Abstract
Tropospheric delay is a major error source in the Global Navigation Satellite System (GNSS), and the weighted mean temperature (Tm) is a key parameter in precipitable water vapor (PWV) retrieval. Although reanalysis products like the National Centers for Environmental Prediction (NCEP) and the European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis-Interim (ERA-Interim) data have been used to calculate and model the tropospheric delay, Tm, and PWV, the limitations of the temporal and spatial resolutions of the reanalysis data have affected their performance. The release of the fifth-generation accurate global atmospheric reanalysis (ERA5) and the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) provide the opportunity to overcome these limitations. The performances of the zenith tropospheric delay (ZTD), zenith wet delay (ZWD), Tm, and zenith hydrostatic delay (ZHD) of ERA5 and MERRA-2 data from 2016 to 2017 were evaluated in this work using GNSS ZTD and radiosonde data over the globe. Taking GNSS ZTD as a reference, the ZTD calculated from MERRA-2 and ERA5 pressure-level data were evaluated in temporal and spatial scales, with an annual mean bias and root mean square (RMS) of 2.3 and 10.9 mm for ERA5 and 4.5 and 13.1 mm for MERRA-2, respectively. Compared to radiosonde data, the ZHD, ZWD, and Tm derived from ERA5 and MERRA-2 data were also evaluated on temporal and spatial scales, with annual mean bias values of 1.1, 1.7 mm, and 0.14 K for ERA5 and 0.5, 4.8 mm, and –0.08 K for MERRA-2, respectively. Meanwhile, the annual mean RMS was 4.5, 10.5 mm, and 1.03 K for ERA5 and 4.4, 13.6 mm, and 1.17 K for MERRA-2, respectively. Tropospheric parameters derived from MERRA-2 and ERA5, with improved temporal and spatial resolutions, can provide a reference for GNSS positioning and PWV retrieval.
Highlights
Tropospheric delay and weighted mean temperature (Tm ) are key tropospheric parameters for high-accuracy positioning/navigation and precipitable water vapor (PWV)retrieval in space geodetic techniques [1,2,3,4,5,6]
We comprehensively evaluate the performances of the zenith tropospheric delay (ZTD), zenith wet delay (ZWD), zenith hydrostatic delay (ZHD), and Tm derived from MERRA-2 and ERA5 reanalysis data
To access the performance of the ZTD, ZWD, ZHD, and Tm derived from MERRA-2 and ERA5 reanalysis data, we compared the tropospheric parameters calculated by reanalysis data with those derived from the radiosonde data and Global Navigation Satellite System (GNSS) observation
Summary
Tropospheric delay and weighted mean temperature (Tm ) are key tropospheric parameters for high-accuracy positioning/navigation and precipitable water vapor (PWV). Many global or regional Tm and tropospheric delays models, such as the Global Pressure and Temperature 2 wet (GPT2w) [12], GPT3 [13], TropGrid2 [14], Improved Tropospheric Grid (ITG) [15], Improved GPT2w (IGPT2w) [16], and GGTm models [17], have been established based on reanalysis products This indicates that tropospheric parameters derived from reanalysis products, including ZWD, Tm , and zenith tropospheric delay (ZTD), play an important role in the modeling of tropospheric parameters and GNSS meteorology. GNSS ZTD and radiosonde data have often been used to validate the accuracies of ZWD, ZTD, ZHD, and Tm values calculated from reanalysis products and tropospheric models. The current study aimed to use GNSS ZTD products and radiosonde data to (1) verify the accuracies of ERA5 and MERRA-2 tropospheric parameters over the globe and (2) to analyze the spatiotemporal variation characteristics of the tropospheric parameters from ERA5 and MERRA-2, and compare them with each other.
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