Method for calibrating an ultrasonic sensor of an ultrasonic-based driver assistance system of a vehicle and vehicle

Abstract

Method for calibrating an ultrasonic sensor (16) in which a plurality of ground echoes (34) are detected by a plurality of ultrasonic pulses (30) with the ultrasonic sensor (16). The detection of the ground echoes (34) comprises, for each ground echo (34), measuring an elevation angle (36) of the ground echo (34) and / or an azimuth angle (38) of the ground echo (34) and measuring the duration of a period between the emission of the ultrasonic pulse (30) generating the ground echo (34) and the reception of the ground echo (34) with the ultrasonic sensor (16). The measured elevation angle (36) and / or azimuth angle (38) of those ground echoes (34) are determined whose measured duration represents a distance between the ultrasonic sensor (16) and the ground (22) that deviates from the height (26) of the ultrasonic sensor (16) by less than a predetermined height limit.

Description

State of the art

[0001] The invention relates to a method for calibrating an ultrasonic sensor of an ultrasonic-based driver assistance system of a vehicle and a vehicle.

[0002] Vehicles often have ultrasonic-based driver assistance systems, particularly in the form of ultrasonic-based parking aids, with several, for example 4 or 8, ultrasonic sensors arranged on the vehicle in a row.

[0003] A typical ultrasonic sensor in an ultrasonic parking aid emits an ultrasonic pulse that is reflected by an object as an echo. The ultrasonic sensor can detect this echo, and the distance between the sensor and the object can be determined based on the time interval between the emission of the ultrasonic pulse and the reception of the echo. Additionally, the ultrasonic sensor can detect the incident elevation and azimuth angles of the echo, thus enabling precise determination of the object's position. Disclosure of the invention

[0004] The invention aims to provide a method for calibrating an ultrasonic sensor of an ultrasonic-based driver assistance system of a vehicle, enabling high-accuracy calibration of the ultrasonic sensor. Furthermore, the present invention aims to provide a vehicle equipped to perform the method.

[0005] The problem underlying the invention is solved by a method with the features of claim 1 and by a vehicle with the features of claim 10. Advantageous embodiments of the invention are specified in the dependent claims.

[0006] A method according to the invention serves to calibrate an ultrasonic sensor of an ultrasonic-based driver assistance system of a vehicle. The vehicle is placed on a ground. The method comprises the steps of: a) specifying a height, in particular an installation height, of the ultrasonic sensor from the ground or determining the height of the ultrasonic sensor from the ground; b) detecting a plurality, for example 5 to 100, of ground echoes of a number, for example 1 to 50, of ultrasonic pulses with the ultrasonic sensor, wherein the detection of the ground echoes for each ground echo comprises measuring an elevation angle of the ground echo and / or an azimuth angle of the ground echo and measuring the duration of a period between the emission of the ultrasonic pulse generating the ground echo and the reception of the ground echo with the ultrasonic sensor;c) Determining, in particular selecting, the measured elevation angles and / or azimuth angles of those ground echoes whose duration measured in step b) represents, in particular corresponds to, represents or describes, a distance between the ultrasonic sensor and the ground that deviates from the height of the ultrasonic sensor by less than a predetermined height limit; and d) Determining and storing a correction value for detecting the elevation angle with the ultrasonic sensor and / or determining and storing a correction value for detecting the azimuth angle with the ultrasonic sensor based on the elevation angles and / or azimuth angles determined, in particular selected, in step c).

[0007] Advantageously, by restricting step c) to those ground echoes whose distance between the ultrasonic sensor and the ground is approximately equal to the height of the ultrasonic sensor from the ground, the requirements for the ground for successful calibration can be reduced. In particular, the area of ​​the ground from which the ground echoes used for calibration originate can be reduced in size. Only the area of ​​the ground from which the ground echoes used for calibration originate can meet the requirements for successful calibration. For example, the method can successfully calibrate an ultrasonic sensor even if only the area of ​​the ground from which the ground echoes used for calibration originate is flat.

[0008] Another aspect of the method may be that the use of ground echoes for calibrating the ultrasonic sensor is particularly cost-effective and achieves a particularly high level of accuracy.

[0009] Another aspect of the procedure is that it can be carried out while the vehicle is in use, for example during a parking maneuver.

[0010] The ultrasonic sensor can be calibrated by saving the correction values. After calibration, the elevation and / or azimuth angles of additional echoes can be detected with high precision using the ultrasonic sensor and these correction values.

[0011] The floor can be level. The floor can be level. The floor can be level. The floor can be level with respect to the longitudinal axis of the vehicle. Preferably, the floor can be parallel to the longitudinal axis of the vehicle.

[0012] The procedure may include the step of emitting the number of ultrasonic pulses using the ultrasonic sensor prior to step b).

[0013] A ground echo can be understood as an ultrasound pulse reflected by the ground. The ultrasound pulse can be reflected from the ground at a reflection point and propagate as a ground echo.

[0014] The duration of the period can be representative of a distance between the ultrasonic sensor and the ground.

[0015] The height limit can be set to a value equal to, or specifically representing, 10%, 5%, or 3% of the height of the ultrasonic sensor from the ground. The height limit defines the size of an area on the ground from which the ground echoes for calibration are taken. The height limit also allows ground echoes whose reflection points are too far from the ultrasonic sensor to be excluded. Excluding a ground echo means that the excluded echo is not considered when determining correction values.

[0016] Determining the height of the ultrasonic sensor from the ground in step a) can include emitting an ultrasonic pulse at a maximum elevation angle of the ultrasonic sensor towards the ground and receiving a ground echo, wherein determining the height of the ultrasonic sensor from the ground is based on a measured duration of the period between emitting the ultrasonic pulse and receiving the ground echo.

[0017] Step c) can be performed, for example, by calculating the duration of a period of time for the ultrasonic sensor's altitude, representing the time between the transmission of the ultrasonic pulse and the reception of the ground echo of that pulse. A threshold duration can be calculated by adding the calculated duration to the altitude threshold. The altitude threshold can be a time interval. Subsequently, ground echoes with a measured duration greater than or equal to the threshold duration can be filtered out.

[0018] Alternatively, step c) can be performed, for example, by calculating a limit distance by adding the height of the ultrasonic sensor and the height limit value. The height limit value can be a distance. For each ground echo, a distance can be calculated from the measured time between transmission and reception of the ground echo. Subsequently, those ground echoes whose calculated distance is greater than or equal to the limit distance can be filtered out.

[0019] The method may include the steps: f) detecting a temperature during the execution of at least one of steps b) to d); and g) storing the temperature detected in step f).

[0020] The correction value determined in step d) for detecting the elevation angle and / or the correction value determined for detecting the azimuth angle may be temperature-dependent.

[0021] The ultrasonic sensor has a detection range of 180°. This allows echoes with elevation and / or azimuth angles to be detected with the ultrasonic sensor, even if the value falls within the range of +90° to -90°.

[0022] If the correction value for elevation angle detection and the correction value for azimuth angle detection are both angles, the azimuth angle measurement can depend on the correction value for elevation angle detection, and vice versa. Therefore, the correction value for elevation angle detection can be determined and stored. Subsequently, the azimuth angles measured in step b) can be corrected based on the correction value for elevation angle detection, and the following steps of the azimuth angle procedure can be performed.

[0023] If the correction value for detecting the elevation angle and the correction value for detecting the azimuth angle are in phase, the measurement of the azimuth angle can be independent of the correction value for detecting the elevation angle and the measurement of the elevation angle can be independent of the correction value for detecting the azimuth angle.

[0024] The procedure may include the following steps: verifying the correction value for detecting the elevation angle and verifying the correction value for detecting the azimuth angle. This verification can be performed using a reference object placed in front of the sensor at a defined angle.

[0025] After executing the procedure, the ultrasonic sensor can detect an elevation angle and / or an azimuth angle of an echo, wherein the detected elevation angle is corrected by the correction value for the detection of the elevation angle determined in step d) and / or the detected azimuth angle is corrected by the correction value for the detection of the azimuth angle determined in step d).

[0026] In a further development of the method, the detection of the majority of ground echoes in step b) includes measuring the amplitude of each ground echo. In step c), the measured elevation angles and / or azimuth angles of those ground echoes whose amplitude measured in step b) exceeds a predefined amplitude threshold are determined. This advantageously allows artifacts to be suppressed. Furthermore, it ensures a high signal-to-noise ratio.

[0027] In a further development of the method, step c) determines the measured elevation angles and / or azimuth angles of those ground echoes whose elevation angle falls within a predefined range and / or whose azimuth angle falls within a predefined range. Advantageously, this allows outliers that lie outside the predefined elevation angle and / or azimuth angle range to be filtered out. It also allows measurement errors, such as those caused by interference, to be filtered out. Interference can be caused, for example, by small objects, potholes, or interference from other ultrasonic sensors.

[0028] In a further development of the procedure, determining the correction value for detecting the elevation angle in step d) includes calculating an elevation median value and an elevation standard deviation based on the elevation angle determined in step c). Additionally or alternatively, determining the correction value for detecting the azimuth angle in step d) includes calculating an azimuth median value and an azimuth standard deviation based on the azimuth angle determined in step c). The elevation median value and elevation standard deviation can be calculated for a predetermined number of ground echoes, for example, 30 or 50. Additionally or alternatively, the elevation median value and elevation standard deviation can be calculated for a predetermined travel distance or time interval.The median azimuth and standard deviation can be calculated for a given number of ground echoes, for example, 30 or 50. Additionally or alternatively, the median azimuth and standard deviation can be calculated for a given travel distance or time interval.

[0029] In a further development of the procedure, the process includes, prior to step d), the following step: Calculating an elevation difference and / or an azimuth difference for each ground echo determined in step c). Each elevation difference is calculated by subtracting the measured elevation angle from a predetermined target elevation angle. Each azimuth difference is calculated by subtracting the measured azimuth angle from a predetermined target azimuth angle. The elevation median value is the median of the elevation differences, and the elevation standard deviation is the standard deviation of the elevation differences. The azimuth median value is the median of the azimuth differences, and the azimuth standard deviation is the standard deviation of the azimuth differences.Advantageously, this allows for a particularly simple determination of the correction value for detecting the elevation angle and / or a particularly simple determination of the correction value for detecting the azimuth angle.

[0030] In a further development of the method, in step d) the elevation median value, preferably with an inverted, particularly reversed, sign, is stored as a correction value for detecting the elevation angle. Additionally or alternatively, in step d) the azimuth median value, preferably with an inverted, particularly reversed, sign, is stored as a correction value for detecting the azimuth angle. For example, the elevation median value can have a positive value, which is stored as a negative value as a correction value for detecting the elevation angle.

[0031] In a further development of the procedure, step d) stores an elevation product as a correction value for detecting the elevation angle and / or an azimuth product as a correction value for detecting the azimuth angle. The elevation product is calculated by multiplying the median elevation value by a predefined elevation weighting factor. The azimuth product is calculated by multiplying the median azimuth value by a predefined azimuth weighting factor. Advantageously, the weighting factors can improve the robustness of the calibration algorithm.

[0032] The elevation weighting factor can have a value in the range of -1 to +1, preferably from +0.3 to +0.7. The azimuth weighting factor can have a value in the range of -1 to +1, preferably from +0.3 to +0.7.

[0033] The elevation weighting factor and / or the azimuth weighting factor can be a negative value. This means that the correction value for detecting the elevation angle can have a sign inverted, or in particular reversed, to the elevation median value, and / or the correction value for detecting the azimuth angle can have a sign inverted, or in particular reversed, to the azimuth median value. This allows the correction of a measured elevation angle and / or azimuth angle to be performed by addition.

[0034] In a further development of the procedure, step d) stores the correction value for detecting the elevation angle if the elevation standard deviation is less than a predefined maximum elevation standard deviation. Additionally or alternatively, step d) stores the correction value for detecting the azimuth angle if the azimuth standard deviation is less than a predefined maximum azimuth standard deviation. This advantageously prevents an incorrect correction value for detecting the elevation angle and / or an incorrect correction value for detecting the azimuth angle from being stored. If the elevation standard deviation is greater than or equal to the predefined maximum elevation standard deviation, at least steps b) and c) can be executed again.If the azimuth standard deviation is greater than or equal to the specified maximum azimuth standard deviation, at least steps b) and c) can be repeated.

[0035] In a further development of the procedure, step d) involves storing the correction value for detecting the elevation angle if the elevation median value exceeds a predefined elevation median threshold. Additionally or alternatively, step d) also stores the correction value for detecting the azimuth angle if the azimuth median value exceeds a predefined azimuth median threshold. This advantageously avoids the unnecessary storage of either correction value. The procedure can be executed continuously in the background during vehicle operation, with one of the two correction values ​​being stored as needed.

[0036] A vehicle according to the invention, in particular a motor vehicle, has an ultrasound-based driver assistance system which is configured to perform a previously described method.

[0037] The ultrasound-based driver assistance system can be designed as an ultrasound-based parking aid.

[0038] The ultrasound-based driver assistance system may include a control unit designed to perform the procedure described above.

[0039] Possible embodiments of the invention are explained below with reference to the accompanying drawings. These show: Fig. 1 A schematic top view of a vehicle with an ultrasound-based driver assistance system, Fig. 2 a schematic side view of the vehicle from Fig. 1, Fig. 3 a schematic rear view of the vehicle from Fig. 1, and Fig. 4 A schematic top view of an ultrasonic sensor of the ultrasonic-based driver assistance system of Fig. 1.

[0040] Fig. Figure 1 shows a vehicle 10 with an ultrasound-based driver assistance system 12. The ultrasound-based driver assistance system 12 has a control unit 14 and eight ultrasound sensors 16. The ultrasound sensors 16 are connected to the control unit 14 via signal transmission.

[0041] The ultrasound-based driver assistance system 12 is designed as an ultrasound-based parking aid. The ultrasound sensors 16 are arranged at the rear of the vehicle 10. The ultrasound sensors 16 can be arranged in an ultrasound sensor array 18.

[0042] The ultrasound-based driver assistance system 12 is configured to perform a procedure for calibrating an ultrasound sensor 16 of the ultrasound sensor series 18. In particular, the ultrasound sensors 16 are calibrated successively using the procedure.

[0043] Fig. Figure 2 shows the vehicle 10 with an ultrasonic sensor 16 of the ultrasonic sensor series 18 in an xz-plane spanned by a longitudinal and a vertical direction of the vehicle 10. The calibration of the sensor is described below as an example. Fig. The calibration of the ultrasonic sensor 16 shown in section 2 is described using the method. The remaining ultrasonic sensors 16 can be calibrated accordingly.

[0044] Vehicle 10 is placed on a floor 22. The floor 22 is flat. The floor 22 runs parallel to a longitudinal axis 24 of vehicle 10.

[0045] The ultrasonic sensor 16 is positioned at a height 26 above the ground 22. This height 26 can be referred to as the installation height. A value for this height 26 is stored in a memory 28 of the control unit 14.

[0046] In an alternative embodiment not shown, the control unit determines the height of the ultrasonic sensor from the ground. For this purpose, the control unit can control the ultrasonic sensor such that it emits an ultrasonic pulse towards the ground at a maximum evolution angle. The control unit can determine the height of the ultrasonic sensor from the ground based on a measured duration of the time interval between the emission of the ultrasonic pulse and the reception of a ground echo of the ultrasonic pulse by the ultrasonic sensor that has the shortest duration of all received ground echoes.

[0047] Fig. Figure 2 shows that the ultrasonic sensor 16 is configured to emit an ultrasonic pulse 30. The ultrasonic pulse 30 strikes the ground 22 and is reflected by the ground 22 at a reflection point 32 as a ground echo 34. The ultrasonic sensor 16 is configured to detect the ground echo 34. Detecting the ground echo 34 involves measuring the elevation angle 36 of the ground echo 34 at which the ground echo 34 strikes the ultrasonic sensor 16.

[0048] Fig. Figure 3 shows vehicle number 10 of Fig. 2 in a rear view, whereby for the sake of clarity only the one in Fig. Figure 2 shows the ultrasonic sensor 16, while the other ultrasonic sensors 16 are hidden. Detecting the ground echo 34 involves measuring an azimuth angle 38 of the ground echo 34, see Figure 2. Fig. 4, under which the ground echo 34 meets the ultrasonic sensor 16.

[0049] The ultrasonic sensor 16 emits a plurality, for example 10 or 40, of ultrasonic pulses 30 in succession. The ultrasonic pulses 30 strike the ground 22 and are reflected from the ground 22 as ground echoes 34 at different reflection points 32. An ultrasonic pulse 30 can be reflected at one or more reflection points 32. Each ground echo 34 can be assigned to one, in particular a single, reflection point 32.

[0050] The ultrasonic sensor 16 detects the majority of ground echoes 34 and measures the elevation angle 36, the azimuth angle 38, and the amplitude of each ground echo 34. Additionally, the ultrasonic sensor 16 detects a temperature when a ground echo 34 is detected. For each detected ground echo 34, the ultrasonic sensor 16 measures the duration of the period between the emission of an ultrasonic pulse 30 and the reception of the ground echo 34 associated with that ultrasonic pulse 30.

[0051] The control device 14 calculates from the height 26 a duration of a period that elapses between the emission of an ultrasonic pulse and the detection of its ground echo, if the reflection point of the ground echo is spaced at a height 26 from the ultrasonic sensor 16.

[0052] The control unit 14 identifies those ground echoes 34 whose measured duration between the emission of the ultrasonic pulse 30 and the reception of the ground echo 34 is less than the sum of the calculated duration for the altitude 26 and a predefined altitude threshold. The altitude threshold is a time duration, for example, 50 µs (microseconds). The remaining ground echoes 34 are suppressed.

[0053] Fig.Figure 4 shows a schematic top view of the ultrasonic sensor 16. The size of a region 40 on the ground 22, from which the ground echoes 34 for calibration are derived, can be defined by the value of the specified height limit. This filters out ground echoes 34 whose reflection points 32 lie outside the region 40. Filtered-out ground echoes 34 are no longer considered.

[0054] The control unit 14 identifies, from the detected ground echoes 34, those ground echoes 34 whose measured amplitude is greater than a predefined amplitude limit. The remaining ground echoes 34 are suppressed.

[0055] The control unit 14 calculates an elevation difference for each detected ground echo 34 by subtracting the measured elevation angle 36 from a predetermined target elevation angle. The target elevation angle can be, for example, 90°. The control unit 14 also calculates an azimuth difference for each detected ground echo 34 by subtracting the measured azimuth angle 38 from a predetermined target azimuth angle. The target azimuth angle can be, for example, 90°.

[0056] The control unit 14 identifies those ground echoes 34 whose evaluation difference and / or azimuth difference fall within a predefined range. The remaining ground echoes 34 are ignored. This advantageously allows outliers or erroneous measurements to be filtered out.

[0057] Control unit 14 calculates an elevation median value and an elevation standard deviation for the elevation differences of the detected ground echoes 34 that have not yet been hidden. Control unit 14 also calculates an azimuth median value and an azimuth standard deviation for the azimuth differences of the detected ground echoes 34 that have not yet been hidden. The elevation median value and elevation standard deviation can be calculated, for example, if the detected number of ground echoes 34 is greater than or equal to a predefined value, such as 30 or 50. Similarly, the azimuth median value and azimuth standard deviation can be calculated if the detected number of ground echoes 34 is greater than or equal to a predefined value, such as 30 or 50.

[0058] The control unit 14 compares the elevation standard deviation value with a predetermined maximum elevation standard deviation value. If the elevation standard deviation value is greater than the predetermined maximum elevation standard deviation value, the control unit 14 terminates the elevation angle calibration procedure. In the illustrated embodiment, the elevation standard deviation value is less than the predetermined maximum elevation standard deviation value, so the determination of the correction value for detecting the elevation angle 36 continues.

[0059] The control unit 14 compares the value of the azimuth standard deviation with a predefined maximum azimuth standard deviation. If the value of the azimuth standard deviation is greater than the predefined maximum azimuth standard deviation, the control unit 14 terminates the azimuth angle calibration procedure. In the illustrated embodiment, the value of the azimuth standard deviation is less than the predefined maximum azimuth standard deviation, so the determination of the correction value for detecting the azimuth angle continues.

[0060] The control unit 14 calculates an elevation temperature mean based on the measured temperatures detected during the detection of the ground echoes 34, which are used to calculate the elevation median and elevation standard deviation. The control unit 14 also calculates an azimuth temperature mean based on the measured temperatures detected during the detection of the ground echoes 34, which are used to calculate the azimuth median and azimuth standard deviation.

[0061] The control unit 14 calculates an elevation product by multiplying the median elevation value by a predefined elevation weighting factor. The elevation weighting factor can have a value in the range of -1 to +1, preferably from +0.3 to +0.7. The control unit 14 also calculates an azimuth product by multiplying the median azimuth value by a predefined azimuth weighting factor. The azimuth weighting factor can have a value in the range of -1 to +1, preferably from +0.3 to +0.7.

[0062] The control unit 14 stores the elevation product as a correction value for detecting the elevation angle 36 with the ultrasonic sensor 16 and / or the azimuth product as a correction value for detecting the azimuth angle with the ultrasonic sensor 16 in the memory 28 and / or in a memory of the ultrasonic sensor 16.

[0063] The control unit 14 stores the elevation temperature mean value and / or the azimuth temperature mean value in the memory 28 and / or in a memory of the ultrasonic sensor 16.

[0064] The calibration of the ultrasonic sensor 16 is completed by saving the elevation product and / or the azimuth product.

[0065] The procedure is repeated for the remaining ultrasonic sensors 16 of the ultrasonic sensor series 18.

[0066] After calibration, an echo can be detected with the ultrasonic sensor 16.

[0067] The measured elevation angle and / or azimuth angle of the echo is corrected by the stored elevation product and / or azimuth product. This correction can be achieved, for example, by calculating the difference between the measured elevation angle and the stored elevation product, and / or by calculating the difference between the measured azimuth angle and the stored azimuth product. This results in particularly precise detection of the echo's elevation angle and / or azimuth angle.

[0068] In an embodiment not shown, a correction value for elevation angle detection and a correction value for azimuth angle detection can be stored for different temperature ranges. This allows different correction values ​​to be used for different temperature ranges. For example, a temperature can be measured while the elevation angle and / or azimuth angle is being detected, and a correction value for elevation angle detection and / or azimuth angle detection can be determined based on the measured temperature, by which the measured elevation angle and / or azimuth angle is corrected.

Claims

[1] Method for calibrating an ultrasonic sensor (16) of an ultrasonic-based driver assistance system (12) of a vehicle (10), wherein the vehicle (10) is placed on a floor (22), the method comprising the steps: a) Specifying a height (26) of the ultrasonic sensor (16) from the ground (22) or determining the height (26) of the ultrasonic sensor (16) from the ground (22), b) Detecting a plurality of ground echoes (34) from a number of ultrasonic pulses (30), wherein the detection of the ground echoes (34) for each ground echo (34) comprises measuring an elevation angle (36) of the ground echo (34) and / or an azimuth angle (38) of the ground echo (34) and measuring a duration of a period between an emission of the ultrasonic pulse (30) generating the ground echo (34) and a reception of the ground echo (34) with the ultrasonic sensor (16), c) Determining, in particular selecting, the measured elevation angles (36) and / or azimuth angles (38) of those ground echoes (34) whose duration measured in step b) represents a distance between the ultrasonic sensor (16) and the ground (22) that deviates from the height (26) of the ultrasonic sensor (16) by less than a predetermined height limit value, and d) Determining and storing a correction value for detecting the elevation angle (36) with the ultrasonic sensor (16) and / or determining and storing a correction value for detecting the azimuth angle (38) with the ultrasonic sensor (16) based on the elevation angle (36) and / or azimuth angle (38) determined, in particular selected, in step c). [2] Method according to claim 1, - wherein detecting the plurality of ground echoes (34) of step b) includes measuring an amplitude of the ground echo (34) for each ground echo (34), - wherein in step c) the measured elevation angles (36) and / or azimuth angles (38) of those ground echoes (34) are determined whose amplitude measured in step b) is greater than a predetermined amplitude limit. [3] Method according to claim 1 or 2, - wherein in step c) the measured elevation angles (36) and / or azimuth angles (38) of those ground echoes (34) are determined whose elevation angle (36) has a value within a specified elevation angle value range and / or whose azimuth angle (38) has a value within a specified azimuth angle value range. [4] Method according to any of the preceding claims, - wherein determining the correction value for detecting the elevation angle (36) in step d) includes calculating an elevation median value and calculating an elevation standard deviation based on the elevation angle (36) determined in step c), and / or - wherein determining the correction value for detecting the azimuth angle (38) in step d) includes calculating an azimuth median value and calculating an azimuth standard deviation based on the azimuth angle (38) determined in step c). [5] Method according to claim 4, - wherein the procedure before step d) includes the step: calculating an elevation difference and / or an azimuth difference for each ground echo determined in step c) (34), - wherein each elevation difference is formed by subtracting the measured elevation angle (36) from a predetermined target elevation angle, - wherein each azimuth difference is formed by subtracting the measured azimuth angle (38) from a predetermined target azimuth angle, - where the elevation median is a median of the elevation differences and the elevation standard deviation is a standard deviation of the elevation differences, - where the azimuth median value is a median value of the azimuth differences and the azimuth standard deviation is a standard deviation of the azimuth differences. [6] Method according to claim 5, - wherein in step d) the elevation median value, in particular with an inverted sign, is stored as a correction value for detecting the elevation angle (36), and / or - wherein in step d) the azimuth median value, in particular with an inverted sign, is stored as a correction value for detecting the azimuth angle (38). [7] Method according to claim 5, - wherein in step d) an elevation product is stored as a correction value for detecting the elevation angle (36) and / or an azimuth product is stored as a correction value for detecting the azimuth angle (38), - where the elevation product is formed by multiplying the elevation median value by a predetermined elevation weighting factor, - where the azimuth product is formed by multiplying the azimuth median value by a given azimuth weighting factor. [8] Method according to any one of claims 4 to 7 above, - wherein in step d) the correction value for detecting the elevation angle (36) is stored if the elevation standard deviation is less than a predetermined maximum elevation standard deviation, and / or - wherein in step d) the correction value for detecting the azimuth angle (38) is stored if the azimuth standard deviation is less than a predetermined maximum azimuth standard deviation. [9] Method according to any one of claims 4 to 8 above, - wherein in step d) the correction value for detecting the elevation angle (36) is stored if the elevation median value exceeds a predefined elevation median limit, and / or - wherein in step d) the correction value for detecting the azimuth angle (38) is stored if the azimuth median value exceeds a predetermined azimuth median limit. [10] vehicle (10), in particular motor vehicle, comprising: - an ultrasound-based driver assistance system (12) that is configured to perform a method according to one of the preceding claims.

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