Analysis of the accuracy of GNSS inferred precipitable water vapour against that from a 210 GHz WVR at the H.E.S.S. site
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Date
2025
Journal Title
Journal ISSN
Volume Title
Publisher
Oxford University Press
Abstract
The High Energy Stereoscopic System (H.E.S.S.) site and the Gamsberg Mountain have been identified as potential sites for the Africa Millimetre Telescope (AMT). The AMT is poised to observe at millimetre and possibly at submillimetre wavelengths. At these wavelengths, precipitable water vapour (PWV) in the atmosphere is the main source of opacity during observations and therefore needs to be accurately assessed at the potential sites for the AMT. In order to investigate the PWV conditions for the AMT, identical Global Navigation Satellite System (GNSS) stations were installed and used to assess the PWV at the two potential sites. In this study, the accuracy of those PWV measurements by the GNSS stations was assessed by comparing the H.E.S.S. installed GNSS station PWV measurements to that from a 210 GHz Water Vapour Radiometer (WVR) also installed at the H.E.S.S. site. A correlation of 98 per cent and an offset of 0.34 mm was found between the GNSS station and the 210 GHz WVR PWV data when on-site pressure and the Nevada Geodetic Laboratory (NGL) weighted mean temperature (
) were used to calculate the GNSS station PWV data. In comparison, the offset reduces to 0.15 mm when on-site derived
and pressure were used to calculate the GNSS station PWV. The results show that the GNSS station with on-site meteorological data can be used with high accuracy to reliably determine the PWV conditions at the H.E.S.S. site
Description
In this study, a 210 GHz WVR was installed in situ at the H.E.S.S. site and used to investigate the accuracy and reliability of the GNSS-derived PWV results by Frans et al. (2025) of both the H.E.S.S. site and the Gamsberg Mountain. Since the
used in the calculation of the GNSS PWV was determined through interpolation by the NGL, the study would also look into improving the GNSS station PWV measurement by developing a
with respect to on-site
for the H.E.S.S. site and the region in general by using the 210 GHz WVR and GNSS station data
Keywords
Atmospheric effects, Instrumentation, Site testing, Opacity, Submillimetre: general, Telescopes, Namibia, University of Namibia