Orbital Effects on ERS-1 SAR Temporal Backscatter Profiles of Agricultural Crops

Abstract

Multitemporal radar backscatter characteristics of crops and their underlying soils were analyzed for an agricultural area in southwestern Ontario, Canada. Nine dates of ERS-1 SAR imagery were acquired for two descending passes during the 1993 growing season. These data were corrected for SAR antenna pattern and compensated for range-spreading loss at ESA D-PAF. SAR temporal backscatter profiles were then generated for each crop type. It was found that the radar backscatter coefficients varied considerably from one date to the next. Given the absolute calibration accuracy of +/- 0.42 dB, these variations could not be related to SAR calibration. Attempts to explain the variations based on changes in environmental conditions, such as local meteorological conditions and crop development, were also unsuccessful.

Attention was then turned to potential variations due to characteristics of the SAR system. For individual crop types, SAR temporal backscatter profiles were generated separately for each orbit. It was found that the profiles were relatively smooth when the two orbits were separated. The average differences in backscatter coefficients between orbits were approximately 3 dB. These results indicated that small changes in incidence-angle could have strong impacts on radar backscatter. Therefore, attention must be given to local incidence-angle effects when using ERS-1 SAR data, especially when comparing fields from different scenes or different areas within the same scene.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry