ABSTRACT
In synthetic aperture radar (SAR) data acquisition and processing, the Doppler frequency is one of the most vital parameters known for focusing the image. For SAR, the Doppler shift is determined by the radial velocity and is profoundly associated with the motion of the platform. This implies that the time and position of the platform must be known. Subsequently, it is important to understand to what extent the
motion trajectory affects the image focusing. Recall that f dR
dt ud r= − = −
2 2 λ λ . The
radar’s radial velocity ur, the relative velocity between the sensor and the target, is determined from u u Rr = − ⋅
ˆ , where
u is the radar velocity and Rˆ is the unit range vector. For accurate azimuthal positioning of the target, it is critical and essential to estimate the position vectors of the radar and target as accurately as possible under a reference time and space coordinate systems. To uniquely describe and determine the SAR sensor position, velocity, and attitude requires a coordinate system or reference frame [1,2]. For a SAR system under study, we assume Newtonian mechanics is valid. Here the coordinate system refers to both time and space coordinates. For space coordinates, both satellite and airborne systems will be described in Chapters 5 and 6 to facilitate the discussions of SAR image focusing and motion compensation.
