Analysis of Temporal Backscattering of Cotton Crops Using a Semiempirical Model.

To develop an operational methodology for estimating soil moisture and crop biophysical parameters and to generate a crop cover map, backscattering signatures of vegetation canopies are investigated using multitemporal Radarsat synthetic aperture radar (SAR) data over a predominantly cotton-growing area in India during low to peak crop growth stage. A simple parameterization of the water-cloud model with volumetric soil moisture content (mv) and leaf area index (LAI) is used to simulate the microwave backscattering coefficient (σ0), as it is found to be a good candidate for operational purposes as demonstrated by several workers in past. The influence of crop height (H), LAI, and mv on σ0 is investigated during peak crop growth stage. A linear relationship between LAI and crop height is derived semiempirically, and a linear zone is chosen for analysis during the peak crop-growing stage. Estimation of average volume fraction of leaves (&Vsline;l) and attenuation factor (L) by two different approaches is discussed: 1) using linear relationship between LAI versus crop height and 2) from the water-cloud model parameter (κ) estimation by iterative minimum least square error approach. It is observed that model-estimated parameters agree well with the measured values within an acceptable error limit. At tower soil moisture, mv ≅0.02 (cm³ · cm-3), the dynamic range of &cigma;0 is found to be about +5 dB for 0-70 cm of crop height but monotonously decreases to null at a transition point, having mv ≈ 0.38 (cm³ · cm-3). A positive correlation is found between backscattering coefficient and crop height fill this transition point but shows a negative correlation beyond that, signifying the predominant attenuation by vegetation over soil. [ABSTRACT FROM AUTHOR]