Remote Microwave Soil Drought Index Considering Dielectric Properties of Soil

The article presents the innovative remote microwave soil drought index (RMSDI) developed for assessing intensity of soil drought (SD) and tested in the Kulunda arid steppe (West Siberia). RMSDI is based on satellite measurements of brightness and thermodynamic temperatures, including dependences of radio-emissivity on volume fraction of water (
$W$
) in soil calculated from soil dielectric characteristics. To define
${W}$
and RMSDI, we employ the data on brightness temperatures obtained from soil moisture and ocean salinity (SMOS) and thermodynamic temperatures–from moderate resolution imaging spectroradiometer (MODIS). The territories falling within a SMOS pixel are major objects of our study (cell 4010458 discrete geodetic grid (DGG) icosahedral Snyder equal area (ISEA) 4H9). According to the MODIS data, the lakes and water source areas in a SMOS pixel makes up less than 0.1%. The total area of forest and water sources is insignificant (less than 0.1%). By granulometric composition, soils are referred to slit loam and loam ones. We offer the constructed for the test area graphs of seasonal dynamics of brightness and thermodynamic temperatures, radio-emissivity (
$\chi$
),
$W$
, and RMSDI. Dependences of
$W(\chi)$
are given for soils with different values of bound water (
$W_{t}$
). The established standardized dependence
$\chi _{t}(W_{t})$
makes it possible to express the value of
$\chi _{t} $
via
$W_{t}$
. The satellite sensing data and dielectric characteristics of soils are used to calculate the values of
$W$
and RMSDI.