SAR calibration using frequency-tunable active radar calibrators

In this paper, the impulse response function (IRF) of a synthetic aperture radar (SAR) image of frequency-tunable reference point targets [e.g., active radar calibrator (ARC)] is analyzed. The frequency-tunable ARC is an effective SAR calibration device that can yield a larger radar cross section (RCS or σ) than a corner reflector, and it displaces the response to a desirable background area for isolation from brighter man-made targets (e.g., buildings). SAR calibration accuracy is degraded by frequency shift, however, because of less correlation gain and broader IRF. We compared the theoretically derived IRF with the measurement data and drew the following conclusions: first, the location shift and the peak gain loss can be theoretically estimated within 4.2 m and 1.6 dB (one standard deviation); second, the peak calibration method is degraded by the defocused IRF; third, the integral method, which is not sensitive to defocusing, is recommended for SAR calibration; and fourth, the frequency shift should be less than 40 Hz for the satellite-based L-band SAR calibration