! ne Le A minimum as compared with the correspcnding close-in bhangmeter measurements at the Nevada Proving Ground. For Snapper, stations at the following locations were manned initizlly: Ephrata, _ Washington (1,160 km); Mountain Home, Idaho (692 km); Flagstaff, Airzona (447 km}; Pyote, Texas (1,420 kz), and Del Rio, Texas (1,640 km).«For the last two shots (No.7 : and No.8) Pyote and Del Rio were abandoned because it became apparent that no detections would be made at the two spots. The equipment at the two castern locations was added to the Mountain Home station, and a new location added at Baker, Oregon (845 km) tuirmediate between the two northern locations. The time constants of the circuitry were set to admit only the frequencies ~ 100 cycles to 30 ke in order to discriminate against natural light scintillation; this bandpass does not accurately reproduce the ght minimum and, hence, in these experiments, good estimates of yield were not possible. Equipment sensitive to both blue (~ 4,000 A ) and red ( ~ 8,000 A) was used. Experiments with a polarizer for maximum discrimination from background were also performed. Detections at Flagstaff and Mountain Home were generally successful. Baker was successful one time out of two tries. No detections were made at Del Rio, Pyote, and Ephrata. The red cells showed approximately two orders of magnitude less absorption than the blue cells, although the signal-to-noise ratio was approximately the same for both color senvitivities. Because we do not know the precise mechaniam of transmission, the light source is treated as a directly viewed point source. The relationship then follows the farniliar: Wr kp Wn = ———-e~ D 4 p ° Where: 1 (4) Wp = irradiance per spectrum band at distance D from the point source W7 = total emitted radiant flux of the source in the band k » absorption constant per unit distance This relationship holds reasonably well for distances up to a few kilometers. How- ever, when the source is below the horizon, and not directly viewed, it ia obvious that it ig not proper to expect the relationship to hold. tions as though the relationship did apply. We have treated the data of past opera- As distance increases, with receptions made beyond line-of-sight and below the horizon, k decreases, which seems to indicate that the path for transmission of the light is at higher aliitudes where absorption would be less. Two empirical formulas for the relationship between time to minimum, t, and energy yield in kilotons-equivalent, E, from reference 1 are: * E = 1.88 x 1077 (t + 7)? (2) E=0.10 (3) é OPERATIONS Criteria for selection of a site for an experiment in long-range light detection includes the following; (1) lack of clouds; (2) little movement in the foreground, (3) clear atmosner mews: phere; (4) low wind velocities; and (5) freedom from man-made light flashes such as airplane beacons, reflectiona from moving objects and automobile lights. attteglately eaeaite dees ee teas eecerene ee ne Since experimental atomic detonations usually take place in the morning, the observing 10 ee ny