they would be not less than 350Kg which give Laser(fanbeam) Multi Fanbeam directional target essel Installation ereby a scanning head fires a laser beam through one lens The targets reflective mounting these prisms on a tube. Position reference is by the laser this is a class one low power unit similar to that in CD players)scanning for the target.In b I rererence unit movemen hetw n the two points is known.Differential GPS The GPS signal from a satellite does not give the degree of accuracy required for a vessel positioning system.To improve accuracy differential GPS is used GPS Signal rror nsatio 3 they would be not less than 350Kg Described is a vertical taut wire system. Also avaible are horizontal taut wires which give the same degree of reliability without the need for the clump weight. The disadvantage is that they must be manually tethered. Laser (fanbeam) This is an auto tracking system whereby a scanning head fires a laser beam through one lens and receives a reflecion of it through a second The targets must be equiped with reflectors, reflective white tpae may be used but the range is very limited. Greater distance is achieved prisms. 360' coverage is achieved by mounting these prisms on a tube. Position reference is by the laser ( this is a class one low power unit similar to that found in CD players) scanning for the target. The bearing and range of the target is found and by calculation using error correction from the vertical reference units the movement between the two points is known. Differential GPS The GPS signal from a satellite does not give the degree of accuracy required for a vessel positioning system. To improve accuracy differential GPS is used 3