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Open AccessArticle

Intercomparison of Soil Moisture Retrieved from GNSS-R and from Passive L-Band Radiometry at the Valencia Anchor Station

1
Department of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China
2
Meteorological Observation Centre, China Meteorological Administration, Beijing 100081, China
3
Faculty of Physics, Earth Physics and Thermodynamics Department, Climatology from Satellites Group, University of Valencia, Burjassot, 46100 Valencia, Spain
4
European Space Agency, ESA-ESTEC, 2200 AG Noordwijk, The Netherlands
5
College of Information Science and Engineering, Shandong Agricultural University, Tai’an 271018, China
6
IRTIC, University of Valencia, C/. Catedrático José Beltrán, 2, 46980 Paterna, Spain
7
Starlab-Living Science, 08035 Barcelona, Spain
8
Earth Observation Research Group, Institute of Space Sciences (ICE, CSIC), 08193 Barcelona, Spain
9
School of Electronic and Information Engineering, Beihang University, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Now at Image Processing Laboratory, University of Valencia, C/Catedrático José Beltrán, 2, 46980 Paterna, Spain.
Now at Global Science and Technology, Inc., Greenbelt, MD 20770 USA, appointed at the Laboratory for Satellite Altimetry, National Oceanographic and Atmospheric Administration, College Park, MD 20740, USA.
§
Now at Neuroelectrics Barcelona, 08035 Barcelona, Spain.
Sensors 2019, 19(8), 1900; https://doi.org/10.3390/s19081900
Received: 28 February 2019 / Revised: 11 April 2019 / Accepted: 18 April 2019 / Published: 22 April 2019
(This article belongs to the Special Issue Satellite Remotely Sensed Soil Moisture)
In this paper, the SOMOSTA (Soil Moisture Monitoring Station) experiment on the intercomparison of soil moisture monitoring from Global Navigation Satellite System Reflectometry (GNSS-R) signals and passive L-band microwave radiometer observations at the Valencia Anchor Station is introduced. The GNSS-R instrument has an up-looking antenna for receiving direct signals from satellites, and a dual-pol down-looking antenna for receiving LHCP (left-hand circular polarization) and RHCP (right-hand circular polarization) reflected signals from the soil surface. Data were collected from the three different antennas through the two channels of Oceanpal GNSS-R receiver and, in addition, calibration was performed to reduce the impact from the differing channels. Reflectivity was thus measured, and soil moisture could be retrieved. The ESA (European Space Agency)-funded ELBARA-II (ESA L Band Radiometer II) is an L-band radiometer with two channels with 11 MHz bandwidth and respective center frequencies of 1407.5 MHz and 1419.5 MHz. The ELBARAII antenna is a large dual-mode Picket horn that is 1.4 m wide, with a length of 2.7 m with −3 dB full beam width of 12° (±6° around the antenna main direction) and a gain of 23.5 dB. By comparing GNSS-R and ELBARA-II radiometer data, a high correlation was found between the LHCP reflectivity measured by GNSS-R and the horizontal/vertical reflectivity from the radiometer (with correlation coefficients ranging from 0.83 to 0.91). Neural net fitting was used for GNSS-R soil moisture inversion, and the RMSE (Root Mean Square Error) was 0.014 m3/m3. The determination coefficient between the retrieved soil moisture and in situ measurements was R2 = 0.90 for Oceanpal and R2 = 0.65 for Elbara II, and the ubRMSE (Unbiased RMSE) were 0.0128 and 0.0734 respectively. The soil moisture retrievals by both L-band remote sensing methods show good agreement with each other, and their mutual correspondence with in-situ measurements and with rainfall was also good. View Full-Text
Keywords: ELBARA-II radiometer; GNSS-R; L-band radiometry; Oceanpal; soil moisture; Valencia Anchor Station ELBARA-II radiometer; GNSS-R; L-band radiometry; Oceanpal; soil moisture; Valencia Anchor Station
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Yin, C.; Lopez-Baeza, E.; Martin-Neira, M.; Fernandez-Moran, R.; Yang, L.; Navarro-Camba, E.A.; Egido, A.; Mollfulleda, A.; Li, W.; Cao, Y.; Zhu, B.; Yang, D. Intercomparison of Soil Moisture Retrieved from GNSS-R and from Passive L-Band Radiometry at the Valencia Anchor Station. Sensors 2019, 19, 1900.

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