of the fluctuations of the physical quantity, and the model that best matches the plurality of detected valleys can be selected to estimate the height of the target, each model corresponding to a given height of the target.

[0021] Alternatively, at least one of the target distances of the detected valleys and the fluctuations of the physical quantity with the target distance can be provided as input data to a machine learning module, and the machine learning module outputs the height of the target.

[0022] The present disclosure also relates to a detection device having a transmitter unit for transmitting a wave signal, two vertically aligned receiver units spaced apart at a given distance for receiving the wave signal, and a processor for controlling the execution of the steps of the previously defined method.

[0023] The present disclosure also relates to: a computer program comprising instructions for causing the detection device defined above to perform the steps of the method defined above; a computer readable medium storing the computer program defined above.

[0024] The present disclosure also relates to a vehicle comprising the detection device previously defined. BRIEF DESCRIPTION OF DRAWINGS

[0025] Other characteristics, objects and advantages of the present disclosure will become more apparent from the detailed description of non-limiting embodiments, made with reference to the attached drawings.

[0026] Figure 1 A system comprising a detection device, a target and the path taken by the waves transmitted by the detection device to the target and reflected by the target is shown.

[0027] Figure 2 An example of fluctuations (perturbations) of the estimated target elevation angle as a function of the target distance is shown.

[0028] Figure 3 A functional block diagram of a detection device according to a specific embodiment is shown.

[0029] Figure 4 A flow chart showing a method for estimating a target height according to a first embodiment is shown. DETAILED DESCRIPTION

[0030] The present disclosure relates to estimating the height of a target 2 above a reflecting surface 3 by a detection device 1 that sends waves to the target 2 and then receives waves reflected by the target 2. The target 2 may be any object or element above the reflecting surface 3, such as the ground.

[0031] The detection device 1 includes a transmitter unit 10 for transmitting waves and two vertically aligned receiver units 11A, 11B for receiving waves. The two receiver units 11A, 11B are separated by a given spacing d. The detection device 1 may include more than two vertically aligned receiver units 11A, 11B for receiving waves and / or more than one transmitter unit 10 for transmitting waves. In some embodiments, the detection device 1 may include a transmitter-receiver unit that both transmits and receives waves.

[0032] like Figure 1 As shown, there are two propagation paths between the respective receiver units 11A, 11B (point A) and the target 2 (point B): a direct propagation path r DP and the indirect propagation path r via the reflecting surface 3 IDP (Point C). Two propagation paths r DP and r IDP Waves are taken in two directions: from detection device 1 to target 2, and from target 2 to detection device 1. Detection device 1 appears to see two targets: real target 2 (at point B) above reflective surface 3, and artificial target 2' (at point B'), which corresponds to the mirror image of target 2 below reflective surface 3. These two targets, real target 2 and artificial target 2', cause an interference phenomenon. Detection device 1 uses this interference phenomenon to determine information about the height of target 2, as described below.

[0033] In operation, the transmitter unit 10 sends a wave that is reflected by the target 2 and then received by each of the two receiver units 11A, 11B. The wave propagates via multiple paths by reflection of the reflecting surface 3. After the wave is sent to the target 2, each of the two receiver units 11A, 11B receives a wave signal reflected by the target 2. Each received wave signal has amplitude and phase information. The detection apparatus 1 measures the phase difference Δφ between the two wave signals received by the two receiver units 11A, 11B, respectively, continuously in real time. As the target distance D between the detection apparatus 1 and the target 2 changes, the detection apparatus 1 measures the phase difference Δφ between the two wave signals received by the two receiver units 11A, 11B, respectively. As shown in Figure 1 , the target distance D can be the distance between the detection apparatus 1 and the target 2 in relation to the reflecting surface 3. When the reflecting surface is a road surface, the target distance D is the ground distance (also referred to as “ground range” or “range”).

[0034] Then, the detection apparatus 1 determines a physical quantity fluctuation as a function of the target distance D (range) from the measured phase difference. It can be determined that the physical quantity fluctuates as a function of the target distance (i.e., the physical quantity changes as a function of the target distance). The physical quantity can be the phase difference or derived from the phase difference. Then, information about the height of the target 2 is obtained from the determined physical quantity fluctuation as a function of the target distance. For example, a valley search is performed in the physical quantity fluctuation. In other words, one or more valleys are searched for in the determined physical quantity fluctuation. A valley corresponds to a local minimum point in the physical quantity fluctuation. If there is some ε > 0 such that all physical quantities within a distance ε of a point x m in the target distance range are equal to or greater than the physical quantity at the point x m , the physical quantity fluctuation is considered to have a local (or relative) minimum point (valley) at the point x m , i.e., at a certain target distance. An appropriate ε value is chosen to detect the minimum point. Such a valley is caused by an interference phenomenon.

[0035] As will be explained in more detail later, information about the height of the target 2 is determined (i.e., obtained) from the results of the valley search.

[0036] As shown in Figure 3 , the detection apparatus 1 also has a processor 13 (i.e., a control processing unit) and a transceiver block 12 connected to the transmitter unit 10 and the two receiver units 11A, 11B.

[0037] The transceiver block 12 controls the transmission of the wave and processes the received wave to extract the amplitude and phase information.

[0038] The processor 13 controls the operation of the detection device 1 and performs wave signal processing to estimate the height of the target. Specifically, as described below, the processor 13 controls the execution of the steps of the method for determining information on the height of the target 2.

[0039] The transceiver block 12 and the processor 13 can be fused in one control processing unit.

[0040] In the first embodiment, the detection device 1 is a radar device. The radar device can be installed on a vehicle. In this case, the reflecting surface 3 is usually a road surface.

[0041] In the radar device 1, the two receiver units 11A, 11B are two receiver antenna units for receiving radar waves (i.e. radar signals), and the transmitter unit 10 is a transmitter antenna unit for transmitting radar waves (radar signals).

[0042] The method for determining information on the height of the target performed by the radar device 1 according to the first embodiment will now be described with reference to Figure 4

[0043] In a first step S1, the transmitter antenna unit 10 transmits a radar wave signal S t to the target 2. Next, the receiver antenna units 11A, 11B receive two radar wave signals S r1 , S r2 reflected by the target 2. As described previously, the waves (i.e. wave signals) propagate via multiple paths due to the reflection by the reflecting surface 3, and an interference phenomenon occurs.

[0044] In a step S2, the target distance D, which is also currently referred to as range, i.e. the distance between the radar device 1 and the target 2, is determined as a function of time. For example, when the radar device 1 approaches the target 2, the target distance D decreases.

[0045] In a step S3, the wave signals S r1 , S r2 received by the respective receiver antenna units 11A, 11B as a function of the target distance (range) D are processed by the transceiver block 12 to determine the phase information of the respective wave signals S r1 , S r2 , and to measure the phase difference Δφ between the two wave signals S r1 , S r2 received by the two receiver antenna units 11A, 11B, respectively.

[0046] ​In step S4, based on the calculated relationship between the separation d between the receiver antenna units 11A and 11B and the phase difference Δφ, the fluctuation of the estimated elevation angle over the target distance D (within the target distance interval or within the range covered by the change in target distance) is determined based on the measured phase difference Δφ. The calculated relationship is as follows:

[0047]

[0048] Where Δφ is the radar wave signal S received by the two vertically aligned receiver antenna units 11A and 11B respectively. r1 、S r2 The phase difference between

[0049] θ is the elevation angle θ g estimates;

[0050] λ is the wavelength of the radar wave;

[0051] d is the spacing (distance) between the two receiver antenna units 11A, 11B.

[0052] As an illustrative and non-limiting example, the vertical spacing d between the two receiver antenna elements 11A, 11B is equal to the wavelength λ multiplied by a given factor k. That is, d = kλ. In an illustrative and non-limiting example, k = 2, so d = 2λ. In such an example, equation (1) can be simplified as follows:

[0053] Δφ=4πsin(θ)(1')

[0054] like Figure 1 As shown, a geometric elevation angle θ is formed between a horizontal plane including the detection device 1 (i.e., extending through the detection device 1) and a line from the detection device 1 to the target 2 (or to the top of the target). g For the two receiver antenna units 11A, 11B, the geometric elevation angle θ of the target 2 is g are considered to be the same because the distance d between the receiver antenna units 11A, 11B is very small (negligible) compared to the target distance D. The estimated elevation angle θ obtained from the measured phase difference is Figure 1 The geometric elevation angle θ shown g Estimation of . Figure 2 As shown, the estimated elevation angle θ is disturbed by interference caused by the indirect path of the radar wave. The estimated elevation angle θ (obtained from the measured phase difference between the receiving antennas) shows the disturbance caused by the interference phenomenon in the form of a valley.

[0055] For example, the detection device 1 determines the fluctuations (i.e. the evolution) of the estimated elevation angle Θ of the target 2 over time (i.e. as a function of time) from the measured phase difference based on equation (1). Then, the detection device 1 obtains the fluctuations of the estimated elevation angle Θ over the target distance (i.e. as a function of the target distance) from the knowledge of the variations of the target distance over time based on the fluctuations of the estimated elevation angle Θ over time.

[0056] Figure 2 An example of fluctuations of the estimated (perturbed) elevation angle Θ over the target distance in the range of distances between 0 and 200 m is shown. For example, when the vehicle having the radar device 1 approaches the target 2, the range of distances goes from 200 m to 0 m (i.e. from the right to the left of the graph in Figure 2 The fluctuations of the estimated elevation angle Θ over the target distance (i.e. the variations or the trend of the estimated elevation angle Θ depending on the target distance) in the range of variations of the target distance D have a plurality of valleys VI, V2, V3... (i.e. a plurality of local minima) due to the perturbation phenomenon. The successive valleys VI, V2, V3... have respective theoretical positions DI, D2, D3... in the interval of target distances (range). In other words, each valley V n is characterized by a particular target distance D n and has an order index n in the series of valleys VI, V2, V3.... The first valley VI is characterized by the highest target distance DI. For each valley V n , the order index n of the valley V n , the target distance D n of the valley V n and the height h of the target 2 are in a theoretical relationship. A simplified version of the theoretical relationship between the order index n of the valley V n , the target distance D n of the valley V n and the height h of the target 2 can be expressed as follows:

[0057]

[0058] where h is the height of the target;

[0059] n is the valley index (or order index), the first index n = 1 corresponding to the first valley observed when the target distance decreases from a long range (i.e. far) distance (for example, the first valley is the farthest to the right in Figure 2 );

[0060] D n is the target distance of the valley (i.e. the position of the valley in the interval of target distances);

[0061] λ is the wavelength of the radar wave;

[0062] H is the height of the radar device 1 above the reflecting surface 3.

[0063] The simplified relation (2) can be used as a calculation relation or calculation rule for estimating the height of the target 2 as explained later.

[0064] In step S5, the detection device 1 performs a valley search using the fluctuations of the estimated elevation angle Θ over the target distance D (range), the valley search comprising searching for at least one valley V in the fluctuations of the estimated elevation angle Θ n .

[0065] In step S6, information about the height of the target is determined (obtained) from the result of the valley search S5.

[0066] The steps S4, S5 and S6 can be performed in real time as the target distance changes, for example as a vehicle with the detection device 1 approaches the target 2, to determine information about the height of the target in real time.

[0067] In steps S5 and S6, different implementations can be implemented to determine information about the height of the target 2 from the fluctuations of the estimated elevation angle Θ over the target distance. Some implementations can be used cumulatively by the radar device 1.

[0068] In a first implementation, the detection device 1 is a long-range detection device 1. The detection range of the detection device 1 covers long target distances (ranges) of 80 m to 200 m and more depending on the range detection of the detection device 1. For example, the detection device 1 is a long-range radar (LDD). Such a long-range radar can detect distant objects (targets) and provide target distances of 80 m to 200 m and more.

[0069] In the first implementation, long-range measurement data is obtained by the radar device 1. In this case, as the target distance D decreases (for example because the vehicle approaches the target 2), in the search step S5, a first valley V1 at a range position D1 can be detected.

[0070] In step S6, the height of the target 2 is estimated by a calculation with the equation (2) and the values n = 1 and D n = D1. The detection of the first valley V1 allows to estimate the height of the target 2 precisely.

[0071] Alternatively, in the search step S5, then a second valley V2 at a range position D2 is detected, and in step S6, the height of the target 2 is estimated again by a calculation with the equation (2) and the values n = 2 and D n = D2.

[0072] Then, the first and second estimates of the target height can be checked for consistency. If the two estimates are the same or substantially the same, they are considered to be mutually confirmed. A difference between the two estimates equal to or less than a predetermined maximum percentage (e.g. a percentage between 5% and 20%) can be tolerated.

[0073] In the second embodiment, the detection device 1 is also a long-range detection device. In this case, if in step S5 the target distance decreases from a long-range distance (i.e. from 200 m and above to 80 m and above), in a given reference target distance (range) D ref1 , D ref2 ... the estimation of the elevation angle Θ does not find a valley in the fluctuations of the estimation of the elevation angle Θ, in step S6 the height of the target 2 is estimated to be less than one or more corresponding reference heights h ref1 , h ref2 ... The relationship between the reference target distance (range) D ref1 , D ref2 ... and the corresponding reference heights h ref1 , h ref2 ... is given by equation (2) for n = 1 as follows:

[0074] For example, in the case where the height H of the detection device is 0.5 m and λ is equal to 0.004 m:

[0075] At a reference target distance D ref1 of 70 m, if no valley is detected, the object height is determined to be less than 30 cm;

[0076] At a reference target distance D ref2 of 45 m, if no valley is detected, the object height is determined to be less than 20 cm;

[0077] At a reference target distance D ref3 of 25 m, if no valley is detected, the object height is determined to be less than 10 cm.

[0078] The third embodiment can be used when the long-range data of the measurement are not available. The detection device 1 can be a short-range detection device. However, the third embodiment can be implemented by a long-range detection device.

[0079] In the third embodiment, in step S5 the detection device 1 detects a plurality of valleys V j , V j+1 , V j+2… , typically a set of m valleys V j , V j+1 , V j+2… In step S6, the detection device 1 estimates the height h of the target 2 from the detected plurality of valleys V j , V j+1 , V j+2… , and the corresponding target distances (ranges) D j , D j+1 , D j+2 … It is possible to use different methods for estimating the target height h based on the detected plurality of valleys V j , V j+1 , V j+2… . In this approach, it is not necessary to know the value of the index of the detected valleys.

[0080] In a first method for estimating the target height h based on the detected plurality of valleys V j , V j+1 , V j+2… , a plurality of models M1, M2… estimating the fluctuations of the elevation angle Θ over the range (target distance) are compared to the detected plurality of valleys V j , V j+1 , V j+2… . Each model M1, M2… corresponds to a given target height h1, h2… The model Mx that best matches the position (in other words: the target distance) of the detected plurality of valleys V j , V j+1 , V j+2… is selected. It is possible to use a least square (LS) based method, or an iterative least square based method, or a filtering method that makes use of a Kalman filter for example, to select the model Mx that best matches the detected valleys. The estimate of the height h of the target 2 is obtained from the target height hx corresponding to the selected model Mx. The height h of the target 2 can be considered equal or substantially equal to the target height hx of the selected model Mx. Optionally, a similarity score between the detected plurality of valleys V j , V j+1 , V j+2… and the selected model Mx can be computed. The similarity score can be used to determine the level of accuracy of the estimate of the target height h or to improve the estimate accuracy.

[0081] In a second method for estimating the target height h based on the detected plurality of valleys V j , V j+1 , V j+2… , the target distances (i.e. the range positions, or positions) of the detected valleys V j , V j+1 , V j+2… are transferred as input data to a machine learning module. For example, a machine learning module is trained with N detected valleys V j , V j+1 , V j+2…the range position D j , D j+1 , D j+2… The feature vector (i.e. the target distance corresponding to the N detected valleys) is sent as input to the machine learning module. It is not required to know the indices of the detected valleys. It is only required that the indices of the consecutively detected valleys are consecutive. The length N of the feature vector can be 2, 3 or larger. For example, in case N = 3, the feature vector can be represented as follows: [j+2nd valley position, j+1st valley position, jth valley position] = [D j+2 , D j+1 , D j ].

[0082] Additionally or alternatively, the fluctuations of the physical quantity over the target distance are provided as input to the machine learning module.

[0083] In step S6, the machine learning module generates an estimate of the target height h as output.

[0084] In the training phase, the machine learning module can be trained with training data containing feature vectors of length N (as input data) and target heights (as reference data).

[0085] The detection apparatus 1 has software units and hardware units to implement the method of estimating the target height as described before. The present disclosure also relates to a computer program comprising instructions to cause the detection apparatus 1 to perform the steps of the described method, and to a computer readable medium having stored thereon the instructions of the computer program.

[0086] In the description of embodiments, the information about the height h of the target 2 is derived from fluctuations of the estimated elevation angle θ within the range (i.e. over the target distance), the estimated elevation angle θ being derived from the phase difference Δφ between the two receiver antenna elements 11A, 11B measured consecutively (at a given sampling frequency). Alternatively, the information about the height h of the target 2 can be derived directly from fluctuations of the estimated elevation angle θ over the range D (i.e. over the target distance D).

[0087] The fluctuations of the physical quantity (e.g. fluctuations of the estimated elevation angle or fluctuations of the phase difference) derived from the measured phase difference can be determined to vary in dependence on the inverse of the target distance 1 / D (or “inverse of the range”) (rather than the target distance D).

[0088] The present method of determining information about the target height based on the measured phase difference between the two receiver elements 11A, 11B can be used in combination with a method of determining information about the target height based on the measured intensity or amplitude of the wave signal received by one or both receiver elements 11A, 11B.

[0089] The detection device is not limited to a radar device. It can be any type of detection device having at least one transmitter unit for transmitting a wave signal and at least two vertically aligned receiver units for receiving the wave signal, which results in a phase difference between the reflected wave signals received by the at least two receiver units.

Claims

1. A method for determining information about the height (h) of a target (2) above a reflecting surface (3), the method being performed by a detection device (1) having a transmitter unit for transmitting a wave signal and two receiver units vertically aligned and spaced apart by a given interval (d) for receiving the wave signal, the method comprising the steps of: At the sender unit, a wave signal (S t ) is transmitted, which is to be reflected by the target (2); receiving, at each receiver unit, a reflected wave signal reflected by the target (2), the reflected wave signal being propagated via a plurality of paths generated by the reflecting surface (3); measuring, while the target distance (D) between the detection device (1) and the target (2) varies over time, a phase difference (Δφ) between the reflected wave signal received by one of the two receiver units and the reflected wave signal received by the other one of the two receiver units; determining, from the measured phase difference (Δφ), a physical quantity fluctuation as a function of the target distance (D); deriving, from the physical quantity fluctuation, information about the height (h) of the target (2).

2. The method according to claim 1, wherein The physical quantity fluctuation is the elevation angle (θ g ) fluctuates with the target distance, the elevation angle (θ g ) is formed between a horizontal plane including the detection device and a line from the detection device to the target, and the fluctuation of the estimated elevation angle (θ) is determined based on the measured phase difference (Δφ) and in accordance with a calculated relationship between the spacing (d) between the receiver units and the phase difference (Δφ).

3. The method according to any one of claims 1 and 2, further comprising a valley search step of searching for at least one valley in the physical quantity fluctuation, and wherein, The information about the height (h) of the target (2) is determined from the result of the valley search.

4. The method of claim 3, wherein, When no valley is found in the physical quantity fluctuation as the target distance (D) decreases, it is determined that the height of the target (2) is less than one or more reference heights.

5. The method of claim 3, wherein, In case a first valley is detected in the physical quantity fluctuation as the target distance decreases from a long-range target distance, the height of the target (2) is calculated from the target distance (D) of the first valley in accordance with a calculated relationship between the target distance (D) of the first valley and the height of the target (2).

6. The method of claim 5, wherein, In case a second valley is detected in the physical quantity fluctuation as the target distance (D) continues to decrease, the height of the target (2) is again calculated from the target distance of the second valley in accordance with a calculated relationship between the target distance of the second valley and the height of the target, and the heights of the target calculated both times are compared to check whether the heights are consistent.

7. The method of claim 3, further comprising: detecting a plurality of valleys in the physical quantity fluctuation; estimating the height of the target (2) from the respective target distances of the detected plurality of valleys.

8. The method of claim 7, wherein, comparing the detected valleys to a plurality of pre-stored models of the physical quantity fluctuation, and selecting the model that best matches the detected plurality of valleys to estimate the height of the target, wherein each model corresponds to a given target height.

9. The method of claim 1 or 7, wherein, sending, as input data, at least one of the target distances of the detected valleys and the physical quantity fluctuation as a function of the target distance to a machine learning module, and the machine learning module outputs the height of the target.

10. A detection device (1) comprising: a transmitter unit for transmitting a wave signal and two receiver units vertically aligned and spaced apart by a given interval (d) for receiving the wave signal, and a processor (13) for controlling the steps of performing the method according to any one of claims 1 to 9.

11. A computer readable medium storing a computer program comprising instructions for causing the detection device (1) according to claim 10 to perform the steps of the method according to any one of claims 1 to 9.

12. A vehicle comprising the detection device (1) according to claim 10.

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