Monitoring local environmental conditions with SIR-C/X-SAR

This article examines temporal changes in the Spaceborne Imaging Radar-C (SIR-C) C- and L-band radar backscatter over an agricultural test site centred on Altona, Manitoba, Canada in relation to changing environmental conditions during April and October 1994. The results indicate that environmental events such as frost and rain can be monitored. However, care must be taken as some soil targets at high moisture contents may behave as specular reflectors at longer wavelengths, such as L-band at large incidence angles, thus masking soil moisture effects. The strongest correlation between radar backscatter and soil moisture (r=0.84) was obtained for the 0–2.5 cm soil profile at HH polarizations. The strength of the correlation was approximately the same at C- and L-band. All polarizations displayed a decrease in soil moisture correlation with increasing soil profile depth. It was observed that soil texture effects on the estimation of soil moisture from radar backscatter were relatively small and consequently can be neglected. Although the sensitivity to surface roughness is greater at HV and VV than at HH polarization, results indicate that roughness could be neglected when measuring soil moisture over relatively short periods of time at a given site, without significantly reducing the sensitivity of the relationship between radar backscatter and soil moisture.