Method of passive range determination using only two bearing measurements

Abstract

A method of determining range from a moving vessel to an approaching object sing only two bearing measurements is provided. At a first point in time, a first bearing measurement to the approaching object is obtained using the vessel's conventional bearing sensor. The vessel and approaching object are then postulated to be on an intercept course based on the vessel's first velocity vector and first bearing measurement. At a second point in time, the vessel commences a maneuver to a known second velocity vector different from the first velocity vector. Then, at a third point in time, a second bearing measurement to the approaching object is obtained using the vessel's bearing sensor. At the same third point in time, a virtual bearing to the approaching object is provided as if the vessel and the approaching object were on the postulated intercept course. A time difference is computed between the second and third points in time and standard trigonometric methods are applied to determine the range to the approaching object. The determined range is accurate when the approaching object is on an actual intercept course.