OASIS: Oklahoma Atmospheric Surface-layer Instrumentation System

Summary

The Oklahoma Mesonet (Brock et al., 1995), a system of 115 automated measurement stations across Oklahoma, is serving as the foundation for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project. OASIS (Brotzge et al. 1999a; Richardson et al., 1999) is a 3-year project (October 1997 to October 2000) designed to enhance the Mesonet's capability to measure boundary layer fluxes of sensible, latent, and ground heat, as well as the radiation balance. Approximately 90 Mesonet sites will directly measure the net radiation and ground heat flux and indirectly estimate the sensible heat flux (using similarity theory); latent heat flux will be calculated as a residual from the conservation of energy equation. In addition, nine of the 90 sites also will use eddy correlation techniques to determine the sensible and latent heat fluxes and measure net radiation using a four-way net radiometer.

The two main objectives of the OASIS surface-layer Intercomparison of Fluxes (SIF) Project were to:

* 1.Examine theuncertainties associated with the measurement of surface fluxes made in the OASIS Project

* 2.Validate the reference sensorsused at the OASIS intercomparison facility.

NCAR's ASTER facilities were requested to provide a reference for intercomparison with OASIS-measured fluxes. This was done by carefully comparing the estimated surface fluxes obtained using OASIS instrumentation with those directly measured by ASTER. Measurement of the following parameters by ASTER were required: momentum, sensible heat, and water vapor fluxes by eddy-correlation; vertical profiles of wind, temperature, and humidity; net radiation, soil heat flux, soil temperature, and soil moisture.

The OASIS intercomparion facility was developed for the OASIS Project in which high quality reference sensors are being used to verify the accuracy of potential OASIS instrumentation (e.g., high quality 4-way net radiation measurements are being compared with measurements from lower quality, less expensive net radiation sensors). ASTER measurements were compared with the OASIS reference sensors. In addition, ASTER's ability to measure profiles of temperature, water vapor, humidity, and wind at multiple levels made it possible to assess the quality of the fetch at the OASIS intercomparison facility. Finally, ASTER's mechanically-aspirated temperature and relative humidity measurements were compared with naturally-ventilated measurements made by OASIS.