{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T03:48:26Z","timestamp":1760240906524,"version":"build-2065373602"},"reference-count":19,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2019,10,17]],"date-time":"2019-10-17T00:00:00Z","timestamp":1571270400000},"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":["61571447"],"award-info":[{"award-number":["61571447"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The subaperture processing is one of the essential strategies for low frequency ultrawideband synthetic aperture radar (LF UWB SAR) imaging, especially for the real-time LF UWB SAR imaging because it can improve the parallelization of the imaging algorithm. However, due to the longer synthetic aperture of LF UWB SAR, the traditional subaperture imaging encounters an azimuth ambiguities problem, which severely degrades the focused quality of the imaging results. In this paper, the reason for the presence of azimuth ambiguities in the LF UWB SAR subaperture imaging and its influence on image quality is first analyzed in theory. Then, an extended subaperture imaging method based on the extension of subaperture length before Range Cell Migration Correction (RCMC) was proposed. By lengthening the subaperture length, the azimuth ambiguities are effectively eliminated. Finally, the extended part of subaperture is wiped off before the azimuth compression (AC), and the LF UWB SAR image of high focused quality is obtained. The correctness of the theory analysis and the effectiveness of the proposed method have been validated through simulated and real LF UWB SAR data.<\/jats:p>","DOI":"10.3390\/s19204516","type":"journal-article","created":{"date-parts":[[2019,10,17]],"date-time":"2019-10-17T11:07:59Z","timestamp":1571310479000},"page":"4516","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Extended Subaperture Imaging Method for Airborne Low Frequency Ultrawideband SAR Data"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1363-9140","authenticated-orcid":false,"given":"Daoxiang","family":"An","sequence":"first","affiliation":[{"name":"College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7606-695X","authenticated-orcid":false,"given":"Wu","family":"Wang","sequence":"additional","affiliation":[{"name":"College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2742-0326","authenticated-orcid":false,"given":"Leping","family":"Chen","sequence":"additional","affiliation":[{"name":"College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China"}]}],"member":"1968","published-online":{"date-parts":[[2019,10,17]]},"reference":[{"doi-asserted-by":"crossref","unstructured":"Davis, M.E. (2011). Foliage Penetration Radar Detection and Characterization of Objects Under Trees, SciTech Publishing.","key":"ref_1","DOI":"10.1049\/SBRA007E"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3799","DOI":"10.1109\/TGRS.2010.2048572","article-title":"Detection of moving targets by focusing in UWB SAR\u2014Theory and experimental results","volume":"48","author":"Vu","year":"2010","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"243","DOI":"10.1109\/TAES.2003.1238734","article-title":"Synthetic-aperture radar processing using fast factorized back-projection","volume":"39","author":"Ulander","year":"2003","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"678","DOI":"10.1109\/JSTARS.2013.2265272","article-title":"Performance evaluation of frequency-domain algorithms for chirped low frequency UWB SAR Data Processing","volume":"7","author":"An","year":"2014","journal-title":"IEEE J. Sel. Topics Appl. Earth Obs. Remote Sens."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"714","DOI":"10.1109\/36.158865","article-title":"Real-time Synthetic Aperture Radar (SAR) processing with a new subaperture approach","volume":"30","author":"Moreira","year":"1992","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"unstructured":"Impagnatiello, F. (1995, January 10\u201314). A precision chirp scaling SAR processor extension to subaperture implementation on massively parallel supercomputers. Proceedings of the 1995 International Geoscience and Remote Sensing Symposium, IGARSS \u201995. Quantitative Remote Sensing for Science and Applications, Firenze, Italy.","key":"ref_6"},{"unstructured":"Huang, Y., and Moreira, A. (1993, January 18\u201321). Airborne SAR processing using the chirp scaling and a time domain subaperture algorithm. Proceedings of the IGARSS \u201993\u2014IEEE International Geoscience and Remote Sensing Symposium, Tokyo, Japan.","key":"ref_7"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1123","DOI":"10.1109\/36.536528","article-title":"Extended chirp scaling algorithm for air- and spaceborne SAR data processing in stripmap and scanSAR imaging modes","volume":"34","author":"Moreira","year":"1996","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"doi-asserted-by":"crossref","unstructured":"Sun, G., Liu, Y., Xing, M., Wang, S., Guo, L., and Yang, J. (2018). Real-Time Imaging Algorithm Based on subaperture CS-Dechirp for GF3-SAR Data. Sensors, 18.","key":"ref_9","DOI":"10.3390\/s18082562"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"6718","DOI":"10.1109\/TGRS.2015.2447393","article-title":"Subaperture approach based on azimuth-dependent range cell migration correction and azimuth focusing parameter equalization for maneuvering high-squint-mode SAR","volume":"52","author":"Zeng","year":"2015","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1323","DOI":"10.1109\/LGRS.2017.2711005","article-title":"Extended autofocus backprojection algorithm for low frequency SAR imaging","volume":"14","author":"Chen","year":"2017","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_12","first-page":"1814","article-title":"New subaperture imaging algorithm and geometric correction method for high squint diving SAR based on equivalent squint model","volume":"37","author":"Li","year":"2015","journal-title":"J. Electron. Inf. Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"389","DOI":"10.1109\/TAES.1983.309319","article-title":"Ambiguities in spaceborne synthetic aperture radar systems","volume":"19","author":"Li","year":"1983","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2889","DOI":"10.1109\/TGRS.2011.2174460","article-title":"Extended two-step focusing approach for squinted spotlight SAR imaging","volume":"50","author":"An","year":"2012","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"885","DOI":"10.1109\/36.239912","article-title":"Suppressing the azimuth ambiguities in synthetic aperture radar images","volume":"34","author":"Moreira","year":"1993","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"doi-asserted-by":"crossref","unstructured":"Wang, J., Xue, G., Zhou, Z., and Song, Q. (2006, January 16\u201319). A new subaperture nonlinear chirp scaling algorithm for real-time UWB-SAR Imaging. Proceedings of the 2006 CIE International Conference on Radar, Shanghai, China.","key":"ref_16","DOI":"10.1109\/ICR.2006.343125"},{"unstructured":"Cumming, I.G., and Wong, F.W. (2005). Digital Processing of Synthetic Aperture Radar Data Algorithm and Implementation, Artech House.","key":"ref_17"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1109\/7.481254","article-title":"A chirp scaling approach for processing squint mode SAR data","volume":"32","author":"Davidson","year":"1995","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"doi-asserted-by":"crossref","unstructured":"Yi, T., He, Z., He, F., Zhen, D., and Wu, M. (2017). Generalized Nonlinear Chirp Scaling Algorithm for High-Resolution Highly Squint SAR Imaging. 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