Radioactive debris from nuclear detonations may fall out over an extensive area. A rapid evaluation of the distribution of such surface contamination cam be obtained by an aircraft mounted detector. The gamma field measured in the aircraft can be related to the intensity on the ground. The HASL Top Hat'' system measures the radiation intensity, in an aircraft, at any altitude up to 1500 feet. The data are continuously compensated to the reading that would be obtained if the measurements were taken at three feet from thc ground surface. It will record the ground radiation field intensities from 0.01 mr/hr to 1000 r/hr. The Telepulse Coding Unit converts this information to a signal suitable for transmission to a plotting center via a standard voice radio transmitter. The transmitted signal is decoded by a Telepulse Receiving Unit and is automatically recorded on a strip chart. The radiation data must be correlated with the aircraft position to determine the location amd intensity distribution of the contaminated area. (auth)