FALLWV

Water Vapor IOP

18 September 2000 - 8 October 2000

Lead Scientist: Henry Revercomb

Observatory: SGP (Southern Great Plains)

Scientific hypothesis: 1. Microwave radiometer (MWR) observations of the 22 GHz water vapor line can accurately constrain the total column amount of water vapor (assuming a calibration accuracy of 0.5 degC or better, which translates into 0.35 mm PWV). 2. Continuous profiling by Raman lidar provides a stable reference for handling sampling problems and observes a fixed column directly above the site only requiring a single height- independent calibration factor. 3. Agreement between the salt-bath calibrated in-situ probes, chilled mirror hygrometers, DIAL, and MWR can be achieved. All of these techniques are considered capable of measuring water vapor with a high absolute accuracy. More details are given in the Science Plan. Approach to test hypothesis: Operate the CART, ETL CSR, and JPL J-unit MWRs in continuous TIP-cal mode so that their calibration can constantly be monitored. Periodically, use a LN2 blackbody target on the MWRs to verify their calibration. Utilize the scanning capability of the NASA/GSFC Raman lidar to investigate the horizontal homogeneity of the sky during several periods when the MWRs are collecting TIP-cal data. Operate the MPI DIAL, comparing it to the MWR-calibrated CART Raman lidar and tower-calibrated NASA/GSFC Raman lidar. Launch dual-sondes (with the new RS-90s) to continue the characterization of the radiosondes performed during the first two WVIOPs. GPS measurements at the CF and/or Lamont to provide a data set which can be compared and evaluated against the other measures of PWV. Chilled mirrors at the surface and 60-m tower levels to demonstrate repeatability of the agreement between the chilled mirrors and the Vaisala in-situ probes at those levels shown in the 1997 WVIOP. More details are given in the Science Plan.