Abstract
The aim of this research is to analyze the potential use of Global Navigation Satellite System (GNSS) signals for the monitoring of in situ vegetation characteristics. An instrument, based on the use of a pair of low-cost receivers and antennas, providing continuous measurements of all the available Global Positioning System (GPS) satellite signals is proposed for the determination of signal attenuation caused by a sunflower cover. Experimental campaigns with this instrument, combined with ground truth measurements of the vegetation, were performed over a nonirrigated sunflower test field for a period of more than two months, corresponding to a significant portion of the vegetation cycle. A method is proposed for the analysis of the signal attenuation data as a function of elevation and azimuth angles. A high correlation is observed between the vegetation’s water content and the GPS signals attenuation, and an empirical modeling is tested for the retrieval of signal behavior as a function of vegetation water content (VWC). The VWC was estimated from GNSS signals on a daily basis, over the full length of the study period.
Highlights
As the vegetation cover affects various physical exchange processes, in particular the water cycle, absorption and reemission of solar radiation, carbon cycling, and latent and sensible heat fluxes, it plays a key role in land surface processes [1, 2]
The attenuation maximum is reached during the third week of July, several days before the maximum value of vegetation water content (VWC) is reached. This could be caused by a signal saturation linked to the additional distance travelled in the vegetation by the signal at lower elevation. These results provide a clear illustration of the considerable potential of Global Navigation Satellite System (GNSS) signal analysis for the retrieval of vegetation cover properties and VWC in particular
We discuss the potential of GNSS signals for the monitoring of vegetation dynamics
Summary
As the vegetation cover affects various physical exchange processes, in particular the water cycle, absorption and reemission of solar radiation, carbon cycling, and latent and sensible heat fluxes, it plays a key role in land surface processes [1, 2]. Any change in vegetation cover can have a strong influence on the environment, at local, regional, and even global scales. Over the last three decades, optical and microwave remote sensing techniques have been used to retrieve global vegetation characteristics [3,4,5]. Optical observations have made a considerable contribution to the estimation of biophysical vegetation parameters, such as the Leaf Area Index (LAI) and vegetation water content. In this context, it has been proposed to use various indices, such as the Normalized Difference Vegetation Index (NDVI), to analyze the distribution and potential photosynthetic activity of vegetation [4]. It is known that the behavior of backscattered radar signals is directly related to the dielectric constant and geometric structure of the vegetation cover
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