1. aNTRCDUCTICN The several purposes of studying the radioactivity background and oceanogriuphic conditions of the Pacific Proving Ground are: (1) Te evaluate effects of RELWING events on the radioactivity content in water, marine organisms, eat bottom % ter m3 Cc 4 a (2 ww sedinents. litate accurate recenstructicn fF tho equivalent lend falicut patterm from measureneats by ships and airereft and enable future fallout surveys to be mace with less effort. (3) To unde'stend the fallout problen at see ‘se, and to provide cceavo.vaphic assistance to the Task Force. Previous oceénograrmic deta in the PPG are primerily fron collections made during the period Merch to August, 29:6, in connection with CROSSPO4DS aia from Japanese hydrogranhie These ere mostly measure $ investigations during 1933-1ch1. menis of density end thermal i:teucture and cf some checice constituents. Although the ¢ita are many, they are nehurer closely spaced mer synoptic. The sapanese made several crouse procurs fe ings in, the area with a reseurch vessel curing June 195: to information in suoport of a claim of damage to their tuna fishery. In analyzing the CASTLE :'allout results, the need was evident for more explicit date on currents, rates of vertice: penetration and acorizontal mixing to properly interpret fallout measurements in the cper sea. COp. LinyHeug ii / [