Kashima Ray-tracing Service (KARATS)On-line provision of total troposphere slant delay corrections for East Asian sites

摘要

In recent years numerical weather models (NWM) have undergone an improvement of spatial and temporal resolution. This makes them not only useful for the computation of mapping functions but also allows slant troposphere delays from ray-tracing to be obtained. Such ray-traced troposphere corrections can be applied to GNSS by reduction of atmospheric path delays from code and phase observations. In order to obtain highly accurate troposphere slant delays the weather model needs to have a sufficiently high spatial and temporal resolution which reflects the complex weather situation at the concerned receiver locations. The meso-scale analysis model from the Japanese Meteorological Agency (JMA) with its three hourly time-update interval provides a good trade-off between the area which is covered by the model and its spatial resolution and thus has been chosen as input for the computation of the 4D refractivity field. As set of tools, named "Kashima Ray-tracing Tools" (KARAT) are capable of handling all necessary steps including NWM handling, ray-tracing and reduction of the original observations. In order to enable a large number of users to benefit from the use of ray-traced observations it was decided to provide the reduction of troposphere delays from user's observations files as a service. The National Institute of Information and Communications Technology (NICT) will launch the "Kashima Ray-tracing Service" (KARATS) in the last quarter of 2008, providing a web-based interface which enables the user to submit his RINEX data and receive the reduced observation files free of charge. Thus, we briefly discuss KARAT and its components and present how KARATS is planned to operate. Additionally we discuss how observations which have been reduced by ray-traced delays have to be handled in GNSS processing and we show how this strategy improves space geodetic estimates.