Synthetic aperture inversion for arbitrary flight paths and nonflat topography

Abstract

This paper considers synthetic aperture radar (SAR) and other synthetic aperture imaging systems in which a backscattered wave is measured from positions along an arbitrary (known) flight path. The received backscattered signals are used to produce an image of the terrain. We assume a single-scattering model for the radar data, and we assume that the ground topography is known but not necessarily flat. We focus on cases in which the antenna footprint is so large that the standard narrow-beam algorithms are not useful. We show that certain artifacts can be avoided if the antenna and antenna footprint avoid particular relationships with the ground topography. We give an explicit backprojection imaging algorithm that corrects for the ground topography, flight path, antenna beam pattern, source waveform, and other geometrical factors. For the case of a non-directional antenna, the image produced by the above algorithm contains artifacts. For this case, we analyze the strength of the artifacts relative to the strength of the true image. The analysis shows that the artifacts can be somewhat suppressed by increasing the frequency, integration time, and the curvature of the flight path.

Bistatic Synthetic Aperture Hitchhiker Imaging

“…Mircolocal analysis of (22) tells us that an edge at point z is visible if the direction nz normal to the edge is contained in the union ∪ s Ω z,s [10,8,9]. Thus by (22) one can only reconstruct the edges of RG that are visible.…”

“…In particular, we have combined the "correlation" methods presented in [1,3] with microlocal techniques [8,9] to develop FBPtype reconstruction methods for BISAH. Given a pair of receivers, the spatial-correlation method compares the received signals to identify a target within the illuminated scene, eliminating the need for knowledge about the transmitter location and waveform.…”

Microlocal analysis of synthetic aperture radar imaging in the presence of a vertical wall

“…The antenna emits pulses of electromagnetic radiation, which scatter off the terrain and the scattered waves are detected with the same antenna. The received signals are then used to produce an image of the terrain (see [1], [5], [6], [7]). …”

“…Here we are interested in the case where the antenna has poor directivity and a typical example of that is the foliage-penetrating radar (see [6], [10], [11]), whose low frequencies do not allow for much beam focusing.…”

<title>Microlocal high-range-resolution ISAR for low signal-to-noise environments</title>

“…Restricting our attention to the singular structure-specifically, to a certain set in phase space called the wavefront set-allows us to use the tools of microlocal analysis. [8][9][10][11] This strategy was first applied to imaging problems by Beylkin 12 ; its uses in seismic prospecting, [13][14][15][16] X-ray tomography, 17,18 sonar, 19 and synthetic-aperture radar 20,21 are active areas of research. An approach similar to the one we pursue here, in which we use microlocal analysis not to do imaging but instead to study the connection between features of the target and the data, was considered for the X-ray tomography problem by Quinto.…”