A Novel Three-Step Image Formation Scheme for Unified Focusing on Spaceborne Sar Data

Abstract

Abstract-Current advanced spaceborne synthetic aperture radar (SAR) systems may operate at multiple imaging modes, including conventional modes as stripmap, ScanSAR and spotlight, as well as the state-of-the-art SAR modes, e.g., sliding spotlight, TOPS (Terrain Observation by Progressive Scans) and inverse TOPS etc. A novel image formation scheme for unified processing spaceborne SAR data was proposed, which significantly simplified complexity of SAR processor sub-system. The unified-model-coefficient (UMC) was defined for modeling all SAR modes by means of analyzing both imaging geometry and time-frequency diagram corresponding to each imaging mode, respectively. The unified mathematical formula for modeling all SAR modes echo signal was derived as a function of UMC. Consequently, a unified image formation scheme for accurately focusing spaceborne SAR data in an arbitrary mode was proposed, which integrates all of SAR image formation procedures into a standard three-step processing framework, namely, de-rotation, data focusing and re-sampling, which evidently improve efficiency and robustness of data processing sub-system. Computer simulation experiment results verify the effectiveness of the proposed scheme.

A High-Order Imaging Algorithm for High-Resolution Spaceborne SAR Based on a Modified Equivalent Squint Range Model

“…However, in most cases, the above equation can not be satisfied. Therefore, an azimuth re-sampling operation is applied to overcome the constraint on the azimuth swath in equation (37) [40]. The operation begins with de-rotation processing, with the de-rotation phase function given by…”

A Wide-Swath Spaceborne TOPS SAR Image Formation Algorithm Based on Chirp Scaling and Chirp-Z Transform

“…As shown in Figure 2, assuming a linear frequency modulated (LFM) pulse is transmitted by the radar, after demodulation to the baseband, the received signal for point target $A$ can be described as [13]: $\begin{array}{ll}S\left(\tau ,\eta ;x_a,r\right)& =rect\left[\tau -\frac{2r\left(\eta ;x_a,r\right)}{c}\right]\cdot rect\left[\frac{v_e\eta /\gamma \left(r\right)-x_a}{X_f}\right]\cdot rect\left[\frac{\eta }{T_B}\right]\cdot rect\left[\frac{x_a}{X_s}\right]\\ & \cdot \text{exp}\left\{-j\pi b{\left(\tau -\frac{2R\left(\eta ;x_a,r\right)}{c}\right)}^2\right\}\cdot \text{exp}\left\{-j\frac{4\pi R\left(\eta ;x_a,r\right)}{\lambda }\right\}\end{array}$ where $rectfalse[\cdot false]$ represents the rectangular window, b is the signal frequency modulation rate, c is the speed of light, $\lambda$ is the carrier frequency, $\tau$ and $\eta$ are range time and azimuth time, respectively, $X_f=\lambda r/D$ is the length of azimuth antenna beam footprint, and $R\left(\eta ;x_a,r\right)$ is the distance between the satellite and the point target $A\left(x_a,r\right)$. Defining $x_a=v_e{\eta }_a$, $R\left(\eta ;x_a,r\right)$ can be...…”

“…Therefore, sub-aperture recombination has to be performed during data processing. In addition to the sub-aperture algorithms, full-aperture algorithms were also proposed, such as the three-step algorithm [12,13], which employ the derotation technique and the deramp technique to avoid the Doppler frequency spectrum aliasing problem and image folding, respectively. However, the deramp operation will introduce a time shift [14], resulting in the appearance of ghost targets and azimuth resolution reduction at the scene edge, especially in the wide-swath coverage case.…”

Novel Jamming Suppression Method Using Polarization Sar Data

“…During the past fifty years, synthetic aperture radar (SAR) has become an important tool for information acquisition and been widely utilized in various fields [1]. On the other hand, there exist many kinds of jamming which may prominently worsen the imaging performance of SAR.…”