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OMEGA-Optimized Method for Estimated Guidance Accuracy basics

OMEGA avionic system is a long range navigational aids and it stands for Optimized Method for Estimated Guidance Accuracy. It provides 2D Aircraft position fix. This technology is based on navigation using a hyperbolic grid, which is quite similar to the LORAN-C.

To obtain the Aircraft position fix at least two LOPs are required. The only difference is that in the OMEGA process we need three ground stations without tagging them as master or slave like we did using LORAN-C.

OMEGA,Optimized Method for Estimated Guidance Accuracy

Following are features of OMEGA system on the Ground:
•  OMEGA Tx: Only 8 OMEGA transmit systems exist in the world.
•  Frequency of operation: VLF from 10.2 to 13.6 kHz
•  OMEGA signals propagate using sky waves.
•  Each GND station could transmit 4 possible time shared signals(e.g. 10.2, 13.6, 11.33, or 11.05 kHz).
•  In addition to the signals above a unique ID signal is emitted from each station.
•  Transition time from one signal Freq to another is approx. 0.2 seconds.
•  The signal transmission scheme repeats every 10 seconds.
•  GND based atomic clocks are used to synchronize stations among each other.

Following are features of OMEGA system in the Aircraft:
•  Rx: OMEGA-Rx system.
•  Frequency: VLF
•  Range of Operation: 6,000 miles (approx. 10,000 km)
•  Highly selective Rx in order to avoid interference from other signals.

Advantages

•  OMEGA does not suffer from LOS since it operates at VLF band.
•  Hyperbolic grid navigation provides a more direct route similar to WPT NAV.
•  Sky wave propagation uses the reflective property of the ionosphere layer; hence large travel ranges are possible.

Disadvantages

•  Error in this system can be about+/-- 0.5 miles (approx.+/-1 1km)
•  Sky Wave Propagation Error: The velocity at which the signal travels may vary, and hence some offset may be introduced.
•  Diurnal Error: The ionosphere layer varies in height during day and night and therefore errors are generated. That is for position fix, 3-stations are needed, and in most cases these GND stations are not aligned within the same time zone; therefore different ionosphere heights will result at different geographical locations.
•  Maintenance of the OMEGA GND stations is quite costly.

OMEGA was in use until sep.30-1997. It has been replaced by GPS system. The North Dakota station is still used by US navy for VLF submarine communications.

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