Validation of observer and aircraft calibration for aerial surveys of animals

Calibration procedures to determine strip widths for use by the Department of Resource Surveys and Remote Sensing (DRSRS) in its aerial surveys are validated by statistical analysis. Tests were made for differences in observer, aircraft and between using photography (camera) and direct observation (naked eye) in the determination of strip widths on the ground. The relationship between strip widths measured on the ground and in the air was determined using regression analysis. Tests were also made for differences between population estimates reported by DRSRS and those recalculated using reported strip widths for elephant, kongoni, wildebeest and cattle. There appears to be no significant differences between observer performance and between reported and recalculated population estimates for all species except cattle. A significant difference was found between strip widths obtained by photography and those through direct observation, with photography values being 14% higher at ground level. Strip widths measured while the aircraft was in the air were highly correlated to those measured while on the ground (r = 0.97). Overall, it can be concluded that the DRSRS standardization of observers, calibration of the aircraft and calculation of population estimates were carried out correctly. Finally, it is recommended that the difference in strip widths determined from photography and through direct observation needs to be considered in the final calculation of population estimates.