The Water Vapor Sensing System (WVSSII) is an innovative application of tunable diode laser (TDL) technology, mounted on commercial aircraft, developed to measure a wide range of atmospheric moisture conditions. The WVSSII observing system has the potential to change the paradigm of how the world's National Meteorological Services gather in situ atmospheric soundings if it can be shown to produce consistent, high quality, moisture observations.

The technological challenges for WVSSII are not trivial. The range of moisture conditions the sensor will operate within be greater than 35,000 ppmv in in the high humidities of Miami to less than 50 ppmv in the cold and dry environment of the upper troposphere (13 km AGL). Additionally, the WVSSII laser will experience the full range of moisture conditions over short time increments of less than 90 minutes, while also operating in a large range in ambient thermal conditions from +35C on the runway to -60C at aircraft cruise level during this time period. This range of thermal conditions pose a significant technical hurdle for TDL sensors.

The WVSSII, flying on United Parcel Service (UPS) aircraft since 2005, had a significant design upgrade in 2008 by SpectraSensors, Inc', to address minimize the sensitivity of the WVSSII to the atmospheric thermal conditions described above while providing accurate moisture observations. This re-engineering activity was initiated through a contract funded by NOAA's National Weather Service (NWS), with ARINC, Inc, serving as contractor lead. The goal of this contract will be to install 56 WVSSII updated sensors on 31 Southwest Airlines B-737 aircraft and 25 UPS B-757 aircraft resulting in a capacity to gather over 600 atmospheric soundings per day which include temperature, moisture, and wind parameters, three times more data gathered than the current U.S. radiosonde daily sounding capability.

The focus of this paper is to describe the testing and validation of sensor performance associated with deployment of the re-engineered WVSSII sensor. Description of testing and validation will include the following:

1. SpectraSensors, Inc, (SSI) factory re-design and production testing

2. Independent chamber tests between WVSSII and reference sensors at the NWS Sterling Upper Air Test Facility and at the Deutscher Wetterdienst (DWD).

3. Field assessment comparisons of WVSSII observations from commercial aircraft with co-incident radiosonde soundings generated by Cooperative Institute for Meteorological Satellite Studies (CIMSS)

4. Collection of co-incident observations gathered from NOAA research aircraft flying WVSSII and reference sensors.

Finally, this paper will summarize preliminary results of available tests and provide an outline of next steps needed for the WVSSII sensor to become an integral component of NOAA's Integrated Upper-Air Observing Systems.