Tham khảo tài liệu 'geoscience and remote sensing, new achievements part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 238 Geoscience and Remote Sensing New Achievements of India provided a suitable condition for vegetation growth. By early April 2008 plants throughout the country were responding to the plentiful water supply that led to record of harvest yield in April NASA-EO . Soil Water index SWI The C-band scatterometer derived soil moisture represent only top few centimeter of soil. Nevertheless thanks to the high temporal sampling of scatterometers about 80 global daily coverage for ASCAT soil moisture in plant root zone can be estimated by using an infiltration model. Wagner et al. 1999b proposed a simple two-layer water balance model to estimate profile soil moisture. The remotely sensed topsoil represents the first layer and the second layer extends downwards from the bottom of the surface layer. In this model the water content of the reservoir layer is described in terms of a Soil Water Index SWI which is controlled only by the past soil moisture conditions in the surface layer in a way that the influence of measurements decreases by increasing the time a July 2007 July 28 - August 12 2007 b March 2008 April 2008 Snow Cover Frozen Soil Indian Ocean Indian Ocean April 1-10 2008 Vegetation Anomaly NDVI low average high NASA s Earth Observatory MODIS instrument ASCAT Soil Moisture Monthly Anomaly -4 -2 0 2 Fig. 6. Examples of the ASCAT soil moisture anomalies showing extreme dry top and wet conditions bottom compared with NDVI anomalies extracted from MODIS data. C-band Scatterometers and Their Applications 239 Ề e. . e - i SWI t t - n i for t. t i n 6 T 0 t is the surface soil moisture measured at time and T is the characteristic time 5 i i length connected to the depth of reservoir which describes the linkage between the surface layer and the reservoir by T L 1 C L d0 t dt C . 0 5 t -0 r t 7 where L is the depth of the reservoir layer and C is a pseudo-diffusivity coefficient that depends on soil properties. 05 and 0r are the volumetric moisture content of the surface
