title: Impact of Soil Moisture Dynamics on ASAR σoSignatures and Its Spatial Variability Observed over the Tibetan Plateau.
abstract: This paper reports on the analysis of a 2.5 year-long time series of ASAR wide swath mode (WSM) observations for characterizing the soil moisture dynamics. The employed ASAR WSM data set consists of 152 VV-polarized scenes acquired in the period between April 2005 and September 2007 over the Naqu river basin located on the Tibetan Plateau. For four different spatial domains, with areas of 30x30 km², 5x5 km² and (two domains of) 1x1 km², the mean backscatter (σo) and the standard deviation (stdev) have been computed for each ASAR acquisition. Comparison of the mean σovalues with the stdev values results in a specific triangular distribution of data points for all spatial domains. Analysis of the mean σoand stdev with respect to in-situ soil moisture measurements demonstrates that this triangular shaped distribution can be explained by soil moisture dynamics during monsoon and winter periods. This shows that the relationship between the spatial mean soil moisture and variability is not uniquely defined and may change throughout seasons. Downscaling of coarse resolution soil moisture products should, therefore, be ideally based on additional near real time data sources. In this context, the presented results could form a basis for the development of SAR-based soil moisture downscaling methodologies.
authors.affiliation: International Institute for Geo-Information Science and Earth Observation (ITC), Hengelosestraat 99, P.O. Box 6, 7500 AA Enschede, The Netherlands. velde@itc.nl.
authors.forename: Rogier
authors.initials: R
authors.lastname: Van der Velde
authors.affiliation: International Institute for Geo-Information Science and Earth Observation (ITC), Hengelosestraat 99, P.O. Box 6, 7500 AA Enschede, The Netherlands. b_su@itc.nl.
authors.forename: Zhongbo
authors.initials: Z
authors.lastname: Su
authors.affiliation: Institute of Tibetan Plateau Research (ITP/CAS), P.O. Box 2871, Beijing 100085, P.R. China. ymma@itpcas.ac.cn.
authors.forename: Yaoming
authors.initials: Y
authors.lastname: Ma
keywords: ASAR; Soil moisture dynamics; Tibetan Plateau; Time series