ERC ere mee nen, Chapter 4 METHODS AND ANALYSIS The photographic study of cloud-rise phenomenadiffers in several important respects from the customary aerial survey or photogrammetric mapping problem. It is not enough simply to establish accurate scale factors for distance. Customary mapping procedures always reduce the three spatial dimensions to two by employing a system of contours to represent the relatively slight variations in the third. Here refuge cannot be taken in such a device; the three spatial dimensions, and also time, must be considered as four separate, independent, and irreducible variables. A complete analysis of all phases of this problem would be laborious and unjustifiably expensive; even a limited study, however, requires accurate and complete controlof all four variables for every photograph exposed. In addition, it requires experience and judgment.on the part of the analyst to: (1) interpret the séries of pictures, (2) identify irregularities in the poorly defined and sometimes nebulous cloud surface, (3) evaluate the relative importances of prominences in the cloud, and (4) estimate probable features which-are hidden from the camera. 4.1 SPATIAL CONTROL | weet It is necessary to know thefollowing for each photograph: (1) horizontal distance . from ground. zero, (2) altitude of the camera platform, (3) horizontal aiming angle ‘(bearing), (4) vertical aiming angle (tilt), (5) focal length of the lens, (6) distortion ‘ characteristics of the camera,. (7) location of the optic-axis on the film (fiducial marks), and (8) earth curvature and atmospheric refraction. In addition to the above, it is desired to make sure that the field.of view of the camera is large enough. A photograph in which cloud-cover, perspective difficulties and curvature-refraction effects are all minimized is preferred. These are contra- PINE SP PRL Hoven dictory effects, and the optimum distance for multimegaton bombs is of the order 75 to 150 miles. In practice, Items 2, 4, 5, 7, and 8 are usually quite well known. Hem 6 is neglected; Item 1 is known to about +2 percent; but Item 3 is too poorly known (+ 4 degrees or so) to permit any true three~dimensional analysis. Lack of this information requires that the cloud phenomenabeevaluated in the vertical plane through ground zero. The loss of any of these data, for any given photograph, seriously impairs: the value of that picture to the study. Data regarding camera position for the Castle detonations were derived from the navigation logs furnished from the field.. The given data were plotted for each mission "as a series of arrows originating at the given position and terminating at the expected position 1 minute later. Since the terminus almost invariably differs from the actual position given by the log for that time, by 1 to 10 miles, it must ‘be concluded that the data are not internally consistent. Therefore, a smoothed curve is drawn through the data to represent the probable course of the ship. An adjusted time scale is constructed along this curve, with equal increments of distance to take account of the nearly constant velocity and with minimum deviation from the logged time scale. This curve is felt good 17 SECRET aeeee a te oti Rm ut ane ne meeterr Soael