The link between daily rainfall and satellite radar backscatter data from the ERS-2 scatterometer in the Free State Province, South Africa

Abstract

Radar backscatter intensity data from the ERS-1 and ERS-2 scatterometers are compared with daily rainfall data in two areas in the Free State province of South Africa. Knowledge of the relation between daily rainfall data and ERS C-band scatterometer data for a specific area can be useful to make reliable soil moisture measurements. The assumption is made that an increase in rainfall will lead to higher radar backscatter data values. This is based on the fact that moisture increases the dielectric properties of surfaces. This leads to higher backscatter intensities when incident radar energy is reflected back to the sensor. Various techniques are used to study the relationship between daily rainfall data and ERS scattrerometer data. It includes correlations, interpolations, visual interpretations, statistical analysis, and a simple model. Weak positive correlations were found between radar and rainfall data in arid areas. This is supported by literature regarding the Sahel. No correlation was found in agricultural areas receiving more rainfall. Vegetation also increases radar backscatter intensities, even in the absence of rain. There is thus a relationship between rainfall and radar data but it is more visible in arid areas and over longer periods of time.