{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,20]],"date-time":"2025-11-20T12:52:58Z","timestamp":1763643178028,"version":"build-2065373602"},"reference-count":23,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2021,4,23]],"date-time":"2021-04-23T00:00:00Z","timestamp":1619136000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Academy Of Finland","award":["336145"],"award-info":[{"award-number":["336145"]}]},{"name":"Academy of Finland","award":["337656","314312"],"award-info":[{"award-number":["337656","314312"]}]},{"name":"Chinese Academy of Science","award":["181811KYSB20160040","XDA22030202"],"award-info":[{"award-number":["181811KYSB20160040","XDA22030202"]}]},{"name":"Jihua Lab","award":["X190211TE190"],"award-info":[{"award-number":["X190211TE190"]}]},{"name":"Huawei","award":["9424877"],"award-info":[{"award-number":["9424877"]}]},{"name":"National Natural Science Foundation of China","award":["41971302"],"award-info":[{"award-number":["41971302"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The paper investigates the penetration properties of an airborne Ku-band frequency modulated continuous waveform (FMCW) profiling radar named Tomoradar and a satellite near-infrared lidar into the boreal forest of Finland. We achieve the accumulative energy distributions based on the Tomoradar waveforms and the satellite lidar waveforms generated from the high-density airborne lidar data within Tomoradar footprints. By comparing two groups of the height percentiles and energy percentiles derived from the accumulative energy distributions, we evaluate the relationship of penetrations between the Ku-band microwave and near-infrared laser according to the coefficients of the determination (COD), and the root mean square errors (RMSE) of linear regression analyses. The quantitative analysis results demonstrate that the height and energy percentiles derived from Tomoradar waveforms correlate well with those from satellite lidar waveforms with the mean correlation coefficients of more than 0.78 and 0.85. The linear regression models for the height and energy percentile produce excellent fits with the mean CODs of 0.95 and 0.90 and the mean RMSEs of 1.25 m and 0.03, respectively. Less than 15% of height percentiles and 87.54% of the energy percentiles in the sixth stratum near the ground derived from Tomoradar waveforms surpass those from satellite lidar waveforms. Hence, the Ku-band microwave can penetrate deeper into the forest than the near-infrared laser at the same spatial scale. In addition, quadratic fitting models are established to describe the differences of the height percentile (DHP) and the energy percentile (DEP) to expound the canopy height and closure contributions numerically. The facts that the CODs of the DHP and DEP individually are more than 0.96 and 0.89 and the fitting residual histograms approximate to normal distributions reveal the reliabilities of the proposed fitting models. Thus, the penetration analyses are valid for the explorations on the FMCW radar applications and the data fusion of the Ku-band radar and near-infrared lidar in the forest investigations.<\/jats:p>","DOI":"10.3390\/rs13091650","type":"journal-article","created":{"date-parts":[[2021,4,25]],"date-time":"2021-04-25T02:12:57Z","timestamp":1619316777000},"page":"1650","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["The Penetration Analysis of Airborne Ku-Band Radar Versus Satellite Infrared Lidar Based on the Height and Energy Percentiles in the Boreal Forest"],"prefix":"10.3390","volume":"13","author":[{"given":"Hui","family":"Zhou","sequence":"first","affiliation":[{"name":"Electronic Information School, Wuhan University, Wuhan 430079, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0148-3609","authenticated-orcid":false,"given":"Yuwei","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]},{"given":"Teemu","family":"Hakala","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]},{"given":"Ziyi","family":"Feng","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]},{"given":"Changhui","family":"Jiang","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4366-4547","authenticated-orcid":false,"given":"Jianxin","family":"Jia","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]},{"given":"Haibin","family":"Sun","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"},{"name":"Key Laboratory of Intelligent Infrared Perception, Shanghai Institute of Technical Physics, Chinese Academy of Sciences (CAS), Shanghai 200043, China"}]},{"given":"Juha","family":"Hyypp\u00e4","sequence":"additional","affiliation":[{"name":"Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute, Geodeetinrinne 2, 02431 Kirkkonummi, Finland"}]}],"member":"1968","published-online":{"date-parts":[[2021,4,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1016\/S1462-9011(03)00070-4","article-title":"A review of remote sensing technology in support of the Kyoto Protocol","volume":"6","author":"Rosenqvist","year":"2003","journal-title":"Environ. Sci. Policy"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"511","DOI":"10.1641\/0006-3568(2004)054[0511:HSRRSD]2.0.CO;2","article-title":"High spatial resolution remotely sensed data for ecosystem char-acterisation","volume":"54","author":"Wulder","year":"2004","journal-title":"BioScience"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"49","DOI":"10.1109\/LGRS.2005.856706","article-title":"Inversion of a lidar waveform model for forest bio-physical parameter estimation","volume":"3","author":"Koetz","year":"2006","journal-title":"IEEE Geosci. Remote Sens. Lett."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1016\/j.agrformet.2003.08.027","article-title":"Review of methods for in situ leaf area index determination: Part I. Theories, sensors and hemispherical photography","volume":"121","author":"Jonckheere","year":"2004","journal-title":"Agric. Forest Meteorol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"249","DOI":"10.14358\/PERS.69.3.249","article-title":"Model-Based Conifer canopy Surface Reconstruction form Photographic Imagery: Overcoming the Occlusion, Foreshortening, and Edge Effects","volume":"69","author":"Sheng","year":"2003","journal-title":"Photogramm. Eng. Remote Sens."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"5605","DOI":"10.1080\/01431160802060904","article-title":"Extracting forest canopy structure from spatial information of high resolution optical imagery: Tree crown size versus leaf area index","volume":"29","author":"Song","year":"2008","journal-title":"Int. J. Remote Sens."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"138","DOI":"10.1016\/j.rse.2009.08.018","article-title":"Estimating forest canopy height and terrain relief from GLAS waveform metrics","volume":"114","author":"Duncanson","year":"2010","journal-title":"Remote Sens. Environ."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"144","DOI":"10.1016\/j.isprsjprs.2015.03.001","article-title":"Validation of Canopy Height Profile methodology for small-footprint full-waveform airborne LiDAR data in a discontinuous canopy environment","volume":"104","author":"Fieber","year":"2015","journal-title":"ISPRS J. Photogramm. Remote Sens."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Harkel, J.T., Bartholomeus, H., and Kooistra, L. (2019). Biomass and Crop Height Estimation of Different Crops Using UAV-Based Lidar. Remote Sens., 12.","DOI":"10.3390\/rs12010017"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"112165","DOI":"10.1016\/j.rse.2020.112165","article-title":"Mapping global forest canopy height through integration of GEDI and Landsat data","volume":"253","author":"Potapov","year":"2021","journal-title":"Remote Sens. Environ."},{"key":"ref_11","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_12","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1016\/S0034-4257(01)00329-7","article-title":"Stem volume retrieval in boreal forests from ERS-1\/2 interferometry","volume":"81","author":"Santoro","year":"2002","journal-title":"Remote Sens. Environ."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2283","DOI":"10.1109\/TGRS.2017.2778024","article-title":"Estimating Ground Level and Canopy Top Elevation With Airborne Microwave Profiling Radar","volume":"56","author":"Feng","year":"2018","journal-title":"IEEE Trans. Geosci. Remote Sens."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Chen, Y., Hakala, T., Karjalainen, M., Feng, Z., Tang, J., Litkey, P., Kukko, A., Jaakkola, A., and Hyypp\u00e4, J. (2017). UAV-borne profiling radar for forest research. Remote Sens., 9.","DOI":"10.3390\/rs9010058"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3590","DOI":"10.1109\/JSTARS.2018.2865624","article-title":"Estimation of Canopy Height Using an Airborne Ku-Band Frequency-Modulated Continuous Waveform Profiling Radar","volume":"11","author":"Zhou","year":"2018","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Du, K., Huang, H., Feng, Z., Hakala, T., Chen, Y., and Hyypp\u00e4, J. (2021). Using Microwave Profile Radar to Estimate Forest Canopy Leaf Area Index: Linking 3D Radiative Transfer Model and Forest Gap Model. Remote Sens., 13.","DOI":"10.3390\/rs13020297"},{"key":"ref_17","unstructured":"Weishampel, J.F., Ranson, K.J., and Harding, D.J. (1996). Remote sensing of forest canopies. Selbyana, 6\u201314."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"116","DOI":"10.5589\/m06-011","article-title":"Investigating laser pulse penetration through a conifer canopy by integrating air-borne and terrestrial lidar","volume":"32","author":"Chasmer","year":"2006","journal-title":"Can. J. Remote Sens."},{"key":"ref_19","first-page":"836008","article-title":"Lidar flecks: Modeling the influence of canopy type on tactical foliage penetration by airborne, active sensor platforms","volume":"8360","author":"Massaro","year":"2012","journal-title":"SPIE Def. Secur. Sens."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"2786","DOI":"10.1016\/j.rse.2011.01.026","article-title":"Satellite lidar vs. small footprint airborne lidar: Comparing the accuracy of aboveground biomass estimates and forest structure metrics at footprint level","volume":"115","author":"Popescu","year":"2011","journal-title":"Remote Sens. Environ."},{"key":"ref_21","first-page":"102133","article-title":"Lidar-aided analysis of boreal forest backscatter at Ku band","volume":"91","author":"Chen","year":"2020","journal-title":"Int. J. Appl. Earth Obs. Geoinf."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Zhou, H., Chen, Y., Hu, N., Dong, Y., Xu, X., Feng, Z., Hakala, T., and Hyypp\u00e4, J. (2020). The Determination of Effective Beamwidth of Ku Band Profiling Radar Based on Waveform Matching Method in the Boreal Forest of Finland. Remote Sens., 12.","DOI":"10.3390\/rs12172710"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"924","DOI":"10.1109\/JSTARS.2012.2211863","article-title":"Stem Volume and Above-Ground Biomass Estimation of Individual Pine Trees From LiDAR Data: Contribution of Full-Waveform Signals","volume":"6","author":"Allouis","year":"2012","journal-title":"IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/9\/1650\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T05:51:54Z","timestamp":1760161914000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/9\/1650"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,4,23]]},"references-count":23,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2021,5]]}},"alternative-id":["rs13091650"],"URL":"https:\/\/doi.org\/10.3390\/rs13091650","relation":{},"ISSN":["2072-4292"],"issn-type":[{"type":"electronic","value":"2072-4292"}],"subject":[],"published":{"date-parts":[[2021,4,23]]}}}