A novel model of the platform attitude drift for SAR

Abstract

For a synthetic aperture radar (SAR) system, the platform attitude drift will affect the image qualities. During SAR system design computer simulation can be used to determine the attitude stability which can satisfy the users' demands. In the computer simulation, the first step is to create the mathematic model. General models of platform attitude drift are usually created in the time domain, such as the sinusoid one, and the model presented is done in the frequency domain. For each attitude angle (roll, yaw, pitch), the amplitude and phase values are first generated in the frequency domain. Because the attitude parameters are sampled with PRF (pulse repetition frequency) in SAR system, the maximum frequency is set to PRF/2. The amplitude may be changed with the frequency (for example, inversely proportional to the square of frequency), while the phase may be uniformly distributed between 0 to 2/spl pi/. Then the inverse Fourier transformation converts this data into the time domain. Because the phase center of the SAR's antenna is usually offset from the platform center, the attitude drift will change the slant range between the antenna's phase center and the target on the ground. These changes will affect the Doppler history in azimuth direction for the SAR. After these changes are simulated, the SAR raw data of a point target can be generated. With the general SAR procession, the simulated image is obtained. Using the analysis software, the authors can get the effects on the image qualities of the attitude drift. At last, the simulation steps and an example are also presented.