| Paper: | WE-P1.1 |
| Session: | Biosphere Applications of Radiometry |
| Time: | Wednesday, March 28, 13:20 - 13:40 |
| Presentation: |
Oral
|
| Topic: |
Soil moisture, soil state and vegetation: |
| Title: |
SMOS-IC: A new tool to monitor Vegetation Optical Depth at L band (L- VOD) |
| Authors: |
Jean-Pierre Wigneron; INRA Bordeaux-Aquitaine | | |
| | Arnaud Mialon; Centre d'Etudes Spatiales de la Biosphère | | |
| | Yann Kerr; Centre National d'Etudes Spatiales | | |
| | Nemesio Rodriguez-Fernandez; CNES | | |
| | Ali Mahmoodi; CESBIO | | |
| | Amen Al-Yaari; INRA Bordeaux-Aquitaine | | |
| | Roberto Feranandez Moran; INRA Bordeaux-Aquitaine | | |
| | Fan Lei; INRA Bordeaux-Aquitaine | | |
| Abstract: |
Monitoring large scale anomalies in vegetation functioning is crucial to evaluate the response and role of vegetation in climate studies. Such a monitoring is challenging. The use of large in situ networks over long time period is limited to a very few sites. Remote sensing (RS) systems can provide observations at global scale with a good temporal and spatial resolution. However such systems have their own limitations. Optical observations can be limited by cloud cover and saturation effects over dense canopies. Observations based on microwave systems can sense deeper within the canopy layer. However, the relative high frequency bands used so far (wavelengths smaller than ~ 5 cm) [Liu et al. 2015, Brandt et al., 2016] may be a limitation to sense the whole vegetation layer.
To overcome these limitations, we developed a new vegetation index (L-VOD) from the multi-angular passive microwave observations at L-band of the SMOS (Soil Moisture and Ocean Salinity) satellite, which was launched end of 2009. Based on observations at longer wavelength (lambda ~ 21 cm) and its multi-angular viewing capabilities, SMOS allows monitoring surface soil moisture (SM) and the vegetation optical depth (L-VOD) over most of the vegetation canopies worldwide with a spatial sampling of about 25 km x 25 km (Kerr et al., 2016). The L-VOD product can be related to the vegetation water content and to biomass (Wigneron et al., 2017) and the low frequency (L-band) SMOS L-VOD time series are now available since mid of 2010.
We computed L-VOD from the new algorithm (SMOS-IC) developed specifically for SMOS to retrieve both soil moisture and VOD, using as little ancillary data as possible (presently only ECMWF temperature data are used). The SMOS-IC SM and L-VOD data were computed on a ~ weekly basis at global scale, except over regions strongly affected by man-made interferences mostly in regions of central Asia, Japan, China and India). At global scale, the spatial patterns of the global map of the yearly average SMOS-IC VOD values can be related to those of vegetation biomass: highest VOD values in the tropical regions (Amazon and Congo basins, Indonesia, etc.), high values in the forested regions of the Northern Hemisphere, lower values in arid and semi-arid regions. In addition, The SMOS -IC soil moisture retrievals were validated against ground measurements delivering very good results as well.
The presentation will depict the SMOS-IC approach and its validation together with interesting new results obtained from L-VOD in monitoring vegetation water content and biomass at global scale. |
