Deutsche Forschungsanstalt Fur Luft-und Raumfahrt E.v.

Deutsche Forschungsanstalt Fuer Luft- Und Raumfahrt E.v.

Joao Moreira

Wolfgang Keydel

Bernd-Peter Noichl

In a method for the detection, localization and velocity determination of moving targets from raw radar data from a coherent, single- or multi-channel image system (SAR), for representing the surface of the earth with different backscatter ratios, chronologically successive azimuth spectra are continuously formed during a defined period of time and a frequency shift of the backscatter ratio portion is obtained by determining the position of the maximum of the correlations between respectively two azimuth spectra formed chronologically directly in succession. Then the frequency shifts of the entire raw radar data set are evaluated for producing a frequency shift map. By searching for values deviating from the nominal Doppler rate in the Doppler rate map, a respective moving target is detected and the center of an image of the detected moving target is formed from this. By neglecting its radial acceleration, the tangential velocity of the moving target is determined by means of a Doppler rate taken from the Doppler rate map, and finally the radial velocity of the moving target is determined from the ratio of a length of the moving target in the range direction on the Doppler rate map and the duration of a scanning time by the antenna.

Method for the detection, localization and velocity determination of

In a method of extracting motion errors of a carrier bearing a coherent imaging radar system from radar raw data, after calculating the entire azimuth spectrum (S(f,i)) and before correlation the azimuth spectrum is broken down over the entire bandwidth into n subspectra (S.sub.1 (f,i) . . . . S.sub.n (f,i)). Associated time-consecutive n subspectra of the two azimuth spectra are correlated with each other; by means of an expected frequency shift (v.sub.er) a window width is defined. From the curve (K.sub.0 (f,i)) obtained by correlation of the azimuth spectrum and from the subcurves (K.sub.i (f,i) . . . . K.sub.n,(f,i)) obtained by subcorrelations the maximum curve value within the window is determined. From the expected frequency shift (v.sub.er) and a just calculated frequency shift (V(i)) the new frequency shift (v'.sub.er) to be expected is determined. After simultaneous performing of the method steps described above over several strips of range gates (N.sub.s), a frequency shift (V(i,m) is calculated for each strip and a matrix is formed therefrom, from which all the values equal to zero are sought, whilst from adjacent positions of each zero position a new value is interpolated.

Method of extracting motion errors of a carrier bearing a coherent

For the imaging of terrains with varied ground reflectivity, azimuth spectra continuously following each other in time are formed over a set period of time in a method for extracting motion errors of a platform carrying a coherent imaging radar system from raw radar data. By determining the position of the maximum of the correlation between two azimuth spectra formed immediately following each other in time, the frequency shift of the ground reflectivity part is obtained. Then a separation of a velocity V.sub.v (t) in the forward direction from an acceleration V.sub.b (t) in the direction of LOS of the antenna is performed by filtering and the acceleration V.sub.b (t) obtained is subjected to normalization after two-fold integration, by means of which the displacement in LOS, i.e. the motion errors in the line of sight direction of the antenna, is obtained. In contrast to GPS systems, all information is taken from the raw radar data and no ground station is required, so that the present method can be used much more flexibly and is more self-sufficient. Furthermore, in comparison with the autofocus method, the present method has a much greater band width and can be performed in real time, which cannot be realized with the autofocus method.

Method for extracting motion errors of a platform carrying a coherent

In a method for extracting motion errors of a platform carrying a coherent imaging radar system from raw radar data, azimuth spectra continuously following each other in time are formed over a set period of time for the imaging of terrains with mainly homogeneous ground reflectivities. An estimate of the ground reflectivity part is performed with a Kalman filter and with the aid of the azimuth spectra represented and system parameters entered. Then the antenna pattern part is obtained by dividing the azimuth spectrum by the estimated ground reflectivity part. By frequency filtering a separation of the drift angle .phi.(t) from the velocity V.sub.b (t) in the LOS- direction of the antenna is subsequently performed and then the velocity obtained is subjected to normalization after having been integrated, from which results the displacement in the line of sight direction of the antenna.

In a sensitivity time control device for an imaging radar system with an automatic gain control attenuator, a sensitivity time control attenuator and an analog-digital converter, output signals of the analog-digital converter are applied, via a device (20) generating an average value and a comparator device, to a control device, which has a ideal on-off relay connected with a device for determining its control parameter, an integrating member, switched downstream, and a device for calculating the operating point of the automatic gain control attenuator device. Furthermore, an n-bit digital analog converter is switched downstream of the control device, by means of the analog output voltage of which the sensitivity time control attenuator is controlled. It is possible, with the aid of the sensitivity time control device, to evaluate continuously the backscatter signal of an imaging radar system in real time, so that it is continuously possible in this way to determine an optimal sensitivity time control curve. By means of such an optimal sensitivity time control it is always possible to obtain the average value of the backscatter signal output independent of the range.

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Landsberg, Germany

Joao Moreira