THE SENSITIVITY OF MULTI-FREQUENCY (X, C AND L-BAND) RADAR BACKSCATTER SIGNATURES TO BIO-PHYSICAL VARIABLES (LAI) OVER CORN AND SOYBEAN FIELDS

The objective of this study is to investigate the sensitivity of synthetic aperture radar (SAR) backscatter signatures to crop biophysical variables. The experimental data were collected over corn and soybean fields in eastern Ontario (Canada) during the 2008 growing season. Remote sensing acquisitions consisted of TerraSAR-X dual-polarized stripmap data ( X-band), RADARSAT-2 Fine beam quad-polarized data (C-band) and ALOS PALSAR dual-pol data (L-band), as well as the Compact Airborne Spectragrahic Imager (CASI) and SPOT-4 multi-spectral data. Plant variables, such as leaf area index (LAI) and surface volumetric soil moisture were measured to coincide with these acquisitions and key phenological growth stages. Analyses were conducted based on statistical correlation and a simple backscatter process model (the water cloud model). The results of this study show that the lower frequency bands, such as L and C, were closely related with LAI. For both corn and soybean crops, most C-band linear (HH, VV, HV) backscatter coefficients were correlated with LAI; backscatter increased with increasing LAI. L-band backscatter at HH and HV polarizations produced the highest correlations with corn LAI (r=0.90—0.96). Conversely, these L-band polarizations were only weakly correlated with soybean LAI. The higher frequency X-band was poorly correlated with both corn and soybean LAI. Based on these findings, the water cloud model was used to express C-band and L-band backscatter for the whole canopy as a function of LAI and surface soil moisture.

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