Measuring Changes in Vegetation Moisture from Insar Closure Phase Time Series

Remotely measuring changes in vegetation moisture is important for agricultural and environmental applications. While radiometry is sensitive to moisture, the resolution is low; optical and infrared measurements can be very fine-resolution but cannot directly measure moisture, instead relying on proxies such as brightness at wavelengths sensitive to chlorophyll. InSAR (interferometric synthetic aperture radar) produces images at fine resolution, and its measurement frequencies are sensitive to water. InSAR closure phase, a measurement of the residual phase from a circular combination of three multilooked interferograms, has been shown to relate to changing moisture content within a radar image. Here, we show that InSAR closure phase tracks several metrics of vegetation moisture from in situ measurements. In a forest in central Massachusetts, cumulative InSAR closure phase at C-band, while not correlated with soil moisture or L-band vegetation optical depth, is anticorrelated with the canopy wetness and well- correlated with the xylem dielectric constant.