摘要(英) |
Synthetic Aperture Radar (SAR) is a payload on aircrafts or satellites for surveillance. It transmits signals to the earth′s surface as the platform moves. The echo signals are processed through imaging algorithms to generate high-resolution 2D image that is unaffected by weather. Two types of radar scan modes are studied. In spotlight scan mode, we investigate Polar Format Algorithm (PFA) and Back Projection Algorithm (BPA). In stripmap scan mode, the BPA and the Range Doppler Algorithm (RDA) are employed and compared. First, the imaging performance is evaluated through simulation of reflection from a point target. Next, the real satellite SAR data in the stripmap scan mode are used. Although the BPA requires additional radar position and digital elevation model for imaging, a linear geographic relationship model is developed to address this issue. The imaging performance of the BPA is compared to that of RDA. Based on the simulations, BPA is ultimately selected for its compatibility with both scan modes and superior imaging performance. To achieve real-time imaging, a hardware accelerator is designed to reduce processing time. The hardware consists of range compression and azimuth processing blocks. In range compression, a frequency domain matched filter is used to improve efficiency. To enhance configurability, the COordinate Rotation DIgital Computer (CORDIC) is adopted to replace multipliers and look-up tables. In azimuth processing, signal grids are transformed into image grids through signal interpolation, Doppler compensation, and accumulation. To reduce frequent data access from external high bandwidth memory and the energy consumption, the imaging size 1024×1024 is divided into multiple fixed-size tiles. Based on data scheduling procedure analysis, a rectangular tile size with diagonal lower left processing sequence can effectively eliminate data reloading redundancy and achieve a reduced data access ratio of only 8/896. |
參考文獻 |
[1] 陳柏達, "適用於合成孔徑雷達之即時都普勒參數估測硬體設計與實作, " 碩士論文, 國立中央大學電機工程學系, 2024
[2] 林家兆, "適用於合成孔徑雷達之測距都普勒演算法即時成像硬體實作與系統整合, " 碩士論文, 國立中央大學電機工程學系, 2022
[3] Ian G. Cumming, Frank H. Wong , "Digital Processing of Synthetic Aperture Radar Data – Algorithms and Implementation," Artech House Publishers, Jan. 2005.
[4] Alaska Satellite Facility, Jun. 2014, “Alaska Satellite Facility Data Search” Available: https://asf.alaska.edu/
[5] A. W. Doerry, "Basics of polar-format algorithm for processing synthetic aperture radar images", Sandia National Laboratories Report No. SAND2012-3369, 2012.
[6] A. Doerry, E. Bishop and J. Miller, "Basics of backprojection algorithm for processing Synthetic Aperture Radar images", Sandia National Laboratories Report No. SAND2016-1682, 2016.
[7] M. I. Duersch, "Backprojection for Synthetic Aperture Radar", Ph.D. thesis, 2013.
[8] M. Horowitz, "Computing’s energy problem (and what we can do about it)", Proc. International Solid-state Circuits Conference (ISSCC), pp. 10-14, Feb. 2014.
[9] L. Gorham and L. Moore, "SAR image formation toolbox for MATLAB", Proc. SPIE, vol. 7699, pp. 46-58, Apr. 2010.
[10] Y. Wang, J.-w. Li, J. Chen, H.-p. Xu and B. Sun, "A parameter-adjusting polar format algorithm for extremely high squint SAR imaging", IEEE transactions on geoscience and remote sensing, vol. 52, no. 1, pp. 640-650, 2013.
[11] D. Zhu, S. Ye and Z. Zhu, "Polar format algorithm using chirp scaling for spotlight SAR image formation", IEEE Trans. Aerosp. Electron. Syst., vol. 44, no. 4, pp. 1433-1448, Oct. 2008. |