The NASA Pathfinder water vapor project (NVAP) is a global, daily, 4-layer, satellite-derived water vapor dataset that currently covers the time period from 1988 – 1999. NVAP is currently being extended several years into the 21st century with a multitude of infrared and microwave satellite instruments, a project called NVAP – Next Generation. NVAP plays a key role in addressing Earth science questions such as “How are global precipitation, evaporation, and the cycling of water changing?” “What trends in atmospheric constituents and solar radiation are driving global climate?” and “How well can long-term climatic trends be assessed or predicted?”

NVAP – Next Generation (NVAP-NG) will incorporate additional sensors not available in previous versions of NVAP. These include operational ATOVS soundings and microwave-only retrievals from AMSU and SSM/T-2. Heritage retrievals such as SSM/I precipitable water, HIRS moisture profiles, and TOVS Pathfinder soundings will be included. The retrieval results will be blended to produce a global, 50 km resolution, twice daily water vapor product for July 1999 – June 2001. Total precipitable water vapor will be produced as well as 5 layer values (1000 – 850, 850 – 700, 700 – 500, 500 – 300, < 300 mb).

In order to explore the temporal consistency of NVAP-NG, 1999 has been chosen as a “bridge” year. We will produce NVAP using the heritage approach and compare it to the NVAP-NG product. This will serve as a first look at systematic or regional differences between the two data sets which could affect future users. Future objectives to overlap NVAP with Aqua instruments (AIRS, AMSR) in the year 2002 will be discussed.