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TRMM Visible and Infrared Scanner (VIRS) Level 1 Calibrated Radiance Product 1B01

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The TRMM Visible and Infrared Scanner (VIRS) Level 1B Calibrated Radiance Product (1B01) contains calibrated radiances and auxiliary geolocation information from the five channels of the VIRS instrument, for each pixel of each scan. The data are stored in the Hierarchical Data Format (HDF), which includes both core and product specific metadata applicable to the VIRS measurements. A file contains a single orbit of data with a file size of about 95 MB. The EOSDIS "swath" structure is used to accommodate the actual geophysical data arrays. There are 16 files of VIRS 1B01 data produced per day.

For channels 1 and 2, Level 1B radiances are derived from the Level 1A (1A01) sensor counts by computing calibration parameters (gain and offset) derived from the counts registered during space and solar and/or lunar views. New calibration parameters are produced every one to four weeks. Channels 3, 4, and 5 are calibrated using the internal blackbody and the space view. These calibration parameters, together with a quadratic term determined pre-launch, are used to generate a counts vs. radiance curve for each band, which is then used to convert the earth-view pixel counts to spectral radiances.

Geolocation and channel data are written out for each pixel along the scan, whereas the time stamp, scan status (containing scan quality information), navigation, calibration coefficients, and solar/satellite geometry are specified on a per-scan basis. There are in general 18,026 scans along the orbit pre-boost and 18,223 post-boost, with each scan consisting of 261 pixels. The scan width is about 720 km pre-boost and 833 km post-boost.

Data Flow Description

VIRS Level 1A (1A01) ==> VIRS Level 1B Calibrated Radiance (1B01)

The data flow of all products are shown in the Satellite Algorithm Flow Diagram.

Data Set Description

Data Characteristics

VIRS Channels
Channel Spectral Region Wavelength (µm)
1 Visible 0.63
2 Near Infrared 1.60
3 Near Infrared 3.75
4 Near Infrared 10.8
Infrared 12.0

TRMM 1B01 (VIRS) Data Characteristics
Characteristic Pre-boost (before 08-07-2001) Post-boost (after 08-24-2001)
Temporal Coverage Start Date: 12-20-1997
Stop Date: 08-07-2001
Start Date: 08-24-2001
Stop Date: -
Geographic Coverage Latitude:     38°S   -  38°N
Longitude: 180°W - 180°E
Latitude:     38°S   -  38°N
Longitude: 180°W - 180°E
Temporal Resolution About 91.5 minutes per orbit
About 16 orbits per day
More information about revisit frequency
About 92.5 minutes per orbit
About 16 orbits per day
More information about revisit frequency
Spatial Resolution 2.2 km 2.4 km
Scan Characteristics Swath Width: 720 km
Pixels/Scan: 261
Scans/Second (SS): 2*98.5/60
Seconds/Orbit (SO): 5490
Average Scans/Orbit: nscan = SS*SO = 18026
Swath Width: 833 km
Pixels/Scan: 261
Scans/Second (SS): 2*98.5/60
Seconds/Orbit (SO): 5550
Average Scans/Orbit: nscan = SS*SO = 18223
Average File Size Original:        ~137 MB Original:        ~138 MB
File Type HDF HDF

Data Format Structure

The following table summarizes the contents and structure of the VIRS Calibrated Radiance (1B01) product. Further information can be found in File Specifications for TRMM Products - Version 7.00

Data Format Structure for VIRS Calibrated Radiance (1B01) Product
Name Type Record
Dim Size/
# of Records
Scaled by Range Unit Description
ECS Core Metadata Char Attribute 10,000  - - - - ECS Core Metadata
PS Metadata Char Attribute 10,000  - - - - Product Specific Metadata
Swath Structure Char Attribute 5,000  - - - - Specifications for the swath geometry
Scan Time Vdata Table nscan - - - Time associated with each scan

Float SDS

4 261*nscan - - degree Earth location of the center of the IFOV at the altitude of the earth ellipsoid
Longitude Float SDS 4 261*scan - - degree Earth location of the center of the IFOV at the altitude of the earth ellipsoid
Scan Status Vdata Table 19  nscan - - - Status of each scan
Navigation Vdata Table 88  nscan - - - Spacecraft geocentric information
Solar Cal Vdata Table 32  nscan - - - Solar unit vector in Geocentric Inertial Coordinates, and the Sun-Earth distance
Calibration Counts Integer SDS 5*2*3*nscan - - - Raw calibration counts data
Temperature Counts Integer SDS 6*nscan - 0 - 4095 counts Primary and redundant temperatures for the black body, radiant cooler, and the electronics module
Local Direction Float SDS 2*2*27*nscan - - degree Angles to the satellite and sun from the IFOV pixel position on the earth
Channels Float SDS 4 5*261*nscan depends on channels depends on channels (mW cm-2µm-1 sr-1) Scene data for the five channels (mW = milliwatts, sr = steradian). Accuracy depends on channels
TRMM 1B01 can be accessed and ordered from
Goddard Earth Sciences Data and Information Services Center (GES DISC) TRMM Data Search and Order System at

.For more details about the data structures: File Specifications for TRMM Products - Version 7.00

Solar Unit Vector
Name Format Description
Solar Position [3] 3*8-byte float Sun Unit Vector (X-component)
Sun Unit Vector (Y-component)
Sun Unit Vector (Z-component)

(Geocentric Inertial Coord)
Distance 8-byte float Sun-Earth Distance (m)

Raw Calibration Counts Data
Dimension Data Stored
1 Channel number
2 Data word
3 Blackbody, space view, solar diffuser
4 Number of scans

Local Direction Angles
Dimension Data Stored Description
1 zenith, azimuth Zenith angle is measured between the local pixel geodetic zenith and the direction to the satellite. Azimuth angle is measured clockwise from the local North direction around toward the local East direction.
2 object The object to which the directions point, namely the satellite and the sun
3 pixel number Angles are given only for every tenth pixel along a scan: pixel 1, 11, 21, ..., and 261.
4 scan number Scan line number

VIRS Range and Accuracy
Channel Minimum
(mW cm-2 µm-1 sr-1)
(mW cm-2 µm-1 sr-1)
1 0 65.5 10%
2 0 32.7 10%
3 0 0.111 2%
4 0 1.371 2%
5 0 1.15 2%



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Last updated: Mar 14, 2013 03:59 PM ET