This experiment examined the relative effects of (1) image size and (2) number of TV raster lines making up the image upon an observer's ability to identify 16 different geometric symbols on TV. Four raster-line values per symbol height were each tested at three image angular subtenses. Eight subjects were told to identify 25 symbols for each of the 12 conditions; all had 20/12 near and far visual acuity or better. The forced-choice method was used; no limits were placed on response times. The results showed that (1) at least eight raster lines per symbol height and (2) a symbol subtense of 10' of arc are necessary to obtain good symbol legibility on TV. An equation is developed from these and other data which quantifies the tradeoff between line number and angular subtense for different levels of performance.
This paper presents a review of experimental data from tests of target acquisition with electro-optical, raster scan systems. These data, as well as equipment parameters such as sensor field of view, system line number, display size, and target size on the display, can be used to estimate target acquisition performance by system operators. The paper lists the equations required to make such performance estimations, and several examples are given. The procedure can be used to compute equipment characteristics required to insure prescribed levels of target acquisition performance.
This report discusses many o^ the aspects of air-to-ground visual search for targets. Curves are presented that can be used for estimating the probability that a ground target is within view and for determining the angular rate of the target as measured with respect to the air observer. Optical aspects (clouds, atmospheric attenuation, reflectance factors) of visual detection are discussed briefly and references from which data can be obtained are cited. A number of laboratory experiments concerning visual detection are described, and some of the results are given. Examples of simulation, operational, and mathematical methods of obtaining estimates of search performance are given and compared.
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