Communications: directive radio wave systems and devices (e.g. – Determining distance – Height finder
Reexamination Certificate
1999-12-08
2001-07-24
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining distance
Height finder
C342S02500R, C342S070000, C342S118000, C342S127000, C342S156000, C342S175000, C342S195000
Reexamination Certificate
active
06266005
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a radar signal processing method for estimating the height of an object above a reflecting surface.
In addition to measuring the distance to the target, it is frequently desirable if radar devices can locate objects in the azimuth and the elevation or height in order to provide a better assessment of the situation in the surveillance range. A number of realized designs are known for this. Such known realized designs as a rule are connected to an expanded aperture of the antenna arrangement, which results in a focusing of the radiation output and makes it possible to purposefully detect a segment of the total surveillance range. Subsequently, the surveillance range is divided into several solid angle segments, which make it possible to provide more exact information on the position of an object. This aperture can either be real or artificial (SAR principle). However, at times it can be difficult to reconcile with the available space for installing the antenna arrangement, especially in the frontal area of motor vehicles.
The amplitude principle or the phase-monopulse operation principle, which permits small antenna dimensions, is furthermore known for the directional resolution in radar devices. In that case, the antenna must have at least two different individual patterns, which overlap.
As a result, known solutions for locating objects within the surveillance range generally are very involved with respect to the necessary device and have disadvantages concerning the costs for the device and/or its space requirement, particularly when used in motor vehicles.
Thus, it is the object of the present invention to specify a method for processing radar signals that permit locating objects, particularly an estimation of the height of the object above a reflecting surface, even if radar devices with little complexity and little space requirement are used.
SUMMARY OF THE INVENTION
The above object generally is achieved according to the invention by a radar signal processing method for estimating the height of an object above a reflecting surface, for which: a change over time in the distance between object and radar device is determined and an intensity modulation of the received signal is measured. Thereafter, information on the object height above the reflecting surface is derived from the course of the intensity modulation over the object distance. Advantageous embodiments and modifications of the invention are disclosed.
The locating of objects with the method according to the invention occurs only on the signal processing level and permits the use of inexpensive radar devices with small dimensions, for which the antenna arrangement predetermines no directional resolution or only a rough one. In particular, it does not require a multi-beam capacity and a pivoting of the antenna diagram.
The method according to the invention is provided for use in situations where the radar device and the objects to be detected are located above an essentially level surface with reflecting characteristics for the signals transmitted by the radar device and/or the echo signals scattered back by the objects. Thus, the method according to the invention makes use of a characteristic of the aforementioned surface, which otherwise is primarily viewed as interfering. A complete specular reflection of signals at the surface is not assumed in this case. The share of object echoes in the total receiving signal, which goes back to the reflection at the surface, should only influence the sum-formation to a measurable degree. Surfaces meeting these requirements are, for example, asphaltcovered or concrete-covered road surfaces, the surfaces of bodies of water or also the surface of the earth, depending on the frequency range of the radar signals and the angle of incidence for the reflection. The degree of roughness or unevenness of the surface that can be tolerated primarily depends on the operating-wave length of the radar device and the angle of incidence.
The invention makes use of the fact that if a radar device is located above such a reflecting surface, the sensitivity of the radar device in the surveillance range shows an interference pattern, owing to the superimposition of direct signal path and reflected signal path. This effect, which can lead to signal breakdowns in the object detection because of the destructive interference points that occur during the process, is purposely utilized in the present invention for detecting and evaluating the chronological course of the intensity of echo signals.
The invention furthermore utilizes the fact that for typical uses of radar devices, particularly radar devices in motor vehicles, the primary objects of interest are those that show an essential component of the relative speed between object and radar device. This component is the result of a reduction in the distance between object and radar device, meaning objects traveling with a relative speed toward the radar device, which can include in particular oncoming vehicles or locally fixed objects. The height of the object above the road surface can provide an essential evaluation criterion for judging the relevance of such objects in a traffic situation.
Given a predetermined height of the antenna above the reflecting surface, the interference pattern is fixed per se and can be computed, simulated or measured. The requirement of having a nearly level reflecting surface for the distance ranges to be considered is generally met in most situations.
The relative movement of an object within the interference pattern of the radiation field for the antenna arrangement leads to an intensity modulation of the receiving signal to be assigned to this object. The intensity modulation pattern depends on the distance between the object and the radar device, the height of the object above the reflecting surface, as well as the value for and the direction of the relative movement and is characteristic for any combination of values for these parameters. Thus, if the interference pattern of the radiation field is specified, one of the aforementioned target parameters can be determined from the intensity modulation of the receiving signal if the other parameters are known. With a first example of a typical use of the method according to the invention, in a vehicle moving along a road surface, it is furthermore assumed that the h eight of the object above the reflecting surface does not change significantly during the evaluation time and that the relative movement between object and radar device is essentially a purely radial movement. Within the distance range and the angle sector of interest, these assumptions are normally justified for the relevant targets of a motor vehicle radar device, namely fixed obstacles or objects in the environment, preceding vehicles or oncoming vehicles. The target distance and its time-dependent changes are provided by the ability of the radar device to continuously measure the distance to an object. The height of the object as unknown variable can then be at estimated least approximately by measuring the pattern of the intensity modulation and the link to the specified interference pattern and the measured relative movement of the object. As a rule, an approximate estimation value for the height of the object is sufficient to evaluate the relevance of the object, particularly its grouping into one of several object groups.
In particular, a calculation rule can be provided for obtaining an estimated value of the object height. In that case, the distance to the object, the cycle length of the intensity modulation and the section of path traveled by the object during a cycle length can be used as input variables that provide an estimated value for the object height as starting value. Alternatively, the height can also be estimated by using a cross-referencing table rule. Finally, it is possible to skip the estimation of the object height as explicit variable by entering the measured variables into a target classifier and assigning an object directl
DaimlerChysler AG
Gregory Bernarr E.
Kunitz Norman N.
Venable
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