Abstract
The aim of this study is to analyze the sensitivity of airborne Global Navigation Satellite System Reflectometry (GNSS-R) on soil surface and vegetation cover characteristics in agricultural areas. Airborne polarimetric GNSS-R data were acquired in the context of the GLORI’2015 campaign over two study sites in Southwest France in June and July of 2015. Ground measurements of soil surface parameters (moisture content) and vegetation characteristics (leaf area index (LAI), and vegetation height) were recorded for different types of crops (corn, sunflower, wheat, soybean, vegetable) simultaneously with the airborne GNSS-R measurements. Three GNSS-R observables (apparent reflectivity, the reflected signal-to-noise-ratio (SNR), and the polarimetric ratio (PR)) were found to be well correlated with soil moisture and a major vegetation characteristic (LAI). A tau-omega model was used to explain the dependence of the GNSS-R reflectivity on both the soil moisture and vegetation parameters.
Highlights
In agricultural areas, soil surface and vegetation cover conditions play an essential role in the understanding of processes related to the soil-vegetation-atmosphere interface, and in different applications related to agricultural management [1,2,3,4]
The Global Navigation Satellite System-Reflectometry (GNSS-R) is a microwave technique based on bistatic radar observations, which appeared at the beginning of the 1990s
In an effort to validate these results over a larger area, including various crops and several forest sites, the instrument described in [16] was upgraded and installed on an aircraft for the GRASS campaign organized in Italy [25,26], during which GNSS-R measurements were recorded from an aircraft at 150 m above ground level (AGL)
Summary
Soil surface and vegetation cover conditions play an essential role in the understanding of processes related to the soil-vegetation-atmosphere interface, and in different applications related to agricultural management [1,2,3,4]. GNSS-R makes opportunistic use of the signals emitted by global satellite navigation constellations, such as the Global Positioning System (GPS) [13] This technique was initially used for oceanographic applications, various experimental in situ and airborne campaigns have led to a considerably improved understanding of the interaction of these signals with the Earth’s surface, and their potential for monitoring land surface conditions, including that of the cryosphere [14]. In an effort to validate these results over a larger area, including various crops and several forest sites, the instrument described in [16] was upgraded and installed on an aircraft for the GRASS campaign organized in Italy [25,26], during which GNSS-R measurements were recorded from an aircraft at 150 m AGL These observations confirmed the strong potential of GNSS-R techniques for the estimation of soil moisture, and forest biomass.
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