Vegetation optical depth and soil moisture retrieval using L-band radiometry over the entire growing season of a winter wheat

This paper describes the first results of a field experiment conducted at the TERENO test site in Selhausen (Germany) over the entire growing season of a winter wheat canopy. The measurements were performed with the passive microwave L-band radiometer ELBARA-II. The data were collected above two footprint types (natural and manipulated), in order to disentangle between the radiation originating from the soil and the radiation originating from the vegetation. Using the brightness temperature (TB) measurements of the manipulated plot (i.e., only vegetation emission) the simple zero-order τ-ω model was used to retrieve a time-, polarization-, and angle- dependent vegetation optical depth value at nadir angle (τNAD). The results show that a time-, polarization-, and angle dependent τNAD is able to improve the soil moisture and vegetation properties retrieval. Furthermore, the correlation between τNAD and different vegetation indices is analyzed and highlights the potential of τNAD in terms of vegetation monitoring