Production of LORAN-C Reliability Diagrams at the Defense Mapping Agency,
DEFENSE MAPPING AGENCY HYDROGRAPHIC/ TOPOGRAPHIC CENTER WASHINGTON DC ELECTRONIC NAVIGATION DIV
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LORAN-C reliability diagrams depict two types of data the maximum usable groundwave signal limit, which aids the LORAN-C user in determining which transmitters provide coverage in his area of operation, and the predicted uncertainty of a LORAN-C hyperbolic fix. Signal limits are computed using Bremmers field prediction formula and an algorithm that predicts the range for a signal of predetermined signal-to-noise ratio propagating along an electrically inhomogeneous transmission path. Fix uncertainty predictions are based on a formula relating fix uncertainty to crossing angle between lines of position, system standard deviation, and the divergence of hyperbolic lines of position. Actual range and fix uncertainty may differ from values shown on reliability diagrams, depending on such factors as weather, the occurrence of geomagnetic disturbances, and the users direction of travel. Reliability diagrams currently produced show signal limits and fix uncertainties for LORAN-C chains at a scale of 15,000,000 a new generation of reliability diagrams could show data at a reduced scale 110,000,000 for each LORAN-C triad one master and two slave transmitters, making more chain and transmitter selection information available to the user.
- Cartography and Aerial Photography
- Direction Finding