GNSS-based bistatic SAR: a signal processing view

Abstract

This article presents signal processing algorithms used as a new remote sensing tool, that is passive bistatic SAR with navigation satellites (e.g. GPS, GLONASS or Galileo) as transmitters of opportunity. Signal synchronisation and image formation algorithms are described for two system variants: one where the receiver is moving and one where it is fixed on the ground. The applicability and functionality of the algorithms described is demonstrated through experimental imagery that ultimately confirms the feasibility of the overall technology.

A Novel General Imaging Formation Algorithm for GNSS-Based Bistatic SAR

“…In addition, GNSS constellations consist of over 100 satellites (GPS, GLONASS, Galileo and BeiDou), and multi-angle observation from over 20 satellites in any given area is attainable [11], which could potentially be used for increasing the imaging formation space [12,13,14,15]. Furthermore, GNSS-based bistatic SAR can achieve easy synchronization aided by the GNSS time service [16,17]. …”

“…For GNSS-based bistatic SAR, however, none of the above-mentioned algorithms is applicable due to its unique topology and non-designed radar signal. Based on the assumption of parallel flight paths of transmitter and receiver, a modified RDA is proposed in [23], and a modified BPA is presented in [16], which has a high computational complexity for interpolation. Due to the unique range history, no frequency domain algorithm without any approximation has been proposed yet in the literature.…”

“…The receiver is assumed to fly in a straight line, without any atmospheric turbulence during its flight. For motion error compensation, which is outside the scope of this paper, adequate processing algorithms about bistatic SAR motion compensation have been proposed [16,26,27] and they are relatively mature nowadays. Besides, other receiver and atmospheric errors (like clock slippage and local oscillator) compensation methods have been proposed in [16].…”

GNSS Imaging: A Case Study of Tree Detection Based on Beidou Geo Satellites

“…When GLONASS P code (bandwidth, 5.11 MHz) is applied, the corresponding range resolution is 30 m. For GPS, the bandwidth of C/A code is 1.023 MHz [19] which leads to the range resolution of 150 m. Although the bandwidth of GPS P code can reach 10.23 MHz, the encoding rules of GPS P code are not open to the public, thereby limiting the application of GPS P code in scientific research. Secondly, traditional imaging formation algorithms based on the hypotheses of linear transmitter trajectories and equal platform velocities are not applicable because navigation satellites have nonlinear trajectories in the long coherent accumulation time [20]. Thirdly, in the traditional imaging geometrical model, the posterior ephemeris data or broadcast ephemeris is required to calculate the position of the satellite before the calculation of path delay.…”

Beam Footprint Detection and Tracking for Non-cooperative Bistatic SAR

“…One of which is the real-time detection for the arrival time of the transmitter's beam footprint [3][4][5]; the other is the computation of the relative position between the transmitter and the receiver [6], [7]. As the anticipative observational area can be forecasted, so the main work of the beam synchronization for non-cooperative bistatic SAR is to realize transmitter's beam detection and tracking in the azimuth direction.…”