{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,14]],"date-time":"2026-02-14T10:26:11Z","timestamp":1771064771308,"version":"3.50.1"},"reference-count":26,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2019,1,16]],"date-time":"2019-01-16T00:00:00Z","timestamp":1547596800000},"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":["61571421"],"award-info":[{"award-number":["61571421"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["61501210"],"award-info":[{"award-number":["61501210"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["61431018"],"award-info":[{"award-number":["61431018"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["61331017"],"award-info":[{"award-number":["61331017"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>In conventional synthetic aperture radar (SAR) working modes, targets are assumed isotropic because the viewing angle is small. However, most man-made targets are anisotropic. Therefore, anisotropy should be considered when the viewing angle is large. From another perspective, anisotropy is also a useful feature. Circular SAR (CSAR) can detect the scattering variation under different azimuthal look angles by a 360-degree observation. Different targets usually have varying degrees of anisotropy, which aids in target discrimination. However, there is no effective method to quantify the degree of anisotropy. In this paper, aspect entropy is presented as a descriptor of the scattering anisotropy. The range of aspect entropy is from 0 to 1, which corresponds to anisotropic to isotropic. First, the method proposed extracts aspect entropy at the pixel level. Since the aspect entropy of pixels can discriminate isotropic and anisotropic scattering, the method prescreens the target from the isotropic clutters. Next, the method extracts aspect entropy at the target level. The aspect entropy of targets can discriminate between different types of targets. Then, the effect of noise on aspect entropy extraction is analyzed and a denoising method is proposed. The Gotcha public release dataset, an X-band circular SAR data, is used to validate the method and the discrimination capability of aspect entropy.<\/jats:p>","DOI":"10.3390\/s19020346","type":"journal-article","created":{"date-parts":[[2019,1,17]],"date-time":"2019-01-17T11:30:27Z","timestamp":1547724627000},"page":"346","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":25,"title":["Aspect Entropy Extraction Using Circular SAR Data and Scattering Anisotropy Analysis"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1592-5933","authenticated-orcid":false,"given":"Fei","family":"Teng","sequence":"first","affiliation":[{"name":"Key Laboratory of Technology in Geospatial Information Processing and Application System, Chinese Academy of Sciences, Beijing 100190, China"},{"name":"Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China"},{"name":"School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 101408, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wen","family":"Hong","sequence":"additional","affiliation":[{"name":"Key Laboratory of Technology in Geospatial Information Processing and Application System, Chinese Academy of Sciences, Beijing 100190, China"},{"name":"Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yun","family":"Lin","sequence":"additional","affiliation":[{"name":"School of Electronic Information Engineering, North China University of Technology, Beijing 100144, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2019,1,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6","DOI":"10.1109\/MGRS.2013.2248301","article-title":"A tutorial on synthetic aperture radar","volume":"1","author":"Moreira","year":"2013","journal-title":"IEEE Geosci. Remote Sens. Mag."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"224","DOI":"10.1109\/TGRS.2008.2000837","article-title":"Four-dimensional SAR imaging for height estimation and monitoring of single and double scatterers","volume":"47","author":"Fornaro","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"506","DOI":"10.1109\/TGRS.2006.888097","article-title":"SAR polarimetry to observe oil spills","volume":"45","author":"Migliaccio","year":"2007","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1823","DOI":"10.1109\/83.806628","article-title":"Adaptive target detection in foliage-penetrating SAR images using alpha-stable models","volume":"8","author":"Banerjee","year":"1999","journal-title":"IEEE Trans. Image Process."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Lin, Y., Hong, W., Tan, W., Wang, Y., and Xiang, M. (2012, January 22\u201327). Airborne circular SAR imaging: Results at P-band. Proceedings of the 2012 IEEE International Geoscience and Remote Sensing Symposium, Munich, Germany.","DOI":"10.1109\/IGARSS.2012.6352051"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Dupuis, X., and Martineau, P. (2014, January 13\u201318). Very high resolution circular SAR imaging at X band. Proceedings of the 2014 IEEE Geoscience and Remote Sensing Symposium, Quebec City, QC, Canada.","DOI":"10.1109\/IGARSS.2014.6946578"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2192","DOI":"10.1109\/36.789616","article-title":"Experimental studies on circular SAR imaging in clutter using angular correlation function technique","volume":"37","author":"Chan","year":"1999","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_8","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":"52","author":"Ponce","year":"2014","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"164","DOI":"10.1117\/12.544935","article-title":"Wide-angle SAR imaging","volume":"5427","author":"Moses","year":"2004","journal-title":"Proc. SPIE"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1406","DOI":"10.1049\/el.2016.1764","article-title":"Adaptive imaging of anisotropic target based on circular-SAR","volume":"52","author":"Zhao","year":"2016","journal-title":"Electron. Lett."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"2264","DOI":"10.1109\/TGRS.2003.817188","article-title":"Scene characterization using subaperture polarimetric SAR data","volume":"41","author":"Reigber","year":"2003","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Ferro-Famil, L., and Pottier, E. (2007, January 11\u201313). Urban area remote sensing from L-band PolSAR data using time-frequency techniques. Proceedings of the 2007 Urban Remote Sensing Joint Event, Paris, France.","DOI":"10.1109\/URS.2007.371769"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"34296","DOI":"10.1109\/ACCESS.2018.2838329","article-title":"An Improved H\/\u03b1 Unsupervised Classification Method for Circular PolSAR Images","volume":"6","author":"Xue","year":"2018","journal-title":"IEEE Access"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1575","DOI":"10.1109\/LGRS.2018.2850859","article-title":"Anisotropy Scattering Detection from Multiaspect Signatures of Circular Polarimetric SAR","volume":"15","author":"Li","year":"2018","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Stojanovic, I., Cetin, M., and Karl, W.C. (2008). Joint space aspect reconstruction of wide-angle SAR exploiting sparsity. Proc. SPIE, 6970.","DOI":"10.1117\/12.786288"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"948","DOI":"10.1109\/19.543991","article-title":"Radar cross section measurements using near-field radar imaging","volume":"45","author":"Odendaal","year":"1996","journal-title":"IEEE Trans. Instrum. Meas."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"623","DOI":"10.1002\/j.1538-7305.1948.tb00917.x","article-title":"A mathematical theory of communication","volume":"27","author":"Shannon","year":"1948","journal-title":"Bell Syst. Tech. J."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1599","DOI":"10.1117\/12.202062","article-title":"Concept of polarization entropy in optical scattering","volume":"34","author":"Cloude","year":"1995","journal-title":"Opt. Eng."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"75","DOI":"10.1109\/LGRS.2011.2160837","article-title":"Improved four-component model-based target decomposition for polarimetric SAR data","volume":"9","author":"Shan","year":"2012","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2412","DOI":"10.1109\/TGRS.2004.836259","article-title":"Polarimetric characteristics of sea ice in the sea of Okhotsk observed by airborne L-band SAR","volume":"42","author":"Wakabayashi","year":"2004","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"769","DOI":"10.1109\/TAES.2003.1238734","article-title":"Sythetic-aperture radar processing using fast factorized back-projection","volume":"39","author":"Ulander","year":"2003","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Ponce, O., Prats, P., Rodriguez-Cassola, M., Scheiber, R., and Reigber, A. (2011, January 24\u201329). Processing of circular SAR trajectories with fast factorized back-projection. Proceedings of the 2011 IEEE International Geoscience and Remote Sensing Symposium, Vancouver, BC, Canada.","DOI":"10.1109\/IGARSS.2011.6050026"},{"key":"ref_23","unstructured":"Kuttikkad, S., and Chellappa, R. (1994, January 13\u201316). Non-Gaussian CFAR techniques for target detection in high resolution SAR images. Proceedings of the 1st International Conference on Image Processing, Austin, TX, USA."},{"key":"ref_24","unstructured":"Lombardo, P., Sciotti, M., and Kaplan, L.M. (2001, January 1\u20133). SAR prescreening using both target and shadow information. Proceedings of the 2001 IEEE Radar Conference, Atlanta, GA, USA."},{"key":"ref_25","unstructured":"Zhao, Y., Lin, Y., Hong, W., Shen, W., and Xue, F. (2017, January 23\u201328). Target aspect feature extraction and application from multi-aspect high resolution SAR. Proceedings of the 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Fort Worth, TX, USA."},{"key":"ref_26","first-page":"656","article-title":"GOTCHA experience report: Three-dimensional SAR imaging with complete circular apertures","volume":"6568","author":"Ertin","year":"2007","journal-title":"Proc. SPIE"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/2\/346\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:26:32Z","timestamp":1760185592000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/2\/346"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,1,16]]},"references-count":26,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2019,1]]}},"alternative-id":["s19020346"],"URL":"https:\/\/doi.org\/10.3390\/s19020346","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,1,16]]}}}