Study On Doppler Parameters Estimation Of Airborne SAR Raw Data And Imaging Algorithms

Airborne Synthetic Aperture Radar (SAR) is a kind of active remote sensor, which works in the microwave band and takes aircraft as the working platform. SAR has the whole weather and the whole day characteristics that observing two dimensions high resolution image of the object, now which has widely been applied in many fields. This paper mainly investigated the estimation methods of doppler parameters and the imaging algorithms of airborne stripe SAR.First, we go over the basic theory of SAR making a theoretical preparation for following chapters, introducing the principle of SAR, range and azimuth resolution ,range migration, principle of the stationary phase. The radar which is embedded on platform sidelooking, but the platform will be disturbed by airflow inevitably. So, the radar will have a small sloping angle, thereby, the doppler centroid that is not zero and doppler frequency rate need to be estimated from the raw echo data in order to focus in azimuth commendably. In the following parts, the paper gives some methods to estimate doppler parameters. At the doppler centroid aspect, this paper make use of Maximum value method; Energy method and autocorrelation function method to estimate doppler centroid. At the doppler frequency aspect, this paper make use of Image offset method; Time-frequency method; Minimum entropy and fractional fourier transformation method to estimate doppler frequency rate. Maximum value method is fast but not accurate, autocorrelation function method is accurate and have a good effect form radar image according to their estimate methods. Image offset method that is also fast can be applied to motion compensation, time-frequency method is intuitionistic and have a better accurate, which is applied extensively on offline. Fractional fourier transformation method is not accurate, but which have some now application in signal processing. We can obtain the velocity of aircraft and the angle of radar antenna phase center in order to focus in azimuth accurately.Finally, this paper actualize RD algorithm, improved RD algorithm, CS algorithm, RM algorithm, and then processing raw echo data make use of some algorithms that have been introduced and adopt doppler parameter that have been estimated above. From radar images, we can find that CS algorithm is more...