Wet path delay and delay gradients inferred from microwave radiometer, GPS and VLBI observations

Abstract

Very Long Baseline Interferometry (VLBI) is collocated with a permanent Global Positioning System (GPS) receiver and a Water Vapor Radiometer (WVR) at the Onsala Space Observatory in Sweden. Both space geodetic techniques are affected by the propagation delay of radio waves in the atmosphere, while the remote sensing technique is sensitive to the atmospheric emission close to the center of the 22 GHz water vapor emission line. We present a comparison of estimated equivalent zenith wet delay and linear horizontal delay gradients from an independent analysis of simultaneous VLBI, GPS, and WVR observations. Using different constraints for the variability of the delay and the horizontal gradient in the analysis of the VLBI and the GPS data did not have a large influence on the agreement with the WVR estimates. We found that the weighted rms differences between wet delay estimates from the geodetic techniques and the WVR estimates generally increased for an increased variability in the atmosphere.

An inter-comparison study to estimate zenith wet delays using VLBI, GPS, and NWP models

“…But since the VLBI vs. GPS comparisons obtained with the short data set (cf. Table 2) agree reasonably well with results reported in Haas et al (1999), Gradinarsky et al (1999), Behrend et al (1999), and Gradinarsky et al (2000), the comparison results may at least be considered indicative. The VLBI experiment was run in a period of low moisture during which MM5 tends to underestimate the ZWDs (see above).…”

Systematic errors between VLBI and GPS precipitable water vapor estimations from 5-year co-located measurements

“…Nowadays, GPS and VLBI have been widely used to determine the tropospheric zenith total delay (ZTD) (Davis et al, 1985;Gradinarsky et al, 2000;Niell et al, 2001;Jin et al, 2007) through mapping functions (Niell, 1996). The ZTD is the sum of the hydrostatic or 'dry' delay (ZHD) and non-hydrostatic or 'wet' delay (ZWD), due to the effects of dry gases and water vapor, respectively.…”

Diurnal and semidiurnal atmospheric tides observed by co-located GPS and VLBI measurements

“…Recently, VLBI has been widely used to determine the tropospheric zenith total delay (ZTD) (e.g., Davis et al, 1985;Gradinarsky et al, 2000;Krü gel et al, 2007) through mapping functions (Niell, 1996). ZTDs from VLBI were compared with different techniques by various authors.…”