Triangulation is a well established method for determining the range to a contact based on bearing information from multiple sources. The theory is simple; bearings on a contact are plugged into a trigonometric formula which accounts for array geometry (i.e., distance between arrays) with the net result being the contact’s range (Figure 1).
This can be a useful complement to other range information. The primary advantage of triangulation ranging is time. While most other techniques require multiple legs, contact may be triangulated in the time it takes to process the sonar data. With detection and counterdetection ranges growing ever closer, this time factor becomes even more critical; seconds could make the difference.
This was the primary motivation for the creation of the triangulation rangefinder (Fig.2) It affords the fire control party the most rapid means of calculating triangulation range. Using readily available bearing informationt anyone can complete this task in approximately ten seconds.
Spherical array relative bearings on contact = 040°
Spherical array/towed array bearing difference = 2°
Range = 12.5 KYD
To use the rangefinder:
1. Place the moveable pointer to the hull mounted array’s relative bearing.
2. Find the intersection of the pointer with the applicable line of constant bearing difference (i.e. difference between the two bearing sources).
3. Read the range directly off the moveable pointer scale (at the point of intersection).
It should be noted that the limitations normally associated with triangulating a contact (i.e. bow/stern bearing and long ranges) still exist; the rangefinder merely gives the fire control party the ability to calculate the range, probably less accurately, but more expeditiously.
Robert F. Gazdzinsld