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2 results on '"equivalent range model"'

1. A Novel Frequency-Domain Focusing Method for Geosynchronous Low-Earth-Orbit Bistatic SAR in Sliding-Spotlight Mode.

Author

Sun, Zhichao, Chen, Tianfu, Sun, Huarui, Wu, Junjie, Lu, Zheng, Li, Zhongyu, An, Hongyang, and Yang, Jianyu

Subjects
*SYNTHETIC aperture radar, *BEAM steering, *DIRECTIONAL antennas, *SLIDING mode control, *IMAGE analysis, *AZIMUTH
Abstract

The low-earth-orbit synthetic aperture radar (SAR) can achieve enhanced remote-sensing capabilities by exploiting the large-scale and long-duration beam coverage of a geosynchronous (GEO) SAR illuminator. Different bistatic imaging modes can be implemented by the steering of an antenna beam onboard the LEO receiver, such as high-resolution sliding-spotlight mode. In this paper, the accurate focusing of GEO-LEO bistatic SAR (GEO-LEO BiSAR) in sliding-spotlight mode is investigated. First, the two major problems of the accurate bistatic range model, i.e., curved trajectory within long integration time and 'stop-and-go' assumption error, for sliding-spotlight GEO-LEO BiSAR are analyzed. Then, a novel bistatic range model based on equivalent circular orbit trajectory is proposed to accurately represent the range history of GEO-LEO BiSAR in sliding-spotlight mode. Based on the proposed range model, a frequency-domain imaging method is put forward. First, a modified two-step preprocessing method is implemented to remove the Doppler aliasing caused by azimuth variance of Doppler centroid and beam steering. Then, an azimuth trajectory scaling is formulated to remove the azimuth variance of motion parameters due to curved trajectory. A modified frequency-domain imaging method is derived to eliminate the 2-D spatial variance and achieve accurate focusing of the echo data. Finally, imaging results and analysis on both simulated data and real data from an equivalent BiSAR experiment validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Published
2022
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2. Generalized PFA for Air-Missile Borne Bistatic Forward-Looking Beam-Steering SAR With Accelerations

Author

Linrang Zhang, Shiyang Tang, Yachao Li, Ping Guo, and Huan Deng

Subjects
Synthetic aperture radar, General Computer Science, Computer science, Acoustics, equivalent range model, Beam steering, azimuth scaling, 0211 other engineering and technologies, General Engineering, generalized polar formation algorithm, 020206 networking & telecommunications, 02 engineering and technology, Acceleration, Bistatic radar, Missile, Aliasing, 0202 electrical engineering, electronic engineering, information engineering, General Materials Science, lcsh:Electrical engineering. Electronics. Nuclear engineering, Antenna (radio), lcsh:TK1-9971, Bistatic forward-looking beam-steering SAR, 021101 geological & geomatics engineering, Interpolation
Abstract

For air-missile borne bistatic forward-looking beam-steering synthetic aperture radar (BFLBS-SAR), the receiver platform moves along a curve track due to the existence of accelerations. Besides, transmitting and receiving antenna beams rotate around a certain rotary center during the process of data collection to extend or shorten synthetic aperture time. These characteristics imply that the echo signal suffers serious range–azimuth coupling and aliasing problems of azimuth spectrum. Worse still, the echo process has problems of double-radical sign and high-order terms, which makes the rotary beam center unable to be obtained directly, and thus, the traditional polar formation algorithm (PFA) cannot be applied directly to BFLBS-SAR. To solve these problems, this paper proposes a generalized PFA (GPFA) for air-missile borne BFLBS-SAR. The algorithm uses the equivalent bistatic linear range model first to separate platform acceleration errors. By equating the bistatic mode to the monostatic one, an equivalent rotary center is obtained, and a new azimuth Deramp function is introduced to eliminate aliasing. Then, spectrum utilization and azimuth sampling rate are improved by spectral rotation and interpolation, and the image format is changed. In the azimuth focusing phase, azimuth aliasing is avoided by means of azimuth scaling, which makes azimuth focusing possible eventually. Numerous simulation experiments verify the effectiveness of the proposed GPFA.

Published
2018

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