Vibration phases estimation based on multi-channel interferometry for ISAL

Abstract

Target vibration introduces unexpected vibration phases in the echo signal of inverse synthetic aperture LADAR (ISAL). The vibration phases cause the imaging results to be defocused. How to estimate the vibration phases has always been one of the difficulties in ISAL imaging, and there has not been an effective solution. In this paper, two methods are proposed to estimate the vibration phases in different situations. The method based on multi-channel along-track interferometry (MCATI method) is for some cases that the target velocity vector is parallel to some baselines of ISAL. The method based on orthogonal interferometry (OI method) is for other cases that the target velocity vector is not parallel to any baseline of ISAL. In addition, a high signal to noise ratio (SNR) is essential for the MCATI and OI methods to get high estimation accuracy. Therefore, a large power-aperture product should be carefully considered in the ISAL system design. Furthermore, on the condition of low SNR, range cell accumulation is also helpful to reduce the influence of noise. Take the ISAL, which is utilized to image the satellite in 500 km orbit, as an example, the estimation accuracy can satisfy the demand of synthetic aperture imaging with 0 dB single-pulse SNR and 300 range cell accumulation. The proposed methods are verified with simulation and experiment.

Varying Amplitude Vibration Phase Suppression Algorithm in ISAL Imaging

“…There are two points that need to be noted. First, the vibration amplitude should be smaller than a range resolution of ISAL [16]. Second, to avoid the phase self-coupling in Equation ( 16), the vibration amplitude and the vibration frequency should meet the following condition:…”

“…On the other hand, there are also some studies on the vibration phase compensation of ISAL, but the application of them is limited by special conditions. One study [16] proposed a vibration phase compensation method based on multichannel interference in which the vibration phase is estimated by high-order polynomial fitting, but this method works only for multichannel systems and not for single-channel systems. Another study [17] proposed a vibration phase compensation method based on the instantaneous ranging model for triangular frequency-modulated continuous wave (FMCW) signals.…”

Imaging and detection method for low signal-to-noise ratio airborne synthetic aperture ladar signals

“…In the case of a low SNR, the coherence between channels becomes worse, and the vibration phase-error compensation method based on interferometry is difficult to apply 7 – 10 Therefore, it is important to study the SAL signal processing methods of airborne SAL low SNR signals under vibration and beam-broadening conditions.…”