Subjects: Astronomy >> Astrophysical processes submitted time 2025-07-09
Abstract： Five decades after the discovery of radio pulsars, main stream theories based on polar cap still suffer from difficulties in both self-consistency and confrontation with observations[1]. Increasing observation of individual subpulses of pulsars, i.e., high brightness temperature, highly polarized, and narrowband nanoshots of the Crab pulsar[2, 3] indicate that they relate with basic emission elements in a pulse window. Moreover, high degree of circular polarization, and rapid orthogonal jump in the position angle of linear polarization are observed in micropulses of both pulsars and Fast Radio Bursts (FRBs)[3–6], which further requires that such a small element of emission has a rapid variable conal-core pattern rather than a simple bunch of high energy density widely accepted. These are both unprecedented challenges and chances to understand the origin of pulsar coherent emission. This paper confronts with those difficulties by a simple model of alternative emission site and mechanism, in which pulsar wind is launched from open field line region and the coherent emission is triggered by a forced magnetic reconnection occurring at the tip of last closed field line near the light cylinder. The high energy density at such a tiny reconnection site automatically invokes Alfven waves, creates electron-positron pair, and accelerates them into relativistic speed. The resultant particle-wave interaction gives rise to coherent bunches inborn a conal-core structure responsible for observations on pulsars, magnetars and FRBs. For the first time, puzzles on coherency, polarization, correlation of coherent emission with wind, and energy budget of pulsars, magnetars, and FRBs are interpreted by a unified model.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes Subjects: Survey & Drawing Science and Technology >> Geodetic Surveying submitted time 2025-04-14
Abstract： In Global Navigation Satellite System - Reflectometry (GNSS - R) studies, polarization was once overlooked. However, in recent years, it has attracted growing attention. This paper focuses on exploring dual polarization for single - frequency data from the airborne GLORI experiment.
Based on theoretical analysis, several retrieval algorithms for soil moisture estimation were applied. Initially, only the surface reflectivity of Left - Right (LR) and Right - Right (RR) polarizations was examined. As additional surface parameters, such as surface roughness and vegetation, were integrated into the algorithm, the retrieval accuracy, measured by RMSE, improved significantly from approximately 0.07 to 0.03. The retrieval accuracy of RR polarization is slightly better than that of LR polarization. Nevertheless, when both dual polarizations were considered, the retrieval accuracy was comparable to that of using only one polarization. When surface roughness, Leaf Area Index (LAI), and incidence angle are taken into account, the retrieval accuracy, indicated by RMSE, reaches 0.0344. This clearly demonstrates the great potential of dual polarization in soil moisture estimation.
GLORI data is the first publicly available dual - polarization GNSS - R data that encompasses both coherent and non - coherent scattering. This paper further discusses the non - coherent scattering properties of LR and RR polarizations. In the context of coherent scattering, it is found that the scattering properties at LR polarization are stronger than those at RR polarization. Conversely, for non - coherent scattering, the scattering properties at LR polarization are weaker than those at RR polarization for corresponding land surface types.
The analysis of dual - polarization data will contribute to future data mining for more accurate soil moisture retrieval and the design of future polarization GNSS - R payloads. The retrieval accuracy considering non - coherent scattering properties implies that both coherent and non - coherent scattering should be incorporated into future GNSS - R data sets, as they are comparable for future soil moisture retrieval algorithms.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes Subjects: Geosciences >> Geodestics submitted time 2024-02-05
Abstract： —LR polarization is commonly used for the
corresponding geophysical parameters retrieval in GNSS#2;
R(Global Navigation Satellite System-Reflectometry) or SoOP-R
(Signal of Opportunity-Reflectometry) . However, the other
polarization of the reflected signals has attracted more and more
attention with the development . The popular used equation for
RR polarization demonstrates that it decreases as the soil
moisture content increase and this is in contradiction with the
experiment data. Here, three new models have been developed:
Spec4PolR (Specular reflectivity model for polarization GNSS#2;
R), SPM4Pol (small perturbation model for polarization GNSS#2;
R), and Umich4Pol (Umich model for polarization GNSS-R).
The Mueller matrix of these three models has been presented
and the wave synthesis technique is employed to calculate the
reflectivity at RR polarization. Spec4polR employs only three
elements in the Mueller matrix for the final reflectivity, while
five elements for Umich4polR participate in the calculation and
although all the elements of the SPM4Pol have constructed the
Mueller matrix and only nine elements have been employed for
calculation. Each elements' effects on the soil moisture content
are presented and the final reflectivity at RR polarization has
been illustrated. However, due to the simple formulations of
Spec4Pol, its reflectivity at RR polarization still decreases as the
soil moisture content increase. while the results of SPM4Pol and
Umich4Pol are consistent with the measured data and the
reflectivity at RR polarization increase as the soil moisture
content increase. The accurate forward calculation of RR
polarization is crucial for the subsequent retrieval algorithm of
polarization GNSS-R/SoOP-R.
Peer Review Status:Awaiting Review
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