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The Support Product includes higher vertical resolution profiles of the quantities
found in the Standard Retrieval Product, plus intermediate output (e.g., microwave-only retrieval),
research products such as the abundance of trace gases, and detailed quality assessment
information. The Support Product profiles contain 100 levels between 1100 and .016 mb;
this higher resolution will simplify the generation of radiances using forward models,
though the vertical information content is no greater than in the Standard Product
profiles. The intended users of the Support Product are researchers interested in
generating forward radiance, or in examining research products, and the AIRS algorithm
development team. The Support Product is generated at all locations as
Standard Products.
AIRS
The AIRS infrared
spectrometer acquires 2378 spectral samples at resolutions, l/Dl, ranging from
1086 to 1570, in three bands: 3.74 µm to 4.61 µm, 6.20 µm to
8.22 µm, and 8.8 µm to 15.4 µm. A 360 degree rotation of the
scan mirror generates a cross-track Earth-scene scan line of IR data every
2.667 seconds. The spatial resolution at nadir is 13.5 km. This instrument
provides fine vertical scale resolution soundings of atmospheric temperature
and water vapor, and integrated column burden for trace gases. Cold space-views
for calibration of data are taken at the beginning and end of the Earth-scene
when the mirror sweeps through space-view scenes.
The IR focal plane is cooled
to 60 K by a Stirling/pulse tube cryocooler. The scan mirror operates at
approximately 265 K due to radiative coupling to the Earth and space and to the
150 K IR spectrometer. Cooling of the IR optics and detectors is necessary to
achieve the required instrument sensitivity.
AIRS VIS/NIR
The Visible/Near-IR (VIS/NIR)
photometer contains four spectral bands, each with nine pixels along track,
with a 0.185 degree instantaneous field-of-view (FOV). It is boresighted to the
IR spectrometer to allow simultaneous measurements of the visible and infrared
scene. The VIS/NIR photometer uses optical filters to define four spectral
bands in the 400 nm to 1000 nm region. The VIS/NIR detectors are not cooled and
operate in the 293 K to 300 K ambient temperature range of the instrument
housing. The spatial resolution at nadir is 2.3 km. The primary function of the
AIRS VIS/NIR channels is to provide diagnostic support to the infrared
retrievals: setting flags that warn of the presence of low-clouds or highly
variable surface features within the infrared FOV.
AMSU-A
The AMSU-A microwave
multichannel radiometer consists of two physically separate units, AMSU-A1 and
AMSU-A2. Together they have 15 channels, measuring radiation in the frequency
span of 23 GHz to 90 GHz. Twelve channels (between 50 GHz and 60 GHz) are
predominantly used for atmospheric temperature sounding. The remaining three
channels (24 GHz, 31 GHz and 89 GHz) are predominantly used for atmospheric
water vapor sounding. The rotating scanning mirror generates a cross-track scan
line every 8 seconds. The spatial resolution at nadir is 40.5 km.
HSB
The HSB microwave
multichannel radiometer has 4 channels. One channel measures radiation at 150
GHz and the other three are centered on 183.31 GHz.All channels are used for
atmospheric water vapor sounding. The rotating scanning mirror generates a
cross-track scan line every 2.667 seconds. The spatial resolution at nadir is
13.5 km.
HSB ceased operation on
February 5, 2003. We are continuing investigation with the hope of recovering
the instrument at some future date. The impact on AIRS core products
(temperature profile, water vapor profile, ozone burden) is negligible. Some
future research products (cloud liquid water and precipitation) are adversely
effected.
For more detail information, see the following instrument guide below:
The AIRS Level2 Support Retrieval data is in Hierarchical Data Format-Earth
Observing System (HDF-EOS)
swath format. The swath concept for HDF-EOS is based on a typical satellite
swath, where an instrument takes a series of scans perpendicular to the
ground track of the satellite as it moves along that ground track (
Diagram). As the AIRS is profiling instrument
that scans across the ground track, the data would be a three dimensional
array of measurements where two of the dimensions correspond to the standard
scanning dimensions (along the ground track and across the ground track),
and the third dimension represents a range from the sensor. The "horizontal" dimensions can be handled as normal geographic dimensions,
while the third dimensions can be handled as a special "vertical" dimension.
An AIRS Level 1B data granule contains data fields, geolocation fields,
dimension, and swath attributes for a single swath. A detailed description of each
attribute can be found in
AIRS Processing Files Descriptions.
Each file contains a single 6-minute swath data and files are named using the following convention:
6-minute granule:
AIRS.{Year}.{Mon}.{Day}.{Gran}.{Level}.{FileType}.{VerID}.{PGenFac}{Cycle#}.hdf
where:
Year is 4 digit year of data; e.g., 2003.
Month is 2 digit month (1-based); e.g., 08
Day is 2 digit day of month (1-based); e.g.,18
Gran is 3 digit granule of day (001-240) for standard (45 scanset) granules.
Level is product level; e.g., L2 is for Level 2
FileType is a string defining the product file type; for example,Sup.
VerID is the PGEVERSION.
PGenFac is the PRODUCTGENERATIONFACILITY char. "G" for GSFC DAAC.
Cycle# is set during production using the "Times Processed" input field
(Cycle# = Times Processed - 1) and is used by the data creator to assure
uniqueness of the LOCALGRANULEID; Cycle# is 3 digits and 0-based; e.g., 002.
hdf is the format of the file
Examples: AIRS.2003.08.18.240.L2.Sup.v3.0.12.0.G03087153709.hdf
Volume average of data files:
- AIRS Level2 Support Product: 18.2 MB
The geolocation data fields of immediate interest to the user are:
- Latitude FOV boresight geodetic latitude
(degrees North, -90->+90), dimension (30,45)
- Longitude FOV boresight geodetic longitude
(degrees East, -180->+180), dimension (30,45)
The attribute of immediate interest to the user are
- pressSupp
standard pressure (mb) for each of 100 levels in atmosphere associated with
temperature, moisture and ozone profiles. The array order is from the top of
atmosphere downward. This is the reverse of pressStd ordering. Note that
topography may place some of these levels below the surface, dimension (100)
The swath data fields of immediate interest to the user are:
- RetQAFlag always check this, dimension (30,45)
- PsurfStd surface pressure, interpolated from forecast and mean topography of FOV (mb), dimension (30,45)
- nSurfSup index of last physically meaningful profile entries. Retrieved profile entries
beyond this index are filled with diagnostic values that may appear to be
physically meaningful but are not. It may be level just above or just below the
surface, dimension (30,45)
- TSurfStd retrieved surface skin temperature (K), dimension (30,45)
- TSurfAir retrieved surface air temperature (K), dimension (30,45)
- TAirSup retrieved atmospheric temperature profile (K) at the pressSupp pressures. Array
values below the surface (index < nSurfStd) are not physically meaningful.
In particular, the first level below the surface contains an extrapolated
value. Always check nSurfSup to identify this extrapolated. The surface value
(at PsurfStd) must be calculated by interpolating in the log(pressure) domain
between this value and the value in the next level up (index = nSurfSup-1),
dimension (100,30,45)
- H2OCDSup retrieved layer column water vapor (molecules/cm-2). The layer corresponding to
value H2OCDSup(index) is bounded by pressSupp(index) at the bottom and
pressSupp(index-1) at the top. Array values below the surface (index < nSurfStd) are not physically meaningful. In particular, the first level below
the surface contains an extrapolated value. Always check nSurfSup to identify
this extrapolated. The surface value (at PsurfStd) must be calculated by
interpolating in the log(pressure) domain between this value and the value in
the next level up (index = nSurfSup-1), dimension (100,30,45)
- lwCDSup retrieved layer column cloud liquid water (molecules/cm-2). The layer
corresponding to value lwCDSup(index) is bounded by pressSupp(index) at the
bottom and pressSupp(index-1) at the top. Array values below the surface (index < nSurfStd) are not physically meaningful. In particular, the first level
below the surface contains an extrapolated value. Always check nSurfSup to
identify this extrapolated. The surface value (at PsurfStd) must be calculated
by interpolating in the log(pressure) domain between this value and the value
in the next level up (index = nSurfSup-1). Missing if HSB instrument is not
operational, dimension (100,30,45)
- O3CDSup retrieved layer column ozone (molecules/cm-2). The layer corresponding to value
O3CDSup(index) is bounded by pressSupp(index) at the bottom and
pressSupp(index-1) at the top. Array values below the surface (index < nSurfStd) are not physically meaningful. In particular, the first level below
the surface contains an extrapolated value. Always check nSurfSup to identify
this extrapolated. The surface value (at PsurfStd) must be calculated by
interpolating in the log(pressure) domain between this value and the value in
the next level up (index = nSurfSup-1), dimension (100,30,45)
See V3.0_Release_ProcFileDesc.pdf
for complete list of variables.
Contacts for Archive/Data Access Information:
Atmospheric Dynamic Data Support Team
Goddard Distributed Active Archive Center
NASA/Goddard Space Flight Center
Code 610.2
Greenbelt, MD 20771
Phone: (301) 614-5323
Fax: (301) 614-5268
Email: atmdyn-dst@disc.gsfc.nasa.gov
You may access the AIRS data from:
Search and Order
1. AIRS Algorithm Theoretical Basis Document, AIRS Team Unified Retrieval for Core
Products (Level 2 ATBD) JPL D-17006, Version 2.1 15 December 1999
2. AIRS Version 3.0 L2 Data Release Documentation 11 August 2003
3. AIRS Version 3.0 Processing Files Description
Contact for Data Center Access Information:
The Goddard Earth Sciences Data and Information Services Center
Distributed Active Archive
Center (GES DISC DAAC)
Phone: (301) 614-5224
Fax: (301) 614-5268
E-mail: help-disc@listserv.gsfc.nasa.gov
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Atmos Composition
