Towards Using Radar to Detect Water Stress: Observations of an Agricultural Maize Canopy from the SnowScat Scatterometer

Abstract:

Recent field experiments and numerical simulations have demonstrated that leaf water content can vary considerably in response to plant water status and that these variations have a significant impact on backscatter, particularly at higher frequencies (>5GHz). The goal of this study is to characterize the radar backscatter response of vegetation in response to natural variations in moisture availability. This is an essential step to determine if there is role for radar in the detection and monitoring of water stress in vegetation.

The SnowScat scatterometer was installed on a tower above a maize canopy in Flevoland in the Netherlands from July to September 2013. Snowscat is a ground-based, fully polarimetric, coherent stepped frequency continuous wave scatterometer operating in the range of 9-18GHz. Since 2009, it has been employed in several field campaigns in Switzerland and Finland to investigate the backscatter characteristics of snow. This study is its first deployment in an agricultural setting.

Backscatter was measured hourly at a range of azimuth and elevation angles. Regular destructive vegetation sampling and dielectric property measurements are used to monitor variations in the canopy water content, dielectric properties, and canopy growth. Meteorological data, soil moisture and temperature profiles, canopy air temperature profiles and NDVI data were also collected. Results will be presented to show the influence of canopy growth, hydrometeorological conditions and the canopy moisture content distribution on the radar backscatter as a function of frequency, polarization and elevation angle.