Effect of Dew and Interception on the Backscattering Behaviour of Crops
A major application field of radar polarimetry is the interpretation of SAR data from agricultural areas. Of special interest is the understanding of the scattering mechanisms, that contribute to the received radar signal. In recent years many studies have been published investigating the scattering behaviour of crops. Polarimetric parameters such as the phase difference, the correlation coefficient, the circular backscatter and the pedestal height were analysed to derive information about the effective scattering mechanism. Furthermore, scattering models and different target decomposition theorems were applied to improve the understanding about the backscattering from crops. Indeed, until today only few studies have been published analysing the effect of dew and interception on the radar backscatter and on the effective scattering mechanisms. Due to missing experimental data, it is still impossible to draw a general conclusion about this topic. The effect of dew and interception on crop recognition is a crucial issue for orbit planning issues, such as the German TerraSAR Project, and initiated the TerraDew project. The project is funded by the German Ministry of Education and Research (BMBF, FKZ 50EE0035).It aims to quantify and systematically evaluate and model the effects of free vegetation water on multifrequency and polarimetric microwave data for different crop types. The investigations were carried out using polarimetric L-band data from the airborne E-SAR system of the German Aerospace Center (DLR), which were recoded on the 14th and 16th June 2000 at 6, 9 and 12 am. During the flight campaign extensive field data were obtained, i.e. land use, vegetation parameters, soil moisture and micro-climatologic conditions to retrieve e.g. the dew point. Objective of this study is to analyse and interpret the diurnal changes in the backscattering behaviour of crops due to dew and interception. Therefore different target decomposition theorems, i.e. the Pauli, the eigenvector and the model based decomposition approach, were applied to the polarimetric SAR- data at L-band. For each field the mean values were calculated and the diurnal changes of the parameters were analysed and interpreted. First analyses show that the influence of dew and interceptions differ for various crop types. The visual interpretation of the Pauli-decomposition indicates a strong increase in volume scattering processes for some vegetation types, such as barley and grassland. This is in agreement with the results obtained by the model based decomposition approach. Contrary, the polarimetric parameters derived by the eigenvector decomposition show no significant diurnal variations, except the beta-information.