Multichannel Ground-Based Bistatic SAR Receiver for Single-Pass Opportunistic Tomography

This article presents a multichannel ground-based bistatic synthetic aperture radar (SAR) receiver architecture designed to perform single-pass tomography using the Sentinel-1 satellites as transmitters of opportunity. The bistatic receiver presents only three imaging channels, which is an extreme case for single-pass tomographic estimation. The three antennas are placed in a nonuniform configuration such that the two antenna separations are in a 2:1 ratio. For a fixed array length, the nonuniform three-element array will extend the maximum unambiguous height (relative to the three-element uniform array) while keeping the elevation resolution cell around the Rayleigh limit. In the proposed processing flow, for each Sentinel-1 overpass on the envisaged orbits, the bistatic SAR image of each channel is focused on a 2-D grid, and afterward, the elevation profile of a given area is computed using the Capon estimator. The proposed architecture was evaluated in a measurement campaign performed between June and November 2021 using an electronic target with two transmit antennas placed on a vertical pole situated 58.5 m from the ground receiver. For an array length of 2.6 m, the overall root mean square error of the relative height was below 10 cm, while the unambiguous interval and the height resolution cell were around 3.75 and 1.2 m, respectively. The experimental data from this measurements campaign provide the first quantitative assessment of spaceborne transmitter/stationary receiver single-pass bistatic SAR tomography in a controlled environment. In the long term, these results may contribute to future multistatic spaceborne SAR missions for which a single-pass tomographic capability is envisioned.