Relating Surface Reflectance and Near-Surface Soil Moisture to Improve Ground Truth Calibration of Optical Remote Sensing.

Optical remote-sensing (RS) provides an exceedingly powerful means for monitoring spatial surface (skin) soil moisture distributions. However, the relatively small penetration depth of electromagnetic radiation within the optical domain (400-2500 nm) and limited near-surface resolution of moisture sensors employed for ground truth calibration of RS observations provide a challenge for accurate near-surface moisture estimations. To better understand the relationship between skin and near-surface soil moisture we employed a benchtop hyperspectral line-scan imaging system to generate high resolution surface reflectance maps during evaporation from a soil column instrumented with a novel time domain reflectometry (TDR) sensor array that allows monitoring of near surface moisture at 1-cm or better resolution. A recently developed physically-based model for skin soil moisture predictions from shortwave infrared reflectance was applied to estimate skin soil moisture from surface reflectance and to explore the relationship between skin and near-surface moisture distributions during soil drying. Preliminary results will be presented and the potential of obtained findings for ground truth calibration of RS observations will be discussed.