Abstract
Abstract The aim of this paper is to compare the validity of six recent symmetric mapping functions. The mapping function models the elevation angle dependence of the tropospheric delay. Niell Mapping Function (NMF), Vienna Mapping Function (VMF1), University of New Brunswick- VMF1 (UNB-VMF1) mapping functions, Global Mapping Function (GMF) and Global Pressure and Temperature (GPT2)/GMF are evaluated by using ray tracing through 25 radiosonde stations covering different climatic regions in one year. The ray-traced measurements are regarded as “ground truth”. The ray-tracing approach is performed for diverse elevation angle starting at 5° to 15°. The results for both hydrostatic and non-hydrostatic components of mapping functions support the efficiency of online-mapping functions. The latitudinal dependence of standard deviation for 5° is also demonstrated. Although all the tested mapping functions can provide satisfactory results when used for elevation angles above 15°, for high precision geodetic measurements, it is highly recommended that the online-mapping functions (UNBs and VMF1) be used.The results suggest that UNB models, like VMF have strengths and weaknesses and do not stand out as being consistently better or worse than the VMF1. The GPT2/GMF provided better accuracy than GMF and NMF. Since all of them do not require site specific data; therefore GPT2/GMF can be useful as regards its ease of use.
Highlights
Radiometric space geodesy systems such GPS, Very Long Baseline Interferometry (VLBI) and InSAR technique are complicated by Earth's troposphere
Niell Mapping Function (NMF) is outdated because it has high total error at low elevation angles by relative to the Global Mapping Function (GMF) and GPT2/GMF that do not require site specific data
GPT2 has been shown to improve upon the original atmospheric model used for the GMF
Summary
Radiometric space geodesy systems such GPS, Very Long Baseline Interferometry (VLBI) and InSAR technique are complicated by Earth's troposphere. The mapping functions that are independent of the azimuth of the observation have been calculated for the hydrostatic and the non-hydrostatic component separately by fitting coefficients of a continued fraction form (Marini, 1972) to ray-traced measurements performed through radiosonde data or numerical weather models. A group of mapping function is based on raytracing through monthly mean profiles or standard profiles including NMF (Niell, 1996), GMF (Boehm, J. et al, 2006a) and GPT2/GMF (Lagler et al, 2013) They do not need any additional data as an input. A wide variety of mapping function before 1996 has been tested by (Mendez, 1999) For both hydrostatic and non-hydrostatic mapping functions, it was concluded that NMF performed the best accuracy when compared to 32,467 ray-traced measurements through 50 radiosonde stations at diverse elevation angles. VMF1 was compared to NMF in global GPS analysis and an average relative improvement (about 6%) was achieved (Boehm et al, 2007)
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