Aircraft based observation systems (termed Aircraft Meteorological Data Relay or AMDAR) for acquiring weather data from aircraft in flight have been shown to be an efficient and cost effective method of collecting atmospheric metrological data. This study looked at the capabilities of the global airline industry to provide further AMDAR coverage around the world.
At present, AMDAR coverage is highly localized around countries that have airlines participating in AMDAR programs. As a result, the majority of AMDAR data comes from the US, Europe, Australia and New Zealand, South Korea, Japan and China. Other parts of the world have less coverage which depends on the routes and destinations of AMDAR participant airlines. The large parts of the world without regular AMDAR data have been termed “Data Sparse Regions”.
This report investigated how to target airlines in the data sparse region s to AMDAR programs. Key findings in this report include:
In addition to appropriate aircraft instrumentation, automated digital communications from the aircraft to a ground telecom network is essential for AMDAR, with AMDAR data is usually being transmitted via VHF ACARS.
VHF ACARS communication is limited or missing in many parts of the Data Sparse Regions so satellite based ACARS communications are frequently required in these areas.
There are no lists of ACARS customers available from the ACARS telecom providers (ARINC and SITA). However, using a number of sources, a global database of airlines, aircraft operating ACARS and airlines’ routes was assembled for this report.
It was found that there are sufficient airlines, with modern aircraft capable of reliably acquiring AMDAR data, within the data sparse regions of the world.
The airlines most useful to AMDAR will be the more sophisticated airlines that have VHF ACARS installed on their aircraft but use satellite ACARS given their operational areas. These airlines are considered as the best targets for future airline recruitment to AMDAR programs.
Large improvements to global AMDAR coverage could be made by recruiting a few select airlines from these regions.
The findings within this report should be used in conjunction with weather data requirements that the meteorological community has in each geographic region to streamline the process of targeting airlines to recruit. Furthermore, the associated database that accompanies this report contains further detailed information on fleets and routes that is not summarized in this report.
The AMDAR System: General description
The advent of powered flight drastically increased the importance of reliable weather forecasting. It seems only fitting that aircraft be used to provide some of the data required for modern weather forecasting.
AMDAR, or Aircraft Meteorological Data Relay, had its start with ad hoc pilot observations of weather conditions but it was the ASDAR (Aircraft to Satellite Data Relay) system that began automated aircraft based weather reporting. ASDAR started in the 1970s when a small number of wide-body jet aircraft were outfitted with equipment that allowed transmission of data to the WMO GTS (Global Telecommunications System) via geostationary meteorological satellites (Painting, 2003).
The first AMDAR program was started in 1986 with just 5 aircraft but has grown immensely to provide over 300,000 observations daily via over 2,800 aircraft. As shown in Figure 1, the number of reports has varied considerably over time, reflecting the economic condition of the airlines involved as well as local and global economic conditions.
Like ASDAR, AMDAR utilizes aircraft instruments to provide accurate static air temperature and winds aloft. This data is transmitted to the ground usually by VHF radio on the aircraft’s ACARS system (Aircraft Communications, Addressing and Reporting System), and from ground stations to meteorological processing via the airline’s data processing centre.
In the early years of commercial jet aviation it became apparent that voice communication was not adequate for air traffic control. The time required for controller – pilot communication, and the unstructured nature of voice communication, limited the number and type of communications and, ultimately, the number of aircraft that could be managed by a controller. The ACARS (Aircraft Communications, Addressing and Reporting System) system was designed to address issues of volume and accuracy in the Air traffic Control System, and made automatic meteorological reporting possible.
Figure 2: Schematic of the basic AMDAR system (WMO AMDAR Flyer, 2007)
The general scheme of the AMDAR system is shown in Figure 2. In some cases the data may be transmitted through ACARS by satellite or by an independent system such as AeroMechanical Services (now FLYHT Aerospace Solutions Ltd.) AFIRS system. While similar, AIRDAT LLC’s TAMDAR system was originally designed to provide observation data independent of the aircraft instrumentation.
The basic data collected by the AMDAR system is indicated in Table 1.
(2) WMO requirement for Numerical Weather Predisction (NWP) in troposphere.
(3) 2ms-1 (4kt) vector error.
(4) 5Nm equivalent (specified for ASDAR).
Table 1: Basic AMDAR parameters and primary data sources.(AMDAR Reference Manual, Painting, 2003)
AMDAR data is passed through rigorous quality checks prior to its distribution or use in Numerical Weather Prediction (NWP) models. Quality checks compare the AMDAR observation to “first guess” results from the model at that location and time. The difference must be smaller than set values depending on the location and model to be acceptable and assimilated. There are also geographic and speed checks performed to ensure that erroneous data is not incorporated.
Several other atmospheric parameters may be acquired in flight. The parameters most desired by the meteorological community are listed in Table 2. These additional parameters are generally not derived from primary flight instrumentation and require additional sensors be installed on the aircraft or additional programming within the aircraft avionics.
Many studies have shown the positive improvement to forecast accuracy provided by the inclusion of AMDAR data in numerical weather prediction models as part of the forecast process. While these improvements benefit the public and industry in general, there are special benefits to aviation including the forecasting of turbulence and icing, or weather that might affect operational aspects of an airline. In some cases AMDAR data is used by the airline’s Meteorological and Flight Planning units to plan more efficient routes with less exposure to in-flight turbulence and icing.
0 to 800
-3 to 6
0 to 20
0 to 1
0 to 100
Humidity (dew pt)
-99 to +49
Humidity (mixing ratio)
0 to 100
(1) Determined by output categories required.
(2) WMO requirement for NWP in troposphere.
(3) To meet stratospheric humidity requirement.
(4) Acceleration due to gravity. ‘Zero’ reference on aircraft is usually +1.
Another reason for AMDAR’s success with the airlines has been that there is a two way flow of information between the meteorological services and the airlines involved. The AMDAR Quality Control process helps to ensure that data quality remains high by alerting airlines to issues with aircraft instrumentation.