{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,20]],"date-time":"2026-02-20T06:22:42Z","timestamp":1771568562529,"version":"3.50.1"},"reference-count":36,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2019,7,2]],"date-time":"2019-07-02T00:00:00Z","timestamp":1562025600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000844","name":"European Space Agency","doi-asserted-by":"publisher","award":["Contract 4000115192\/15\/NL\/AF\/eg"],"award-info":[{"award-number":["Contract 4000115192\/15\/NL\/AF\/eg"]}],"id":[{"id":"10.13039\/501100000844","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The simultaneous availability of observations from space by remote sensing platforms operating at multiple frequencies in the microwave domain suggests investigating their complementarity in thematic mapping and retrieval of biophysical parameters. In particular, there is an interest to understand whether the wealth of short wavelength Synthetic Aperture Radar (SAR) backscatter observations at X-, C-, and L-band from currently operating spaceborne missions can improve the retrieval of forest stem volume, i.e., above-ground biomass, in the boreal zone with respect to a single frequency band. To this scope, repeated observations from TerraSAR-X, Sentinel-1 and ALOS-2 PALSAR-2 from the test sites of Remningstorp and Krycklan, Sweden, have been analyzed and used to estimate stem volume with a retrieval framework based on the Water Cloud Model. Individual estimates of stem volume were then combined linearly to form single-frequency and multi-frequency estimates. The retrieval was assessed at large 0.5 ha forest inventory plots (Remningstorp) and small 0.03 ha forest inventory plots (Krycklan). The relationship between SAR backscatter and stem volume differed depending on forest structure and environmental conditions, in particular at X- and C-band. The highest retrieval accuracy was obtained at both test sites at L-band. The combination of stem volume estimates from data acquired at two or three frequencies achieved an accuracy that was superior to values obtained at a single frequency. When combining estimates from X-, C-, and L-band data, the relative RMSE for the 0.5 ha inventory plots at Remningstorp was 31.3%. For the 0.03 ha inventory plots at Krycklan, the relative RMSE was above 50%. In a retrieval scenario involving short wavelength SAR backscatter data, these results suggest combining multiple frequencies to ensure the highest possible retrieval accuracy achievable. Retrievals should be undertaken to target spatial scales well above the size of a pixel.<\/jats:p>","DOI":"10.3390\/rs11131563","type":"journal-article","created":{"date-parts":[[2019,7,2]],"date-time":"2019-07-02T12:11:17Z","timestamp":1562069477000},"page":"1563","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":43,"title":["Complementarity of X-, C-, and L-band SAR Backscatter Observations to Retrieve Forest Stem Volume in Boreal Forest"],"prefix":"10.3390","volume":"11","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3339-6991","authenticated-orcid":false,"given":"Maurizio","family":"Santoro","sequence":"first","affiliation":[{"name":"Gamma Remote Sensing, Worbstrasse 225, 3073 G\u00fcmligen, Switzerland"}]},{"given":"Oliver","family":"Cartus","sequence":"additional","affiliation":[{"name":"Gamma Remote Sensing, Worbstrasse 225, 3073 G\u00fcmligen, Switzerland"}]},{"given":"Johan E. S.","family":"Fransson","sequence":"additional","affiliation":[{"name":"Department of Forest Resource Management, Swedish University of Agricultural Sciences, SE-901 83 Ume\u00e5, Sweden"}]},{"given":"Urs","family":"Wegm\u00fcller","sequence":"additional","affiliation":[{"name":"Gamma Remote Sensing, Worbstrasse 225, 3073 G\u00fcmligen, Switzerland"}]}],"member":"1968","published-online":{"date-parts":[[2019,7,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"945","DOI":"10.1111\/j.1365-2486.2005.00955.x","article-title":"Aboveground Forest Biomass and the Global Carbon Balance","volume":"11","author":"Houghton","year":"2005","journal-title":"Glob. Chang. Biol."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"405","DOI":"10.5194\/essd-10-405-2018","article-title":"Global Carbon Budget 2017","volume":"10","author":"Andrew","year":"2018","journal-title":"Earth Syst. Sci. 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