The main objective of this study is to estimate the errors in the measurement of lengths of missiles or satellite launch vehicles from digital images available in the public domain when the scale or the pixel sizes of the images are not known. The present report is an attempt to validate the methodology used in previous ISSSP studies by estimating the measurement error. We estimate the error by making measurements on images of missiles whose dimensions are known apriori with confidence.
Images are selected carefully so that geometric and scale effects are minimal. In each of the images, the diameter of the missile or launch vehicle is measured in pixels and since the actual diameter is known, the pixel size is estimated. Pixel size is the actual diameter in meters divided by the diameter in pixels. Once the pixel size is known the relevant length is measured in terms of number of pixels and then converted to meters using the estimated pixel size. Since the actual length is known the measurement error is obtained as the difference between the actual length and the measured length.