Dual-Frequency GPS Derived Precipitable Water Vapor and Comparison with ERA-Interim Reanalysis Data Over Indian stations

Abstract

Apart from positioning, velocity and time transfer applications, the Global Position System (GPS) offers an exceptional opportunity for probing the space weather as well as atmospheric weather as the signals traverse various layers of earth's atmosphere. Following ionosphere delay, the troposphere delay is regarded as a non-negligible propagation threat to GPS and other navigation system performances. Present paper focuses on estimating Precipitable Water Vapour (PWV) which along with the dry gas pressure is responsible for total zenith tropospheric delay (ZTD) in GPS positioning. GPS observables at seven different locations in and around Indian subcontinent are processed through GAMIT that involves phase double difference positioning solution along through modeling of the delay parameters. With additional observed/modeled temperature and pressure parameters, the zenith hydrostatic delay (ZHD), zenith wet delay (ZWD), and PWV are estimated. The GPS- PWV is further validated with the ERA-Interim reanalysis data for investigating the disparity over the region. We noticed an acceptable agreement between the two at Bangalore (towards the equator) followed by underestimation at Hyderabad and overestimation at the farthest location Lucknow, through straddling across the average minimum values is perceived at KLU- Guntur location in India. The interpretation from the observations motivates further analysis of the GPS-based water vapor parameter at diverse locations involving the tropical wet and dry climate over Hyderabad and Guntur, semi-arid climatic conditions over Bangalore, and humid-subtropical climate over Lucknow. The outcomes of the paper would support lower atmospheric climatology as well as better mitigation of tropospheric delay errors ensuing relatively precise regional positioning services.