What Is a Doppler Map?

Since the 1970s, a multifunctional aviation integrated system combining Doppler navigation system and other airborne electronic systems has appeared. The Doppler navigation system uses the Doppler effect to measure the Doppler frequency shift, thereby calculating the current speed and position of the aircraft for navigation (see Radio Navigation). When the aircraft is yawing due to crosswind, Doppler radar is also used to measure the value of the drift angle and correct the course. The advantages of the Doppler navigation system are: no ground equipment is required to work with it; it is not limited by regional and climatic conditions; and the accuracy of the measurement of aircraft speed and drift angle is high. The disadvantages are: when the attitude of the aircraft exceeds the limit, the Doppler radar cannot work because it cannot receive echoes; the positioning error increases with time; the operation of the Doppler radar is related to the condition of the reflective surface.

The Doppler navigation system refers to a general term for a self-contained navigation device using Doppler effect for navigation. It usually consists of Doppler navigation radar, heading and attitude system, navigation computer, control display and so on. The Doppler frequency shift (ie, the difference between the frequency of the ground echo and the frequency of the radio wave emitted by the radar) corresponding to the aircraft ground speed and deflection angle measured by the Doppler navigation radar, and the aircraft provided by the heading attitude system The heading, pitch, and tilt signals are sent to the navigation computer together to calculate the ground speed and deflection angle. The aircraft position and other navigation parameters are obtained, and the display of various navigation parameters is controlled by the display, and the system is controlled and controlled. ^[1]

Doppler navigation system

FM CW

Band Ku

Singer Company, Kearfott Division

Developed in 1972

Equipped in 1978

Equipment models YAH-60A, AH-1S, UH-60A, CH-47D, CH-46E, BO-105VBH, BO-105PAH, CH-53D, UH-1H, etc.

Work status navigation

Production status, in service

AH-64 Apache-Helicopter with Doppler Navigation System

The AH-64 Apache is an advanced attack helicopter developed by the United States McDonnell Douglas under the Advanced Attack Helicopter (AAH) plan proposed by the United States Army. The aircraft can perform anti-tank missions day and night under severe weather conditions, and has strong combat, lifesaving and survivability. In September 1975, the prototype flew for the first time and was officially delivered in 1984. In December 1989, it entered the war for the first time in Panama. The Gulf War in 1991 and the NATO military strike against Yugoslavia in 1999 showed a great deal Combat capabilities. Existing types: AH-64A, "Advanced Apache", "Multi-stage Improvement Plan" (MSIP); AH-64B, which is a modification of AH-64A, is equipped with Global Positioning System (GPS) and has target handover capability AH-64C, which is a modification of AH-64A; AH-64D "Longbow Apache", equipped with "Longbow" radar, "Helfa" missile that can carry RF seeker; plan to retrofit more power General Dynamics' T700-GE-701C engine, a new power distribution system, a large generator doubled to 70 kVA, and an AN / ASN-157 Doppler navigation system.

The AN / ASN-128 Doppler navigation system was developed by the U.S. Army in 1972. Through three rounds of hardware design and the final competitive engineering development phase, it won the 1976 tender. The Army awarded a contract to produce 300 systems. By the mid-1980s, the system had also been transferred to West Germany's SEL and produced 470 units. It is listed by the US Army as a standard helicopter Doppler navigation system. This system has a simple design, a low speed measurement threshold, and its signal-to-noise ratio is almost constant at low altitudes, so it has good low-altitude performance and high hovering accuracy. Therefore, it is used by armed helicopters that require ground-based flight in many countries. In addition, the system has a small radiant energy and is highly resistant to electronic reconnaissance on the battlefield. Because of its simple structure, it is relatively inexpensive to construct, has a simple power supply, and high reliability.

The system has the capability of automatic ocean correction, without the need for additional sea / land correction switches. It can use the wind and ocean currents set to correct the effects of ocean wind and ocean current. In the event of a sensor failure, it has a spare way to navigate. It can hover in three dimensions over all landscapes. Its computer has fast speed, low speed fluctuation and time delay, low noise power spectral density, and can meet the cross-linking with autopilot and fire control system. It can set moving targets for correction. The position can be updated by passing the known waypoint over the waypoint to be flown. The target can be stored when flying over the aircraft target, and it has the function of freezing the instant position display screen.

With the increase of the production batch, the actual reliability has been improved. From 1979 to 1981, its mean time between failures remained at around 500 hours. After 1981 the actual reliability continued to improve. Due to the different conditions of use and maintenance in various countries, the reliability statistics are also different. The MTBF value of the West German Army has exceeded 2000 hours. Some military forces have conducted many tests when selecting the system. For example, the West German Army conducted a Doppler navigation system work evaluation test, extended evaluation test, missile launch test, soldier trial test, and joint tactical evaluation test.

The US Army's order for AN / ASN-128 has been lined up to the early 1990s, and to date the system has produced more than 3,000 sets. Because it uses surface mount technology in production, it is suitable for mass production. It is currently produced at a rate of 50 units per month, of which about 40 are for the US Army and 10 are for export. The system has been exported to Greece, West Germany, Spain, Japan, Nigeria, Australia and some other countries. It is the world's most productive helicopter Doppler navigation system.

LRU 3

Antenna print antenna

Beam configuration time-division four-beam

Beam

Conversion rate

Transmit power is less than 100mW, more than 20mW

Transmitting frequency 13325Hz ± 75MHz

Speed measurement range -93 650km / h

Lateral ± 185km / h

Vertical ± 25.4m / s

Height range 0 4267m

When the attitude range is 0 3048m

Land roll ± 45 °

Tilt ± 30 °

Rolling at sea ± 30 °

Tilt ± 20 °

Speed measurement accuracy: 0.25% Vt + 0.368km / h

(1) 0.25% Vt + 0.368km / h

0.15% Vt + 0.184km / h

Where Vt = Vx2 + Vy2 + Vz2 warm-up time is less than 5s

No cooling required

Power spectrum for vertical and horizontal 0.005kn2 / rad / s / kn

Density vertical 0.002kn2 / rad / s / kn

Linear acceleration longitudinal -1g + 2g

± 2g

Vertical -1g to + 2g

Bearing change

Speed up to 10 ° / s

Pitch change

Speed up to 20 ° / s

Roll change

Speed up to 20 ° / s

Navigation accuracy CEP 0.7 1.9% varies with heading system accuracy, CEP is 1.3% at heading accuracy of 1

Power requirements RTA 12W

SDC 56.6W

CDU 30W

Option SHIU 15W

Volume RTA 7752cm3

SDC 9296cm3

CDU 3676cm3

Option SHIU 1067cm3

Weight RTA 4.76kg

SDC 5.67kg

CDU 3.18kg

Option SHIU 0.91kg

MTBF system (calculated value) 2121h

System (84-year field statistics) 1250.9h

With option SHIU (calculated value) 1750h

Of which RTA 12237h

SDC 7744h

CDU 3838h

SHIU 10000h

Maintainability level 1 (estimated) 15min

(Statistics) 9min

Level 2 (estimated) 30min

(Statistics) 13min

Automatic interception

Tracking time <10s

BITE 95% confidence

Extension Overview

RTA

The antenna is a printed antenna, and its design can automatically compensate for the sea surface deviation of the Doppler shift caused by the change of the water surface scattering coefficient. The transmitting and receiving antenna uses the same antenna, and the radome and the antenna are integrated. The antenna is simple to manufacture, low in cost, small in size, and light in weight. The cost is 1/5 of the waveguide antenna, and the error caused by the terrain is 1/6 of the average antenna.

The transmitter uses a body-effect Gunn diode oscillation source, and uses a varactor to modulate the transmission source. Its modulation frequency is 30 GHz and its modulation coefficient is 0.92% ± 15%. The integrated transceiver circuit consists of a directional coupler, a ferrite duplexer, a bridge, and a balanced mixer.

The above components form a transceiver antenna unit together with a pre-IF amplifier circuit, an FM drive circuit, a beam drive circuit, and an antenna correction unit.

SDC

The signal-to-data converter consists of a leakage suppression filter, a frequency tracker, a timing interface circuit, a power supply, and an analog-to-digital signal converter. The filter is used to suppress the leaked carrier, but to ensure the detection of the Doppler signal when the helicopter is flying at low speed to meet the required helicopter hovering accuracy. SDC also provides power for each unit of the system.

CDU

The computer display unit uses the special chip of Singer Company as the CPU, and the word length of its instruction word and data word is 16 bits. The capacity of ROM is 16K bytes. The capacity of the RAM is also 16K bytes. All the internal self-test results are displayed on the CDU. The entire process is only 18 seconds. It can perform self-tests without interrupting navigation and guiding calculations. Can use latitude and longitude coordinates and UTM coordinates, can store 10 waypoints, the computer has room for further expansion.

Option SHIU

The driving hover indicator is used for driving and hovering instructions. It has two working modes of navigation and hover.