DE102017123901B4 - Method for collecting environmental information - Google Patents

Abstract

Method for detecting environmental information in the area of a moving object using a radar system (1), comprising the following steps:
- Acquiring spatially resolved radar information at different times (S10);
- Detecting movement information of the moving object (S11);
- Calculating accumulated radar information by correctly adding up the spatially resolved radar information received at different times or information derived therefrom, taking into account the movement information of the moving object (S12); characterized in that when adding up the spatially resolved radar information, only the radar information that results from reflections from static, non-moving surrounding objects is taken into account.

Description

The invention relates to a method for acquiring environmental information using a radar system and a radar system for acquiring environmental information.

Radar techniques are known from the prior art, by means of which high-resolution radar information, hereinafter also referred to as a radar image, can be obtained. Such high-resolution radar images are particularly relevant for autonomous driving of vehicles. In particular, synthetic aperture radar (SAR) enables high spatial resolution. The calculation of high-resolution radar information, especially in SAR radar systems, requires a very high computational effort because the radar image is calculated pixel by pixel based on measurements taken at different locations as the object moves. It is important that the object's path of movement, also known as its trajectory, is known as best as possible.

Radar systems with a real aperture are also known (RAR: Real Aperture Radar). In contrast to SAR radar systems, in RAR radar systems the antenna aperture is not increased arithmetically, so that significantly less computer power is required to record the surrounding information, but losses in the resolution of the radar image must be accepted.

Pamphlet DE 10 2014 223 432 A1 discloses a radar device and a method for generating high-resolution environmental information.

Based on this, it is the object of the invention to provide a method for acquiring environmental information that enables the most complete representation of the environment with reduced computing effort.

The task is solved by a method with the features of independent patent claim 1. Preferred embodiments are the subject of the subclaims. A radar system for recording environmental information is the subject of independent patent claim 13.

• Zunächst werden ortsaufgelöste Radarinformationen zu unterschiedlichen Zeitpunkten erfasst. Diese Radarinformationen resultieren vorzugsweise aus mehreren Messungen bzw. Messzyklen, die zeitlich nacheinander vollzogen werden. Während dieser Messzyklen bewegt sich das Objekt vorzugsweise weiter, so dass sich das die Messungen vollziehende Radarsystem an unterschiedlichen Orten (bezogen auf einen geographischen Referenzpunkt) befindet.

According to a first aspect, the invention relates to a method for detecting environmental information in the area of a moving object, for example a vehicle, using a radar system. The procedure includes the following steps:

• First, spatially resolved radar information is recorded at different times. This radar information preferably results from several measurements or measurement cycles that are carried out one after the other. During these measurement cycles, the object preferably moves further, so that the radar system carrying out the measurements is at different locations (relative to a geographical reference point).

In addition, movement information of the moving object is recorded. In particular, this movement information indicates the movement path (also called trajectory) on which the object moves. The movement information can come, for example, from an odometry system of a vehicle that has one or more sensors for detecting the movement information.

Accumulated radar information is then calculated by correctly adding up the spatially resolved radar information received at different times or information derived therefrom, taking into account the movement information of the moving object. In other words, the spatially resolved radar information obtained from different measurements or measurement cycles is superimposed in the correct position by compensating for the movement of the object and the radar information from the different measurements or measurement cycles assigned to the respective discrete location areas (e.g. correlating with grid areas of a radar grid) is added up. The environmental information can then advantageously be derived from this accumulated radar information, for example using suitable image or pattern recognition algorithms.

The main advantage of the method according to the invention is that the accumulated radar information represents the environment more completely than the radar information of the respective individual measurements, since detections occurring in a specific location area with a lower signal strength, which come, for example, from a surrounding object with a small reflecting area, are due to the addition are amplified, whereas detections that only occur sporadically due to noise typically do not accumulate because they usually do not occur in successive measurements in the same spatial area. This means that, compared to a SAR radar system, environmental information can be determined with less computational effort, which can be used, for example, to distinguish between trafficable and non-trafficable surfaces, for curb classification (e.g. height of the curb). or can be used to classify the road surface (e.g. asphalt, cobblestones, etc.).

According to one embodiment, the spatially resolved radar information includes spatially resolved power density spectral values that contain information as to how much power of a radar signal was reflected at a specific discrete spatial area. The accumulated radar information thus contains information about how much power of the radar signal was reflected in a specific discrete location area over several measurements or measurement cycles. This enables better interpretability of the environment based on the accumulated radar information.

According to one embodiment, the spatially resolved radar information is raw radar data obtained at an output interface of a fast Fourier transform unit (FFT unit). These raw radar data are spatially discrete and preferably structured according to a multi-dimensional data structure (also called radar cube). To sum up, the radar information assigned to a discrete location area is added up with radar information from the same discrete location area obtained from further measurements or measurement cycles. Before the summation, this radar information is spatially compensated based on the movement information, i.e. the movement in space caused by the movement of the object is arithmetically canceled. In other words, the radar information obtained from different measurements or measurement cycles is, so to speak, “superimposed”.

According to one exemplary embodiment, the accumulated radar information is calculated in such a way that radar information recorded at different times, i.e. in measurements or measurement cycles carried out one after the other, which each result from reflections in a specific, discrete spatial area, is added up. As a result, even reflections from stationary surrounding objects with a small reflection area lead to significant values in the accumulated radar information, making the static environment in the area of the moving object easier to detect.

According to one exemplary embodiment, amounts of the spatially resolved radar information are summed up, i.e. an incoherent summation is carried out without taking phase information into account. Alternatively, the spatially resolved radar information can be summed up taking the phase of complex radar information into account, i.e. a coherent summation is carried out.

According to one embodiment, the accumulated radar information is two-dimensional or three-dimensional information. In other words, the environmental information may be captured either in a horizontal or substantially horizontal plane (e.g. based on azimuth and range as parameters) or three-dimensional (e.g. based on azimuth, elevation and range as parameters) using the accumulated radar information.

According to one embodiment, the radar system includes a real aperture radar. This means that the computing power required to record the environmental information can be significantly reduced.

According to one exemplary embodiment, when adding up the spatially resolved radar information, only the radar information that results from reflections from static, non-moving surrounding objects is taken into account. Since moving environmental objects in the radar information obtained in different measurements or measurement cycles would possibly be assigned to different discrete location areas, these would worsen the detection accuracy, so that preferably only radar information is used whose Doppler shift information indicates a stationary detection.

According to one embodiment, the spatially resolved radar information is subjected to no or substantially no filtering based on a lower threshold or a lower threshold curve before summing. As a result, surrounding objects with a low radar return cross section can also be detected by accumulating the radar information caused by them, which is advantageous, for example, in road detection.

According to one exemplary embodiment, when calculating the accumulated radar information, compensation for the antenna gain in azimuth and/or elevation is carried out. This makes it possible to eliminate the differences in the amounts of the spatially resolved radar information resulting from the direction-dependent antenna gain.

According to one embodiment, when calculating the accumulated radar information, a distance-related decrease in the leis the recorded radar information is compensated. In this way, it can be achieved that the attenuations in the amounts of radar information resulting from the free space attenuation, which result from distant surrounding objects, are eliminated.

According to a further aspect, the invention relates to a computer program product for acquiring environmental information by means of a radar system, the computer program product comprising a computer-readable storage medium with program instructions, the program instructions being executable by a processor in order to cause the processor to carry out a method according to one of the preceding exemplary embodiments to carry out.

• - zumindest einen Radarsensor der zur Erfassung von ortsaufgelösten Radarinformationen zu unterschiedlichen Zeitpunkten ausgebildet ist;
• - eine Schnittstelle, die zum Empfang von Bewegungsinformationen des bewegten Objekts ausgebildet ist; und
• - eine Rechnereinheit, die zum Berechnen von akkumulierten Radarinformationen durch lagerichtiges Aufsummieren der an unterschiedlichen Zeitpunkten empfangenen, ortsaufgelösten Radarinformationen oder davon abgeleiteter Informationen unter Berücksichtigung der Bewegungsinformationen des bewegten Objekts ausgebildet ist.

According to a further aspect, the invention relates to a radar system for detecting environmental information in the area of a moving object, comprising:

• - at least one radar sensor which is designed to record spatially resolved radar information at different times;
• - an interface designed to receive movement information of the moving object; and
• - a computer unit which is designed to calculate accumulated radar information by summing up the spatially resolved radar information received at different times or information derived therefrom, taking into account the movement information of the moving object.

“Static” in the sense of the present invention means “stationary”, i.e., for example, a static environmental object does not move in relation to a fixed reference point in the relevant detection period. Due to the movement of the vehicle on which the radar system is provided, a relative movement can take place between the radar system and the static surrounding object.

For the purposes of the present invention, “moving object” is understood to mean, in particular, a vehicle or an aircraft or flying object (drone, satellite, etc.).

In the sense of the invention, the expressions “approximately”, “essentially” or “approximately” mean deviations from the exact value by +/- 10%, preferably by +/- 5% and/or deviations in the form of changes that are insignificant for the function .

Further developments, advantages and possible applications of the invention also emerge from the following description of exemplary embodiments and from the figures. All described and/or illustrated features, individually or in any combination, are fundamentally the subject of the invention, regardless of their summary in the claims or their relationship. The content of the claims is also made part of the description.

• 1 beispielhaft und schematisch ein Blockdiagramm eines Radarsystems;
• 2 beispielhaft ein Diagramm zur Veranschaulichung eines bei einer ersten Messung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene;
• 2a beispielhaft ein Diagramm zur Veranschaulichung eines nach der ersten Messung aus der Summationseinrichtung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene (identisch zum Diagramm aus 2);
• 3 beispielhaft ein Diagramm zur Veranschaulichung eines bei einer zweiten Messung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene;
• 3a beispielhaft ein Diagramm zur Veranschaulichung eines nach der zweiten Messung aus der Summationseinrichtung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene (identisch zum Diagramm aus 2);
• 4 beispielhaft ein Diagramm zur Veranschaulichung eines bei einer dritten Messung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene;
• 4a beispielhaft ein Diagramm zur Veranschaulichung eines nach der dritten Messung aus der Summationseinrichtung erhaltenen Leistungsdichtespektrums in einer horizontalen Raumebene (identisch zum Diagramm aus 2);
• 5 beispielhaft die den Diagrammen gemäß 2 bis 4 zugrundliegenden, ortsverteilten Reflexionspunkte; und
• 6 beispielhaft ein das Verfahren zur Erfassung von Umgebungsinformationen veranschaulichendes Blockdiagramm.

The invention is explained in more detail below using the figures and exemplary embodiments. Show it:

• 1 by way of example and schematically a block diagram of a radar system;
• 2 By way of example, a diagram to illustrate a power density spectrum obtained during a first measurement in a horizontal spatial plane;
• 2a For example, a diagram to illustrate a power density spectrum obtained after the first measurement from the summation device in a horizontal spatial plane (identical to the diagram). 2 );
• 3 By way of example, a diagram to illustrate a power density spectrum obtained in a second measurement in a horizontal spatial plane;
• 3a For example, a diagram to illustrate a power density spectrum obtained after the second measurement from the summation device in a horizontal spatial plane (identical to the diagram). 2 );
• 4 By way of example, a diagram to illustrate a power density spectrum obtained in a third measurement in a horizontal spatial plane;
• 4a For example, a diagram to illustrate a power density spectrum obtained from the summation device after the third measurement in a horizontal spatial plane (identical to the diagram). 2 );
• 5 for example, those according to the diagrams 2 until 4 underlying, spatially distributed reflection points; and
• 6 By way of example, a block diagram illustrating the method for acquiring environmental information.

1 shows, by way of example and roughly schematically, a block diagram of a radar system 1, which is arranged in a moving object, for example a vehicle. The radar system 1 has a transmission section designated TX, by means of which a radar signal is emitted into the environment at an antenna unit 2.

Furthermore, the radar system 1 includes a reception section designated RX. The reception section RX is coupled to at least one, preferably several, antenna units 2 and can have one or preferably several reception paths. For example, an amplifier 3, a mixer 4 for frequency conversion of the received signal, a filter unit 5, for example a low-pass filter or a band-pass filter, etc. can be provided in the respective reception paths. In addition, one or more analog-digital converters (A/D converters) 6 are provided in the receiving section, by means of which the received analog signals are converted into digital signals. These digital signals are then subjected to digital signal processing, in particular a frequency transformation, particularly preferably a fast Fourier transformation (FFT unit 7).

The radar system 1 is in particular a radar with a real aperture, in which the antenna-related aperture is not synthetically increased, i.e. artificially increased by computational measures. In other words, it is preferred not to use a synthetic aperture radar (SAR) system.

At the output of the FFT unit 7, for example, raw radar data is available, which is preferably structured according to a multi-dimensional, for example cube-like, data structure. In the field of radar technology, this data structure is referred to as a so-called “radarcube”. The data structure can, for example, contain spatially resolved radar information, for example based on a two- or three-dimensional coordinate system (for example Cartesian coordinate system or polar coordinate system). In addition, the data structure can contain information regarding the Doppler shift of the respective received radar signal. The values stored in the data structure can in particular be spatially resolved power density values, i.e. indicate the reflected, spectral power density at the respective reflection location.

2 shows an example of the power density values obtained from an individual measurement of the radar system 1, which are due to reflections at several T-shaped reflection points 5 be received. The power density values determined in a horizontal plane (power density values for different distances and azimuth angles) were entered in a Cartesian coordinate system. The different gray colors reflect the magnitude of the respective power density value, whereby the darker the gray color, the higher the magnitude of the respective power density value. The moving object, in particular the vehicle on which the radar system is provided, is arranged at the origin of the coordinate system (x=0; y=0).

In order to be able to provide data at the output of the radar system that is as sensor-independent as possible, the radar information determined by the radar system is transferred to a stationary radar map, also known as a radar grid. In radar systems known from the prior art, the location-dependent radar information is transmitted to the radar map, taking into account movement data of the moving object, for example obtained from one or more sensors of a vehicle odometry system. Weak detections, i.e. detected reflections with a power density value below a certain threshold value, are neglected in order to only obtain significant delegations in the radar map.

In order to improve the detection result and, in particular, to be able to better represent static environmental information, the location-dependent radar information obtained from the FFT unit 7 is not transferred directly to the radar map (i.e. after the previously described threshold value filtering), but rather the location-dependent radar information is added up over several measurements .

For this, as in 1 shown, a summation device 8 is provided, which sums up the spatially resolved radar information (ie, for example, information contained in the radar cube) over several measurement cycles, ie over several transmit-receive cycles of the radar system 1. This results in accumulated radar information, which can be supplied to a detection system 9, for example, in order to be able to detect environmental information based on the accumulated radar information.

The summation device 8 is designed to add up the spatially resolved radar information from different measurement cycles, preferably from immediately successive measurement cycles, in the correct position. In other words, radar information determined at different times, which is assigned to a specific discrete location area where the reflection occurred, is summed up. The summation can be a complex summation be, ie the spatially resolved radar information is complex quantities that are added up in the correct amount and phase (coherent summation). Alternatively, only a summation in terms of amount can take place, that is, either the spatially resolved radar information is only available as amount information or, in the case of complex, spatially resolved radar information, it is only added up in terms of amount (incoherent summation).

In the event that only static, non-moving objects are to be detected in the surrounding area of the radar system 1, only the radar information that was recognized as stationary objects (velocity v=0) due to the Doppler shift can be used. In other words, only the area of radar information from the radar cube to which the speed v=0 is assigned is used to detect the environment. This can, for example, be a matrix-like area in which the radar information is stored according to its azimuth angle and the radial distance.

By summing up the spatially resolved radar information in the correct position, temporary, non-static environmental objects are filtered out, since these are located at different locations in several consecutive measurements and are therefore assigned to different areas in the radar cube. However, static environmental objects that always fall into the same area of the radar cube are added up over several measurements so that they are easier to detect. This allows a more complete capture of the environmental information in the area around the radar system.

As previously described, shows 2 the power density values obtained from a first individual measurement (ie first measurement cycle) of the radar system 1, which are due to reflections at several reflection points arranged in a T-shape 5 be received. These are fed to the summation device 8. 2a shows the information provided by the summation device 8 after the first individual measurement. Since it is assumed that the summation device 8 did not contain any information before the first individual measurement that is added to the spatially resolved radar information of the first individual measurement, the in 2a The spatially resolved radar information shown is identical to the spatially resolved radar information 2 .

3 shows the radar information (power density values) obtained from a second individual measurement, which was determined after the first individual measurement and which in turn is based on reflections at several T-shaped reflection points 5 be received. Through the summation device 8, the in 2 radar information shown with that of the 3 added up in the correct position, ie while compensating for the movement of the object on which the radar system 1 is arranged. The result of the summation is in 3a shown.

4 shows the radar information (power density values) obtained from a third individual measurement, which was determined after the second individual measurement and which in turn is due to reflections at several reflection points arranged in a T-shape 5 be received. The summation device 8 now calculates the in 2 until 4 The radar information shown is added up in the correct position, that is, while compensating for the movement of the object on which the radar system 1 is arranged. The result of the summation of the individual measurements is in 4a shown.

It is understood that between the in 2 to 4 As shown in the individual measurements shown, a large number of further individual measurements may be present in accordance with the accumulated radar information 4a to obtain.

How out 4a As can be seen, the correct addition of the spatially resolved radar information results in an increasingly sharper radar image in which the in 5 The T-shaped arrangement of the reflection points shown becomes increasingly visible.

Preferably, the spatially resolved radar information can be summed up while compensating for the antenna characteristics. As is known, antennas have a direction-dependent antenna gain, i.e. the antenna gain in a first spatial direction can deviate from the antenna gain that is present in a second spatial direction, which deviates from the first spatial direction, for example by a certain angular difference in azimuth and/or elevation. By moving the radar system 1 relative to an environmental object to be detected, this environmental object can be detected in a changed spatial direction in which the receiving antenna of the radar system 1 has a changed antenna gain. In order to compensate for the influence of the changed antenna gain, the spatially resolved radar information to be summed up can be modified based on information regarding the antenna gain. This modification may be made based on two-dimensional or three-dimensional antenna characteristic information depending on whether two-dimensional or three-dimensional environmental information is being acquired.

Alternatively or additionally, the spatially resolved radar information can be summed up while compensating for the free field attenuation. As is known, received radar signal components that result from more distant reflections are attenuated more strongly than radar signal components that result from reflections in the near field due to the longer propagation path. In order to compensate for the influence of the free field attenuation, the accumulating, spatially resolved radar information can be modified based on information about the distance of the surrounding object causing the reflection.

6 schematically shows a block-based flowchart of a method for acquiring environmental information in the vicinity of a moving object.

In step S10, spatially resolved radar information is first received at different times. This spatially resolved radar information can, for example, result from several individual measurements or measurement cycles carried out one after the other.

In addition, movement information of the moving object is recorded (S11). This movement information can be obtained, for example, from a vehicle odometry system. Based on this movement information, it is possible to compensate for the movement of the object in space during the subsequent summation of the radar information.

In step S12, accumulated radar information is then calculated by adding up the spatially resolved radar information or information derived therefrom (for example through the aforementioned compensations for the direction-dependent antenna gain and/or the free space attenuation) taking into account the movement information of the moving object.

The invention has been described above using exemplary embodiments. It is understood that numerous changes and modifications are possible without departing from the scope of protection defined by the patent claims.

Reference symbol list

1

Radar system

2

Antenna unit

3

amplifier

4

mixer

5

Filter unit

6

A/D converter

7

FFT unit

8th

Summation device

9

Environment detection system

TX

Transmitting unit

RX

Receiving unit

Claims (13)

Method for detecting environmental information in the area of a moving object using a radar system (1), comprising the following steps: - detecting spatially resolved radar information at different times (S10); - Detecting movement information of the moving object (S11); - Calculating accumulated radar information by correctly adding up the spatially resolved radar information received at different times or information derived therefrom, taking into account the movement information of the moving object (S12); characterized in that when adding up the spatially resolved radar information, only the radar information that results from reflections from static, non-moving surrounding objects is taken into account. Procedure according to Claim 1 , characterized in that the spatially resolved radar information includes spatially resolved power density spectral values which contain information as to how much power of a radar signal was reflected at a specific discrete spatial area. Procedure according to Claim 1 or 2 , characterized in that the spatially resolved radar information is raw radar data that is obtained at an output interface of a fast Fourier transformation unit (FFT unit) (7). Method according to one of the preceding claims, characterized in that the accumulated radar information is calculated in such a way that radar information recorded at different times, each resulting from reflections in a specific, discrete location area, is added up. Method according to one of the preceding claims, characterized in that amounts of the spatially resolved radar information are summed up. Procedure according to one of the Claims 1 until 4 , characterized in that the spatially resolved radar information is added up taking the phase of complex radar information into account. Method according to one of the preceding claims, characterized in that the accumulated radar information is two-dimensional or three-dimensional information. Method according to one of the preceding claims, characterized in that the radar system (1) comprises a radar with a real aperture. Method according to one of the preceding claims, characterized in that the spatially resolved radar information is subjected to no or substantially no filtering based on a lower threshold value or a lower threshold value curve before the summation. Method according to one of the preceding claims, characterized in that when calculating the accumulated radar information, compensation for the antenna gain in azimuth and/or elevation is carried out. Method according to one of the preceding claims, characterized in that when calculating the accumulated radar information, a distance-related decrease in the power of the acquired radar information is compensated for. Computer program product for detecting environmental information in the area of a moving object by means of a radar system (1), the computer program product comprising a computer-readable storage medium with program instructions, the program instructions being executable by a processor in order to cause the processor to carry out a method according to one of the preceding claims to carry out. Radar system for detecting environmental information in the area of a moving object, comprising: - at least one radar sensor which is designed to detect spatially resolved radar information at different times; - an interface designed to receive movement information of the moving object; and - a computer unit which is designed to calculate accumulated radar information by summing up the spatially resolved radar information received at different times or information derived therefrom, taking into account the movement information of the moving object; characterized in that the computer unit is further designed to only take into account the radar information that results from reflections from static, non-moving surrounding objects when summing up the spatially resolved radar information.

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