Advanced Microwave Sounding Unit Swath (AMSU-A)

Table of Contents

Advanced Microwave Sounding Unit Swath
AMSU Instrument Platforms
File Naming Convention
Data Format		 Sample Read Routine
Links to other AMSU sites
Contact Information

Important Notices

NOAA-16 AMSU-A1 - Channel 4 out of spec performance confirmed on 4 March 2008. This channel is used for limb correction, and this failure requires GHRC to discontinue the AMSUA16 swath products. This dataset has an end date of 3 Mar 2008.

NOAA-17 AMSU-A1 suffered an instrument failure on October 28, 2003. As a result, AMSU-A channel-3 to channel-15 antenna temperatures are no longer available (AMSU-A channel-1 and channel-2 are working properly). NOAA-17 GHRC products end as of 28 Oct 2003.

Channel 14 on the NOAA-15 AMSU-A instrument stopped working in the Fall of 2000. In an effort to continue the channel 14 data set, we have developed an algorithm that estimates channel 14 measurements using data from AMSU-A channels 11, 12, and 13. The data currently being provided as "channel 14" is computed from this algorithm. This "channel 14" data is an educated estimate of what channel 14 would have measured had it remained operational.

Channel 11 on the NOAA-15 AMSU-A instrument has failed. Effective 25 Apr 2002, the limb correction equations have been modified to reflect an algorithm change for channels 8-14. Note that these corrections provide the 'best estimate' of what a fully functional instrument would provide.

Advanced Microwave Sounding Unit Swath

The Advanced Microwave Sounding Unit, (AMSU-A), is a cross-track, line-scanning instrument designed to measure scene radiances in 15 discrete frequency channels which permit the calculation of the vertical temperature and moisture profile from about 3 millibars (~45 km) to the Earth's surface. Each scan has 30 cells, with a resolution of 3.3 degrees (50 km at nadir). The swath width is 2343 km (96.66 degrees). The AMSU-A instrument is made up of two separate modules, A1 and A2. AMSU-A1 contains the 13 highest frequencies (50.3 - 89 GHz) of various polarizations. AMSU-A2 contains the two lowest frequency channels (23.8 and 31.4 GHz), both vertically polarized.

AMSU Instrument Platforms

AMSU flies on the National Oceanic and Atmospheric Administration (NOAA) polar orbiting spacecraft as part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). Click here for more NPOESS information. An interesting orbital mechanics discussion is found here.

NOAA-15 was the first spacecraft to fly AMSU. Launched on 13 May 1998, NOAA-15 is in a sun synchronous near polar orbit. Flying at approximately 450 nautical miles (~833km) in altitude at an orbital inclination of 98.7 degrees, NOAA-15 completes an orbit every 101.2 minutes. The ascending equator crossing time is at approximately 1920 local time.

Launched on 21 September 2000, NOAA-16 is in a similar orbit, with an ascending equatorial crossing time near 1553 local time.

The Third Advanced Microwave Sounding Unit-A was launched on NOAA 17 on 24 June 2002 from Vandenberg AFB, California on a Titan II booster.

File Naming Convention

From 3 Aug 1998 through 31 May 1999, the AMSU-A Swath Data Product was packaged in HDF-EOS format, one file per day. Each daily file is then compressed using the UNIX 'gzip' command. The file may be uncompressed on a UNIX system, using the 'gunzip' command, or on a PC using the 'WinZip' program. The file naming convention was:

amsu_a_swath_YYYY.JJJ.eos.gz

where

YYYY is the year (e.g., 1999)
JJJ is the day-of-year (e.g., 032)

NOTE: On 1 June 1999 (99.152), the file naming format was changed! The data prior to this date are available by special order only. Please contact User Services to order these preliminary data.

Data collected from 1 Jun 1999 forward have the following format. The Swath Data Products are packaged in HDF-EOS format, with one file per orbit. These daily files are tarred together using the UNIX tar command into a daily file that is then compressed using the UNIX 'gzip' command. The daily file is named:

amsuaSSsp_YYYY.JJJ_daily.tar.gz

where

SS is the platform identifier (e.g., 15 for NOAA-15)
YYYY is the year (e.g., 2000)
JJJ is the day-of-year (e.g., 235)
tar indicates UNIX 'tar'
gz indicates UNIX 'gzipped' (NOTE: this may be 'unzipped' using the UNIX 'gunzip' command, or on a Windows machine using the 'WinZip' program.)

Once a file is 'untarred' and 'unzipped' there will be individual orbit files which are named in the following manner:

amsuaSS_YYYY.JJJ_OOOOO_SSSS_EEEE_GG.eos

SS is the platform identifier (e.g., 16 for NOAA-16)
YYYY is the year of start of orbit (e.g., 2001)
JJJ is the day-of-year of start of orbit (e.g., 045)
OOOOO is the orbit number (e.g., 09453)
SSSS is the start time of orbit, HHMM, UTC (e.g., 0901)
EEEE is the end time of orbit, HHMM, UTC (e.g.,1056)
GG is the ground station identifier (e.g., GC)

Data Format

HDF-EOS objects

For data from dates between 3 Aug 1998 and 31 May 1999, data are contained within a single HDF-EOS swath object named:

DayYYYYJJJ

where YYYY and JJJ have the same meanings as above.

For Data from 1 June 1999 and later, data are contained in a single HDF-EOS swath object named:

Orbitddddd

where ddddd is the orbit number without leading zeroes (e.g. 2143, not 02143).

Dimensions

Two dimensions are defined:

Track - The along-track dimension or number of scans
Xtrack - The cross-track dimension (always 30)

Geolocation fields

Three geolocation fields are defined:

Latitude

Contains latitude values in decimal degrees in the range -90.0 to 90.0, stored as an array of single-precision floating-point values (FLOAT32). The array is dimensioned "Track" by "Xtrack" ("C" order).

Longitude

Contains longitude values in decimal degrees in the range -180.0 to 180.0, stored as an array of single-precision floating-point values (FLOAT32). The array is dimensioned "Track" by "Xtrack" ("C" order).

Time

Contains International Atomic Time values in seconds with 1993-01-01 00:00:00 as the zero base (TAI93), stored as a vector of double-precision floating-point values (FLOAT64). The vector is dimensioned "Track".

Data fields

Fifteen data fields are defined, one per channel. Each data field contains single-precision floating-point values (FLOAT32) stored in an array that is dimensioned "Track" by "Xtrack" ("C" order). Each datum can therefore be geolocated using its row/column index to reference the values in the "Latitude" and "Longitude" geolocation fields. Each row can be temporally located by using its row index to reference the value in the "Time" geolocation field.

The data field names are representative of the channel data they contain, as follows:

Channel 1 23800.37 MHz
Channel 2 31400.42 MHz
Channel 3 50299.91 MHz
Channel 4 52799.39 MHz
Channel 5 53595.41 +- 115 MHz
Channel 6 54399.53 MHz
Channel 7 54940.64 MHz
Channel 8 55498.70 MHz
Channel 9 57290.33 MHz
Channel 10 57290.33 +- 217 MHz
Channel 11 57290.33 +- 322.2 +- 48 MHz*
Channel 12 57290.33 +- 322.2 +- 22 MHz
Channel 13 57290.33 +- 322.2 +- 10 MHz
Channel 14 57290.33 +- 322.2 +- 4.5 MHz*
Channel 15 88997.00 MHz

*NOTE: Channel 14 INOPERATIVE on NOAA-15 as of 30 Oct 2000
               Channel 11 INOPERATIVE on NOAA-15 as of 25 Apr 2002

Sample Read Routine

A sample read routine is shown here, or you may download the sample code, amsuareader.c. This routine must be compiled and linked with the HDF-EOS and HDF libraries.

Links to Other AMSU Sites

The GHRC Data Pool browse page at the Global Hydrology Resource Center contains AMSU-A global imagery.

From the ITSC DISCOVER site, Daily Earth Temperatures from Satellites

From Colorado State Cooperative Institute for Research in the Atmosphere: CIRA's AMSU Website

Occasionally, orbit data is missed for technical reasons, or the satellite performs in a non-optimal manner. In these cases, NESDIS posts a NOAA Satellite Notice. These may be found at http://www.osdpd.noaa.gov/PSB/PPP/PPP.html.

For a history of all user notices, see http://www.ssd.noaa.gov/PS/SATS/messages.html.

For the Office of Satellite Operations morning reports, see http://www.oso.noaa.gov/daily-news.

Contact Information

To order these data or for further information, please contact:

Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/

Citing These data:

To help us best serve the scientific research communities, please cite GHRC data whenever you use them in a published paper or public presentation. We also request that you send us one reprint of any publication that cites our data. Please include the following information in each citation: principal investigators, year of data set release, data set title and version number, dates of the data you used, publisher, and digital media.

Example Citation:

Frank Wentz. 2010, near real-time. NRT AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures V11, May 1-15 2011. Huntsville, Alabama USA: AMSR-E SIPS at the GHRC DAAC. Digital media.

For further information please contact us at ghrcdaac@itsc.uah.edu.