The HSB level 1B data set contains HSB calibrated and geolocated brightness temperatures in degrees Kelvin. This data set is generated from HSB level 1A digital numbers (DN) and contains 4 microwave channels in the 150 - 190 GHz region of the spectrum. A day's worth of data is divided into 240 scenes each of 6 minute duration. For the HSB measurements, an individual scene consists of 135 scanlines containing 90 cross-track footprints; thus there is a total of 135 x 90 = 12,150 footprints per HSB scene, which coincide very closely with the AIRS infrared footprints.
HSB is primarily a humidity sounder that provides information on snow/ice cover and precipitation using the 150 GHz window channel, and the coarse distribution of moisture in the troposphere using the 183 GHz channels. Combined with simultaneous measurements from the AIRS and AMSU-A instruments, the calibrated HSB brightness temperatures will be used to initialize the atmospheric moisture profile required for the retrieval of the final AIRS geophysical products. HSB level 1B daily summary browse product is also available to provide users with a global quick look capability when searching for data of interest.
The HSB is a direct descendant of what was originally intended to form a part of the AMSU system. AMSU-A was to be the temperature sounder and AMSU-B was to be the moisture sounder. HSB is a near identical copy of AMSU-B. The performance of AMSU-B has been disappointing, due to its unanticipated susceptibility to interference from the spacecraft transmitters. However, the RF shielding of HSB has been modified and enhanced, and HSB is not expected to exhibit this susceptibility.
HSB is a four channel version of AMSU-B, designed to detect radiances in the range of 150 to 183.31 GHz. One window channel (at 150 GHz) measures a part of the water vapor continum, while three window channels are grouped around the 183-GHz water vapor absorption line. Like AMSU-B, it samples ninety 1.1 ° scenes per 2.67-second crosstrack scan. Due to the higher spatial resolution (which equals that of AIRS) and a higher scan rate, the measurement density is 2.4 times that of AMSU-A (20 % less than for AMSU-B). HSB is very similar to AMSU-A, except that is contains only one antenna/receiver system.
This microwave humidity sounder is part of a sounding system that acts in a synergic way, and will provide humidity and profile much more accurately than that of other sounders currently in operation. It also has the capability to detecting precipitation under the clouds. The horizontal resolution is 50km for temperature and 15km for humidity, both in the subsatellite point. The temperature error is around 1 K to 1.5 K and 5 to 15 percent for humidity.
AIRS Scan Geometry Diagram (Courtesy of AIRS Science Team, NASA/JPL)
The HSB level 1B 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).
An HSB 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 HSB level1B Radiance file contains a single 6-minute swath data and browse subset contains daily data for ascending or descending node.
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., 2001.
Month is 2 digit month (1-based); e.g., 03
Day is 2 digit day of month (1-based); e.g., 31
Gran is 3 digit granule of day (001-240) for standard (45 scanset) granules.
Level is product level; e.g., L1B is for Level1B
FileType is a string defining the product file type; for example,VIS_Rad.
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.
Examples:
AIRS.2003.03.14.105.L1B.HSB_Rad.v2.7.12.0.G03074131756.hdf
AIRS HSB Level 1B Radiances: 16.0 MB
HSB level 1B data contains calibrated and geolocated brightness temperatures in degrees Kelvin. Brightness temperature is the apparent temperature of the surface assuming a surface emissivity of 1.0. Setting the emissivity to one is equivalent to assuming the target is a blackbody, so the brightness temperature is defined as the temperature a blackbody would be in order to produce the radiance perceived by the sensor.
N.B. Arrays shown below are those most likely of interest to the general user. Array not included are primarily those dealing with statistics of the scene and calibration source counts, radiance statistics, and channel gain/offset statistics, among others.
AIRHBRAD - HSB Geolocated Radiances
| Variable |
Units |
Data Type |
Dimensions |
Description |
| latitude |
degrees |
float64 |
135 x 90 |
footprint latitude |
| longitude |
degrees |
float64 |
135 x 90 |
footprint longitude |
| time |
seconds |
float64 |
135 x 90 |
footprint elapsed time since Jan 1, 1993 (TAI time) |
| antenna_temp |
Kelvins |
float32 |
135 x 90 x 5 |
received antenna temperatures |
| brightness_temp |
Kelvins |
float32 |
135 x 90 x 5 |
Radiances for each channel as brightness temperatures (Channel1:Deleted:Always Invalid) |
| scanang |
degrees |
float32 |
135 x 90 |
footprint scan angle |
| ftptgeoqa |
none |
int32 |
135 x 90 |
footprint geolocation QA bit flags |
| zengeoqa |
none |
int16 |
135 x 90 |
footprint satellite zenith geolocation QA bit flags |
| demgeoqa |
none |
int16 |
135 x 90 |
footprint DEM geolocation QA bit flags |
| satzen |
degrees |
float32 |
135 x 90 |
satellite view angle (degrees from zenith) |
| satazi |
degrees |
float32 |
135 x 90 |
satellite azimuth angle (degrees east of north) |
| solzen |
degrees |
float32 |
135 x 90 |
solar zenith angle (degrees from zenith) |
| solazi |
degrees |
float32 |
135 x 90 |
solar azimuth angle (degrees east of north) |
| sun_glint_distance |
kilometers |
int16 |
135 x 90 |
distance from footprint center to sunglint |
| topog |
meters |
float32 |
135 x 90 |
mean topography above reference ellipsoid |
| topog_err |
meters |
float32 |
135 x 90 |
error estimate for topog |
| landFrac |
none |
float32 |
135 x 90 |
fraction of footprint that is land |
| landFrac_err |
none |
float32 |
135 x 90 |
error estimate for landFrac |
| state |
none |
int32 |
135 x 90 |
data state |
| satheight |
kilometers |
float32 |
135 |
satellite altitude above reference ellipsoid at nadir |
| nadirTAI |
seconds |
float64 |
135 |
TAI time for instrument at nadir |
| satroll |
degrees |
float32 |
135 |
satellite attitude roll angle at nadirTAI |
| satpitch |
degrees |
float32 |
135 |
satellite attitude pitch angle at nadirTAI |
| satyaw |
degrees |
float32 |
135 |
satellite attitude yaw angle at nadirTAI |
| sat_lat |
degrees |
float64 |
135 |
satellite latitude |
| sat_lon |
degrees |
float64 |
135 |
satellite longitude |
| scan_node_type |
N/A |
character8 |
135 |
node during scan (Ascending or Descending) |
| satgeoqa |
none |
int32 |
135 |
satellite geolocation QA bit flags |
| glintgeoqa |
none |
int16 |
135 |
glint geolocation QA bit flags |
| moongeoqa |
none |
int16 |
135 |
moon geolocation QA bit flags |
| glintlat |
degrees |
float32 |
135 |
solar glint latitude at nadirTAI |
| glintlon |
degrees |
float32 |
135 |
solar glint longitude at nadirTAI |
An HSB 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.
Data fields: Data fields are the main part of a swath from a science perspective and all the other parts of the swath exist to provide information about the data fields or to support particular types of access to them. In HSB level 1B data, Along-Track data fields appear once for scanline and Full Swath data fields appear for every footprint of every scanline in granule. Sample.
Geolocation fields: Geolocation fields allow scientific or engineering data to be accurately tied to particular points on the Earth's surface. These fields appear for every foot print and correspond to footprint center coordinates and "shutter" time.
Dimensions: Dimensions define the axes of the data and geolocation fields by giving them names and sizes. Sample .
Swath Attributes: Swath attribute includes DayNight flag, Quality Assessment (QA) flags and other swath information. Sample.
- Spatial Resolution: Size of Field of View (FOV) is 13.5 km in diameter at nadir.
- Temporal Coverage: (Future Entry)
- Temporal Resolution: Twice daily (day and night)
Data Product Readers : A selection of product readers - FORTRAN/C readers for Level 1B and Level 2 data (with accompanying Guide document); IDL procedure to read L1B, L2 and L3 product files; and the MATLAB module to read L1B, L2 and L3 product files.
HDF_READER : This is a command line program developed by the GES DAAC to allow a user to view the contents of an HDF file, as well as to subset the data therein. A list of options controls what is displayed. One may list any of the HDF objects within a file, and the data within them. They may be subsetted along any dimension, or the entire data may be dumped if no subset options are given. There is also a mode to print a heirarchical tree list of the objects in the file. Data can be sent to an ASCII text file, a set of flat binary files, or displayed on the screen (default).
AIRSMETA: This was developed by the GES DAAC to read various components of the data granule (file) and display it in ASCII format. The program was designed and tested on SGI UNIX workstations. The HDF-EOS calling interface library must be installed on your machine and linked to this program during compilation.
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 http://eospso.gsfc.nasa.gov/atbd/airstables.html
2. AIRS Calibration Plan, JPL D-16821, 14 November 1997. http://eospso.gsfc.nasa.gov/calibration/plans.
3. AIRS Team Science Validation Plan, Core Products, JPL D-16822, Version 2.1 15 December 1999 ftp://eospso.gsfc.nasa.gov/sterling/Validation/AIRSplan.pdf
4. AIRS/AMSU/HSB Data Processing and Data Products Quality Assessment Plan, JPL D-20748, Version 2.1 August 28, 2001
5. AIRS Version 2.7 Processing Files Description
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
Atmos Composition
