DETERMINING AN ELEVATION ANGLE OF AN ELECTROMAGNETIC SENSOR MOUNTED IN A VEHICLE
The present invention relates to a method ( 1 o ) for determining an elevation angle of an electromagnetic sensor mounted in a vehicle, wherein the method comprises the steps of exciting ( 11 ) a transmitter of the sensor with a plurality of different frequencies such that the transmitter radiates a plurality of first electromagnetic signals corresponding to the plurality of frequencies onto a target arranged in the field of view of the sensor, wherein each of the plurality of first electromagnetic signals is radiated at a different angle relative to the transmitter; receiving ( 12 ), by the sensor, a plurality of second electromagnetic signals being reflections of the first electromagnetic signals at the target; determining ( 13 - 17 ) the elevation angle of the sensor based on the second electromagnetic signals. The invention also relates to a corresponding sensor and a computer program for performing the method.
1 . A method for determining an elevation angle of an electromagnetic sensor mounted in a vehicle, the method comprising the steps:
exciting a transmitter of the sensor with a plurality of different frequencies such that the transmitter radiates a plurality of first electromagnetic signals corresponding to the plurality of frequencies onto a target arranged in the field of view of the sensor, wherein each of the plurality of first electromagnetic signals is radiated at a different angle relative to the transmitter;
receiving, by the sensor, a plurality of second electromagnetic signals being reflections of the first electromagnetic signals at the target; and
determining the elevation angle of the sensor based on the second electromagnetic signals.
2 . The method of claim 1 , wherein the step of determining the elevation angle comprises:
estimating amplitudes of the received second electromagnetic signals; and
determining the elevation angle of the sensor based on the estimated amplitudes.
3 . The method of claim 2 , wherein the step of determining the elevation angle additionally further comprises:
estimating a maximum amplitude as a function of angle of radiation or as a function of frequency based on the estimated amplitudes;
determining the elevation angle of the sensor based on the angle of radiation and/or frequency corresponding to the estimated maximum.
4 . The method of claim 3 , wherein estimating ( 16 ) the maximum of amplitude comprises:
fitting a curve to the estimated amplitudes as a function of the corresponding angles and/or frequencies; and
determining the maximum of the curve.
5 . The method of claim 1 , further comprising:
mapping at least one frequency at which one of the first plurality of electromagnetic signals is radiated to a corresponding angle of radiation of the corresponding electromagnetic signal.
6 . The method claim 2 , wherein the step of estimating amplitudes of the received second electromagnetic signals comprises:
compensating for the gain of the sensor as a function of frequency.
7 . The method claim 1 , wherein the steps of exciting the transmitter, receiving the second electromagnetic signals and determining the elevation angle are repeated N times and the elevation angle is determined as the mean of the N repetitions.
8 . The method of claim 1 , wherein the transmitter comprises an array of radiator elements.
9 . The method of claim 8 , wherein the radiator elements are excited in series, or wherein the array is excited between two radiator elements or with a feeding network and wherein the transmitter comprises a further array being shifted in elevation relative to the other array and wherein both arrays are excited simultaneously.
10 . The method of claim 2 , wherein the step of estimating amplitudes of the received second electromagnetic signals comprises:
normalizing at least a first amplitude corresponding to a first frequency based on a parameter to obtain a first normalized amplitude.
11 . The method of claim 10 , wherein the step of determining the elevation angle of the sensor comprises:
comparing at least the first normalized amplitude against values in a look-up-table stored in the sensor, wherein the look-up-table contains signal amplitude values corresponding to different radiation angles at at least the first frequency.
12 . The method of claim 11 , wherein the step of comparing comprises:
calculating a difference between at least the first normalized amplitude and the signal amplitude values contained in the look-up-table.
13 . The method of claim 12 , further comprising the step of:
estimating the location of the minimum of the difference as a function of the angle, wherein the location corresponds to the determined elevation angle.
14 . An electromagnetic sensor mountable on a vehicle, wherein the sensor is adapted to perform a method of claim 1 .
15 . A computer program comprising instructions which, when executed on the computer, cause the computer to perform a method of claim 1 .