A new method for remote sensing of moisture profiles in the arable layer at three frequencies; experimental case study.

In this paper, the possibilities of remote sensing of moisture profiles in the arable layer were theoretically and experimentally studied based on the nadir measurements of reflection coefficients at three frequencies of 1.26 GHz, 796 MHz and 641 MHz. The reflection coefficients were measured by the impulse method during natural cycles of evaporation and moistening of an arable layer at the agricultural field being under steam, located at 56°05ʹN, 92°40ʹ E in the area of the Minino village, Krasnoyarsk region, the Russian Federation. The soil moisture profiles were retrieved in the course of solving the inverse problem, in which the reflection coefficients at different frequencies acted as an informative sign. The root-mean-square error and the determination coefficient (R2) between retrieved and measured moisture values in the topsoil thickness of 0.15 m were 3.3% and 0.79, respectively. In the course of theoretical calculations, it was shown that in practice, it is impossible to predict the sensing depth of the arable layer without preliminary information on the form of moisture profile. Moreover, the sensing depth depends not only on the form of soil moisture profile but also on frequency. In this regard, it is impossible to correlate the effective soil moisture, retrieved from single-frequency measurements of the reflection coefficient in the approximation of homogeneous topsoil, with the specific thickness of topsoil. The study shows the promise of developing multi-frequency radar systems for remote sensing of soil moisture profiles in the arable layer, the potential of which can be realized on lightweight unmanned area vehicle (UAV) platforms. [ABSTRACT FROM AUTHOR]