Abstract
Abstract : The three-point sextant fix has been used for the horizontal positioning of vessels in nearshore hydrographic surveys since 1775. However, this method has only recently been modeled mathematically. The accuracy of the three-point fix depends on the magnitude of the random and systematic errors in the angle measurements and the fix geometry. The random errors in horizontal sextant measurements were investigated by analyzing over 1400 angles, both at sea and on land. These random errors were found to vary with the clarity of the signals being observed, the stability of the vessel and the experience of the observer. The upper and lower bounds for one standard deviation were found to be about 2.7 and 0.6 minutes of arc respectively. In addition, angular differences due to the direction of rotation of the micrometer drum were examined as well as the variability in the determination of sextant index error.
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