EP-4231052-B1 - DEVICE AND METHOD FOR CALIBRATING AT LEAST ONE PARAMETER OF A RADAR SYSTEM, AND MOBILE RADAR SYSTEM

Inventors

• PANHUBER, Reinhard

Dates

Publication Date

20260513

Application Date

20230217

Claims (10)

1. A method for calibrating at least one parameter of a radar system, comprising: receiving (110) a plurality of measurements of a radar scene; transforming (120) the plurality of measurements into a representation dependent on the parameter; and varying the parameter (130) to obtain an improved parameter with which an improved representation of the plurality of measurements has a minimum nuclear norm.
2. The method of claim 1, wherein transforming comprises selecting a single distance interval of a plurality of distance intervals of the measurements.
3. The method of claim 1 or 2, further comprising: representing the plurality of measurements such that a first dimension of the representation and a second dimension of the representation each correspond to one information from the group consisting of direction information of the measurements, velocity information of the measurements, and distance information of the measurements.
4. The method of claim 3, further comprising: removing incomplete measurements from the improved representation.
5. The method of claim 4, further comprising: varying the improved parameter to obtain a further improved parameter with which a further improved representation of the plurality of measurements has a minimum nuclear norm.
6. The method of any one of the preceding claims, wherein the at least one parameter is a parameter from the group consisting of relative velocity between radar scene and radar system, relative orientation between radar scene and radar system, position of the phase center of at least one radar antenna, and a complex-valued factor for channel balancing.
7. An apparatus (400) for calibrating at least one parameter of a radar system, comprising: an input interface (410) for receiving a plurality of measurements of a radar scene; an optimization circuit (420) configured to: transform (430) the plurality of measurements into a representation dependent on the parameter; and vary the parameter (440) to obtain an improved parameter with which an improved representation of the plurality of measurements has a minimum nuclear norm.
8. A mobile radar device (510), comprising: a radar front end for generating a plurality of measurements of a radar scene; and an apparatus according to claim 7.
9. An aircraft or spacecraft (500) having a mobile radar device (510) according to claim 8.
10. A computer program having a program code which, when executed on a programmable hardware component, causes the method according to any one of claims 1 to 6 to be carried out.

Description

Technical field Examples of implementation deal with the calibration of one or more parameters of a radar system and with a mobile radar system. background Methods for calibrating one or more parameters of a radar system are used, for example, for the robust estimation of flight and calibration parameters from clutter measurement data in moving radar systems. An example of a moving radar system is an aircraft-mounted ground-observation radar that measures both moving targets and the landscape with stationary targets as a static background, also known as clutter. To successfully detect targets, the signal processing algorithms used require calibrated measurement data. Generating this calibrated data requires precise information about the characteristics of the radar system and the platform supporting it. This information is obtained through system calibration. Calibration determines various parameters (system and process parameters), such as the current airspeed, the platform's yaw, pitch, and roll angles, the precise location of the antenna phase centers, and any other parameters necessary for channel alignment. The platform's yaw, pitch, and roll angles describe the relative orientation between the radar scene and the radar system. Separate measuring equipment, which can provide some of these parameters, such as an inertial measurement unit (IMU) for the platform's longitude information, delivers data with offset errors (caused, for example, by alignment errors during installation). Other potentially required parameters, such as the location of the antenna phase centers, can only be determined conventionally with considerable effort and directly on the ground. Such parameters are therefore advantageously estimated using measurement data from the scene being measured. This also allows for recalibration of the radar system during operation. The estimated parameters can also be used for more advanced signal processing algorithms beyond the application of calibration. These are typically model-based, meaning their performance depends on the quality of the estimated parameters. Radar scenes are extremely diverse. They can depict, for example, meadows, fields, forests, lakes, the sea, cities, roads, etc., with and without moving targets, and any combination thereof. Due to the wide range of possible radar scenes, a robust calibration procedure is required to determine the parameters. Numerous methods exist for estimating parameters. These differ, among other things, in the available measurement data used for their determination. One example of a direct method uses one or more known targets (usually point scatterers) and, in a direct minimization procedure, adjusts the required parameters using a model so that the modeled signal corresponds as closely as possible to the received signal. This allows for absolute calibration of the radar system. If no known targets are available, measurements from unknown radar scenes must be used. Absolute calibration is not possible in this case. Instead, in conventional methods, an antenna channel and the platform itself serve as reference objects. The parameters are then estimated, for example, using iterative methods or approximations. However, even here, measurement data from suitable scenes are a prerequisite for successful calibration. In particular, the presence of moving targets impairs the quality of the parameters estimated in this way. The publication EP 3 364 212 A1 refers to a method for the computer-aided processing of SAR raw data, comprising radar echoes from the ground that are the response to radar pulses transmitted by antenna elements of a radar sensor on at least one flying object moving in an azimuth direction above the ground, and wherein the radar echoes were received by antenna elements of the radar sensor, the SAR raw data containing radar echoes originating from reference targets with known radar cross-sections and positions on the ground and obtained by data acquisitions for several Channels are represented, with each channel referring to radar pulses sent by a specific antenna element and radar echoes received by a specific antenna element. Consequently, there is a need for an improved approach to calibrating a parameter of a radar system. Summary The object of the invention is to perform calibration without a reference object, as is required in the prior art, for example, by a known target or a selected antenna channel. This makes the calibration more robust, for instance, in the event of a fault occurring in the reference object itself. Furthermore, the calibration can be performed with any radar scene without requiring it to meet a specific criterion that would make it suitable for conventional calibration. To achieve this object, a method and a device for calibrating a parameter of a radar system according to claims 1 and 7 are provided. Character description Some examples of devices and/or methods are explained in more detail below with referenc