RIASSUNTO
ABSTRACT
Raydist ""T"" and Micro-Omega are electronic phase comparison systems for marine and aircraft radiolocation and precision navigation. Both systems employ important new advances in electronics technology.
Raydist ""T"" is an outgrowth of Raydist DR-S, a range-range radiolocation system widely used to achieve ten foot positioning accuracy beyond line of sight. While a single Raydist DR-S network serves a maximum of four users, Raydist ""T"" serves an unlimited, ed number. The latter system produces a unique, nearly rectangular ""HALOP"" grid covering 10,000 or more square miles. HALOP coordinate geometry permits the use of simple overlays for geophysical surveys and general navigation, avoiding the need for computer coordinate conversion. Raydist ""T"" is much simpler, more reliable and less expensive than existing navigational aids of less than comparable accuracy.
Micro-Omega provides fully automatic correction of data derived from the U. S. Government';s world-wide Omega system, eliminating the need for manual corrections or the use of sky wave tables. The system achieves a navigational accuracy of three hundred feet. Both Raydist ""T"" and Micro-Omega are exceptionally simple to use; no special calibration, alignment nor table look-up procedures are required.
The state of Virginia has adopted Raydist ""T"" for evaluation as a permanent Radio positioning and navigation system covering the Chesapeake Bay and Continental Shelf waters of Virginia. This paper presents test results from both the Virginia Raydist ""T"" Network and the Micro-Omega evaluation program.
INTRODUCTION
By late 1973, the world-wide Omega navigation network will be fully operational. For the first time, using this eight-station network, it will be possible to obtain a 1-2 mile position fix at ten-second intervals anywhere on earth.
Several existing systems provide continuous or nearly continuous position information with accuracies comparable to Omega. However, none of these furnishes usable coverage of more than about 15 percent of the earth';s surface. To achieve world-wide coverage, all would require prohibitive expenditures for network acquisition and operation, assuming such Coverage would even be feasible. The Navy Navigation Satellite System provides world-wide position fixes at time intervals varying from 30 minutes to several hours. These long updating intervals are unsuitable for most applications, especially general navigation in areas of heavy traffic congestion, such as coastal regions and ports. Furthermore, conversion of raw satellite data to useful navigational information is a complex problem requiring sophisticated and costly receiving, timing and computing equipment.
At present, four of the ultimate total of eight Omega stations are transmitting, providing coverage of roughly 40 percent of the earth';s surface. Several of these stations operate at reduced power or use inefficient antenna configurations that will eventually be much improved. Fully adequate Omega signals will not be available on acontinual basis until 1973.
Omega data, as received, can exhibit errors of eight to ten miles. Skyways Correction Tables published by the U. S. Naval Oceanographic Office are used to achieve one mile accuracy in the daytime and two miles at night. This correction technique is suitable for navigation on the open seas; however, both the inconvenience of table look-up and the limited accuracy which results have generated an urgent need for a fully automatic, high-accuracy Omega correction technique.