DNS-Doppler Navigation System: Basics and Functionality

The DNS avionic system, short for Doppler Navigation System, is a long-range navigational aid used in aviation.

The DNS system provides aircraft velocity (3D) and position fix (3D) information. It is primarily used for military purposes requiring high-speed, low-altitude flights. The system determines the aircraft’s velocity using Doppler radar, and this information is fed into a navigation computer to calculate the position fix. Like INS (Inertial Navigation System), DNS is a self-contained system, meaning it doesn’t rely on any external sources.

The system includes the following features when installed in the aircraft:

• The transmitter (Tx) and receiver (Rx) are part of the DNS radar system.
• It operates at SHF (Super High Frequency) bands (8.8 to 9.8 GHz and 13.25 to 13.40 GHz).
• The aircraft’s Doppler radar transmits a beam towards the ground.
• The beam is reflected and observed at the aircraft receiver, providing velocity information.
• Velocity is then integrated to determine the position.

Advantages

• DNS is a self-contained airborne system that doesn’t require any external navigation sources.
• It operates effectively over both land and water.
• The average velocity information is highly accurate.
• The aircraft’s transmitter and receiver are light, small, and inexpensive due to their low power requirements.
• Sometimes, a combination of INS and DNS is used for more accurate readings. One technology can correct the other because:
  • INS can generate short-term velocity errors.
  • DNS can generate long-term velocity errors.

Disadvantages

• 3D velocities are initially obtained in aircraft coordinates and then transformed to earth coordinates, which can introduce calculation errors. The overall system error is approximately 0.5%.
• DNS performance is reduced in extreme weather conditions, such as heavy rain.
• When operating over water, accuracy can be degraded due to water motion and smooth water surfaces.