Comparison of SMOS and AMSR-E vegetation optical depth to four MODIS-based vegetation indices

2016

Article référencé dans le Web of Science WOS:000366764500007

Grant J. P., Wigneron J. P., De Jeu R. A. M., Lawrence H., Mialon A., Richaume P., Al Bitar A., Drusch M., van Marle M. J. E., Kerr Yann

Remote Sensing of Environment, 2016, 172, p. 87-100 ISSN 0034-4257

The main objectives of this study were to provide a proxy "validation" of the Soil Moisture and Ocean Salinity (SMOS) mission's vegetation optical depth product (tau(SMOS)) on a global scale, to give a first indication of the potential of tau(SMOS) to capture large-scale vegetation dynamics, and to contribute towards investigations into the possible use of optical vegetation indices (VI's) for the estimation of tau. The analyses were performed by comparing the spatial and temporal behaviour of tau(SMOS) relative to four MODIS-based VI's, with that of the vegetation optical depth from a similar sensor, AMSR-E (tau(AMSR-E)). 16-day and annual average values of the passive microwave optical depth (tau) for the year 2010 were obtained from SMOS (1.4 GHz) and AMSR-E (6.9 GHz) observations. The VI's chosen for this study were the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), Leaf Area Index (LAI) and Normalized Difference Water Index (NDWI). The highest global-scale, annual correlation was found between tau(SMOS) and tau(AMSR-E) from ascending orbits (Spearman's R = 0.80). On global, annual scales, tau(SMOS) showed higher correlations with tau(AMSR-E) than with the VI's, while tau(AMSR-E) was more highly correlated with VI's than with tau(SMOS). Timeseries of both tau and the VI's were made per landcover class, for the northern hemisphere, tropics and southern hemisphere. Although the large-scale spatial and spatio-temporal behaviour of tau(SMOS) and tau(AMSR-E) is generally similar, the results highlight some notable differences in observing vegetation with optical vs. passive microwave sensors, and certain crucial differences between the two passive microwave sensors themselves. Overall, the results found in this study give a good first confidence in the SMOS L3 tau product and its potential use in vegetation studies. These results provide an essential general reference for future (global-scale) vegetation monitoring with passive microwaves, for the future inclusion of tau(SMOS) in long-term, multi-sensor datasets, and for passive microwave algorithm development.

Etudes, transformation, conservation du milieu naturel [082] ; Télédétection [126]

PAR00014092