Abstract
The tropospheric delay and gradients can be estimated using Global Positioning System (GPS) observations after removing the ionospheric delay, which has been widely used for atmospheric studies and forecasting. However, high-order ionospheric (HOI) delays are generally ignored in GPS processing to estimate atmospheric parameters. In this study, HOI effects on GPS-estimated tropospheric delay and gradients are investigated from two weeks of GPS data in June 2011 at selected GPS stations in Turkey. Results show that HOI effects are up to 6 mm on zenith tropospheric delay (ZTD), 4 mm on the North-South (NS) gradient and 12 mm on the East-West (EW) gradient during this period, but can reach over 30 mm in slant tropospheric delays. Furthermore, the HOI effects on tropospheric delay and gradient are larger in the daytime than the nighttime. Furthermore, HOI effects on tropospheric delay are further investigated on low and high solar activity days. The HOI effects on GPS estimated tropospheric delay and gradients in high solar activity days are higher than those in low solar activity days.
Highlights
Global Positioning System (GPS) has been widely used for geodetic applications and atmospheric parameter estimations starting from the late 20th century [1,2,3]
Corrected and raw observation files were processed by GAMIT/GlobK software, and zenith tropospheric delay (ZTD) values were estimated for each station to investigate high-order ionospheric (HOI) effects on GPS estimated ZTD values
While the mean values of the ZTD differences at all the GPS stations are close, the root mean square (RMS) of the DIYB station is relatively higher than the other stations
Summary
GPS has been widely used for geodetic applications and atmospheric parameter estimations starting from the late 20th century [1,2,3]. When a GPS signal passes through the atmosphere it is subjected to errors in the atmosphere layers called the ionosphere and the troposphere. With the advancing technology and necessity of accurate GNSS applications such as position or atmospheric parameter estimation, the high-order ionospheric (HOI) effects on GNSS signals are no longer negligible. GPS signals are burdened with an error called the tropospheric delay which cannot be removed but modelled. The dry part is related to the concentration of gases in the atmosphere, while the wet delay is related to atmospheric parameters such as temperature, pressure, and humidity [2,6]
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