Title of article :
Satellite observations of the microwave emissivity of a semi-arid land surface
Author/Authors :
Morland، نويسنده , , June C. and Grimes، نويسنده , , David I.F and Hewison، نويسنده , , T.J، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2001
Pages :
16
From page :
149
To page :
164
Abstract :
Microwave emissivity is an important parameter for rainfall estimation over land, as well as for atmospheric temperature and humidity retrievals. However, over land surfaces, it varies over a considerable range depending principally on vegetation cover and soil moisture. This study examines the feasibility of estimating emissivity from satellite-based vegetation and moisture indicators for a semiarid region in the African Sahel. Microwave emissivity was calculated from SSM/I observations at 19, 37, and 85 GHz horizontal (H) and vertical (V) polarisation. The technique was validated by comparing the measured emissivity of a sea surface area with the theoretically predicted emissivity. For a dry atmosphere, there was good agreement between theory and measurement. However, the discrepancy was considerably higher in an area where the atmosphere was humid, particularly at 85 GHz. This is attributable to increased uncertainty in atmospheric correction. The land surface emissivity over a 5° square area, which included the Hapex Sahel site, was studied from August to October 1992. The horizontally polarised emissivity eH and polarisation difference measured over dry land areas were found to be well-correlated with Normalised Difference Vegetation Index (NDVI) such that NDVI can be used to estimate pixel eH to within ±0.02. For a wet land surface, there is a general trend for the emissivity to increase with increasing NDVI and for the polarisation difference to decrease. However, the trend is much less well defined than in the dry case. A weak relationship was observed between areal averages of previous dayʹs rainfall (PDR) and emissivity for various vegetation cover classes. A similar relationship was observed with ground-based soil moisture measurements. The results show that emissivity can be estimated with a S.E.<0.015 at 19 GHz from a combination of NDVI and rainfall or soil moisture information.
Journal title :
Remote Sensing of Environment
Serial Year :
2001
Journal title :
Remote Sensing of Environment
Record number :
1573640
Link To Document :
بازگشت