{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,10]],"date-time":"2026-01-10T08:15:01Z","timestamp":1768032901103,"version":"3.49.0"},"reference-count":28,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2024,4,15]],"date-time":"2024-04-15T00:00:00Z","timestamp":1713139200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Aeronautics and Space Administration through the Research Opportunities in Space and Earth Sciences","award":["NNH19ZDA001N-SMAP\u2014grant task order 80NM0018F0618"],"award-info":[{"award-number":["NNH19ZDA001N-SMAP\u2014grant task order 80NM0018F0618"]}]},{"name":"National Aeronautics and Space Administration through the Research Opportunities in Space and Earth Sciences","award":["19-SMAP19-0013"],"award-info":[{"award-number":["19-SMAP19-0013"]}]},{"name":"ROSES NRA Program","award":["NNH19ZDA001N-SMAP\u2014grant task order 80NM0018F0618"],"award-info":[{"award-number":["NNH19ZDA001N-SMAP\u2014grant task order 80NM0018F0618"]}]},{"name":"ROSES NRA Program","award":["19-SMAP19-0013"],"award-info":[{"award-number":["19-SMAP19-0013"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The Soil Moisture Active\u2013Passive (SMAP) mission has greatly contributed to the use of remote sensing technologies for monitoring the Earth\u2019s land surface and estimating geophysical parameters that influence the climate system. Since the SMAP mission switched its radar receiver to allow the reception of Global Positioning System (GPS) signals, Global Navigation Satellite System Reflectometry (GNSS-R) configuration has been enabled, providing full polarimetric forward scattering measurements of the Earth\u2019s surface, also known as SMAP Reflectometry or SMAP-R. Polarimetric GNSS-R is beneficial for sensing land surface properties, especially for more accurate estimations of soil moisture (SM) in densely vegetated areas. In this study, we explore the opportunity to enhance SMAP mission soil moisture estimates using reflected GNSS signals. We achieve this by interpolating the sparse reflectivity data with terrain information to disaggregate radiometer brightness temperatures. Our main objective is to present a novel algorithm based on Graph Signal Processing (GSP) that uses reflectometry data to enhance SMAP radiometer observations and ultimately improve SM retrievals. By implementing methods from the GSP field, we formulate the reflectivity interpolation problem as a signal reconstruction on a graph, where the weights of the edges between the nodes are chosen as a function of geophysical information. Subsequently, using the retrieved reflectivity maps, we increase the resolution of the brightness temperature data, leading to an improvement in the SM estimates. Initial findings indicate that our GSP method presents a promising alternative for analyzing sparse remote sensing observations, leveraging Earth\u2019s surface geophysical information. This approach results in a notable improvement, with a reduced Root Mean Square Error (RMSE) of 11.8% compared to SMAP data and a reduction in unbiased RMSE (uRMSE) by 14.7% over vegetated areas.<\/jats:p>","DOI":"10.3390\/rs16081397","type":"journal-article","created":{"date-parts":[[2024,4,15]],"date-time":"2024-04-15T11:53:53Z","timestamp":1713182033000},"page":"1397","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Enhancing Soil Moisture Active\u2013Passive Estimates with Soil Moisture Active\u2013Passive Reflectometer Data Using Graph Signal Processing"],"prefix":"10.3390","volume":"16","author":[{"given":"Johanna","family":"Garcia-Cardona","sequence":"first","affiliation":[{"name":"Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9382-0686","authenticated-orcid":false,"given":"Nereida","family":"Rodriguez-Alvarez","sequence":"additional","affiliation":[{"name":"Planetary Radar and Radio Sciences Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6441-6676","authenticated-orcid":false,"given":"Joan Francesc","family":"Munoz-Martin","sequence":"additional","affiliation":[{"name":"Signal Processing and Networks Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7608-0559","authenticated-orcid":false,"given":"Xavier","family":"Bosch-Lluis","sequence":"additional","affiliation":[{"name":"Signal Processing and Networks Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kamal","family":"Oudrhiri","sequence":"additional","affiliation":[{"name":"Communication Architectures and Research Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,4,15]]},"reference":[{"key":"ref_1","unstructured":"(2023, September 26). 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