Mapping of Amplitude onto CRT Luminance in Frequency-Time-Intensity Displays

Abstract

A common method of presenting passive sonar information on a CRT is the frequency–time–intensity (FTI) display. Detection of targets on an FTI display can be affected by the method used to map the original sonar input onto the visual display. The current study examined the problem of mapping the acoustic amplitude of the incoming sound onto CRT luminance. Detectability of a single target line was measured as a function of the number of quantization levels used to map amplitude onto CRT luminance (2, 4, 8, 16 or 256) and the marking density (percentage of the display set to other than background luminance). Marking density was varied by mapping all amplitude values below a fixed cut-off point (either 3, 1, or 0 S.D. below the mean of the noise) on to the lowest quantization level. On average, detection performance improved more than 3 dB as the number of quantization levels increased from two to eight. If amplitude was mapped onto fewer than sixteen quantization levels, the selection of a cut–off point was important.