Method for monitoring an underbody area below a vehicle using an ultrasonic sensor device by adjusting a reference signal, computing device and ultrasonic sensor device

Abstract

Method for monitoring an underbody area (6) beneath a vehicle (1), in which measurements are carried out using an ultrasonic sensor device (3), wherein at least one ultrasonic sensor (4) is activated in each of the measurements to emit an ultrasonic signal into the underbody area (6) and a sensor signal is determined which describes a temporal profile of the received ultrasonic signal, wherein a reference signal (10) is determined on the basis of a first sensor signal determined in a first measurement and the presence of an object (7) in the underbody area (6) is checked by comparing a second sensor signal (11) determined in a subsequent, second measurement with the reference signal (10), characterized in that the first sensor signal for determining the reference signal (10) is scaled with a scaling function (12),where the amplitude (P) of the scaling function (12) varies depending on time (t).

Description

The present invention relates to a method for monitoring an underbody area beneath a vehicle, in which measurements are carried out using an ultrasonic sensor device. In each measurement, at least one ultrasonic sensor is activated to emit an ultrasonic signal into the underbody area, and a sensor signal is determined that describes the temporal profile of the received ultrasonic signal. Furthermore, a reference signal is determined based on a first sensor signal determined in a first measurement, and the presence of an object in the underbody area is verified by comparing a second sensor signal determined in a subsequent measurement with the reference signal. The present invention also relates to a computing device and an ultrasonic sensor device.Furthermore, the present invention relates to a computer program and a computer-readable (storage) medium. Several methods exist for monitoring the underbody of a vehicle. Besides camera-based solutions, which reach their limits particularly in poorly lit parking garages or at night, infrared-based solutions are also possible. However, as with cameras, these systems can also suffer significant performance losses due to dirt or damage to the sensor housing. The use of ultrasonic sensors offers a cost-effective way to monitor the underbody. Interference factors such as insufficient lighting or poor lighting conditions do not occur with this method. The range of ultrasonic sensors is also generally sufficient for monitoring the underbody. Previous implementations of ultrasonic sensors, for example, use the direct detection of objects to determine the clearance of the underbody area. Ultrasonic sensors can be placed near the wheel arch, and measurements can be taken to check whether objects are in front of or behind the wheel. To achieve complete coverage with such a method, it is necessary to place an ultrasonic sensor in front of and behind each wheel. This entails high installation requirements and limited flexibility, and such an ultrasonic sensor system is also associated with increased costs. To achieve high sensitivity for object detection while maintaining robustness against environmental conditions, online calibration of the ultrasonic sensor device is recommended. Online calibration refers to the process of recording, processing, and storing a reference measurement of the underbody area when the vehicle is stationary or parked. Subsequently, each new measurement, for example, when the vehicle is started, can be compared to this reference measurement. Furthermore, both direct and indirect measurements are used to monitor the underbody area with ultrasonic sensors. A direct measurement, as defined below, is one in which an ultrasonic sensor emits an ultrasonic signal and the same ultrasonic sensor also receives this ultrasonic signal. In contrast, an indirect measurement is one in which an ultrasonic sensor emits an ultrasonic signal and another ultrasonic sensor receives it. According to the current state of the art, a reference signal, against which a current sensor signal is compared, is provided with a constant offset or scaling factor across the entire measurement range or time domain. This scaling is necessary to adapt the robustness and sensitivity of object detection to external conditions. However, since interfering echoes, for example from the floor covering or subfloor, vary in intensity at different distances and also affect object detection due to their amplitude, a constant scaling of the reference is only of limited use for achieving robust detection. In this context, DE 10 2017 111 932 A1 describes a method for operating an ultrasonic sensor device for a motor vehicle. Here, an ultrasonic signal is emitted into a ground area beneath the vehicle, and an ultrasonic signal is received from this ground area. The ultrasonic signal is emitted by a first ultrasonic sensor of the ultrasonic sensor device, and the ultrasonic signal emitted by the first ultrasonic sensor and reflected from a road surface in the ground area is received by a second ultrasonic sensor of the ultrasonic sensor device. Furthermore, it can be provided that a portion of the ultrasonic signal received by the second ultrasonic sensor is stored after the motor vehicle is switched off, and that this portion is subsequently determined again and compared with the stored portion. The object of the present invention is to provide a solution for how monitoring of an underbody area beneath a vehicle can be carried out more reliably using an ultrasonic sensor device of the type mentioned above. This problem is solved according to the invention by a method, a computing device, an ultrasonic sensor device, a computer program, and a computer-readable (storage) medium with the features according to the independent claims. Advantageous embodiments of the present invention are specified in the dependent claims. A method according to the invention serves to monitor an underbody area beneath a vehicle. Measurements are performed using an ultrasonic sensor device, wherein, in each measurement, at least one ultrasonic sensor is activated to emit an ultrasonic signal into the underbody area, and a sensor signal is determined that describes the temporal profile of the received ultrasonic signal. Furthermore, a reference signal is determined based on a first sensor signal determined in a first measurement. The presence of an object in the underbody area is verified by comparing a second sensor signal determined in a subsequent measurement with the reference signal. It is further provided that the first sensor signal used to determine the reference signal is scaled with a scaling function, wherein the amplitude of the scaling function varies depending on time. The method is intended to monitor the underbody area beneath the vehicle. This underbody area preferably extends from the road surface on which the vehicle is currently located to the vehicle's underbody. This allows, for example, the detection of an object in the underbody area. The method can be performed using an ultrasonic sensor device. This ultrasonic sensor device comprises at least one ultrasonic sensor. Alternatively, the ultrasonic sensor device may have at least two ultrasonic sensors. The ultrasonic signal can be emitted into the underbody area using the at least one ultrasonic sensor.This emitted ultrasonic signal, which may be reflected off the ground or road surface and / or the vehicle's underbody, can then be received by the same ultrasonic sensor or a different ultrasonic sensor. The ultrasonic sensor can have a diaphragm that can be excited to mechanical vibrations by a transducer element, in particular a piezoelectric element. This excites the emission of the ultrasonic signal. To receive the ultrasonic signal, the vibration of the diaphragm caused by the ultrasonic signal can be detected by the transducer element and output as a sensor signal. Measurements are continuously performed with the ultrasonic sensor device. During each measurement, the ultrasonic signal is emitted and received. A sensor signal is then determined based on the received ultrasonic signal.The sensor signal can be a raw signal. It can also be a raw signal that is subsequently filtered and / or amplified. Furthermore, the sensor signal can be an envelope or curve of the potentially amplified and / or filtered raw signal. In the first measurement, the reference signal is determined based on the initial sensor signal. This reference signal can be stored and serves as a reference for subsequent measurements. In a second measurement, taken immediately after the first, the second sensor signal can then be determined. To check whether an object is located in the underbody area, the second sensor signal can be compared with the reference signal. For example, depending on the measurement setup, it can be checked whether the second sensor signal exceeds or falls below the reference signal. This allows for the detection of any deviation between the current or second measurement and the reference, and potentially leads to the conclusion that an object is located in the underbody area. According to a key aspect of the present invention, the first sensor signal used to determine the reference signal is scaled by a scaling function, wherein the scaling function varies over time. This scaling function can be composed of a plurality of scaling factors. Using these scaling factors, or the scaling function itself, the first sensor signal can then be scaled accordingly to generate the reference signal. According to the prior art, the scaling function is constant over time, i.e., it does not vary. This means that the first sensor signal used to generate the reference signal is increased or decreased by a certain factor or amount. This allows the overall false-positive rate and the sensitivity of the detection to be varied and optimized depending on the system or vehicle.According to the present invention, it is taken into account that, for example, due to the installation angle of the at least one ultrasonic sensor, significantly more ground reflections can occur in certain distance or time ranges than in other ranges. Additionally, depending on the nature of the subfloor, high reflections occur in certain distance or time ranges. These interfering echoes can cause highly reflective objects to produce only a slight increase in amplitude, while, conversely, weakly reflective objects produce a significant reduction in amplitude. In other areas where fewer interfering echoes occur, the opposite relationship is observed. This can now be taken into account by varying the scaling function as a function of time and thus as a function of the distance ranges.This enables reliable detection of objects in the underbody area. Preferably, the scaling function used to scale the initial ultrasonic signal is non-linear with respect to time. As previously explained, a constant scaling function, or a scaling function that remains constant over time, leads to suboptimal detection in terms of robustness and sensitivity. A solution to this problem is the use of a non-constant scaling function to generate the reference signal, which serves as a threshold for detecting objects in the underbody area. In addition to a linear scaling function, a non-linear scaling function is particularly suitable. This scaling function can then be adapted to the vehicle's design, the installation position and / or angle of the at least one ultrasonic sensor, and / or the road surface characteristics. In principle, it is also possible to provide multiple scaling functions.It is also possible to predefine a number of scaling functions and select one of these depending on the application. Overall, this can improve the monitoring of the underbody area. In one embodiment, the scaling function is determined depending on the installation position of the at least one ultrasonic sensor and / or depending on the surface and / or the design of the vehicle's underbody. The variable scaling function for generating the reference signal, which serves as the detection threshold, allows for improved adaptation to different vehicle models. The installation position and / or angle of the at least one ultrasonic sensor can be taken into account. Furthermore, the design of the vehicle's underbody can be considered. Depending on the measurement, the emitted ultrasonic signal may be reflected by the vehicle's underbody. The non-linear scaling function accounts for the fact that this underbody can exhibit different reflection properties depending on the vehicle model. Furthermore, the system can take into account the reflective properties of the road surface or the ground on which the vehicle is currently located. This road surface can vary in composition. For example, it may be asphalt or paved with cobblestones. It may also consist of a gravel path or a grass surface. These different types differ significantly in their reflective properties. Current weather conditions can also be considered. For example, the road surface may be wet or dry. It may also be covered with ice or snow. In particular, the system can be designed to detect the reflective properties of the road surface based on the initial sensor signal.Depending on this, the scaling function can then be selected. This makes it possible to specifically adapt the monitoring of the underbody area to the vehicle model and / or the environmental conditions. In a further embodiment, the first and second measurements are performed as direct measurements, in which the ultrasonic signal is emitted by the at least one ultrasonic sensor and the ultrasonic signal reflected in the underbody area is received. In the direct measurement, the at least one ultrasonic sensor, or the same ultrasonic sensor, is used as both transmitter and receiver. The first measurement can be performed, in particular, when the vehicle is parked or stops. In this case, it can be assumed that an object is located in the underbody area. The first measurement thus serves as the reference for the condition that an object is located in the underbody area. It may be necessary to detect highly reflective objects in the underbody area.In this case, the scaling function can be generated such that the amplitudes of the reference signal are increased compared to the amplitudes of the first sensor signal. If a highly reflective object is present in the underbody area, the second sensor signal will typically have a higher amplitude than the reference signal. If the second sensor signal, which is determined, for example, before the vehicle starts moving, exceeds the reference signal, it can be assumed that a highly reflective object is present in the underbody area. This enables reliable detection of highly reflective objects, such as metal objects, stones, or similar materials. In this context, it is specifically provided that the scaling function has a first region, a second region which follows the first region in time, and a third region which follows the second region in time, wherein the amplitude of the scaling function in the second region is lower than in the first region and / or the third region. Depending on time, the scaling function can have a predetermined amplitude in the first region, which decreases towards the second region. In the second region, the scaling function can have a minimum. The amplitude of the scaling function can then increase again from the second region to the third region. With such a scaling function, a lower sensitivity can be achieved at the beginning of the signal than in the middle of the time domain.The first range ensures that interference from reflections of the ultrasound signal from the ground is not taken into account. Higher sensitivity can be achieved in the second, or middle, range, which is typically less affected by interference. The high scaling in the third range significantly reduces or completely prevents the detection of objects located outside the underbody area. This results in a substantial overall improvement in the coverage and performance of underbody monitoring. In another embodiment, for the detection of weakly reflective objects in the underbody area, the scaling functions are determined such that the amplitude of the reference signal is lower than the amplitude of the first sensor signal in at least one range. It may also be the case that weakly reflective objects in the underbody area are to be detected. Such weakly reflective objects could be, for example, animals with fur that attenuate the ultrasound signal. A weakly reflective object could also be a person, such as a child, wearing appropriate clothing. In this case, it can be checked whether the sensor signal describing the ultrasound signal reflected by the object exhibits a reduction in amplitude caused by the weakly reflective object.In this case, the scaling function can be chosen so that the reference signal has at least a partially lower amplitude than the first sensor signal. If the second sensor signal describes the reflected ultrasound signal from a weakly reflective object, the second sensor signal, or a portion of it, will be below the reference signal. This allows even weakly reflective objects to be reliably detected. According to a further embodiment, the first and second measurements are performed as indirect measurements, in which the ultrasonic signal is emitted by a first ultrasonic sensor and received by a second ultrasonic sensor. In this case, the first ultrasonic sensor is used as the transmitter, and the second ultrasonic sensor is used as the receiver. Objects in the underbody area can also be detected by this indirect measurement, which essentially simulates a light barrier. It is specifically designed that the scaling function is determined such that the amplitude of the reference signal is lower than the amplitude of the first sensor signal, at least within a range corresponding to the time period for direct transmission of the ultrasonic signal from the first to the second ultrasonic sensor. If an object is located in the underbody area, the direct transmission of the ultrasonic signal from the first to the second ultrasonic sensor is attenuated or blocked. In this case as well, the reference signal is determined to have a lower amplitude, at least partially, compared to the first sensor signal. Therefore, if an object is located in the underbody area or in the area between the first and second ultrasonic sensors, the transmitted ultrasonic signal is blocked or attenuated.This reduces the amplitude of the second sensor signal. If the second sensor signal falls below the reference signal, an object in the underbody area can be reliably detected using indirect measurement. The installation positions of the first and second ultrasonic sensors are known. From this, the transmission time of the ultrasonic signal can be determined. This transmission time correlates with the shortest distance between the first and second ultrasonic sensors. In this time range, the reference signal can have a higher amplitude than in other areas of the reference signal. Overall, however, the reference signal or the scaling function must be selected so that the amplitude of the reference signal is lower than the amplitude of the first sensor signal.This allows objects located between the first and second ultrasonic sensors to be reliably detected. Preferably, the first measurement is taken after the vehicle has been parked, and the second measurement is taken before the vehicle is driven again. When parking, the vehicle can, for example, be parked in a designated parking space or area. Once the vehicle is moved to this space and parked there, it can be assumed that there is no object in the underbody area, as the vehicle has previously driven over this area. Thus, the first sensor signal describes the state in which there is no object in the underbody area. The second measurement can then be taken before the vehicle is driven again or departs. Here, by comparing the second sensor signal with the reference signal, it can be verified whether an object is present in the underbody area. Furthermore, it is advantageous if, during scaling, the respective amplitude values ​​of the first sensor signal are multiplied by certain factors and / or predetermined offset values ​​are added to the amplitude values. The factors or scaling factors can have positive or negative values. A computing device according to the invention for an ultrasonic sensor device for a vehicle is configured to carry out a method according to the invention and its advantageous embodiments. A computing device according to the invention for an ultrasonic sensor device of a vehicle is configured to carry out a method according to the invention and its advantageous embodiments. The computing device can include a processor. The computing device can be formed by an electronic control unit (ECU) of the vehicle. It can also be provided that the computing device is formed by integrated sensor electronics of the ultrasonic sensor. These sensor electronics can be configured as an application-specific integrated circuit. An ultrasonic sensor device according to the invention for a vehicle comprises a computing device according to the invention and at least one ultrasonic sensor. It can also be provided that the ultrasonic sensor device has at least two ultrasonic sensors. The ultrasonic sensors can, for example, be mounted at different installation positions on the underbody of the vehicle. In principle, both direct and indirect measurements can be carried out with the ultrasonic sensor device. The ultrasonic sensor device can be part of a vehicle's driver assistance system. This system can preferably be designed to warn the driver or vehicle user if an object is detected in the underbody area. It can also be configured to prevent the vehicle from continuing to drive or starting as soon as an object is detected in the underbody area. A vehicle according to the invention comprises a driver assistance system or an ultrasonic sensor device according to the invention. The vehicle can, in particular, be designed as a passenger car. The invention also includes a computer program comprising instructions which, when the program is executed by a computing device, cause it to execute a method according to the invention and its advantageous embodiments. Another aspect of the invention relates to a computer-readable (storage) medium comprising instructions which, when executed by a computing device, cause it to execute a method according to the invention and its advantageous embodiments. The preferred embodiments and their advantages presented with reference to the method according to the invention apply accordingly to the computing device according to the invention, to the ultrasonic sensor device according to the invention, to the driver assistance system according to the invention, to the vehicle according to the invention, to the computer program product according to the invention, and to the computer-readable (storage) medium according to the invention. Further features of the invention are evident from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified but also in other combinations without departing from the scope of the invention. Thus, embodiments that are not explicitly shown and explained in the figures but can be derived and generated from the explained embodiments by separate combinations of features are also to be considered as encompassed and disclosed by the invention. Embodiments and combinations of features that do not exhibit all the features of an originally formulated independent claim are also to be considered disclosed.Furthermore, embodiments and combinations of features, in particular those set out above, are to be considered disclosed which go beyond or deviate from the combinations of features set out in the cross-references of the claims. The invention will now be explained in more detail with reference to preferred embodiments and the accompanying drawings. Figure 1 shows a vehicle which has an ultrasonic sensor device for monitoring an underbody area beneath the vehicle, wherein the ultrasonic sensor device comprises an ultrasonic sensor; Figure 2 shows a time course of a second sensor signal from the ultrasonic sensor and a reference signal; and Figure 3 shows a time course of a scaling function for generating a reference signal. In the figures, identical or functionally equivalent elements are given the same reference symbols. Fig. 1 shows a schematic representation of a vehicle 1 from the rear. The vehicle 1 is designed as a passenger car. The vehicle 1 includes a driver assistance system 2 and an ultrasonic sensor device 3. The ultrasonic sensor device 3 can be used to monitor an underbody area 6 beneath the vehicle 1. In particular, the ultrasonic sensor device 3 can be used to check whether an object 7 is located in the underbody area 6. In the present embodiment, the ultrasonic sensor device 3 comprises an ultrasonic sensor 4. As shown schematically in Fig. 1, the ultrasonic sensor 4 can be arranged in a region of the underbody 8 of the vehicle 1. This ultrasonic sensor 4 can emit an ultrasonic signal in the underbody region 6. In this example, the emitted ultrasonic signal is then reflected by the ground 9 or road surface on which the vehicle 1 is currently located and returns to the ultrasonic sensor 4. A sensor signal can then be determined from the reflected ultrasonic signal using the ultrasonic sensor device 3. Furthermore, the ultrasonic sensor device 3 includes an electronic computing unit 5, which is connected to the ultrasonic sensor 4 for data transmission. The computing unit 5 can control the ultrasonic sensor 4 to emit the ultrasonic signal. In addition, the sensor signal can be transmitted from the ultrasonic sensor 4 to the computing unit 5. The computing unit 5 can, for example, be an electronic control unit (ECU). With the aid of the driver assistance system 2, the vehicle 1 can be maneuvered at least semi-autonomously. In order to enable automatic starting with the driver assistance system 2, it is necessary to monitor the underbody area 6 beneath the vehicle 1 or to ensure that no object 7 is located in the underbody area 6. Objects 7 may be in the form of animals or children under the vehicle 1, and it is also possible that objects 7 are located under the vehicle 1 that could damage the vehicle 1 when starting. The present arrangement is to perform an initial measurement using the ultrasonic sensor device 3. This initial measurement can be performed before the vehicle 1 is parked. Based on this initial measurement, or rather the initial sensor signal, a reference signal 10 can then be determined. At a later time, particularly before the vehicle 1 departs, a second measurement can be performed, thereby determining a second sensor signal 11. This second sensor signal 11 can then be compared with the reference signal 10. In this way, it can be verified whether an object 7 is located in the underbody area 6. Figure 2 shows a schematic representation of a reference signal 10 and a second sensor signal 11. The abscissa represents time t or distance, and the ordinate represents amplitude A. To generate the reference signal 10, the first sensor signal, which was determined at the initial time point or before the vehicle 1 was switched off, was scaled using a corresponding scaling function 12. In the example shown in Figure 2, the first sensor signal was scaled with a constant scaling function 12 to generate the reference signal 10. It is already noticeable that in this case, the magnitude of the deviations between the reference signal 10 and the current measurement or the second sensor signal 11 varies considerably, depending on the amplitude value of the reference signal 10.An evaluation of the deviation across all distance ranges or time ranges is not easily carried out, which is why, for object detection with a constant scaling factor for the direct measurement with highly reflective objects 7 shown, only the exceedance of the reference curve by the current measurement can be used. The present application proposes using a non-linear scaling function 12 to scale the first sensor signal and generate the reference signal 10 from it. This non-linear scaling ensures that the amplitude deviations have a normalized value, independent of the amplitude A of the reference signal 10. Figure 3 shows an example of such a non-linear scaling function 12. The abscissa represents time t or the distance, and the ordinate represents the amplitude P. It can be seen that the scaling function 12 has a first region 13, a second region 14, and a third region 15.Thus, in the first region 13, the high amplitude P of the scaling function 12 results in lower sensitivity than in the second region 14, where the scaling function 12 has a lower amplitude P compared to the first region 13. This increases robustness against ground reflections, which typically occur in the first region 13 or for a time period associated with the first region 13. High sensitivity is achieved in the middle, second region 14, which is typically less disturbed. The high scaling in the rear region, or third region 15, can, for example, significantly reduce or completely prevent the detection of objects located outside the subsurface region 6.The non-linear scaling function 12 for determining the reference signal 10 thus has several advantages, which together result in a significant improvement in the coverage and performance of the ultrasonic sensor device 3. In the previously described example, a direct measurement was performed with a single ultrasonic sensor 4 to detect highly reflective objects 7 in the underbody area 6. It can also be intended that the ultrasonic sensor device 3 should be used to detect weakly reflective objects 7 in the underbody area 6. In this case, the scaling function 12 or the reference signal 10 can be determined such that the reference signal 10 has a lower amplitude A than the first sensor signal. If the second sensor signal 11 is now below the reference signal 10, it can be assumed that a weakly reflective object, such as an animal or child, is located in the underbody area 6. Furthermore, the ultrasonic sensor device 3 may be configured to include a first ultrasonic sensor and a second ultrasonic sensor. The ultrasonic signal is emitted by the first ultrasonic sensor and received by the second ultrasonic sensor. In this case, the scaling function 12 or the reference signal 10 can also be determined such that the amplitude A of the reference signal is lower than the amplitude of the first sensor signal. In this case, the scaling function 12 can be configured to exhibit higher sensitivity over a time interval corresponding to the direct transmission time of the ultrasonic signal from the first ultrasonic sensor to the second ultrasonic sensor. Depending on the measurement method used, the reference signal can be adapted to different conditions by using the non-linear scaling function 12. For example, the scaling function can be adapted to the corresponding vehicle model, the design of the underbody 8 of the vehicle 1, the installation position and / or the installation angle of the at least one ultrasonic sensor 4, and the properties of the ground 9.

Claims

Method for monitoring an underbody area (6) beneath a vehicle (1), in which measurements are carried out using an ultrasonic sensor device (3), wherein at least one ultrasonic sensor (4) is activated in each of the measurements to emit an ultrasonic signal into the underbody area (6) and a sensor signal is determined which describes a temporal profile of the received ultrasonic signal, wherein a reference signal (10) is determined on the basis of a first sensor signal determined in a first measurement and the presence of an object (7) in the underbody area (6) is checked by comparing a second sensor signal (11) determined in a subsequent, second measurement with the reference signal (10), characterized in that the first sensor signal for determining the reference signal (10) is scaled with a scaling function (12).where the amplitude (P) of the scaling function (12) varies depending on time (t). Method according to claim 1, characterized in that the scaling function (12) with which the first sensor signal is scaled is non-linear as a function of time (t). Method according to claim 1 or 2, characterized in that the scaling function (12) is determined depending on an installation position of the at least one ultrasonic sensor (4) and / or depending on a base (9) and / or depending on a design of the underbody (8) of the vehicle (1). Method according to one of the preceding claims, characterized in that the first measurement and the second measurement are carried out as direct measurements in which the ultrasound signal is emitted with the at least one ultrasound sensor (4) and the ultrasound signal reflected in the underbody area (6) is received again. Method according to claim 4, characterized in that the scaling function (12) has a first area (13), a second area (14) which follows the first area (13) in time, and a third area (15) which follows the second area (14) in time, wherein the amplitude (P) of the scaling function (12) in the second area (14) is less than in the first area (13) and / or third area (15). Method according to claim 4, characterized in that, for the detection of weakly reflective objects (7) in the subfloor area (6), the scaling function (12) is determined such that an amplitude (A) of the reference signal (10) is less than an amplitude (A) of the first sensor signal at least in one area. Method according to one of claims 1 to 3, characterized in that the first measurement and the second measurement are carried out as indirect measurements, in which the ultrasound signal is emitted with a first ultrasound sensor (4) and the ultrasound signal is received with a second ultrasound sensor (4). Method according to claim 7, characterized in that the scaling function (12) is determined such that an amplitude (A) of the reference signal (10) is less than an amplitude (A) of the first sensor signal, at least in a range which is associated with a time period for a direct transmission of the ultrasound signal from the first ultrasound sensor (4) to the second ultrasound sensor (4). Method according to one of the preceding claims, characterized in that the first measurement is carried out after the vehicle (1) has been parked and the second measurement is carried out before the vehicle (1) continues driving. Method according to one of the preceding claims, characterized in that during scaling, respective amplitude values ​​of the first sensor signal are multiplied by certain factors and / or predetermined offset values ​​are added to the amplitude values. Computing device (5) for an ultrasonic sensor device (3) for a vehicle (1), wherein the computing device (5) is designed to perform a method according to one of the preceding claims. Ultrasonic sensor device (3) for a vehicle (1) with a computing device (5) according to claim 11 and with at least one ultrasonic sensor (4). Computer program comprising instructions which, when the program is executed by a computing device (5), cause it to execute a method according to any one of claims 1 to 10. Computer-readable (storage) medium comprising instructions which, when executed by a computing device (5), cause it to execute a method according to any one of claims 1 to 10.

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