Tomographic Performance of Multi-Static Radar Formations: Theory and Simulations

Ilgin Seker,Marco Lavalle

doi:10.3390/rs13040737

Abstract

3D imaging of Earth’s surface layers (such as canopy, sub-surface, or ice) requires not just the penetration of radar signal into the medium, but also the ability to discriminate multiple scatterers within a slant-range and azimuth resolution cell. The latter requires having multiple radar channels distributed in across-track direction. Here, we describe the theory of multi-static radar tomography with emphasis on resolution, SNR, sidelobes, and nearest ambiguity location vs. platform distribution, observation geometry, and different multi-static modes. Signal-based 1D and 2D simulations are developed and results for various observation geometries, target distributions, acquisition modes, and radar parameters are shown and compared with the theory. Pros and cons of multi-static modes are compared and discussed. Results for various platform formations are shown, revealing that unequal spacing is useful to suppress ambiguities at the cost of increased multiplicative noise. In particular, we demonstrate that the multiple-input multiple-output (MIMO) mode, in combination with nonlinear spacing, outperforms the other modes in terms of ambiguity, sidelobe levels, and noise suppression. These findings are key to guiding the design of tomographic SAR formations for accurate surface topography and vegetation mapping.

Highlights

Airborne and space-based radar imaging of Earth’s surface for scientific, civilian, and surveillance purposes has been an active field of research since the 1950s
The acquisition and processing of these signals that lead to vertical imaging of natural and human-made media is known as synthetic aperture radar (SAR) tomography, or TomoSAR [6,7,8]
The results shown are generated using Equations (6), (11), and (15) by assuming that radar frequency is 1.2 GHz, the platforms’ mean altitude is 700 km and no windowing is applied

Summary

Introduction

Airborne and space-based radar imaging of Earth’s surface for scientific, civilian, and surveillance purposes has been an active field of research since the 1950s. By virtue of the SAR measurement process and side-looking geometry, radar signals scattered from targets located at about the same distance from the radar antenna and within the SAR resolution cell are superimposed and indistinguishable in the final two-dimensional SAR image. At least two interferometric SAR (InSAR) acquisitions are needed to recover the third dimension, i.e., the location or the change of the microwave scattering phase center above the Earth’s surface [2,3,4,5]. In order to resolve distinct targets located at different heights and within the same slant-range resolution cell, multiple radar signals transmitted and/or received from different radar look angles are required. Multiple signals with look-angle diversity can be acquired by the same platform drifting at each pass (repeat-pass TomoSAR), by a multi-static formation of several platforms in which one or more platforms transmit radar pulses and a Remote Sens.

Results

Discussion

Conclusion