Abstract
Nowadays, the space missions employing the global navigation satellite system reflectometry (GNSS-R) are UK TDS-1, NASA CYGNSS, and the Chinese BuFeng-1A/B twin satellites, part of the first Chinese global navigation satellite system reflectometry (GNSS-R) satellite mission. They provide delay-Doppler map (DDM) measurements reflected from the land as well as the ocean. Using land reflected DDMs, several studies have been conducted to retrieve land geophysical parameters, such as soil moisture and biomass. Despite the clear dependence on these parameters, many other parameters impact the DDMs as well, such as topography, surface roughness, etc. The impact of these perturbing factors must be analyzed, and modeled in various conditions. This article presents a comprehensive end-to-end simulator that can generate synthetic DDMs reflected over land. It is an extension of a previously developed simulator validated for ocean applications. This simulator is very generic, and it includes numerous configurable parameters such as arbitrary scattering geometry (transmitter and receiver positions and speeds), arbitrary GPS and Galileo transmitted signals and frequencies, GNSS-R instrument antenna and receiver errors, as well as surface topography, roughness, soil moisture, vegetation cover, etc. The sensitivities of GNSS-R observables with respect to soil moisture and vegetation are obtained and compared to previous experimental results, and synthetic DDMs are compared and validated against TDS-1 ones.
Highlights
T HANKS to the successful operation of the spaceborne global navigation satellite system reflectometry (GNSSR) instrument SGR-ReSI onboard TechDemoSat-1 [1] and CYGNSS [2] missions, many studies have been conducted to Manuscript received December 31, 2019; revised March 13, 2020 and May 5, 2020; accepted May 20, 2020
In the static/parameter sweep mode, the digital elevation model (DEM) (ETOPO1) of the facet is used for the topography, and the geophysical parameters impacting the delay-Doppler map (DDM) are set by user input
This article has presented an efficient simulator to study the impact of the geophysical parameters
Summary
T HANKS to the successful operation of the spaceborne global navigation satellite system reflectometry (GNSSR) instrument SGR-ReSI onboard TechDemoSat-1 [1] and CYGNSS [2] missions, many studies have been conducted to Manuscript received December 31, 2019; revised March 13, 2020 and May 5, 2020; accepted May 20, 2020. A generic E2E simulator is presented for the spaceborne GNSS-R land applications, titled “GARCA/GEROS-SIM4Land.”. It was originally developed for ocean applications [18], and it was progressively improved to include land effects [16]. It is important to highlight that the approach followed avoids as much as possible sophisticated numerical electromagnetic methods (e.g. for vegetation scattering [19]) that will be very time-consuming In practice these methods prove to be quite difficult to use because in general, it is either impossible to know the values of the input parameters, or because these parameters could be adjusted to many sets of values to fit the real data, but may lack the capability to predict the GNSS-R observables in other conditions.
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