UAV

Goals: The focus of the Unmanned Aerospace Vehicle (UAV) IOP will be on shortwave radiation and clear and cloudy sky absorption, consisting of four primary experiments. These four experiments in order of priority include:

• Geostationary satellite interpretation over the Central Facility using (a) surface to Altus (UAV aircraft) radiation budget, (b) radiation field above the clouds, (c) radiation above and below clouds, and (d) cloud microphysics
• Surface characterization using (a) BDRF versus time-of-day, (b) albedo versus cloudiness and sun angle, and (c) skin temperature
• Repeat of ARESE 1995 experiment measuring absorption of shortwave radiation in cloudy and atmospheres
• Diurnal radiation budget quantities: studying the variation of shortwave and longwave radiation in the vicinity of the Central Facility (Altus 24-hour endurance flight)

Activity Summary

The UAV Program operated both the Altus UAV and the Twin Otter chase aircraft during the IOP period. As can be seen in the previous sections, the IOPs on water vapor, clouds, aerosols, and shortwave radiation were all dependent to various degrees on UAV operations.

The advantage of a UAV such as the Altus is that it offers high altitude, long endurance, and unmanned observation of the atmosphere. These are important features when studying evolving cloud fields and their effect on solar and thermal radiation balance. The high-altitude capability of the Altus also provides measurements to calibrate satellite radiance products and validate their associated retrieval algorithms. Indeed, during this IOP, it was possible to coordinate a UAV operation with a LANDSAT overpass.

This particular UAV IOP contained four experimental areas as a focus. These are described briefly below.

Experimental Group I, termed "Geostationary Satellite over the SGP Central Facility", attempted to:

• Characterize the sunset to sunrise radiation budget of the atmospheric column from the surface of the Central Facility to the Altus' service ceiling (approximately 35,000-37,000 ft.) in aerosol-laden clear skies and single-layer extensive cloudy conditions
• Measure the solar noon radiation field above an extensive single solid cloud layer or a broken cloud field, with the Twin Otter near cloud top and the Altus at various altitudes
• Measure the solar noon radiation field above an extensive single solid cloud layer or a broken cloud field, with the Twin Otter and Altus 1-2 km below and above cloud base and top, respectively
• Characterize the sunrise to sunset correlation of microphysics to absorption, with the Altus at its service ceiling and in situ sampling by another aircraft (such as the Gulfstream)

Missions in support of Experiment Group I were flown on September 17, 24, 27, 29, October 1 and 4.

Experiment Group II, "Surface Characterization", measured the effects of surface properties on the solar and infrared radiation budgets in the atmospheric column. Special objectives included building databases of spectrally resolved BDRF (bi-directional reflectance functions) viewed from the tropopause and spectrally-resolved and broadband directional albedo models viewed from near the surface, and to determine the response of skin temperature to cloud shading. These were to be achieved using the following measurements:

• MPIR measurements, with the Altus at its service ceiling over the Central Facility and other diverse sites in northern Oklahoma (grass, soil, forest) for all solar zenith angles; this assesses BDRF versus time of day
• RAMS albedos over the Central Facility, and also soil, grass, forest, water, and salt, with the Twin Otter near the surface under clear, broken, and thin cloud skies for all solar zenith angles
• RAMS infrared measurements, with the Twin Otter flying near the surface when cloud conditions produced large sunlit and shaded areas

Missions in support of Experiment Group II were flown on September 21 (albedos), and September 25 and October 1 (surface characterization).

Experiment Group III, termed "ARESE Re-Reprise", was designed to fill in gaps in the ARESE 1995 IOP data set. However, time did not allow for any flights in support of this experiment. A similar fate befell Experiment Group IV, "Diurnal Radiation Budget Quantities". It sought to intensively study the effect of diurnal cycles on the radiation budget, specifically assessing the variation of shortwave and longwave radiation in the vicinity of the Central Facility. A successful test of the Altus' ability to fly continuously for a 24-hour or longer period occurred in October 1996 over the Central Facility. For this experiment, the Altus was to fly at its service ceiling for an extended period of time. Planning for this exercise occurred during the third week of the IOP, and was planned for execution during October 3-5 window, but unusually windy conditions prevented this from happening.

Formal UAV scientific missions occurred on nine days:

• September 17: Altus/Otter clear-sky mission (Altus was forced down early, but the Otter continued with microwave radiometer calibrations)
• September 21: Otter surface albedo flights with diffuse illumination to support satellite interpretation
• September 24: Otter cloverleaf pattern 1,000 ft. above the Central Facility, over uniform overcast consisting of several layers, in order to make radiometric measurements
• September 25: Otter surface characterization mission over a variety of land surfaces, including plowed soil, grasslands, forest, water, and the Central Facility
• September 26: Altus/Otter joint water vapor profiling mission in generally clear skies, with cirrus above 35,000 ft.
• September 27: Altus/Otter joint clear-sky calibration mission in support of a LANDSAT overpass, with the Altus in a cloverleaf pattern over the Central Facility at 35,000 ft. and another Altus/Otter cloverleaf at 12,500 ft.; the Otter also performed microwave radiometer calibration turns at 1,000 ft. The Gulfstream provided clear-sky aerosol support
• September 29: Altus/Otter clear-sky flux profiling with complementary Gulfstream aerosol profiling; Altus/Otter comparisons occurred at 10,000 ft., then the Altus climbed to 37,000 ft. and remained aloft for 6.5 hours.
• October 1: Otter clear-sky surface characterization mission similar to September 25 mission, carried out at three solar elevation angles (10, 30, 50 degrees) and three altitudes (500, 3,000, 7,000 ft. AGL); it was accompanied by the Gulfstream profiling aerosols both in the morning and afternoon
• October 4: Altus/Otter clear-sky mission, with instrument intercomparison at 15,000 ft. AGL. The Altus subsequently performed clear-sky radiation measurements at 35,000 ft., with the Otter profiling radiative flux from 500 to 10,000 ft. above the Central Facility. The Gulfstream performed complementary aerosol profiling in conjunction with the Otter.

Timeline

Campaign Data Sets