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On the Impact of Sea State on GNSS-R Polarimetric Observations

Hoseini, Mostafa and Semmling, Maximilian and Rennspiess, Erik and Ramatschi, Markus and Haas, Rüdiger and Strandberg, Joakim and Nahavandchi, Hossein and Wickert, Jens (2020) On the Impact of Sea State on GNSS-R Polarimetric Observations. EGU General Assembly 2020, 2020-05-04 - 2020-05-08, Vienna, Austria. doi: 10.5194/egusphere-egu2020-21823.

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Official URL: https://doi.org/10.5194/egusphere-egu2020-21823


We investigate a long-term ground-based GNSS-R dataset to evaluate the effect of sea state on the polarization of the reflected signals. The dataset consists of one-year polarimetric observations recorded at Onsala space observatory in Sweden in 2016 using right- and left-handed circular polarization (RHCP and LHCP) antennas. One up-looking antenna to receive direct signal and two side-looking antennas to collect reflections are installed at about 3 meters above sea level. The data is collocated with the measurements from a nearby tide-gauge and meteorological station. We focus on precise power estimation using a polarimetric processor based on Lomb–Scargle periodogram at precisely observed sea levels. The processor converts 0.1 Hz coherent in-phase and quadrature correlation sums provided by a reflectometry receiver to power estimates of the direct and reflected signals. The power estimates are reduced to three power ratios, i.e. cross-, co-, and cross to co-polarization. A model, describing the elevation dependent power loss due to sea surface roughness, is then utilized to invert the calculated power ratios to the standard deviation of sea surface height. Analysis of about 14000 events found in the dataset (about 40 continuous tracks per day) shows a fair agreement with the wind speeds as an indicator of the sea state. Although an increasing sensitivity to sea state is observed for all the power ratios at elevation angles above 10 degrees, the measurements from the co-polar link seem to be less affected by the surface roughness. The results reveal that the existing model cannot predict the effect of sea surface roughness in a comprehensive way. The different response of RHCP and LHCP observations to roughness is evident, however, the polarization dependence is not covered by the model. The deviations from the model are particularly clear at lowest elevations (<5 deg) where the roughness effect is expected to vanish. The results indicate that roughness also affect observations at lowest elevation angles. In this elevation range the expected dominance of the RHCP component above the LHCP component is not observed. A different approach is required to model the influence of sea state in GNSS-R. The increasing amount of reflectometry data may allow to retrieve an empirical relation between coherent reflection power and sea state in future investigation.

Item URL in elib:https://elib.dlr.de/135332/
Document Type:Conference or Workshop Item (Speech)
Title:On the Impact of Sea State on GNSS-R Polarimetric Observations
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Hoseini, MostafaNorwegian University of Science and Technology NTNU, Trondheim, NorwayUNSPECIFIEDUNSPECIFIED
Semmling, MaximilianUNSPECIFIEDhttps://orcid.org/0000-0002-5228-8072UNSPECIFIED
Rennspiess, ErikGerman Research Centre for Geosciences GFZ, Potsdam, GermanyUNSPECIFIEDUNSPECIFIED
Ramatschi, MarkusGerman Research Centre for Geosciences GFZ, Potsdam, GermanyUNSPECIFIEDUNSPECIFIED
Haas, RüdigerChalmers University of Technology, Gothenburg, SwedenUNSPECIFIEDUNSPECIFIED
Strandberg, JoakimChalmers University of Technology, Gothenburg, SwedenUNSPECIFIEDUNSPECIFIED
Nahavandchi, HosseinNorwegian University of Science and Technology NTNU, TrondheimUNSPECIFIEDUNSPECIFIED
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:GNSS reflectometry polarimetric measurements wind speed sea surface roughness
Event Title:EGU General Assembly 2020
Event Location:Vienna, Austria
Event Type:international Conference
Event Start Date:4 May 2020
Event End Date:8 May 2020
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Monitoring and Data Evaluation (old)
Location: Neustrelitz
Institutes and Institutions:Institute for Solar-Terrestrial Physics
Deposited By: Semmling, Dr. Maximilian
Deposited On:26 Aug 2020 13:52
Last Modified:24 Apr 2024 20:38

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