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Radio Science Applications in GNSS

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Remote Sensors".

Deadline for manuscript submissions: closed (25 January 2022) | Viewed by 3644

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Guest Editor
Geodesy Observatory of Tahiti, University of French Polynesia, BP 6570, Faa’a, Tahiti 98702, French Polynesia
Interests: planetary exploration; planetary geodesy; radio science
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Special Issue Information

Dear Colleagues,

One of the hottest areas in GNSS is now the added value of GNSS-augmented constellations for positioning of course, but also for studies of the atmosphere, and especially atmospheric water vapor.

These augmented constellations, still under phase A development, are based on a flotilla of numerous LEO (low Earth orbit) satellites that will retransmit reference signals (pseudo-range, carrier, clock drifts) from GPS-like high-altitude satellites, with highly precise clocks and orbits, to ground receivers.

These LEO satellites will typically have a ground visibility of the order of a few tens on minutes, while GNSS satellites have a ground visibility of typically several hours.

These LEO constellations will allow a scan of the atmosphere, in terms of radio propagation delays, with a sky coverage (line-of-sight geometries) and time resolution by at least one, or even two orders of magnitude improvement with respect to GNSS-only constellations. Unlike COSMIC satellites, scans will probe the entire atmospheric column, from the ground (boundary layer) to the atmosphere limit (120 km).

GPS satellites revolutionized the way to do positioning in the 1990s, and one of the byproducts of this revolution is now called GNSS meteorology, but this application is still hampered by the low number and slow motion of GNSS satellites. LEO constellations will introduce time-and-space high-resolution GNSS meteorology.

The main topics of interest of this Special Issue include but are not limited to:

- How to obtain post-processed or real-time accurate orbits of these LEO satellites, with the same accuracy that is now attained by PPP products for GNSS satellites, including LEO specialized ionosphere corrections;

- How to improve the mapping functions/gradient approach (VMF3 is the up-to-date family of mapping functions) in order to fully grasp the variability of the atmosphere. Ideally, the separation between the “dry” and wet components of the atmospheric refractivity should be done as the level of the modeling of the carrier phase in GNSS software (such as the Bernese or Gamit software) and not by using external a priori “dry” models, such as the Saastamoinen model acting of the total delays (“dry” + wet);

- How to precisely define and assimilate LEO-augmented meteorology products in numerical weather models (NWM).

Prof. Dr. Jean-Pierre Barriot
Guest Editor

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Keywords

  • GNSS-augmented constellations with LEO sub-satellites
  • Precise orbits for LEO-augmented constellations
  • Time and space dense GNSS-meteorology from LEO-augmented constellations
  • Assimilation of dense GNSS-meteorology products in numerical weather models

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Published Papers (1 paper)

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Research

19 pages, 9124 KiB  
Article
Evaluation of the ZWD/ZTD Values Derived from MERRA-2 Global Reanalysis Products Using GNSS Observations and Radiosonde Data
by Liangke Huang, Lijie Guo, Lilong Liu, Hua Chen, Jun Chen and Shaofeng Xie
Sensors 2020, 20(22), 6440; https://doi.org/10.3390/s20226440 - 11 Nov 2020
Cited by 15 | Viewed by 3052
Abstract
Tropospheric delay is one of the main errors affecting high-precision positioning and navigation and is a key parameter of water vapor detection in the Global Navigation Satellite System (GNSS). The second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) is the latest generation [...] Read more.
Tropospheric delay is one of the main errors affecting high-precision positioning and navigation and is a key parameter of water vapor detection in the Global Navigation Satellite System (GNSS). The second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) is the latest generation of reanalysis data collected by the National Aeronautics and Space Administration (NASA), which can be used to calculate tropospheric delay products with high spatial and temporal resolution. However, there is no report analyzing the accuracy of the zenith tropospheric delay (ZTD) and zenith wet delay (ZWD) calculated from MERRA-2 data. This paper evaluates the performance of the ZTD and ZWD values derived from global MERRA-2 data using global radiosonde data and International GNSS Service (IGS) precise ZTD products. The results are as follows: (1) Taking the precision ZTD products of 316 IGS stations from around the world from 2015 to 2017 as the reference, the average root mean square (RMS) of the ZTD values calculated from the MERRA-2 data is better than 1.35 cm, and the accuracy difference between different years is small. The bias and RMS of the ZTD values show certain seasonal variations, with a higher accuracy in winter and a lower accuracy in summer, and the RMS decreases from the equator to the poles. However, those of the ZTD values do not show obvious variations according to elevation. (2) Relative to the radiosonde data, the RMS of the ZWD and ZTD values calculated from the MERRA-2 data are better than 1.37 cm and 1.45 cm, respectively. Furthermore, the bias and RMS of the ZWD and ZTD values also show some temporal and spatial characteristics, which are similar to the test results of the IGS stations. It is suggested that MERRA-2 data can be used for global tropospheric vertical profile model construction because of their high accuracy and good stability in the global calculation of the ZWD and ZTD. Full article
(This article belongs to the Special Issue Radio Science Applications in GNSS)
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