Deutsche Forschungsanstalt Fur Luft-und Raumfahrt E.v.

Deutsches Zentrum Fur Luft-und Raumfahrt E.v.

Wolfgang Keydel

Joao Moreira

Joao R Moreira Neto

Karl-Heinz Zeller

Helmut Suss

Reinhard Schr&ouml;der

In the inventive aircraft based or spacecraft based radar system with synthetic antenna aperture (SAR&equals;Synthetic Aperture Radar) a transmit antenna and a receive antenna are provided according to a bistatic radar, which are arranged above the earth's surface, physically separate and on different platforms of which at least one is moving, so that a relative movement results between the transmit antenna and the receive antenna. Either the transmit antenna, the receive antenna, or both antennas are designed for ambiguity suppression. The radar system according to the invention is useful particularly for the systematic imaging of the earth's surface.

Aircraft or spacecraft based synthetic aperture radar

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 phase errors caused by the atmosphere in the backscatter signal of an on-board coherent imaging radar system from radar raw data, firstly to image areas with different backscatter ratios over a predetermined period of time consecutive azimuth spectra are continuously formed. Thereupon, a frequency offset (.DELTA.F(t)) of the backscatter ratio component is obtained by determining the location of the maximum of the correlations between two respective immediately consecutively formed azimuth spectra. Then, a double integration for the difference of the frequency offset (.DELTA.F(t)) and a desired value (.DELTA.F.sub.soll) of the frequency offset is carried out, the frequency offset desired value (.DELTA.F.sub.soll) being determined either from the carrier forward velocity (V.sub.v) or by a low-pass filtering of the frequency offset (.DELTA.F(t)), and finally for standardization the result of the double integration is multiplied by a constant (2.pi./.DELTA.t) to obtain thereby the phase error (.phi..sub.e (t)).

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Hechendorf, Germany

Wolfgang Keydel