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A classification of a navigation system with respect to availability. A continuous system gives the capability to deter- mine position at any time.



Related Terms

PREDICTABILITY

In a navigation system, the measure of the accuracy with which the system can define the position in terms of geographical coordinates.

GNSS

Global Navigation Satellite System a worldwide position and time determination system that includes one or more satellite constellations and receivers

WWRNS

World-Wide Radio Navigation System terrestrial and satellite radio-navigation systems that have been accepted by IMO as capable of providing adequate position information to an unlimited number of ships

ELLIPTICAL SYSTEM

A tracking or navigation system where ellipsoids of position are determined from time or phase summation relative to two or more fixed stations which are the focuses for the ellipsoids.

RELATIVE ACCURACY

The accuracy with which a user can measure current position relative to that of another user of the same navigation system at the same time. Hence, a system with high relative accuracy provides good rendezvous capability for the users of the system. The correlation between the geographical coordinates and the system coordinates is not relevant.

CHART CLASSIFICATION BY SCALE

  1. Charts are constructed on many different scales, ranging from about 1:2,500 to 1:14,000,000 (and even smaller for some world charts). Small-scale charts are used for voyage planning and offshore navigation. Charts of larger scale are used as the vessel approaches land. Several methods of classifying charts according to scale are in use in various nations. The follow- ing classifications of nautical charts are those used by the National Ocean Survey: Sailing charts are the smallest scale charts used for planning, fixing position at sea, and for plotting while proceeding on a long voyage. The scale is generally smaller than 1:600,000. The shoreline and topography are generalized and only offshore soundings, the principal navigational lights, outer buoys, and land- marks visible at considerable distances are shown. General charts are intended for coastwise navigation outside of outlying reefs and shoals. The scales range from about 1:150,000 to 1:600,000. Coast (coastal) charts are intended for inshore coastwise navigation where the course may lie inside outlying reefs and shoals, for entering or leaving bays and harbors of considerable width, and for navigating large inland waterways. The scales range from about 1:50,000 to 1:150,000. Harbor charts are intended for navigation and anchorage in harbors and small waterways. The scale is generally larger than 1:50,000. 2. The classification system used by the National Imagery and Mapping Agency differs from the system in definition 1 above in that the sailing charts are incorporated in the general charts classification (smaller than about 1:150,000); those coast charts especially useful for approaching more confined waters (bays, harbors) are classified as approach charts.

G.N.S.S.

Global Navigation Satellite System Worldwide position and time determination system that includes one or more satellite constellations and receivers.

REPEATABLE ACCURACY

In a navigation system, the measure of the accuracy with which the system permits the user to return to a position as defined only in terms of the coordinates peculiar to that system. For example, the distance specified for the repeatable accuracy of a system such as Loran C is the distance between two Loran C positions established using the same stations and time-difference readings at different times. The correlation between the geographical coordinates and the system coordinates may or may not be known.

NAVSTAR GLOBAL POSITIONING SYSTEM

A satellite navigation system developed by the Department of Defense. The system is provides highly accurate position and velocity information in three dimen- sions and precise time and time interval on a global basis continuously, to an unlimited number of users. It is unaffected by weather and provides a worldwide common grid reference system. The objective of the program is to provide very precise position information for a wide spectrum of military missions. In addition, current policy calls for civil availability with a slight degradation in system accuracy required to protect U.S. national security interests.

ABSOLUTE ACCURACY

The ability of a navigation or positioning system to define an exact location in relation to a coordinate system.

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