air flow pattern induced by the wind impinging on the wind-shielded platform. This paper presents the results of a study to define and to correlate the sampling bias with certain air flow characteristics above the platform. From the analyses of the air flow pattern above the standard platform and the REDWING sampling data it was possible to define the collection bias within &@ platform by certain parameters. The values of these parameters were determined from the properties of a collection curve describing the variation. Where more than one wind is involved the observed sampling bias within the platforms was further correlated to the properties of the prevailing winds. In certain cases the effects of particle size and density were noted. It is also the objective of the study to determine the equivalent ground value associated with each shipboard platform of collections, i.e. the value that would be collected by the earth's surface (at the same location). FALLOVET COLLECTION Fallout was collected from four events and for this study they are designated as Shots A, B, C and D. The relative quantity of fallout particles collected by the receiving tray of each instrument was determined by measuraug their total activity in a gamma crystal counter know colloquially as the Goghouse counter. All activity units are in terms of net doghouse counts per min at H + 100 per tray. Standare Pletform The standard piatforms, comprising Project 2.63 major collecting stations, were located on HOW Island and on the following vessels: YAG-4O, YAG-39, LST- 611, YFNB-13, YFNB-29 (2 platforms). To specify the platform and event under discussion, designating terms such as YAG-40-A are used. Platform dimensions, geometry, and pertinent instrumentation are depicted in Fig. 1 for the ship- board stations and Fig. 2 for the barge (YFNB) end land stations. With the exception of the differences in size and some additional instruments on the larger platform, the two platforms are geometrically similar and can be considered identical with respect to sampling and bias characteristics. On the YAG's the platform was mounted on the forward kingpost approximately 60 ft apove the water line. The LST platform, placed on a tower above the ship's bow, was 35 ft above the water line. The platforms on the two anchored YFNB's were also 35 ft above the water line, being situated on towers located on the vessel bows as well as on the YFNB-29 stern. The HOW platform, mounted on a tower similar to those used on the barges, was 27 ft above ground and associated with this particular platform was an array of ground collectors. This arrangement of platform and surrounding ground collectors provided the only comparison between platform collections and ground collections. iocation and geometry of the ground array are depicted in Ref. 3. The