Extrapolating continuous vegetation water content to understand sub-daily backscatter variations

Abstract. Microwave observations are sensitive to vegetation water content (VWC). Consequently, the increasing temporal and spatial resolution of spaceborne microwave creates a unique opportunity study dynamics its role in diurnal cycle. However, we currently have limited understanding sub-daily variations VWC how they affect observations. This is partly due challenges associated with measuring internal for validation, particularly non-destructively, at timescales less than day. In this study, aimed (1) use field sensors reconstruct continuous records corn (2) these interpret behaviour 10 d time series polarimetric L-band backscatter high resolution. Sub-daily were calculated based on cumulative difference between estimated transpiration sap flow rates base stems. Destructive samples used constrain estimates validation. The inclusion surface canopy (dew or interception) soil moisture allowed us attribute hour-to-hour either VWC, water, variations. Our results showed that varied by %–20 % during day non-stressed conditions, effect was significant. Diurnal nocturnal dew formation affected vertically polarized most. Moreover, multiple linear regression suggested cycle typical dry leads 2 (HH, horizontally, cross-polarized) almost 4 (VV, vertically, polarized) times higher variation drydown does. These demonstrate radar potential provide unprecedented insight into land–atmosphere interactions timescales.