Chapter 4 DISCUSSION The accuracy of the dose-rate measurements depends on the navigation, instrumentation, and correction factors that refer the aircraft readings to the 3-foot references plane. The isodose plots most closely represent the actual fallout distribution in the region where the flight legs are close together. Less information is available in the far-out areas, because of the greater distances between the legs of the flight patterns. The position of isodose lines are estimated between the measured equal dose-rate points. 4.1 OPERATIONAL PERFORMANCE The records of the Top Hat aerial survey meters indicate that their calibrations remained stable throughout the surveys. Complete and frequent calibrations were made to insure optimum operation of the equipment. Only one breakdo..n, an interconnecting cable break on Zuni D-day, occurred during the entire operation. The failure of the automatic telemetering link between the aircraft and the control center created the requirement for more intensive clerical effort in the data-collection period. Voice transmission of the data provided immediate information for the tactical isodose plot and the flight-control chart, but the aircraft positions and radiation records had to be reviewed durée the development of the survey plots. The airborne radioactivity encountered after Shot Flathead limited the contaminated-area survey. The EOB of the fallout could not be detected after the aircraft became contaminated; however, high-value isodose data were obtained, and a partial plot was developed. 4.2 DATA RELIABILITY Errors in delineation of areas enclosed by isodose lines depend on variations during the survey and on the estimates of isodose positions between measured points. Navigational accuracy, variations in the individual radiation detectors, and the accuracy of determining the aircraft altitude contribute to the accuracy of the primary measurements. Determinations of surface dose rate and contamination are dependent on the primary measurements and the accuracyof the theoretical calculations. 4.2.1 Isodose Determinations. Navigation was based on Loran fixes at the end, and at points during each flight leg. Each transit along a flight leg was flown at constant speed and course heading. The aircraft positions are estimated to be within a 3-mile error circle at any time. The radiation response of the Top Hat detectors was assumed to be represented by the cali- bration curve (Figure 3.1). Reproducibility of all instruments was within 10 percent for over 87 percent of the calibrations, and no instrument exceeded 25 percent at any time. in radiation intensity at the edges of the highly contaminated sections is rapid. The change A 20-percent error in the reading will not displace the 0.25 to 1 mr/hr isodose contour by over a mile. This is well within navigational accuracy. The aircraft ate assumed to have been within 5 percent of their reported altitude BOEARGHIVES Specified accuracy of the APN-1 radio altimeter. This altimeter indicates the altitude between surface and aircraft directly and is not dependent on atmospheric pressure. Altimeter error does not appear directly in the results, rather the error is modified by the slope of the altitude 55 2 -7