Improving the Airborne Remote Sensing of Soil Moisture: Estimating Soil Effective Temperature

Obtaining measurements of the near-surface soil water content from passive microwave observations requires knowledge of the soil effective temperature, which is a function of the soil temperature and moisture profiles. Detailed information on these profiles is not available from airborne remote sensing, but the effective temperature can be estimated via thermal infrared observations of the land surface. Current estimation techniques were developed for bare soil only, and do not account for the effects of vegetation. We have performed a simulation study which investigates the influences of vegetation and intra-day soil temperature and moisture variations. We find that, unless vegetation is taken into account, the so-called ‘C parametrisation’ performs poorly for leaf area index values &3. We introduce a technique that models the intra-day variations in the ratio between the effective and surface temperatures. This technique performs particularly well if a term for the near-surface soil moisture is included and vegetation information in available.