In an extensive observer experiment, identification and classification performance with a CCD camera system was measured for ship targets. The experiment was specifically designed for target acquisition (TA) model validation and improvement. Target type, target aspect angle, viewing depression angle, target contrast and range were varied systematically, and 50% correct acquisition ranges were determined. The observer data were used to validate several basic assumptions in the TA model ACQUIRE and to test whether the recently developed triangle orientation discrimination (TOD) system performance characterization curve (Bijl and Valeton, 1998), when implemented in ACQUIRE, leads to performance predictions similar to or better than the minimum resolvable contrast (MRC) does. The results of the study are (1) the TOD curve predicts the effect of target contrast very well while the MRC curve is too steep, thus proving the value of characterizing a sensor with the new procedure; (2) ACQUIRE predicts the effect of target orientation on acquisition range quite well, using the square-root area of the target as characteristic size; (3) the Johnson cycle criteria for identification and classification of sea targets are 9 and 4, respectively, which means that angular dimensions for sea targets must be 1.5 to 2 times larger than for ground targets to obtain the same level of acquisition performance; (4) similar TOD acquisition criteria were defined, and these appeared to be quantitatively the same as the Johnson criteria; and (5) in 95% of the conditions, the ratio between predicted and measured range falls between 0.5 and 2.0 when the MRC is used, and between 0.6 and 1.6 when the TOD is used. Overall, considering the simplicity of ACQUIRE, its predictions are reasonable, especially when the TOD is used. © 1998 Society of Photo-Optical Instrumentation Engineers.