{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T03:57:19Z","timestamp":1760241439067,"version":"build-2065373602"},"reference-count":26,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2018,2,21]],"date-time":"2018-02-21T00:00:00Z","timestamp":1519171200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["61601470"],"award-info":[{"award-number":["61601470"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Natural Science Foundation of Tianjin, China","award":["16JCYBJC41200 (20162898)"],"award-info":[{"award-number":["16JCYBJC41200 (20162898)"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Synthetic Aperture Radar (SAR) imaging with a non-zero (forward) squint angle is capable of providing a longer time for reaction than that of the broadside mode. However, due to the large squint angle, there will be severe coupling between range and azimuth samples in the echoed data, which is known as the problematic Range Cell Migration (RCM) in the SAR community. Especially when the SAR sensor mounted on an airborne platform encounters unexpected motion deviations\/errors, the coupling becomes more complicated, and it is difficult to differentiate the systematic RCM for the SAR Image Formation Processing (IFP) and the non-systematic RCM error to be compensated. To this end, a novel and accurate SAR imaging algorithm is proposed in this paper to facilitate the processing of airborne SAR data collected at a high-squint angle. Firstly, the proposed algorithm is established under a Fast Time-Domain Back-Projection (FTDBP) framework for the SAR IFP. FTDBP paves the way to avoid the complicated processing for the systematic RCM as for the conventional SAR IFP in the Doppler processing manner. It is capable of generating a high-resolution SAR image efficiently under more general geometries and configurations. Secondly, regarding the non-systematic RCM errors, the proposed algorithm realizes the compensation by correcting both the Non-systematic Range Cell Migration (NsRCM), as well as Azimuthal Phase Error (APE) in a coherent manner. It is consequently capable of auto-calibrating the effects of the motion error completely without being dependent on the airborne navigation unit. Finally, both simulated and raw data collected by the airborne squinted SAR are applied to evaluate the proposed algorithm. Comparisons with conventional algorithms are carried out to reveal the superiority of the proposed algorithm.<\/jats:p>","DOI":"10.3390\/rs10020321","type":"journal-article","created":{"date-parts":[[2018,2,21]],"date-time":"2018-02-21T06:33:39Z","timestamp":1519194819000},"page":"321","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Coherent Auto-Calibration of APE and NsRCM under Fast Back-Projection Image Formation for Airborne SAR Imaging in Highly-Squint Angle"],"prefix":"10.3390","volume":"10","author":[{"given":"Lei","family":"Yang","sequence":"first","affiliation":[{"name":"Tianjin Key Laboratory for Advanced Signal Processing, Civil Aviation University of China, Tianjin 300300, China"}]},{"given":"Song","family":"Zhou","sequence":"additional","affiliation":[{"name":"School of Electronic Information and Engineering, Nanchang University, Nanchang 330031, China"}]},{"given":"Lifan","family":"Zhao","sequence":"additional","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, S2-B3a-06, 639798, Singapore"}]},{"given":"Mengdao","family":"Xing","sequence":"additional","affiliation":[{"name":"National Key Lab for Radar Signal Processing, Xidian University, Xi\u2019an 710071, China"}]}],"member":"1968","published-online":{"date-parts":[[2018,2,21]]},"reference":[{"key":"ref_1","unstructured":"Carrara, W.G., Goodman, R.S., and Majewski, R.M. (1995). Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, Artech House."},{"key":"ref_2","unstructured":"Cumming, I.G., and Wong, F.H. (2004). Digital Signal Processing of Synthetic Aperture Radar Data: Algorithms and Implementation, Artech House."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1320","DOI":"10.3390\/rs70201320","article-title":"Integration of Optical and SAR Data for Burned Area Mapping in Mediterranean Regions","volume":"2","author":"Stroppiana","year":"2015","journal-title":"Remote Sens."},{"key":"ref_4","first-page":"1","article-title":"An Adaptive Fast Factorized Back-Projection Algorithm With Integrated Target Detection Technique for High-Resolution and High-Squint Spotlight SAR Imagery","volume":"99","author":"Ran","year":"2017","journal-title":"IEEE J. Sel. Top. Appl. Earth Observ. Remote Sens."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"6063","DOI":"10.3390\/rs5116063","article-title":"Autonomous Navigation Airborne Forward-Looking SAR High Precision Imaging with Combination of Pseudo-Polar Formatting and Overlapped Sub-Aperture Algorithm","volume":"11","author":"Peng","year":"2013","journal-title":"Remote Sens."},{"key":"ref_6","first-page":"1574","article-title":"Wavenumber-Domain Autofocusing for Highly Squinted UAV SAR Imagery","volume":"5","author":"Zhang","year":"2011","journal-title":"IEEE Sensors J."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"4339","DOI":"10.1109\/TGRS.2013.2281454","article-title":"Azimuth Resampling Processing for Highly Squinted Synthetic Aperture Radar Imaging With Several Modes","volume":"7","author":"Xing","year":"2014","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2308","DOI":"10.1109\/TGRS.2010.2102040","article-title":"Focus Improvement of Highly Squinted Data Based on Azimuth Nonlinear Scaling","volume":"6","author":"Sun","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Wu, J., Xu, Y., Zhong, X., and Yang, J.M. (2017). A Three-Dimensional Localization Method for Multistatic SAR Based on Numerical Range-Doppler Algorithm and Entropy Minimization. Remote Sens., 9.","DOI":"10.3390\/rs9050470"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2225","DOI":"10.1109\/LGRS.2017.2758386","article-title":"A New Nonlinear Chirp Scaling Algorithm for High-Squint High-Resolution SAR Imaging","volume":"12","author":"Wang","year":"2017","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_11","first-page":"1","article-title":"Efficient and precise processing for squinted spotlight SAR through a modified Stolt mapping","volume":"1","author":"Vandewal","year":"2007","journal-title":"EURASIP J. Adv. Signal Process."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"724","DOI":"10.1109\/LGRS.2017.2676118","article-title":"Spectrum-Oriented FFBP Algorithm in Quasi-Polar Grid for SAR Imaging on Maneuvering Platform","volume":"5","author":"Yang","year":"2017","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"7053","DOI":"10.1109\/TGRS.2017.2739133","article-title":"Quasi-Polar-Based FFBP Algorithm for Miniature UAV SAR Imaging Without Navigational Data","volume":"12","author":"Zhou","year":"2017","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2949","DOI":"10.1109\/TAES.2011.6034676","article-title":"Efficient Time-Domain Image Formation with Precise Topography Accommodation for General Bistatic SAR Configurations","volume":"4","author":"Rodriguez","year":"2011","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3074","DOI":"10.1109\/TGRS.2013.2269194","article-title":"Fully Polarimetric High-Resolution 3-D Imaging With Circular SAR at L-Band","volume":"6","author":"Ponce","year":"2014","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"760","DOI":"10.1109\/TAES.2003.1238734","article-title":"Synthetic-aperture radar processing using fast factorized back-projection","volume":"3","author":"Ulander","year":"2003","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1460","DOI":"10.1109\/LGRS.2013.2295326","article-title":"A Fast BP Algorithm With Wavenumber Spectrum Fusion for High-Resolution Spotlight SAR Imaging","volume":"9","author":"Zhang","year":"2014","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"457","DOI":"10.1109\/TSP.2014.2375157","article-title":"Nyquist sampling requirements for polar grids in bistatic time-domain algorithms","volume":"2","author":"Vu","year":"2015","journal-title":"IEEE Trans. Signal Process."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1394","DOI":"10.1109\/LGRS.2013.2258886","article-title":"Integrating Autofocus Techniques With Fast Factorized Back-Projection for High-Resolution Spotlight SAR Imaging","volume":"6","author":"Zhang","year":"2013","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_20","unstructured":"Yegulalp, A.F. (1999, January 22). Fast backprojection algorithm for synthetic aperture radar. Proceedings of the 1999 IEEE Radar Conference on Radar into the Next Millennium, Waltham, MA, USA."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1109\/LGRS.2012.2196676","article-title":"Compensation for the NsRCM and Phase Error After Polar Format Resampling for Airborne Spotlight SAR Raw Data of High Resolution","volume":"1","author":"Yang","year":"2013","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"5031","DOI":"10.1109\/TGRS.2013.2276112","article-title":"Robust Autofocusing Approach for Highly Squinted SAR Imagery Using the Extended Wavenumber Algorithm","volume":"10","author":"Xu","year":"2013","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_23","first-page":"1","article-title":"Application of fast factorized back-projection algorithm for high-resolution highly squinted airborne SAR imaging","volume":"6","author":"Zhang","year":"2017","journal-title":"Sci. China"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"3202","DOI":"10.1109\/TGRS.2011.2180392","article-title":"A Robust Motion Compensation Approach for UAV SAR Imagery","volume":"8","author":"Zhang","year":"2012","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2870","DOI":"10.1109\/TGRS.2009.2015657","article-title":"Motion compensation for UAV SAR based on raw radar data","volume":"8","author":"Xing","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"627","DOI":"10.1049\/iet-rsn.2011.0078","article-title":"Entropy-based motion error correction for high-resolution spotlight SAR imagery","volume":"7","author":"Yang","year":"2012","journal-title":"IET Radar Sonar Navig."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/2\/321\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T14:55:45Z","timestamp":1760194545000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/2\/321"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,2,21]]},"references-count":26,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2018,2]]}},"alternative-id":["rs10020321"],"URL":"https:\/\/doi.org\/10.3390\/rs10020321","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2018,2,21]]}}}