Efforts by the U.S. government to detect the first Soviet atomic test began at least as early as 1946. Interception of radioactive debris from the first test was made by the Air Weather Service B-29 weather reconnaissance aircraft, which was equipped to filter particles from the air, on 3 September 1949 at 500 mb east of Kamchatka. The U.S. Weather Bureau was charged with trying to find the likely testing grounds from this first interception and a few later ones. The test site was found using backward air trajectories from the radioactivity detection line and a time of detonation to determine where to stop the backward trajectories. The explosion time, with large error bars, was obtained from radiochemical analysis of the particulate debris. In 1949, best time was estimated to be about 1500 UTC on 27 August. This was then combined with 500-mb backward trajectories to place the likely test site, incorrectly, near the northern part of the Caspian Sea. The uncertainties in the test time and in the calculated trajectories allowed the test site to be possible over a much larger region.
Subsequently, the real explosion time was found to be about 0100 UTC 29 August, placing the most likely test site, from the 1949 Weather Bureau trajectories, just south of Lake Balkash. The true test site has also been revealed to be the Khazakh Test Site, and is 250 to 275 miles north of this latter calculated position. The percentage error between the calculated and correct source position relative to the trajectory distance is about 5%. This value, 5%, is much smaller than the more typical 20% errors found by other studies.
