Sensitivity analysis of X-band SAR to wheat and barley leaf area index in the Merguellil Basin

Abstract

Remote sensing of vegetation by using active microwave sensors is important for the management of land and water resources. Microwave radiation at X-band penetrates only the upper part of the canopy; thus, radar backscattering comes mainly from the top vegetation layer, making the scattering from soil almost negligible. Fourteen in situ measurement campaigns were carried out during which sixteen SAR images of COSMO-SkyMed and TerraSAR-X were acquired on the test site of Merguellil Basin, in the centre of Tunisia, from March to May 2012. A clear sensitivity of the backscattering coefficient, measured by both sensors, to the leaf area index (LAI) of green plants of wheat and barley (at both HH and VV polarizations) was observed, and it did not seem to be greatly affected by the variations in soil moisture, even in HH polarization. As expected, the sensitivity to LAI of dry plants was, instead, almost negligible. The decreasing trend of backscattering as vegetation grows, which has already been observed in past investigations, also at lower frequencies, was confirmed. Due to the similar geometry and dimensions of the two crop types, none of the sensors succeeded in separating the two crop types.

Acknowledgements

This research was partially supported by the ASI through the Hydro-Cosmo 1720 project. ASI also provided the COSMO-SkyMed X-band SAR images necessary for the analysis. TerraSAR-X images were obtained through the CAL1279. The authors would like to thank IRD staff for their kind assistance in gathering and interpreting ground parameters.