An Improved Frequency-Domain Image Formation Algorithm for Mini-UAV-Based Forward-Looking Spotlight BiSAR Systems

Tao Zeng,Feifeng Liu,Zhanze Wang,Chenghao Wang

doi:10.3390/rs12172680

Tao Zeng, Feifeng Liu + Show 2 more

Open Access

https://doi.org/10.3390/rs12172680

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Journal: Remote sensing	Publication Date: Aug 19, 2020
Citations: 8	License type: CC BY 4.0

Affiliation: Beijing Institute of Technology

Abstract

Mini-unmanned aerial vehicle (UAV)-based bistatic forward-looking synthetic aperture radar (SAR) (mini-UAV-based BFSAR) is much more attractive than the monostatic one because of the flexibility of the system geometry selection as well as its simplicity of system operation, especially with the mini-UAV platform. However, the trajectory of the mini-UAV needs to be accurately modeled since it is very sensitive to the external environment, and the forward-looking configuration results in more severe spatial variance in image formation processing. In the paper, an improved frequency-domain imaging algorithm based on a very accurate slant range model is proposed for mini-UAV-based BFSAR with spotlight illumination. First, a more accurate slant range expression considering the motion characteristics of the UAV and bistatic spotlight configuration is re-derived. Second, a new range nonlinear chirp scaling (NLCS) operator was derived based on the accurate bistatic slant range model. Third, an improved azimuth NLCS operator in the Doppler frequency domain was established for the spotlight illumination of the transmitter and receiver in mini-UAV based BFSAR systems. Finally, the proposed algorithm is validated by both simulations and real datasets.

Highlights

Synthetic aperture radar (SAR) [1,2] has become a very attractive technique because it can provide high-resolution images during the day and night regardless of weather conditions
The transmitter and receiver are mounted on two mini-unmanned aerial vehicle (UAV), respectively
Because the experimental site was selected in the suburbs, the wind was relatively strong, which meant that the mini-UAV carrier itself shook seriously, resulting in higher system acceleration and jerk compared to large aircraft

Summary

Introduction

Synthetic aperture radar (SAR) [1,2] has become a very attractive technique because it can provide high-resolution images during the day and night regardless of weather conditions. In the forward-looking case, monostatic SAR cannot achieve high-resolution imaging along the azimuth direction because it cannot form an effective Doppler bandwidth, and mirror effects occur in this scenario. To solve these difficulties, bistatic forward-looking SAR (BFSAR) has been introduced as a working mode, in which the receiver adopts forward-looking and spotlight reception while the transmitter adopts broadside or squint illumination to simultaneously form an effective Doppler bandwidth and avoid mirror effects [3,4,5,6,7,8,9,10,11]. The back-projection (BP) algorithm is a theoretically accurate image formation algorithm for any SAR system, but it is limited by its inefficiency [13,14,15]

Results

Discussion

Conclusion