High resolution atmospheric modelling of a tropical island for space geodesy

Temporal variations in water vapour distribution cause delays in phase used in the space geodetic InSAR technique. To correct for this, NWP is used to simulate water vapour distribution and hence variable refractive phase delay over a small volcanic island in the humid tropics, Montserrat. Initialised by ECMWF data at ~ 16 km resolution, the WRF model is nested to 300 m resolution. Synthetic simulations of trade wind flow tests the WRF Montserrat Model (WMM) demonstrating its ability to replicate gravity waves. WMM simulates atmospheric delay fields during the InSAR imaging of Montserrat by X-band radar (COSMO) from two viewing geometries during December 2014. Field measurements during imaging and the recording of zenith wet delay (ZWD) by a 14-receiver GPS network are used for comparison with the WMM and COSMO. WMM and ZWD delay difference images show two main influences: topographic modulation and dynamic modulation due to the trade winds flowing over and around the island. Statistical calculation of pixel-wise delay estimates place model accuracy in the range 64-81%. The reasons for this level of mitigation may be truncation of initial conditions to WMM, the large amount of liquid water in the atmosphere and simulation of trade wind flow across Montserrat.