Relationships between Radarsat SAR data and surface moisture content of agricultural organic soils

Abstract

A time series of 10 C-band fine beam images were acquired over the West Monteregie region (Quebec) in 1999 to examine the potential of Radarsat to detect surface moisture content of cultivated organic soils. Soil moisture data were simultaneously collected from 10 fields cropped to carrots, potatoes, lettuces, and onions. The analysis was conducted at two levels: (i) a temporal scale (daily average value); and (ii) a spatial scale (10 fields). At the first level, we found that the average radar backscatter ) was quite well correlated to the seasonal change of the average moisture content (R 2=0.75), although the dates with a strong vegetation growth decreased the relationship. Comparison with data acquired for mineral soils indicates that organic soils exhibit a lower backscatter, especially at lower moisture content levels, suggesting that soil types should be considered prior to map soil moisture changes. At the field scale, the relationship was much lower (R 2=0.44). The quality of the relationship was proportional to vegetation cover and appeared to be crop-dependent. Best results were obtained with onions and carrots. Considering only bare organic soils, the result was satisfactory (R 2=0.79) and similar to those published on mineral soils.