dese rates resulting frum fellout in the sea. Only those Subsiciary m- asurcimen’s which w directly applicable to an understanding of the aerial-survey technique were uedertaken. 2.4.1 Distribution of Contamination ian the Sea. The gamma isoduse plots maybe directly related tothe surface layer of contamination in the sea. To obtain these plots, gamma dose rate was recurded in the aircraft as it was flown on a Search pattern. The aircraft flew between designited points at constant speed. The plot of the flight leg was then marked with time divisions. The recorder chart is calibrated in time, so the gamina reading can be relatedto the position of the aircraft. Readings were plotted on the flight chart, and points of equal dose rate connected to develop the isodose chart. The values of these isudoses were then corrected to H + 24 hours and to 3 feet above the surface. 2.4.2 Altitude Absorption. To refer the aircraft readings to 3 feet above the surface, veri- fication of the attenuation resulting from air absorption was required. Survey aircraft and heli- copter passes at varying altitudes were made over fixed locations to obtain the gamma dose rate as a function of altitude. 2.4.3 Stability of Contaminated Area. Variations in the density of surface contamination duringan aerialsurveycan modifytheestimates of the location on an isodose line, because various points along this isodose must necessarily be determined at different times. The surface stability is directly influenced both by surface ocean currents that horizontally translate the contamination, and by mixing which removes contamination from the surface. The gammaintensity measurements made by aerial surveys cannot view the gamma activity of contamination more than a few fect below the surface of the sea. A measure of the stability of a contaminated area may be achieved by comparing the aerial-survey results over a period of several days. The change in position of the isodose lines provides information on the horizontal translation of the surface contamination. The area enclosed by a given isodose pattern is proportional to the amount of surface contamination. Data on the vertical-mixing function may be obtained directly by the analysis of samples taken from varied depths at a specific location. The analysis is included as Appendix D. 23