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DNS-Doppler Navigation System basics

DNS avionic system is a long range navigational aids and it stands for Doppler Navigation System.

DNS,Doppler Navigation System

DNS system provides Aircraft velocity (3D) and position fix (3D). This system is primarily used for military purposes requiring high speed low altitude flights. First, the aircraft velocity is obtained using the doppler radar, then the information is inputted to a NAV computer so that the position fix can be calculated. Also, similar to INS, this technology is a self contained system and therefore, does not depend on any outside source.

In the Aircraft the system has following features.
•  Tx and Rx is referred as DNS radar system.
•  Operates at SHF frequency band (8.8 to 9.8 GHz and 13.25 to 13.40 GHz)
•  Aircraft doppler radar transmits a beam to Ground.
•  The beam is reflected and observed at the Aircrfat receiver with velocity information.
•  Velocity is then integrated to obtain position.

Advantages

•  DNS is a self-contained airborne system that does not need any outside NAV source.
•  DNS operates over land and water.
•  Average velocity information is extremely accurate.
•  Aircraft Tx-Rx is light, small, and cheap since it requires a small amount of power for operation.
•  Sometimes a combination of INS-DNS is used to obtain more accurate readings since one technology could correct the other due to the fact that:
•  •  INS will generate a short-term velocity error
•  •  DNS will generate a long-term velocity error

Disadvantages

•  3D velocities are first obtained in A/C coordinates and then transformed to earth coordinate and therefore calculation errors will be present. Overall system error is about 0.5 %
•  DNS performance is diminished in extreme conditions of rain.
•  While operation over water, accuracy is degraded due to water motion and smooth water surface.

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