These data are routed by
several cooperating airlines to GSD, and we decode and quality control
Our web site also includes AMDAR data from many
European and Asian air
carriers. The AMDAR data are subjected to the same quality control and
other processing by us as the ACARS data.
Demonstration displays showing past ACARS data are available to all,
java version, or
Because the ACARS data processed at GSD are
proprietary to the airlines providing the data, the following
guidelines have been developed regarding access. (In the statements
below, "ACARS" refers to all aircraft data from GSD,
including AMDAR data.)
- Real-time ACARS data may be made available to those
organizations that are performing research which, in the judgment
of GSD, is likely to benefit the airlines providing the data.
- The data may not be redistributed in real-time. However, the use of
images in research publications is allowed and encouraged.
- Researchers are encouraged to use ACARS data in Numerical Weather
Prediction models. NWP model results may be made available to the
public in real-time provided that all of the following conditions are
met (Adapted 26 April 2001):
- Individual ACARS measurements may not be revealed (though gross
numbers may be).
- ACARS must be one of several kinds of input observations (such as
radiosondes and METARs).
- The model and data may not be used to develop products or services
- Real-time data are available to government agencies such as NOAA in
support of forecasting operations.
- Real-time data may be made available only to those airlines that
provide ACARS meteorological data to the US Government at their own
expense. Data may not be shared with affiliate or code-share airlines.
(Language clarified 26 April 2001.)
- Real-time data may not be made available to commercial entities that
would use them to develop products or services they plan to offer for
sale to the participating airlines.
If you would like to receive GSD ACARS data and believe you are
eligible, please have a faculty member or other responsible official
of your organization send an email to
briefly describing your proposed use of the data (a couple of
sentences should suffice), and agreeing not to
redistribute the data and not to use it to develop commercial
products or services. We will reply by email with access
information, or explaining why we cannot provide access.
Once approved, you can receive ACARS data in several ways:
- Web-based graphical displays, either java-based or not
- Web-based access to binary data in netCDF format
- LDM access to binary data in netCDF format
Frequently Asked Questions
- What variables are
- Most aircraft provide
- wind direction and speed
- Eddy dissipation rate (EDR), a measure of
turbulence, is reported by about 100 UAL aircraft that fly
mostly over the United States. (These data are
experimental and should not yet be relied upon for
turbulence verification. We expect
quality-controlled EDR data to be available in 2005.)
- Derived equivalent vertical gust (DEVG), another
measure of turbulence, is reported by
about 80 international (AMDAR) aircraft that fly over Europe and
The translation between DEVG values and turbulence severity is as
|< 2 m/s||Nil
|2 - 4.5 m/s||Light
|4.5 - 9 m/s||Heavy
|> 9 m/s||Severe
- Water vapor, reported as dewpoint, is provided by a few aircraft.
These data are experimental, have not been validated, and should
be used with caution.
- Icing information (yes/no) is reported by a few aircraft. These
data are experimental, have not been validated, and should be used
- How many data are there?
- Currently, we are getting just about 140,000 wind and temperature
observations per day,
100,000 of which are over the continental United States. These
data come from more than 4000 aircraft. There are
more data during the daytime than at night, but thanks to
participation by some parcel-carrying airlines, nighttime
coverage is substantial.
- What is the storage/data transmission
- about 1.8 megabytes per hour in netCDF format
- 150 kilobytes per hour in the format downloaded to the java
- The non-java display downloads gif images which have sizes from 2 to
75 kilobytes, depending on the amount of data shown and whether a
satellite background image is requested.
- What quality control is applied to the
- The ACARS data stream is very high quality, with less than 2% of
the data showing problems. Nevertheless, all data shown on
the web site or available for download have been
quality-controlled at GSD. This processing includes interpolating
location and time information to those data, such as
high-resolution ascent data, that lack it. Data that fail
quality control are
indicated by a special color on the web plots, and several
quality control and interpolation flags are available in the
netCDF data that
indicate exactly what test(s) and interpolation each datum was
subjected to. Details
of the quality control are available
- What kind of altitude is
- The altitude-determining physical variable is pressure.
This is converted to altitude by using a standard
atmosphere. The standard atmosphere is used at
all altitudes and under all pressure conditions.
Thus, for instance, it is possible to have ACARS altitudes below
ground level on days with high atmospheric pressure. (This is in
contrast to other aviation reports such as voice PIREPS that use
a standard atmosphere
to compute altitude above 18,000 ft (MSL), but use the current
altimeter setting for lower altitudes.)
- Are the data averaged?
- No. All ACARS data are point samples, not
averaged in time or
space. (Specifically, this means that the averaging time is
approximately 1 sec or less.)
- What is the resolution?
- At flight altitudes (above about 23,000 ft), data are generally
taken every 5-6 minutes. Near airports the data spacing is
decreased by some airlines in several different ways:
- 2000 and 1000 ft. vertical resolution below 18,000 ft. is
- On ascent, more than 150 aircraft provide data with a vertical
resolution of 300 ft. for the first minute after take-off
(up to about 2500 ft. AGL).
- What is the accuracy?
- Benjamin, Schwartz, and Cole (1999, Weather and Forecasting, in
review) -- collocation study with ACARS reports. Estimated wind
vector accuracy - 1.8 m/s, estimated temperature accuracy - 0.5 deg C.
These numbers are much lower than the previous ACARS/RAOB differences,
which by definition included RAOB error.
- Decker, R., R.D. Mamrosh, and C.E. Weiss, 1999: ACARS operational
assessment: description and interim results. Preprints, 3rd
Conference on Integrated Observing Systems, Dallas, TX, Amer. Meteor.
- From Richard D.
Mamrosh (1998): "Several studies have compared ACARS with
other data sources. Among these, Lord,
et. al. (1984) compared ACARS flight-level winds with
radiosonde, cloud-motion and VAS thermally-derived winds. When ACARS
was compared to radiosondes, root mean square (RMS) deviations were
7.4 degrees in direction and 5.3 m/s in speed. More recently, Schwartz
and Benjamin (1995) compared ACARS ascent/descent winds and
temperatures with radiosondes and found temperature differences were
less than 2C on 94 percent of all occasions, and less than 1C better
than 68 percent of the time. Wind speed RMS deviations were 4.1 m/s
while direction RMS differences were 35 degrees (mostly due to light
and variable wind situations)."
- How timely are the data?
- Data are processed at GSD every 10 minutes, starting on the hour.
If you access the data shortly after they are processed, the most recent
data may be only a couple of minutes old. However, some airlines
buffer the data on board the aircraft. Reports on ascent and
descent are generally buffered for 0 to 2
minutes (depending on airline and aircraft type), however some
over-ocean reports may be buffered for several hours.
Gruesome additional details: Every 10 minutes,
starting on the hour, data arriving since the end of the last
complete hourly file are processed. Processing takes about
10 seconds. At 18 min past the hour, the last complete
hourly file is generated. I.e.,
at 0118 a file containing data for 0000-0059:59 is generated. In
order to catch late-arriving reports, this file is regenerated
approximately 1,2,3,6, and 12 hours later. (Times are shifted by
a minute or so that jobs don't overlap.) So, if you want to
get the most complete data set, wait at least 12h 22m.
- How is a "sounding"
- A "sounding" is a portion of an ascent or descent flight track
from a single aircraft that can provide a vertical profile of
wind, temperature, and sometimes dewpoint and other variables.
On both the java and non-java displays, a sounding plot will
always be generated when you click on an
ascending or descending portion
of a flight track. However, some flight track portions are
considered by the software to have sufficient resolution and
vertical extent to be a meteorologically useful
sounding. These are indicated on the java display by solid lines
between the data points comprising the sounding. To be considered
a (useful) sounding, the flight track portion must meet all of
- The bottom of the sounding must be <= 2000 ft AGL (and
< 10000 ft MSL)
- The bottom of the sounding must be within 50 nm of a known
- The maximum data gap must be <= 5000 ft in the vertical.
- (The top of the sounding is taken as 500 ft below the
maximum altitude of a flight, or 50 temperature data points
above the lowest point--whichever is less.)
- Are retrospective data
- On the web, 30 days of data are generally kept on line. For the
java display, data back to 1 July 2001 may be downloaded on demand
(from the MADIS archive) although data more than 30 days old take
longer to load, initially.
Data since 1 July 2001 in netCDF format are available through
program. Interested parties may fill out this data
- How have the data been used?
- NOAA forecast offices have been using GSD's ACARS data for several
years. One on-line publication that describes the use of the
data at one forecast office is THE USE OF
HIGH- FREQUENCY ACARS SOUNDINGS IN FORECASTING CONVECTIVE
STORMS by Richard D. Mamrosh of the National Weather Service,
Chicago, Illinois. We also have begin compiling NWS
Forecast Discussions that mention
- ACARS are critical asynoptic data for the Rapid Update Cycle
(RUC), LAPS, and
the Eta models, and are also assimilated into
- What airlines provide GSD with
- Currently-participating U.S. airlines are: American, Delta, Federal
Express, Northwest, Southwest, United, and United Parcel Service. In
addition, the following airlines participate in the
AMDAR program: BA, KLM, Air France, SAS, Lufthansa, Qantas,
Air New Zealand, South African Air, Air Namibia.
AMDAR data sources
explained, by Dave Helms, NWS. (PDF document)
- AMDAR: Aircraft Meteorological Data Reports. The
name used worldwide for automated meteorological reports from aircraft.
- TAMDAR: Tropospheric AMDAR. A commercial
measurement and communications developed by AirDat, LLC,
initially under NASA sponsorship. TAMDAR is designed to be
deployed on regional aircraft, and has been deployed on several
regional fleets. TAMDAR data from the Mesaba Airlines fleet is
available to the U. S. government; data from other fleets is
generally restricted to GSD, for evaluation.
- MDCRS: Meteorological Data Collection and
Reporting System. MDCRS is
funded jointly by the U.S. government and the seven participating
airlines (American, Delta, Federal Express, Northwest, Southwest,
United, and United Parcel Service), and operated by Aeronautical Radio, Inc.
- ACARS: Aircraft Communications Addressing
and Reporting System, a proprietary system run by
Aeronautical Radio, Inc. (ARINC). ACARS is used by
airlines to transmit a variety of proprietary air-to-ground
communications. Seven airlines use ACARS to transmit
meteorological data for the MDCRS system. These airlines also
use ACARS to route their meteorological data directly to GSD
where we also decode the data from the wide variety of formats
used by the airlines. Thus, on the GSD AMDAR display, we refer
to "ACARS" data as those data we decode here, and to MDCRS data
as those data we reveive from the NOAA telecommunications gateway.
- WVSS and WVSS-II: The Water
Vapor Sensing System II (WVSS) has
been developed by SpectraSensors through contracts with NOAA.
The WVSS has undergone a series of engineering changes since its
initial deployment in 2005, culminating with the most design
changes in 2008. The latest design has corrected most problems
with the system, yielding consistent quality mixing ratio
observations for a range of warm/moist and cold/dry airmasses,
probably as good or better than other operational in situ
observing systems. As of August 2010, there are 30 WVSS in
operations, 25 flying on United Parcel Service B-757 aircraft
and another 5 flying on Southwest Airlines B-737 aircraft
generating hundreds of soundings per day. The WVSS fleet will
expand to 100 aircraft in the next year, with on-going
assessments planned by multiple researchers; the results of
these assessments will be published in scientific journal
articles. (August, 2010)