Optical and microwave remote sensing of wheat and canola

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Hochheim, Klaus P.,
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The primary focus of this research is the evaluation of RADARSAT-I (5.3 GHz HH) data to: l) understand the nature of seasonal backscatter from wheat and canola; and 2) determine the extent to which RADARSAT can discriminate variations in biomass at the field scale. This research is necessary because managers, scientists and agricultural producers locally require better information on production related parameters and regionally need to assess the impacts of climate variability on the grain and oil seed producing regions of the Great Plains. In support of the first objective, detailed vertically stratified seasonal representations of wheat and canola representing low and high biomass canopies were generated. These data were used to develop an adaptive multi-layer (4 layer) volumetric moisture model parameterized for wheat and canola to gain an understanding of the nature of RADARSAT- 1 backscatter. The model generates a measure referred to as the TMc (total effective volumetric moisture) that is correlated to RADARSAT-1 backscatter. The model results for wheat were highly correlated to backscatter (r2=0.67-0.97). The results suggest a relatively high extinction coefficient for high biomass wheat canopies. The seasonal backscatter over wheat is bimodal, with the green leafy portion of the canopy driving early season backscatter, and heads driving the end of season backscatter. The early season model results for canola were less promising (r2 = 0.46) suggesting the need to integrate a scattering model based on leaf geometry early in the growing season. Later in the season, when pods dominated the canopy, the volumetric model worked much better (r2 = 0.94). The seasonal backscatter profile for canola was very distinct from wheat. Early season backscatter was driven by the leafy portion of the canopy, maximum backscatter as associated with the reproductive period (pod development). Results associated with objective 2 showed that RADARSAT-1 has a potential to map biomass variation for wheat at the booting and heading stage, and later in the year as the crop senesces. Backscatter is inversely related to biomass (as defined by the normalized difference vegetation index (NDVI)) at the booting to heading stage, and positively correlated at the hard dough stage. The NDVI data and ground confirmation data support the premise that many of the parameters determining the optical reflectance are also directly and indirectly related to factors driving microwave backscatter.