Bistatic scattering simulations of circular and linear polarizations over land surface for signals of opportunity reflectometry

Wu, Xuerui; Song, Yezhi; Xu, Jin; Duan, Zheng; Jin, Shuanggen

doi:10.1186/s40562-021-00182-y

Cited by 8 publications

(5 citation statements)

References 33 publications

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“…Following previous studies on HCP Synthetic Aperture Radar (SAR) 4 , 14 – 18 if cross-polarization is considered negligible, i.e. are at least an order of magnitude smaller than and , which is the case for L-band forward scatter radar 40 , then the reflectivity can be approximated as: …”

Section: Methodsmentioning

confidence: 99%

“…(26), but using as starting point we can write an analogous equation to Eq. ( 3 ) for the SMAP-Reflectometry as: where, for simplicity and in line with the sparse nature of SMAP-Reflectometry and the fact that are at least an order of magnitude smaller than and at L-band 40 , we consider . The coarse and medium data and are obtained by aggregating SMAP-Reflectometry data into 36 km pixels and 9 km pixels, respectively, and then applying a natural interpolator to complete missing data.…”

Section: Methodsmentioning

confidence: 99%

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The first polarimetric GNSS-Reflectometer instrument in space improves the SMAP mission’s sensitivity over densely vegetated areas

Rodriguez-Alvarez

Muñoz-Martín

Bosch-Lluis

et al. 2023

Sci Rep

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The Soil Moisture Active Passive (SMAP) mission has dramatically benefited our knowledge of the Earth’s surface processes. The SMAP mission was initially designed to provide complementary L-band measurements from a radiometer and a radar, producing geophysical measurements at a finer spatial resolution than the radiometer alone. Both instruments, sensitive to the geophysical parameters in the swath, provided independent measurements at different spatial resolutions. A few months after SMAP’s launch, the radar transmitter’s high-power amplifier suffered an anomaly, and the instrument could no longer return data. During recovery activities, the SMAP mission switched the radar receiver frequency facilitating the reception of Global Positioning System (GPS) signals scattered off the Earth’s surface, and enabling the radar to become the first spaceborne polarimetric Global Navigation Satellite System – Reflectometry (GNSS-R) instrument. With more than 7 years of continued measurements, SMAP GNSS-R data are the most extensive existing GNSS-R dataset and the only one providing GNSS-R polarimetric measurements. We demonstrate that the SMAP polarimetric GNSS-R reflectivity, derived from Stokes parameters mathematical formulation, can enhance the radiometer data over dense vegetation areas, recovering some of the original SMAP radar capability to contribute to the science products and pioneering the first polarimetric GNSS-R mission.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

The first polarimetric GNSS-Reflectometer instrument in space improves the SMAP mission’s sensitivity over densely vegetated areas

Rodriguez-Alvarez

Muñoz-Martín

Bosch-Lluis

et al. 2023

Sci Rep

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“…2022, 14, x FOR PEER REVIEW To calculate the scattering properties of different geophysical paramete GNSS-R requires consideration of bistatic scattering. Therefore, the forward sc alignment (FSA) coordinate system should be employed (Figure 1) because FSA applies to the bistatic scattering of nonuniform media [26][27][28][29][30]. Vertical and horizontal vectors in FSA are defined along the direction of wav agation.…”

Section: Coordinate Changementioning

confidence: 99%

“…Using the model described in Section 2.1, we present the bare soil simula ious polarizations [28]. Given that GNSS-R is a type of bistatic radar, the obs ometry will vary considerably and these variations will result in the scatterin Figure 3 illustrates the scattering simulations.…”

Section: Bare Soil Ddm Output At Various Polarizationsmentioning

confidence: 99%

Investigation of Potential of GNSS-R Polarization: Theoretical Simulations

Yan

et al. 2022

Remote Sensing

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Global navigation satellite system (GNSS) reflectometry (GNSS-R) developed into a promising remote sensing technique. However, few previous related studies considered the potential of its polarization. Owing to lack of sufficient in situ measurement data to support comprehensive investigation of GNSS-R polarization, this study used theoretical models and reference to our previous work to explore this topic. The commonly used microwave scattering models are employed to get the bare soil or vegetation scattering properties of GNSS-R configurations, i.e., the random surface scattering model and the first-order radiative transfer equation were improved and then employed to obtain the scattering properties of both bare soil and vegetation. Since the final output of the space-borne GNSS-R missions is a delay Doppler map (DDM), a spaceborne (DDM) simulator, oriented for the Chinese FengYun-3E (FY-3E) GNSS-R payload, was utilized to obtain the final output at different polarizations. Using the developed models (such as the bare soil and vegetation scattering models), corresponding polarization simulations were performed. That is to say, not only the commonly used LR (left hand circular polarizations (LHCP) received and the right hand circular polarizations (RHCP) received) can be presented, but also the scattering properties at RR, VR, and HR (the transmitted signals are RHCP, while the received polarizations are RHCP, vertical (V) and horizontal (H) polarizations, respectively) can be predicted by our developed models. Results reveal obvious polarization differences for the bistatic scattering and DDM. Therefore, the use of GNSS-R polarization information has potential to provide competitive and fruitful results in the future detection of land surface geophysical parameters.

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“…The first Low Earth Orbit satellite carrying a GNSS-R receiver was the UK Disaster Monitoring Constellation (UK-DMC) mission in 2003 [13]. Then, several other missions followed, including the TechDemoSat-1, the NASA's Cyclone GNSS (CYGNSS), the Spire GNSS-R satellites, the Chinese Bufeng-1 satellites [14], the upcoming HydroGNSS and GEROS (GNSS REflectometry, Radio Occultation, and Scatterometry) experiments from ESA, the 3CAT-2 satellite of Polytechnic University of Catalonia (UPC) [15], etc.…”

Section: Introductionmentioning

confidence: 99%

Calibration and Validation of CYGNSS Reflectivity through Wetlands’ and Deserts’ Dielectric Permittivity

et al. 2022

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The reflection of Global Navigation Satellite Systems (GNSS) signals, namely GNSS-Reflectometry (GNSS-R), has recently proven to be able to monitor land surface properties in the microwave spectrum, at a global scale, and with very low revisiting time. Moreover, this new technique has numerous additional advantages, including low cost, low power consumption, lightweight and small payloads, and near real-time massive data availability, as compared to conventional monostatic microwave remote sensing. However, the GNSS-R surface reflectivity values estimated through the bistatic radar equation, and the Fresnel coefficients have shown a lack of coincidence with real surface reflectivity data, mostly due to calibration issues. Previous studies have attempted to avoid this matter with direct regression methods between uncalibrated GNSS-R reflectivity data and external soil moisture content (SMC) products. However, calibration of GNSS-R reflectivity used in traditional inversion models is still a challenge, such as those to estimate SMC, freeze/thaw, or biomass. In this paper, a successful procedure for GNSS-R reflectivity calibration is established using data from the CYGNSS (Cyclone GNSS) constellation. The scale and bias parameters are estimated from the theoretical dielectric properties of water and dry sand, which are well-known and empirically validated values. We employ four calibration areas that provide maximum range limits of reflectivity, such as deserts and wetlands. The CYGNSS scale factor and the bias parameter resulted in a = 3.77 and b = 0.018, respectively. The derived scale and bias parameters are applied to the CYGNSS dataset, and the retrieved SMC values through the Fresnel reflection coefficients are in excellent agreement with the Soil Moisture Active Passive (SMAP) SMC product. Then, the SMAP SMC is used as a reference true value, and provides a standard linear regression with an R-square coefficient of 0.803, a root mean square error (RMSE) of 0.084, and a Pearson’s correlation coefficient of 0.896.

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Bistatic scattering simulations of circular and linear polarizations over land surface for signals of opportunity reflectometry

Cited by 8 publications

References 33 publications

The first polarimetric GNSS-Reflectometer instrument in space improves the SMAP mission’s sensitivity over densely vegetated areas

The first polarimetric GNSS-Reflectometer instrument in space improves the SMAP mission’s sensitivity over densely vegetated areas

Investigation of Potential of GNSS-R Polarization: Theoretical Simulations

Calibration and Validation of CYGNSS Reflectivity through Wetlands’ and Deserts’ Dielectric Permittivity

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