Determination of zenith hydrostatic delay and its impact on GNSS-derived integrated water vapor

摘要

Surface pressure is a necessary meteorological variable for theaccurate determination of integrated water vapor (IWV) using GlobalNavigation Satellite System (GNSS). The lack of pressure observations is abig issue for the conversion of historical GNSS observations, which is arelatively new area of GNSS applications in climatology. Hence the use of thesurface pressure derived from either a blind model (e.g., Global Pressure andTemperature 2 wet, GPT2w) or a global atmospheric reanalysis (e.g.,ERA-Interim) becomes an important alternative solution. In this study,pressure derived from these two methods is compared against the pressureobserved at 108 global GNSS stations at four epochs (00:00, 06:00, 12:00 and 18:00 UTC)each day for the period 2000–2013. Results show that a good accuracy isachieved from the GPT2w-derived pressure in the latitude band between−30 and 30° and the average value of6 h root-mean-square errors (RMSEs) across all the stations in this regionis 2.5 hPa. Correspondingly, an error of 5.8 mm and 0.9 kg m in itsresultant zenith hydrostatic delay (ZHD) and IWV is expected. However, forthe stations located in the mid-latitude bands between−30 and −60° and between30 and 60°, the mean value of the RMSEsis 7.3 hPa, and for the stations located in the high-latitude bands from−60 to −90° and from60 to 90°, the mean value of the RMSEsis 9.9 hPa. The mean of the RMSEs of the ERA-Interim-derived pressure acrossat the selected 100 stations is 0.9 hPa, which will lead to an equivalent errorof 2.1 mm and 0.3 kg m in the ZHD and IWV, respectively, determined from this ERA-Interim-derived pressure.Results also show that the monthly IWV determined using pressure fromERA-Interim has a good accuracy − with a relative error ofbetter than 3 % on a global scale; thus, the monthly IWV resulting fromERA-Interim-derived pressure has the potential to be used forclimate studies, whilst the monthly IWV resulting from GPT2w-derived pressurehas a relative error of 6.7 % in the mid-latitude regions and even reaches20.8 % in the high-latitude regions. The comparison between GPT2w andseasonal models of pressure–ZHD derived from ERA-Interim and pressureobservations indicates that GPT2w captures the seasonal variations inpressure–ZHD very well.