Networks & Measurements Section

Bureau of Meteorology
Aircraft Meteorological Data Relay (AMDAR)

Introduction

A relatively modern development in meteorological observational systems involves the utilisation of commercial aircraft to automatically measure meteorological parameters and transmit them back to ground as the aircraft operates. The collective term used to describe this type of system is: Aircraft Meteorological Data Relay, and is known by the acronym: AMDAR. AMDAR systems take advantage of the fact that commercial airlines operate over large areas of the world where ground-based balloon-borne radiosondes do not, and, as such, offer the opportunity to capture large volumes of upper air data from data-sparse regions throughout the globe.

To date there have been two predominant sources of AMDAR systems: ASDAR (Aircraft to Satellite Data Relay); and more recently, ACARS (Aircraft Communication Addressing and Reporting System). The ASDAR system was developed as a sensor and communications package that is fitted separately to the aircraft. The ACARS system is essentially a software package that utilises the aircraft's own sensors and communications systems to operate. AMDAR systems utilising ACARS operate via VHF communications and a worldwide network of ground-based relay stations that, in most cases, enable the data to be received in close to real time. The network of relay ground stations is operated by a number of international communications companies including: SITA (AIRCOM); ARINC; Air Canada (ACARS); and Japan (AVICOM). The SITA network is the most extensive with some 300 stations in Europe, the Middle East, India, Africa, Central and South America, Far East and the South Pacific.

General schema for AMDAR system utilising ACARS.

The Bureau's AMDAR System

The Bureau of Meteorology developed its own AMDAR/ACARS systems with the cooperation and technical support of Australia's two major airline operators Qantas (from 1990) and, until recently, Ansett (from 1987 until 2001). As at November 2001, the Bureau derives approximately 2,500 AMDAR observations per day from 25 internationally-operating Qantas Boeing 747-400 aircraft.

AMDAR Data

AMDAR messages basically consists of two components: operational and positional data (time, latitude longitude, etc; and, meteorological data (temperature, wind and turbulence). Messages are transmitted at predefined frequencies which vary depending on the aircraft flight phase. Messages are received at a higher frequency and according to pressure level during ascent and descent so that an atmospheric profile is derived, and at a lower frequency dependent on time (currently every 7 minutes in the southern hemisphere) during cruise.

Upon reception of AMDAR messages, the Bureau decodes and archives them for operational purposes and also reformats them into a world standard format whereupon they are relayed on the Global Telecommunications System (GTS) for use by other meteorological agencies throughout the region and the world. The Bureau in turn receives data via the GTS from other meteorological agencies operating AMDAR systems.

The meteorological data derived from the AMDAR program is extremely valuable for various purposes including: input into numerical weather models; climate analysis and research; and, operational forecasting. This means that, by participating in the program, the airlines enable the Bureau to provide a better service to all Bureau clients, including the aviation industry.

Example of AMDAR aircraft tracks over a 24 hour period.

Further information about the AMDAR program can be obtained by contacting the Bureau of Meteorology.