A Doppler velocity sensor (DVS) is a specialized

Doppler radar A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the fr ...

that uses the

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, ...

to measure the three orthogonal

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

components referenced to the

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. ...

. When aircraft true heading, pitch and roll are provided by other aircraft systems, it can function as a navigation sensor to perform stand-alone

dead reckoning In navigation, dead reckoning is the process of calculating current position of some moving object by using a previously determined position, or fix, and then incorporating estimates of speed, heading direction, and course over elapsed time. T ...

navigation calculations as a Doppler Navigation Set (DNS). Doppler navigation systems are independent of surrounding conditions, perform with high accuracy over land and sea anywhere in the world, and are independent of ground-based aids and space-based

satellite navigation A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location ( longitude, latitude, and altitude/ elevation) to hi ...

systems.

Operational principles

To measure an aircraft three-dimensional velocity, a Doppler

radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

antenna is caused to radiate a minimum of three non-coplanar

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequency, frequencies between 300 MHz and 300 GHz respectively. Different sources define different fre ...

electromagnetic beams toward the earth's surface. Some of the energy is backscattered to the radar by the earth surface. With knowledge of the beam angles, three or more beam-Doppler

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is e ...

are combined to generate the components of aircraft velocity. DVS transmission is performed at a center frequency of 13.325

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one ...

in the internationally authorized

Ku band The Ku band () is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). The symbol is short for "K-under" (originally german: Kurz-unten), because it is the lower part of the o ...

of 13.25 to 13.4 GHz.

Uses

DVS are used on helicopters for

navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

, hovering, sonar dropping, target handover for weapon delivery and

search and rescue Search and rescue (SAR) is the search for and provision of aid to people who are in distress or imminent danger. The general field of search and rescue includes many specialty sub-fields, typically determined by the type of terrain the search ...

. Because the Doppler radar measures velocity relative to surface, sea current and

tidal Tidal is the adjectival form of tide. Tidal may also refer to: * ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * Tidal (servic ...

effects create biases. However, for

sonobuoys A sonobuoy (a portmanteau of sonar and buoy) is a relatively small buoy – typically diameter and long – expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic resear ...

dropping and over water search and rescue, velocity of the aircraft relative to water movement is expected. These radars were formally approved under the

FAA The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

TSO-65a until 2013, and are designed in accordance with the Radio Technical Commission for Aeronautics (RTCA) DO-158 standard titled ''Minimum Performance Standards − Airborne Doppler Radar Navigation Equipment.''

Limitations

The functional operation and accuracy of Doppler velocity sensors is affected by many factors, including aircraft velocity, attitude and

altitude Altitude or height (also sometimes known as depth) is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context ...

above terrain. It is also affected by environmental factors, including the type of terrain the radar is illuminating, and precipitation in the atmosphere. As the aircraft moves, the backscattering coefficient changes within the beam width, and this causes a shift and some skewing of the Doppler spectrum, and hence an error in the measurement of velocity. A major limitation of using DVSs for navigation is that they typically suffer from accumulated error. Because the guidance system is continually integrating velocity with respect to time to calculate position ''(see

)'', any measurement errors, however small, are accumulated over time. This leads to 'drift': an ever-increasing difference between where the system thinks it is located and the actual location. Due to integration a constant error in velocity results in a linear error in position.

References

{{Reflist

External links

Doppler Navigation Radar
on Friends of CRC
CMA-2012 Doppler Velocity Sensor and Navigation System
on

CMC Electronics CMC Electronics Inc. (french: CMC Électronique) is a Canadian avionics manufacturer. The company's main manufacturing facility is located in Montreal, Quebec with additional facilities located in Ottawa, Ontario and Sugar Grove, Illinois. Hi ...

AN/ASN-157 Doppler Navigation Set
on BAE Systems
ANV-353
on

Leonardo S.p.A. Leonardo S.p.A., formerly Leonardo-Finmeccanica and originally Finmeccanica, is an Italian multinational company specialising in aerospace, defence and security. Headquartered in Rome, Italy, the company has 180 sites worldwide. It is the eighth ...

Radar Aircraft instruments Avionics Speed sensors Navigational equipment Spacecraft components Navigational aids Motion (physics)

Operational principles

Uses

Limitations

See also

References

External links