Research / Campaigns

AFWEX

ARM-FIRE Water Vapor Experiment

1 November 2000 - 31 December 2000

Lead Scientist: Henry Revercomb

Observatory: SGP

The Water Vapor Working Group conducted a collaborative effort between NASA and the ARM Water Vapor Working Group (overlapping the Fall SCM IOP) focusing on the accurate measurement of upper tropospheric water vapor. In addition to the ARM raman lidar and Vaisala RS-80 radiosondes, the following guest instruments were located at the SGP central facility:

differential absorption lidar (DIAL) from the Max Planck Institute (MPI) in Hamburg, Germany
scanning raman lidar from the NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland
scanning atmospheric emitted radiance interferometer (AERI) spectrometer from the University of Wisconsin
Meteolabor "snow white" chilled mirror radiosondes from NASA Langley Research Center (LaRC) in Hampton, Virginia.

In addition to the ground-based instruments, the NASA DC-8 provided an airborne platform for the following instruments:

differential absorption lidar (LASE) from NASA LaRC
cryogenic chilled mirror hygrometer from NASA LaRC
fast-response ozone sensor from NASA LaRC

Scientific hypothesis: 1. Aircraft with continuous profiling capabilities from DIAL, which parallel the ground-based CART Raman lidar capabilities, will be sufficient to handle sampling related problems to compare observations with the Raman lidar and radiosondes. 2. Coupling the absolute calibration of DIAL with state-of-the- art in-situ sensors is adequate airborne truth 3. Nighttime Raman lidar has adequate sensitivity and stability to transfer IOP-based aircraft truth to long-term observations and to satellite remote sensing validation. More details are given in the Science Plan.

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Related Publications

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Chung et al. "A Satellite-Based Assessment of Upper-Tropospheric Water Vapor Measurements during AFWEX". 2009. 10.1175/2009jamc2250.1.

Activity Summary

This field mission experience indicated that it is possible for several sensors to be used in a coordinated fashion over a period of several weeks to achieve a mean water water profile that is accurate at the +/- 5% level using the ARM microwave radiometer (MWR) as the total water column reference. The fall was chosen for this experiment since this is the season that offers the highest probability of clear skies due to the strong frontal passages that occur then. The winter also possesses these strong fronts but the likelihood of snow or ice is much higher in the winter. AFWEX consisted of both airborne and ground-based instruments. The main result of AFWEX was to demonstrate that, with careful analysis, a core group of 5 instruments was accurate at the 5% level for the profile of water vapor. These 5 instruments were the airborne NASA LaRC LASE water vapor lidar and Diode Laser Hygrometer (DLH), the ground-based Vaisala RS-80H (after application of corrections for time-lag, temperature and total column water), DOE CART Raman Lidar (CARL) and the NASA/GSFC Scanning Raman Lidar (SRL). A follow-on experiment called AIRS Water Vapor Experiment-Ground (AWEX-G) has been scheduled for (held in) October/November 2003.