Interferometric SAR signal analysis in the presence of squint

Abstract

Abstract-This paper develops an analysis of the SAR impulse response function from the interferometric point of view, with the intention of studying its phase behavior in the presence of high squint angle values. It will be pointed out that in this case, a phase ramp is present in the range direction, which, in combination with a certain degree of misregistration between the two images induces an offset in the generated interferometric phase. This behavior, if not compensated, imposes strong limits on the performance of the interferometric techniques in a squinted case, especially for airborne SAR systems. The article proposes two new techniques, which are appropriate to correct the phase bias coming from this source. The first one is based on a modification of the azimuth compression filter, which cancels the phase ramp of the range impulse response function for one specific squint value. In case the SAR processing is performed with variable squint over range, we propose a second method oriented to estimating the expected misregistration and thus, the phase bias by means of an iterative approach. Simulated data as well as real corner reflector responses are used to show that the correct topography can be recovered precisely even in the presence of phase bias coming from the squinted geometry.Index Terms-Digital elevation model, interferometry, remote sensing, synthetic aperture radar (SAR).

Wind‐wave‐induced velocity in ATI SAR ocean surface currents: First experimental evidence from an airborne campaign

“…The single look complex (SLC) images were produced with a ground range resolution between 5.3 m at near range (248) and 1.5 m at far range (458). The azimuth resolution is 1.06 m. The SAR focusing is processed to acquisition Doppler (AD) geometry [Bara et al, 2000;Fornaro et al, 2002] with a bandwidth of 75 Hz. As the processing is done over lines of constant Doppler frequencies, the squint angle on the ground varies across the swath.…”

GMTI for Squint Looking XTI-SAR with Rotatable Forward-Looking Array

“…The response in each channel for a static/moving target in complex image domain could be unified if written as $\begin{array}{c}left{S}_0(x,y,h,v_r)=a_{\mathrm{normals}}\exp \left\{j{\phi }_0\left(x,y,h,v_r\right)\right\}\\ S_1(x,y,h,v_r)=a_{\mathrm{normals}}\exp \left\{j{\phi }_0\left(x,y,h,v_r\right)+j\Delta \phi \left(x,y,B\right)+j\varphi \left(x,y,h,v_r,B\right)\right\}\end{array}$ where $a_{\mathrm{normals}}$ is the consistent amplitude response of the target in each channel, and $\mathrm{normalB}$ is the length of baseline vector $\stackrel{true\to }{{\mathrm{normalA}}_0{\mathrm{normalA}}_1}$ in Figure 1. ${\phi }_0$ is the phase response for the reference channel A 0 , and $\Delta \phi$ is the phase difference caused by location difference and response unbalancing between two channels, which can be compensated by the image co-registration and channel balancing processing [12,24]. $\varphi$ is the interferometry phase caused by the displaced receive antenna, which is a function of the baseline, the target position and the motion parameters.…”

“…From [23,24], the moving targets will shift towards the direction across the radar line of sight (RLOS). Therefore, the cross track shift due to the presence of squint could be determined as: $\Delta x=-\Delta y\frac{{\hat{y}}_0}{{\hat{x}}_0}$ where ${\hat{x}}_0$ and ${\hat{y}}_0$ are the focus position of the moving target.…”

“…Meanwhile, the cross-track interferometry synthetic aperture radar (XTI-SAR) is usually used for the digital elevation model (DEM) generation [16,17,18] in the side-looking application because the interferometry phases among cross-track multiple receivers are sensitive to the target’s height. Nevertheless, few studies can be found on GMTI for XTI-SAR, though many real systems with cross-baselines still only have strong demands on the GMTI [19,20,21,22,23,24,25,26,27,28]. For example, the airborne navigation or fire-control radars are normally mounted on the plane nose with a forward-looking array antenna, where the receivers are all distributed in the plane perpendicular to the flying track.…”

TOPS Interferometry With TerraSAR-X

“…For typical TerraSAR-X TOPS acquisitions, the Doppler centroid can vary by more than 7 kHz within each burst. It is well known that in the presence of squint, linear phase ramps are induced in the focused impulse response both in azimuth and range [4]- [6], where for small squints, the range phase ramp can be usually neglected [2]. Fig.…”