Rangefinder based on intensity gradient measurement

Abstract

An algorithm is derived which enables the range of an object to be measured by passive optical means. It is shown that the distance of an object from an observation point is given by the ratio of the angular intensity gradient to the translational intensity gradient of a segment of the object’s intensity profile, as seen from the observation point. The algorithm is implemented by two rows of photodetectors with angular sensitivity functions g(α) and g′(α), positioned in pairs along a baseline, at equal distances and with parallel optical axes. Weighted sums of the outputs are formed for each row, the weights being defined by a pair of functions of position on the baseline h′(T) and h(T). The ratio of the two sums is proportional to distance, independent of background intensity and contrast. A device based on this principle, using simple analog electronics and commercially available photodetectors, is described, and its performance is evaluated. Show more