Comparison of different techniques for retrieving the ZWD over South America and surrounding oceans, and some proposal for their integrations.

A. CALORI; G. COLOSIMO; M.CRESPI; MACKERN, M.V,

Roma

Simposio; Hotine Marussi Symposium.; 2013

Universita di Roma

Water vapour (WV) plays a fundamental role in several weather processes that deeply influence human activities. Retrieving water vapour content in the atmosphere can be performed in different ways using independent techniques. Radiometers aboard satellites provide WV measurements at different days and times over the entire sea surface of the Earth. Ground based Global Navigation Satellite Systems (GNSS) receivers estimate the delay caused by tropospheric refraction as the signals traverse the neutral atmosphere. Based on the retrieved Zenith Wet Delay (ZWD) the WV content can be achieved applying a scaling factor. Numerical weather models (NWM),which ingest data from many different sources, can provide WV estimations and forecasts. This work presents a two years systematic comparison to address the agreement on the ZWD retrieved by the three mentioned techniques for the very large region of the Central and South America. For the period from June 2008 to June 2010 the Zenith Total Delays (ZTD) of approximately 100 permanent stations belonging to the SIRGAS GNSS networks are estimated. At first, in order to assess the performances of SIRGAS products, the results are compared with the official International GNSS Service (IGS) ZTD and the differences are discussed. Then, 14 SIRGAS stations located along the coastline are selected to check the agreement with the ZWD measured by Jason-1 satellite mission. Further, observations and forecasts data coming from the European Center for Medium-Range Weather Forecasts (ECMWF) are used to retrieve the ZWD and check the consistency with GNSS. All the differences between the techniques, which were considered in order to yield a reliable comparison, are discussed.