Global navigation satellite system-reflectometry (GNSS-R) as an efficient tool for remote sensing has gained increasing interests in the last two decades, due to its unique characteristics. It uses GNSS signals as sources of opportunity, providing precise, continuous, allweather, and 24 hours' detections, which play a key role in many land applications. The fundamental theoretical part of GNSS-R technique is examined at first. Then, GNSS-R methodologies applied in the soil moisture content, vegetation biomass sensing, and altimetry applications are also detailed. One retrieval method uses only RH (right-hand) reflected data. Another retrieval method for soil moisture content (SMC) aimed to calibrate the measurement by using water reflections, based on the bistatic equations with LH (left-hand) reflected and RH direct signals. The other method for SMC retrieval is related to the polarimetric ratio (PR), the ratio of LH/RH reflected signals can reveal the fluctuations of the SMC. Another vital parameter vegetation biomass was observed by using the variation of reflectivity of the LH and RH reflected components. Finally, the C/A code method was used for exploring the possibility to the altimetry estimation. The features of GNSS-R technique made it a promising remote sensing technique in hydrology, climatology carbon cycles, and other potential applications.
ABSTRACT:The depth-averaged shallow water equations based on Godunov-type finite volume method are developed for unsteady flow over arbitrary topography with moving lateral boundaries caused by flooding or recession. An HLLC approximate Riemann solver is invoked to evaluate fluxes. A linear reconstruction procedure with WBAP-L1 limiter and modified 4 stages Runge-Kutta time stepping are employed to provide a second order accuracy that is free from spurious oscillations. Also, a robust technique is presented to efficiently and accurately simulate the movement of wet/dry fronts. The model predictions are compared with analytical solutions, experimental data and a two-dimensional dam-break event. Numerical results show that the model performs satisfactorily with respect to its effectiveness and robustness and thus has good application prospects.
GNSS Reflectometry is an emerging technique used for the remote sensing of soil surfaces. In this contribution an application of dielectric constant retrieval is presented. Both direct and reflected GPS signals were collected by a fully software receiver mounted on-board an aircraft. The reflected signal was processed with an open loop approach, obtaining Delay Doppler Maps (DDMs) and corresponding Delay Waveforms. Signal to Noise Ratios (SNRs) time series were estimated from (non coherently) integrated Delay Waveforms. To take into account variations of system parameters from nominal values, a calibration was performed considering signals reflected from a water lake. Finally, the retrieval process able to estimate dielectric constant of soil surface from evaluated SNR was applied and the results showed good correlation with fields' flooding state.
The use of reflected Global Navigation Satellite System (GNSS) signals for sensing the Earth has been growing rapidly in recent years. This technique is founded on the basic principle of detecting GNSS signals after they have been reflected off the Earth's surface and using them to determine the properties of the reflecting surface remotely. This is the so-called GNSS reflectometry (GNSS-R) technique. In this paper, a new application regarding the detection of metallic buried objects is analyzed and it is validated through several experimental campaigns. Although the penetration depth of GNSS signals into the ground is not optimal and depends on the soil moisture, GNSS signals can likely interact approximately with the first 10 cm of the ground and therefore can be reflected back by any metallic object buried on the first terrain layer. A very light and low-cost GNSS receiver prototype based on a software-defined radio approach was developed. This receiver can be used as a payload on board small drones or unmanned aerial systems to detect metallic objects (mines or other explosive devices). A signal processing tool based on an open-loop GNSS signal acquisition strategy was developed. The results of two experiments which show the possibility of using GNSS-R signals to detect buried metallic objects and to provide an estimate of their dimensions are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.