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sensors-08-08224(Azimuth reference equations)

sensors-08-08224(Azimuth reference equations) - Sensors...

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Sensors 2008 , 8 , 8224-8236; DOI: 10.3390/s8128224 sensors ISSN 1424-8220 www.mdpi.com/journal/sensors Article A Modified Subpulse SAR Processing Procedure Based on the Range-Doppler Algorithm for Synthetic Wideband Waveforms Byoung-Gyun Lim 1, *, Jea-Choon Woo 1 , Hee-Young Lee 2 and Young-Soo Kim 1 1 Division of Electrical and Computer Engineering, Pohang University of Science and Technology, Pohang, Gyungbuk, 790-784, South Korea; E-Mails: [email protected] (J. C. W); [email protected] (Y. S. K.) 2 Agency for Defense Development, Daejeon, South Korea; E-Mail: [email protected] (H. Y. L.) * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +82-54-279-2895; Fax: +82-54-279-2903 Received: 14 October 2008; in revised form: 10 December 2008 / Accepted: 10 December 2008 / Published: 11 December 2008 Abstract: Synthetic wideband waveforms (SWW) combine a stepped frequency CW waveform and a chirp signal waveform to achieve high range resolution without requiring a large bandwidth or the consequent very high sampling rate. If an efficient algorithm like the range-Doppler algorithm (RDA) is used to acquire the SAR images for synthetic wideband signals, errors occur due to approximations, so the images may not show the best possible result. This paper proposes a modified subpulse SAR processing algorithm for synthetic wideband signals which is based on RDA. An experiment with an automobile- based SAR system showed that the proposed algorithm is quite accurate with a considerable improvement in resolution and quality of the obtained SAR image. Keywords: Synthetic Aperture Radar (SAR), Range-Doppler Algorithm (RDA), Synthetic Wideband Waveforms (SWW). 1. Introduction Synthetic aperture radar (SAR) can produce high resolution two-dimensional imagery of the ground surface. The improvement in resolution is normally achieved by increasing the bandwidth, so a high- resolution SAR usually transmits a wideband chirp signal. To increase the range resolution beyond the OPEN ACCESS
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Sensors 2008 , 8 8225 theoretical value of c /2 B , where c is signal propagation speed and B is the chirp bandwidth, synthetic waveforms using a burst of narrowband signals have been suggested [1-3]. These waveforms combine the advantages of a stepped-frequency continuous wave (SF-CW) waveform and a chirp signal waveform without requiring an unrealistically high sampling rate. Such narrowband pulse sequences have many names, including a synthetic wideband signal [4], synthetic bandwidth [2, 5, 6], a stepped chirp signal [7], a stepped frequency train [3, 8, 9], and a frequency-jumped burst [10]. The papers and reports on synthetic wideband waveforms (SWW) have mainly dealt with methods to implement such waveforms [2, 5], and signal processing techniques to reduce the sidelobes and grating lobes [3, 8, 9]. Several methods including nonlinear stepping, linear windowing and spatial variant apodization have also been suggested [4, 7]. However, few studies have reported the actual quality of the SAR images acquired using these synthetic wideband waveforms.
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