The OASIS98 field project was conducted from 27 June to 8 August 1998 at the Norman, Oklahoma Mesonet site. This time period was chosen because it would test the measurement techniques under worst-case conditions of high global solar radiation and low wind speed. Figure 1 is a schematic of the towers and instrumentation used in OASIS98, the towers were erected on an east-west line with the Mesonet tower furthest east. The field site had a flat and uniform fetch of short prairie grass to the south and east for several hundred meters. Due to obstructions from the north (small trees) and west (ISFF base trailer), data with winds from these directions were considered suspect; southerly and southeasterly winds resulted in optimal data collection conditions.

The majority of OASIS measurements were taken on a single 10 m Mesonet tower. Instrumentation on the Mesonet tower included R.M. Young model 3101 cup anemometers at 2 m and 9 m and an R.M. Young model 5103 prop-vane anemometer at 10 m. At 1.5 and 9 m, Thermometric model T5503/D1 temperature sensors were housed in naturally aspirated R. M. Young Gill radiation shields. Eddy correlation flux measurements were made using a Campbell Scientific, Inc. CSAT3 sonic anemometer and Krypton hygrometer mounted at 4.5 m.

OASIS radiation instrumentation was mounted on two 3 m high trusses; one had seven Kipp and Zonen NR-Lite net radiometers and two Kipp & Zonen CNR1 four-component systems. The second truss had a Radiation Energy Balance Systems (REBS) Q*7.1 net radiometer and an Eppley four-component system that used two Precision Infrared Radiometers (PIRs) and two Precision Spectral Pyranometers (PSPs). Ground heat flux was measured using two REBS HFT 3.1 heat flux plates at 5 cm below ground level and the ground heat storage was determined using REBS integrating Platinum Resistance Temperature Detectors at 5-0 cm. Soil moisture was measured at 5 cm using Campbell Scientific 229L heat dissipation sensors.

ISFF instrumentation was mounted on three 10 m towers and one 5 m tower. The flux tower held Atmospheric Technologies Inc. sonic anemometers/ thermometers and Campbell Scientific Krypton hygrometers mounted at 4.5 and 9 m. The wind profile tower was to the east of the flux tower and measured wind speed and direction at five levels (at 1 m, 2 m, 4.5 m, 6.5 m, and 9 m) using propeller-vane anemometers manufactured by R. M. Young. East of the prop tower was the hygrothermometer tower that measured the temperature and moisture profile using Vaisala HMP 50Y temperature and relative humidity sensors. These sensors were placed at 0.5 m, 1.5 m, 4.5 m, 6.5 m, and 9 m agl.

NCAR's radiation stand used an Eppley four-way system and a REBS net radiometer. OASIS' Q*7.1 and Eppley systems are the same models used by NCAR and therefor provided a useful comparison. NCAR also used the same ground heat flux plates and PRTÕs as OASIS.

OASIS data were sampled every 3 s except for the sonic anemometer and Krypton hygrometer which were sampled at 8 Hz. A Campbell Scientific CR10T data logger collected data and five-minute averages were computed. OASIS data was collected, processed, and then relayed to the ISFF base facility every 15 minutes to be included with the ISFF data files.

All ISFF data was sampled at 1 Hz except for the sonic anemometer and krypton hygrometer, which were sampled at 20 Hz. Sampled data was temporarily stored in the ISFF Data Acquisition Module (ADAM) and then averaged over five-minute periods; Businger et al. (1990) gives a description of the ADAM and its functions. Data could be examined in the ISFF base trailer, which allowed for real-time quality assurance.

Weather conditions during OASIS98 were typified by very hot and dry conditions. The average air temperature for the period was 30 ¡ C with a maximum temperature of 40.6 ¡ C, there were 21 days with temperatures in excess of 37.7 ¡ C (100 ¡ F). Wind speeds were often low during the day. This environment represented worst-case conditions for the measurement of the sensible heat flux using the profile method.