L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning
At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscri...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2020-07-01
|
| Series: | Remote Sensing |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2072-4292/12/15/2352 |
| _version_ | 1797561674273652736 |
|---|---|
| author | Adriano Camps Alberto Alonso-Arroyo Hyuk Park Raul Onrubia Daniel Pascual Jorge Querol |
| author_facet | Adriano Camps Alberto Alonso-Arroyo Hyuk Park Raul Onrubia Daniel Pascual Jorge Querol |
| author_sort | Adriano Camps |
| collection | DOAJ |
| description | At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N<sub>0</sub>) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N<sub>0</sub> and NDVI data, obtaining <i>R<sup>2</sup></i> coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θ<sub>e</sub>)), at elevation angles smaller than ~67°, the ω(θ<sub>e</sub>) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning. |
| first_indexed | 2024-03-10T18:18:16Z |
| format | Article |
| id | doaj.art-cbae738cd2d94fbebd4862b01b321b07 |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T18:18:16Z |
| publishDate | 2020-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-cbae738cd2d94fbebd4862b01b321b072023-11-20T07:34:03ZengMDPI AGRemote Sensing2072-42922020-07-011215235210.3390/rs12152352L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and PositioningAdriano Camps0Alberto Alonso-Arroyo1Hyuk Park2Raul Onrubia3Daniel Pascual4Jorge Querol5CommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c/Jordi Girona 1-3, 08034 Barcelona, SpainCommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c/Jordi Girona 1-3, 08034 Barcelona, SpainCommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c/Jordi Girona 1-3, 08034 Barcelona, SpainCommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c/Jordi Girona 1-3, 08034 Barcelona, SpainCommSensLab-UPC, Department of Signal Theory and Communications, UPC BarcelonaTech, c/Jordi Girona 1-3, 08034 Barcelona, SpainInterdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, 29 Avenue John F. Kennedy, Luxembourg L-1855, LuxembourgAt L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N<sub>0</sub>) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N<sub>0</sub> and NDVI data, obtaining <i>R<sup>2</sup></i> coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θ<sub>e</sub>)), at elevation angles smaller than ~67°, the ω(θ<sub>e</sub>) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning.https://www.mdpi.com/2072-4292/12/15/2352GNSSvegetationopacityalbedodepolarizationpropagation |
| spellingShingle | Adriano Camps Alberto Alonso-Arroyo Hyuk Park Raul Onrubia Daniel Pascual Jorge Querol L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning Remote Sensing GNSS vegetation opacity albedo depolarization propagation |
| title | L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning |
| title_full | L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning |
| title_fullStr | L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning |
| title_full_unstemmed | L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning |
| title_short | L-Band Vegetation Optical Depth Estimation Using Transmitted GNSS Signals: Application to GNSS-Reflectometry and Positioning |
| title_sort | l band vegetation optical depth estimation using transmitted gnss signals application to gnss reflectometry and positioning |
| topic | GNSS vegetation opacity albedo depolarization propagation |
| url | https://www.mdpi.com/2072-4292/12/15/2352 |
| work_keys_str_mv | AT adrianocamps lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning AT albertoalonsoarroyo lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning AT hyukpark lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning AT raulonrubia lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning AT danielpascual lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning AT jorgequerol lbandvegetationopticaldepthestimationusingtransmittedgnsssignalsapplicationtognssreflectometryandpositioning |