Extension of Wavenumber Domain Focusing for spotlight COSMO-SkyMed SAR Data

Abstract

In this work we describe a method to handle curved orbits in wavenumber domain focusing algorithm for high-resolution SAR data acquired by Low Earth Orbit satellites using spotlight mode. The standard wavenumber domain focusing algorithm make assumptions that start to be invalid when applied to high-resolution spotlight SAR data acquired in spaceborne low Earth orbit (LEO) configurations. The assumption of a hyperbolic range history is no longer accurate for sub-metric spatial resolutions due to the satellite curved orbit. The proposed method is used to estimate the satellite velocity and closest-approach range distance of the rectified effective orbit which minimizes the phase errors over the whole scene coverage. This allows to use all frequency domain focusing kernels developed to focus SAR images acquired with a stripmap mode. We use this method with the ω-k algorithm, and its approximation Fast ω-k (Fω-k), demonstrating its effectiveness to focus COSMO-SkyMed (CSK) SAR images obtaining, respectively, sub-metric and metric azimuth spatial resolution.

A Modified Cartesian Factorized Backprojection Algorithm Integrating with Non-Start-Stop Model for High Resolution SAR Imaging

“…Synthetic aperture radar (SAR), which can provide remote sensing images during the day and night regardless of weather conditions, plays an important role in Earth and planetary observation [1][2][3]. In recent years, high resolution SAR imaging attracts growing interest due to its wide applications especially in military reconnaissance and disaster monitoring [4][5][6][7][8][9][10]. Several spaceborne SAR systems have the ability of submeter imaging.…”

“…Several spaceborne SAR systems have the ability of submeter imaging. For example, the COSMO-SkyMed SAR can achieve a high azimuth resolution better than 0.9 m [6], while TerraSAR-X can achieve 0.16 m azimuth resolution [7]. In addition, the Gaofen-3 (GF-3) satellite, a C-band multi-polarization SAR of China launched in 2016, can achieve 0.4 m azimuth resolution [5,10].…”

“…Therefore, the non-start-stop model should be used in imaging processing [13]. Additionally, due to the long trajectory, the error introduced by curved orbit should also be corrected [6]. Topography dependence and atmospheric effects should be considered [7,14], which further increases the complexity of imaging processing.…”

Sliding Spotlight Mode Imaging with GF-3 Spaceborne SAR Sensor

“…The feasibility of spotlight was verified by several satellites like Radarsat-2 [ 2 ], Cosmo-Skymed [ 3 , 4 ], ALOS-2 [ 5 ], TerraSAR-X [ 6 , 7 ], and Sentinel-1 [ 8 ], as well as the next generation SAR satellites such as TerraSAR Next Generation (TerraSAR-NG) [ 9 , 10 ]. The sliding spotlight mode in TerraSAR-X [ 11 ] applies a slower antenna steering than staring spotlight mode.…”

A Novel Imaging Algorithm for Focusing High-Resolution Spaceborne SAR Data in Squinted Sliding-Spotlight Mode

“…Another azimuth preprocessing method including the linear range walk correction (LRWC) operation and de-rotation operation can cope with the above two problems simultaneously, but two key issues arise after the azimuth preprocessing. Firstly, the LRWC operation changes the signal property significantly so that the traditional imaging algorithms for high-resolution broadside SAR [8][9] cannot accurately focus the data; secondly, the Doppler rates of the targets located at the same range cell after range compression vary along the azimuth direction, which leads to residual quadratic phases for the targets at azimuth edge if the same matched filter is used. Thus, the azimuth size of the focused scene, which is also called the depth-of-azimuth-focus (DOAF), is seriously limited, especially in high-resolution case.…”