Santa Barbara, CA 93102-0719
Unmanned aerospace vehicles (UAVs) are an important complement to the DOEšs Atmospheric Radiation Measurement (ARM) Program. ARM is primarily a ground-based program designed to extensively quantify the radiometric and meteorological properties of an atmospheric column. There is a need for airborne measurements of radiative profiles, especially flux at the tropopause, cloud properties, and upper troposphere water vapor. There is also a need for multi- day measurements at the tropopause; for example, in the tropics, at 20 km for over 24 hours. UAVs offer the greatest potential for long endurance at high altitudes and may be less expensive than piloted flights.
The ARM-UAV program strategy has three major phases with increasing capability. The first phase, now complete, was a one-year demonstration stage which served to acquire early scientific results and UAV operational experience, using existing UAVs and instruments. The second phase, meant to develop interim capability over the next 2-3 years, will be characterized by sustained operations and near-term UAV construction and use (14+ km for over 24 hours), using existing and near-term instruments. The third, or full capability phase, in years 3 and 4, will be characterized by sustained/autonomous operations, full capability UAVs (20 km, multi-day, 200 kg payloads), and full instrument capability.
The UAV demonstration flights focused on clear-sky flux profiling, flying straight level runs at multiple altitudes. Multi-plane flight patterns with UAVs may be a possibility in the future. The FAA is still considering how it will regulate UAV flights.
Figure 20.1 shows a preliminary comparison between the UAV longwave flux observations and line- by-line model calculations. Figure 20.2 shows the difference between observed and calculated downward flux divergence in two layers. Differences are mostly within 5%.
The program has four new instruments under development: HONER, a novel net flux radiometer, MPIR, a multi-spectral cloud imaging radiometer, CDL , a cloud detection lidar, and UAV-AERI, an IR interferometer. HONER will be able to simultaneously measure upward and downward fluxes and flux divergence. Additional new instruments may also be developed. All flights include a standard meteorological package to measure temperature, pressure, and relative humidity.
Three UAV flight activities are planned: a cloudy skies satellite calibration mission at 14 km in Sept./Oct. 1994 in the U.S.; a sustained operations mission for multi-day coverage, with 2 UAVs flying simultaneously, in the U.S. in the Spring of 1995; and a tropical cirrus mission at 20 km in the tropical Pacific in the Winter of 1995- 96.
