{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,21]],"date-time":"2026-02-21T18:34:08Z","timestamp":1771698848436,"version":"3.50.1"},"reference-count":40,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2021,7,26]],"date-time":"2021-07-26T00:00:00Z","timestamp":1627257600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Natural Science Foundation of China","award":["41804004,41820104005, 41804003"],"award-info":[{"award-number":["41804004,41820104005, 41804003"]}]},{"name":"the Strategic Priority Research Program of the Chinese Academy of Sciences","award":["XDA19070202"],"award-info":[{"award-number":["XDA19070202"]}]},{"name":"Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)","award":["CUG200619, CUG190633"],"award-info":[{"award-number":["CUG200619, CUG190633"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The underlying topography is an important part of the three-dimensional structure of forests, and is used for a variety of applications, such as hydrology and water resource management, civil engineering projects, and forest resource surveying. Due to the three-dimensional imaging ability and strong penetration, the tomographic synthetic aperture radar (TomoSAR) with a long wavelength has been shown to be a useful tool to estimate the underlying topography. At present, most of the current methods use the local means method to estimate the sample covariance matrix, in which the vertical backscattering power is estimated. However, these methods cannot easily obtain high-precision underlying topography, and often lose some detailed information. In this paper, to solve this problem, a non-local means method is introduced to estimate the optimal covariance matrix by combining weighted neighborhood pixels. To validate the feasibility and effectiveness of this proposed method, a BioSAR 2008 campaign L-band dataset acquired from the northern forests of Sweden was used to inverse the underlying topography. The results show that the accuracy of the underlying topography retrieved by the proposed method is improved by more than 30% when compared with the traditional method.<\/jats:p>","DOI":"10.3390\/rs13152926","type":"journal-article","created":{"date-parts":[[2021,7,26]],"date-time":"2021-07-26T22:22:46Z","timestamp":1627338166000},"page":"2926","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Underlying Topography Inversion Using TomoSAR Based on Non-Local Means for an L-Band Airborne Dataset"],"prefix":"10.3390","volume":"13","author":[{"given":"Xing","family":"Peng","sequence":"first","affiliation":[{"name":"School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2461-2477","authenticated-orcid":false,"given":"Youjun","family":"Wang","sequence":"additional","affiliation":[{"name":"School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Shilin","family":"Long","sequence":"additional","affiliation":[{"name":"School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xiong","family":"Pan","sequence":"additional","affiliation":[{"name":"School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4293-3354","authenticated-orcid":false,"given":"Qinghua","family":"Xie","sequence":"additional","affiliation":[{"name":"School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1277-564X","authenticated-orcid":false,"given":"Yanan","family":"Du","sequence":"additional","affiliation":[{"name":"School of Geographical Sciences, Guangzhou University, Guangzhou 510006, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Haiqiang","family":"Fu","sequence":"additional","affiliation":[{"name":"School of Geoscience and Info-Physics, Central South University, Changsha 410083, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jianjun","family":"Zhu","sequence":"additional","affiliation":[{"name":"School of Geoscience and Info-Physics, Central South University, Changsha 410083, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xinwu","family":"Li","sequence":"additional","affiliation":[{"name":"Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2021,7,26]]},"reference":[{"key":"ref_1","first-page":"967","article-title":"Relating P-Band Synthetic Aperture Radar Tomography to Tropical Forest Biomass","volume":"52","author":"Dinh","year":"2013","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"30","DOI":"10.1109\/MGRS.2019.2963093","article-title":"Forest SAR Tomography: Principles and Applications","volume":"8","author":"Aghababaee","year":"2020","journal-title":"IEEE Geosci. Remote Sens. Mag."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"138","DOI":"10.1016\/j.rse.2015.12.037","article-title":"SAR tomography for the retrieval of forest biomass and height: Cross-validation at two tropical forest sites in French Guiana","volume":"175","author":"Dinh","year":"2016","journal-title":"Remote Sens. Environ."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Ngo, Y.-N., Ho Tong Minh, D., Moussawi, I., Villard, L., Ferro-Famil, L., d\u2019Alessandro, M.M., Tebaldini, S., Albinetv, C., Scipal, K., and Le Toan, T. (2018, January 22\u201327). Afrisar-Tropisar: Forest Biomass Retrieval by P-Band Sar Tomography. Proceedings of the IGARSS 2018\u20142018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain.","DOI":"10.1109\/IGARSS.2018.8517464"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Peng, X., Li, X., Wang, C., Zhu, J., Liang, L., Fu, H., Du, Y., Yang, Z., and Xie, Q. (2019). SPICE-Based SAR Tomography Over Forest Areas Using a Small Number of P-band Airborne F-SAR Images Characterized by Non-Uniformly Distributed Baselines. Remote Sens., 11.","DOI":"10.3390\/rs11080975"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2142","DOI":"10.1109\/36.868873","article-title":"First demonstration of airborne SAR tomography using multibaseline L-band data","volume":"38","author":"Reigber","year":"2000","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1344","DOI":"10.1109\/TAES.2002.1145755","article-title":"Layover solution in multibaseline SAR interferometry","volume":"38","author":"Gini","year":"2002","journal-title":"IEEE Trans. Aerosp. Electron. Syst."},{"key":"ref_8","unstructured":"Lombardini, F., and Reigber, A. (2003, January 21\u201325). Adaptive spectral estimation for multibaseline SAR tomography with airborne L-band data. Proceedings of the 2003 IEEE International Geoscience and Remote Sensing Symposium (IEEE Cat. No. 03CH37477), Toulouse, France."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1109\/TGRS.2008.2007846","article-title":"Estimation of the minimum number of tracks for SAR tomography","volume":"47","author":"Nannini","year":"2009","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1857","DOI":"10.1109\/JSTARS.2021.3051081","article-title":"The Performance of Relative Height Metrics for Estimation of Forest Above-Ground Biomass Using L-and X-Bands TomoSAR Data","volume":"14","author":"Yu","year":"2021","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"232","DOI":"10.1109\/TGRS.2011.2159614","article-title":"Multibaseline polarimetric SAR tomography of a boreal forest at P-and L-bands","volume":"50","author":"Tebaldini","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"6774","DOI":"10.1109\/TGRS.2019.2908517","article-title":"Digital terrain model retrieval in tropical forests through P-band SAR tomography","volume":"57","author":"Tebaldini","year":"2019","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"El Moussawi, I., Ho Tong Minh, D., Baghdadi, N., Abdallah, C., Jomaah, J., Strauss, O., and Lavalle, M. (2019). L-Band UAVSAR tomographic imaging in dense forests: Gabon forests. Remote Sens., 11.","DOI":"10.3390\/rs11050475"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"451","DOI":"10.1109\/LGRS.2019.2923252","article-title":"Tropical Forest Height Retrieval Based on P-Band Multibaseline SAR Data","volume":"17","author":"Yang","year":"2019","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Zhang, Q., Huang, Y., Schwaebisch, M., Mercer, B., and Wei, M. (2012, January 22\u201327). Forest height estimation using single-pass dual-baseline L-band PolInSAR data. Proceedings of the 2012 IEEE International Geoscience and Remote Sensing Symposium, Munich, Germany.","DOI":"10.1109\/IGARSS.2012.6351946"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"095048","DOI":"10.1117\/1.JRS.9.095048","article-title":"Multibaseline polarimetric synthetic aperture radar tomography of forested areas using wavelet-based distribution compressive sensing","volume":"9","author":"Liang","year":"2015","journal-title":"J. Appl. Remote Sens."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"3386","DOI":"10.1109\/JSTARS.2018.2847033","article-title":"L-and P-band 3-D SAR reflectivity profiles versus lidar waveforms: The AfriSAR case","volume":"11","author":"Pardini","year":"2018","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"3617","DOI":"10.1109\/JSTARS.2018.2851606","article-title":"In situ reference datasets from the TropiSAR and AfriSAR campaigns in support of upcoming spaceborne biomass missions","volume":"11","author":"Labriere","year":"2018","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_19","first-page":"147","article-title":"Comparison of tomographic SAR reflectivity reconstruction algorithms for forest applications at L-band","volume":"58","author":"Pardini","year":"2019","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2213","DOI":"10.1109\/TGRS.2011.2171494","article-title":"Under-foliage object imaging using SAR tomography and polarimetric spectral estimators","volume":"50","author":"Huang","year":"2011","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Ramachandran, N., Saatchi, S., Tebaldini, S., d\u2019Alessandro, M.M., and Dikshit, O. (2021). Evaluation of P-Band SAR Tomography for Mapping Tropical Forest Vertical Backscatter and Tree Height. Remote Sens., 13.","DOI":"10.3390\/rs13081485"},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Huang, Y., Zhang, Q., and Ferro-Famil, L. (2021). Forest Height Estimation Using a Single-Pass Airborne L-Band Polarimetric and Interferometric SAR System and Tomographic Techniques. Remote Sens., 13.","DOI":"10.3390\/rs13030487"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Ferro-Famil, L., Huang, Y., and Pottier, E. (2015, January 17\u201321). Principles and applications of polarimetric SAR tomography for the characterization of complex environments. Proceedings of the VIII Hotine-Marussi Symposium on Mathematical Geodesy, Rome, Italy.","DOI":"10.1007\/1345_2015_12"},{"key":"ref_24","unstructured":"Guliaev, R., Pardini, M., and Papathanassiou, K. (April, January 28). A Comparison of Function Bases for Polarization Coherence Tomography in Forest Scenarios. Proceedings of the European Conference on Synthetic Aperture Radar, EUSAR 2021, Virtual."},{"key":"ref_25","unstructured":"Cazcarra-Bes, V., Pardini, M., and Papathanassiou, K. (2020). Definition of Tomographic SAR Configurations for Forest Structure Applications at L-Band. IEEE Geosci. Remote Sens. Lett."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"729","DOI":"10.1109\/LGRS.2018.2808681","article-title":"The role of nonlocal estimation in SAR tomographic imaging of volumetric media","volume":"15","author":"Aghababaee","year":"2018","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_27","first-page":"272","article-title":"Nonlocal filtering applied to 3-D reconstruction of tomographic SAR data","volume":"56","author":"Guillaso","year":"2017","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Asopa, U., and Kumar, S. (2020). UAVSAR Tomography for Vertical Profile Generation of Tropical Forest of Mondah National Park, Gabon. Earth Space Sci., 7.","DOI":"10.1029\/2020EA001230"},{"key":"ref_29","first-page":"116","article-title":"Advances in Information Extraction of Surface Parameters Using Tomographic SAR","volume":"10","author":"Li","year":"2021","journal-title":"J. Radars"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"507","DOI":"10.1109\/TGRS.2003.809934","article-title":"Three-dimensional focusing with multipass SAR data","volume":"41","author":"Fornaro","year":"2003","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"5283","DOI":"10.1109\/TGRS.2012.2231081","article-title":"Wavelet-based compressed sensing for SAR tomography of forested areas","volume":"51","author":"Aguilera","year":"2013","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_32","unstructured":"Homer, J., Longstaff, I., and Callaghan, G. (1996, January 31). High resolution 3-D SAR via multi-baseline interferometry. Proceedings of the IGARSS\u201996 1996 International Geoscience and Remote Sensing Symposium, Lincoln, NE, USA."},{"key":"ref_33","unstructured":"Stoica, P., and Moses, R.L. (2005). Spectral Analysis of Signals, Prentice Hall."},{"key":"ref_34","unstructured":"She, Z., Gray, D., Bogner, R., and Homer, J. (July, January 28). Three-dimensional SAR imaging via multiple pass processing. Proceedings of the IEEE 1999 International Geoscience and Remote Sensing Symposium, IGARSS\u201999 (Cat. No. 99CH36293), Hamburg, Germany."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"5175","DOI":"10.1109\/JSTARS.2017.2741723","article-title":"Spaceborne PolSAR tomography for forest height retrieval","volume":"10","author":"Kumar","year":"2017","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1628","DOI":"10.1109\/JSTARS.2013.2256881","article-title":"Iterative bilateral filtering of polarimetric SAR data","volume":"6","author":"Guillaso","year":"2013","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"2363","DOI":"10.1109\/36.789635","article-title":"Polarimetric SAR speckle filtering and its implication for classification","volume":"37","author":"Lee","year":"1999","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Barbaresco, F. (2008, January 18\u201320). Interactions between symmetric cone and information geometries: Bruhat-tits and siegel spaces models for high resolution autoregressive doppler imagery. Proceedings of the LIX Fall Colloquium on Emerging Trends in Visual Computing, Palaiseau, France.","DOI":"10.1007\/978-3-642-00826-9_6"},{"key":"ref_39","unstructured":"European Space Agency (2009). Technical Assistance for the Development of Airborne SAR and Geophysical Measurements during the BioSAR 2008 Experiment, European Space Agency. Final Report."},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Peng, X., Li, X., Du, Y., and Xie, Q. (2021). Forest Height Estimation from a Robust TomoSAR Method in the Case of Small Tomographic Aperture with Airborne Dataset at L-Band. Remote Sens., 13.","DOI":"10.3390\/rs13112147"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/15\/2926\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T06:35:12Z","timestamp":1760164512000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/15\/2926"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,7,26]]},"references-count":40,"journal-issue":{"issue":"15","published-online":{"date-parts":[[2021,8]]}},"alternative-id":["rs13152926"],"URL":"https:\/\/doi.org\/10.3390\/rs13152926","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,7,26]]}}}