ad 4 an Project 1.4 - Free Air Pressure Measurements at Altitudes - Lt. Col. J.A. Fava OBJECTIVE The objective of Project 1.4 was to obtain basic free air peak overpressure measurements vertically above an air burst megaton weapon, Information was sought covering the range of 20 psi to 1 psi. This data was needed to further the study of the effect of altitude on the propagation of the shock wave so that safe ranges for delivery aircraft could be specified more accurately. INSTRUMENTATION Twelve parachute-borne pressure-instrumented telemetering canister, were deployed in a vertical array above intended ground zero. of altitudes at burst time was 930 feet to 33,560 feet. The range The large horizontal bombing error precluded the canisters being in the range of primary interest. RESULTS All twelve canisters telemetered useful data. Ten of the twelve were in the "free air" (regular reflection) region, and two were in the mach reflection region below the triple point path. The assumption MkTLL. whiten::«-: optimum agreement between measured and computed peak overpressures, and with this assumption the r.m.s. percentage deviation between measured and computed values is 7%, which is considered highly satisfactory for measurements of this type. However, if lower estimates of the actual yield obtained by other methods are confirmed, the higher apparent yield obtained from these blast pressure measurements will indicate a need for revision of current methods of calculating the effects } [orienVb, NL Re of altitude on blast overpressures, Measurements of the amplitude and time of arrival of the reflected shock were obtained, but because of the large