Data Access for
2B31:
http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/09_Combined_2B_31/
Contents:
[Skip Contents]
- Summary
- TRMM Satellite Operating Altitude
Change
- Sponsor and
Acknowledgement
- Future Updates
- Data Flow Description
- Data Set Description
-
- Tools for Visualizing Data
-
- Sample Software
-
- Data Access
- Points of Contact
- References
This document provides basic information on 2B31, Combined (PR, TMI)
Rainfall Profile Product.
The TRMM Microwave Imager (TMI) is a nine-channel passive microwave
radiometer, which builds on the heritage of the Special Sensor
Microwave/Imager (SSM/I) instrument flown aboard the Defense
Meteorological Satellite Program (DMSP) platforms.
The TRMM Precipitation Radar (PR), the first of its kind in space, is
an electronically scanning radar, operating at 13.8 GHz that measures the
3-D rainfall distribution over both land and ocean, and defines the layer
depth of the precipitation.
The TRMM combined algorithm (2B31) combines data from the TMI and PR
to produce the best rain estimate for TRMM. Currently, it uses the low
frequency channels of TMI to find the total path attenuation. This
information is used to constrain the radar equation.
The average operating altitude for TRMM was changed from 350 to 403 km
during the period of August 7-24, 2001. This orbit boost maneuver
extended the mission life significantly. All post-boost data products had
been released by the TRMM Science Project, as of early December 2001. All
TRMM data products (post- and pre-boost) are available via the TRMM data
search-and-order system at http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/.
The time period before August 7, 2001 is referred to as
pre-boost, and the time period after August 24, 2001 is
referred to as post-boost.
The characteristics of the three rain instruments for pre- and post-boost
are shown in following table:
| Characteristics of TRMM Instruments |
| |
Swath Width (km) |
Ground Resolution (km) |
| Pre-boost |
Post-boost |
Pre-boost |
Post-boost |
| VIRS |
720 |
833 |
2.2 |
2.4 |
| TMI |
760 |
878 |
4.4* |
5.1* |
| PR |
215 |
247 |
4.3 |
5.0 |
| * Ground resolutions of TMI
are those at 85.5 GHz (highest resolution). |
The pre- and post-boost characteristics of TRMM data are different; their
details are listed in the Data Characteristics table for each orbital
product. Some caveats associated with post-boost TRMM Precipitation Radar
(PR) products have been released by the PR algorithm scientists and are
available at
ftp://disc2.nascom.nasa.gov/data/TRMM/Documentation/TRMM_Boost_PR_Caveats.html.
For TRMM version 5 products, the post-boost filenames all have a "5A"
in the product version part of the name, compared with a "5" in pre-boost
filenames. For version 6, the filenames have no differences for pre-boost
and post-boost.
The distribution of this data set is funded by NASA's Earth Science Enterprise
(ESE). The data are not copyrighted; however, we request
that when you publish data or results using these data, please
acknowledge as follows:
The data used in this study were acquired as part of the Tropical
Rainfall Measuring Mission (TRMM). The algorithms were developed by the
TRMM Science Team. The data were processed by the TRMM Science Data and
Information System (TSDIS) and the TRMM Office; they are archived and
distributed by the Goddard Distributed Active Archive Center. TRMM is
an international project jointly sponsored by the Japan National Space
Development Agency (NASDA) and the U.S. National Aeronautics and Space
Administration (NASA) Office of Earth Sciences.
Please send a copy of your publication to Help Desk, Goddard
DAAC, Code 610.2, NASA GSFC, Greenbelt, MD 20771 or email the
reference of your publication to help-disc@listserv.gsfc.nasa.gov.
It is expected that some of the TRMM algorithms will be refined or
improved as new measurements are gathered and analyzed by the TRMM
Science Team. The data products are expected to be periodically
reprocessed by TSDIS in order to provide the scientific and other user
communities with the most current and best available rainfall products.
The exact reprocessing schedule will be set by a team designated by the
TRMM Project Scientist. This document will be updated in coordination
with the TRMM reprocessing schedule and whenever appropriate as
determined by the Goddard DAAC Hydrology Data Support Team.
PR Level 1A ==> 1B11 TMI Calibrated Brightness Temperature and 1C21 PR
Reflectivities 1C21 ==> 2B31 Combined (PR, TMI) Rainfall Profile
The data flow of all products are shown in Satellite Algorithm Flow Diagram.
Data Characteristics
| TRMM 2B31 Data
Characteristics |
| |
Pre-boost (before 2001-08-07) |
Post-boost (after 2001-0 8-24) |
| Temporal Coverage |
Start Date: 1997-12-08
Stop Date: 2001-08-07 |
Start Date: 2001-08-24
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 |
| Horizontal Resolution |
4.3 km |
5.0 km |
| Scan Characteristics |
Swath Width: 215 km
Rays/Scan: nray = 49
Scans/Second (SS): 1/0.6
Seconds/Orbit (SO): 5490
Average Scans/Orbit: nscan = SS*SO = 9150
|
Swath Width: 247 km
Rays/Scan: nray = 49
Scans/Second (SS): 1/0.6
Seconds/Orbit (SO): 5550
Average Scans/Orbit: nscan = SS*SO = 9250
|
| Average File Size |
Compressed: ~8.2 MB
Original: ~158 MB |
Compressed: ~8.5 MB
Original: ~160 MB |
| File Type |
HDF |
HDF |
Data Format Structure
Further information on the contents and structure of the 2B31 product
can be found in Volume 4 of the "File Specifications for TSDIS Products -
Level 2 and Level3" .
| Data Format
Structure for 2B31, Combined (PR, TMI) Rainfall Profile
|
| Name |
Type |
Record
Size
(byte) |
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 |
- |
- |
- |
- |
Specification of the swath geometry. |
| Scan Time |
Vdata Table |
8 |
nscan |
- |
- |
- |
Time associated with the scan, expressed as 8-byte float UTC
second of the day. |
| Geolocation |
Float SDS |
4 |
2*nray*nscan |
- |
- |
degree |
Geolocation is the earth location of
the center of the IFOV at the altitude of the earth ellipsoid. |
| Scan Status |
Vdata Table |
15 |
nscan |
- |
- |
- |
Status of each scan. |
| Navigation |
Vdata Table |
88 |
nscan |
- |
- |
- |
Spacecraft geocentric information. |
| D-hat |
Integer SDS |
2 |
nray*nscan |
100 |
0.7 ~ 1.8 |
mm* |
Correlation-corrected mass-weighted mean drop diameter.
( more ) |
| Sigma-D-hat |
Integer SDS |
2 |
nray*nscan |
100 |
0.00 ~ 2.00 |
mm* |
RMS uncertainty in D-Hat. The accuracy is 0.01 "normalized"
mm. |
| R-hat |
Integer SDS |
2 |
Nradarrange*nray*nscan |
10 |
0.0 ~ 500.0 |
mm/hr |
Instantaneous rain rate at the radar range gates. The accuracy is
0.1 mm/hr. |
| Sigma-R-hat |
Integer SDS |
2 |
Nradarrange*nray*nscan |
10 |
-125 ~ 125 |
mm/hr |
RMS uncertainty in the R-hat estimated at the radar range gates.
(The negative sign indicating estimates based on a "rain-possible"
detection by the radar rather than the "rain-certain" associated with
positive values). The values -125 and 125 are reserved for cases
where the RMS uncertainty could not be accurately estimated. The
accuracy is 0.5 mm/hr. |
| RR-Surf |
Float SDS |
4 |
nray*nscan |
- |
0.0 ~ 500.0 |
mm/hr |
Surface rain rate. |
| Sigma-RR-Surf |
Integer SDS |
2 |
nray*nscan |
100 |
-125 ~ 125 |
mm/hr |
RMS uncertainty in RR-Surf. (The negative sign indicating
estimates based on a "rain-possible" detection by the radar rather
than the "rain-certain" associated with positive values). The values
-125 and 125 are reserved for cases where the RMS uncertainty could
not be accurately estimated. The accuracy is 0.5 mm/hr. |
| latentHeadHH |
Float SDS |
4 |
nlayer*nray*nscan |
- |
- |
°K/hr |
The "hydrometeor heating" calculated from the vertical fluxes of the
different hydrometeor species and using average archival temperature/
pressure/humidity soundings which depend on longitude and latitude only.
In V6 all the precipitation is assumed to be liquid. Heating is listed
for 13 layers.
|
| spare |
Float SDS |
4 |
4*nray*nscan |
- |
- |
- |
Contents and ranges are not public. |
|
* "normalized units" are defined as follows:
If a variable X, expressed in grams, is correlated with the rain
rate R and a variable Y is defined where Y = X * R0.37
R, then the unit of Y is called "normalized grams".
Nradarrange:
The number of radar range gates, up to about 20 km from the earth
ellipsoid (80). The gates range from gate 0 to gate 79. Each gate
is 250 m apart, with gate 79 at the earth ellipsoid.
|
The Goddard DAAC provides the following tools to help users visualize
data in the Hierarchical Data Format (HDF).
TSDIS Orbit Viewer
The TSDIS Orbit Viewer is a menu-driven graphical interface for
dynamically generating images from TRMM HDF files. The viewer can
display, at the full instrument resolution, TRMM satellite, Ground
Validation, browse, and Coincidence Subsetted Intermediate (CSI)
products, as well as other derived products.
The software runs on Microsoft Windows and UNIX.
The source code and installation instructions for the Orbit Viewer are
available from the Goddard DAAC's TRMM ftp site (ftp://disc2.nascom.nasa.gov/software/trmm_software/Orbit_Viewer).
Please note: TSDIS can provide technical support for
the Orbit Viewer only to certain members of the TRMM Science Team. Other
users should contact the DAAC's Hydrology Data Support
Team (hydrology-disc@listserv.gsfc.nasa.gov).
EOSView
EOSView is a standalone X-based data visualization tool that displays
HDF files. It can be used to view data ordered from the Goddard DAAC. In
addition, it provides a secondary mechanism for previewing browse files
before ordering data. (The primary mechanism is the preview feature of
the TRMM Data
Search and Order System.) EOSView serves as a file verification tool.
The contents of HDF files are displayed and individual objects can be
selected for display. Displayable objects include raster images, data
sets in tables, pseudocolor images of data sets, attributes, and
annotations. Simple animations can be performed for a file with multiple
raster images.
A unique interface has been provided for handling HDF-EOS data
structures. The Swath/Point/Grid interface uses only HDF-EOS library
calls. EOSView users will not see the underlying HDF structures but will
be prompted for what parts of the HDF-EOS object they wish to view. The
EOSView requires at least 4 megabytes of memory and a larger than 24-bit
graphics board.
Download Instructions for the
Software:
-
These tools can be downloaded via anonymous ftp using a command
line ftp client, available on all Unix machines.
The source code, installation instructions, and documentation for
EOSView and Orbit Viewer are available from the Goddard DAAC's
TRMM ftp site
(ftp://disc2.nascom.nasa.gov/software/trmm_software).
The following files should be downloaded for EOSView:
- EOSView (executable)
- eosview.csc (help)
- eosview.uid (user interface description file)
- eosview.dat (IDL commands file)
- How to start EOSView:
-
Start EOSView by typing 'EOSView' at the command prompt. The
current working directory must contain the four EOSView files.
TRMM HDF Data File Read Software
The Goddard DAAC Hydrology Team has developed the TRMM HDF Data File
Read Software, first released in February 1999. The software reads TRMM
HDF data files and writes out to flat binary files. The software has been
tested with most of the TRMM standard products, as well as with some
derived subset products. Both C and Fortran versions are available from
ftp://disc2.nascom.nasa.gov/software/trmm_software/Read_HDF/.
TSDIS Toolkit
TSDIS developed the TSDIS Science Algorithm Toolkit to assist the TRMM
Science Team's algorithm developers. The toolkit provides a library of
commonly used routines, constants, and macros. It also allows seamless
integration of TRMM algorithms into the TSDIS environment.
The toolkit provides routines for reading and writing data to and from
the HDF files; routines are provided for Levels 1-3 products and for both
satellite and GV. Each of the routines in the toolkit are callable in
either C or Fortran. The toolkit also includes routines for reading
land/sea data and topographical data.
The Goddard DAAC maintains archives of all TRMM data products and many
other Hydrology data sets. The archived data can be ordered via FTP network transfer.
| Data Volume Limits By Media |
| CDR |
FTP-Pull |
| Min. |
Max. |
Min. |
Max. |
Min. |
Max. |
Min. |
Max. |
| 0 GB |
3.17 GB |
0 GB |
2 GB |
1 GB |
50 GB |
1 GB |
50 GB |
TRMM 2B31 can be accessed and ordered using the Goddard DAAC's
TRMM Data Search and Order System at
http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/09_Combined_2B_31/.
- For information about or assistance in using any Goddard DAAC data,
contact the DAAC Help Desk at:
-
GES Distributed Active Archive Center (DAAC)
Code 610.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Email: help-disc@listserv.gsfc.nasa.gov.
301-614-5224 (voice)
301-614-5268 (fax)
Tropical Rainfall Measuring Mission Science Data and Information System
(TSDIS) Interface Control Specification Between the TSDIS and the TSDIS
Science User (TSU)
Volume 3: File Specifications for TRMM Products - Level 1.
Volume 4: File Specifications for TRMM Products - Level 2 and Level 3.
Appendix
| TRMM 2B31 Geolocation |
| Geolocation is the earth location of the center of the
IFOV at the altitude of the earth ellipsoid. The first dimension is
latitude and longitude, in that order. The next dimensions are numbers
of pixels and scans. Values are represented as floating point decimal
degrees. Off-earth is represented as -9999.9. Latitude is positive
north, negative south. Longitude is positive east, negative west. A
point on the 180° meridian is assigned to the western
hemisphere. |
| TRMM 2B31 D-hat Description |
| D-hat is the correlation-corrected mass-weighted mean
drop diameter. The accuracy is 0.01 "normalized" mm (the value 0
indicates no rain or bad data). The average value of dHat is around 1.1
"normalized" mm, a unit which comes from the fact that dHat is related
to the true mass-weighted mean drop diameter D* mm by the formula dHat
= D*rHat-0.155 (with rHat in mm/hr). |
|
TRMM Navigation
|
| Name |
Format |
Description |
Spacecraft Geocentric
Position [3] |
3 X 4-byte float |
The position (m) of the spacecraft in Geocentric Inertial
Coordinates at the Scan mid-Time (i.e., time at the middle pixel/IFOV
of the active scan period). The order of components is: x, y, and z.
Geocentric Inertial Coordinates are also commonly known as Earth
Centered Inertial coordinates. These coordinates will be True of Date
(rather than Epoch 2000 which are also commonly used), as interpolated
from the data in the Flight Dynamics Facility ephemeris files generated
for TRMM. |
Spacecraft Geocentric
Velocity [3] |
3 X 4-byte float |
The velocity (ms -1) of the spacecraft in Geocentric
Inertial Coordinates at the Scan mid-Time. The order of components is:
x, y, and z. |
Spacecraft Geodetic
Latitude |
4-byte float |
The geodetic latitude (decimal degrees) of the spacecraft at the
Scan mid-Time. |
Spacecraft Geodetic
Longitude |
4-byte float |
The geodetic longitude (decimal degrees) of the spacecraft at the
Scan mid-Time. Range is -180 to 179.999999. |
Spacecraft Geodetic
Altitude |
4-byte float |
The altitude (m) of the spacecraft above the Earth Ellipsoid at the
Scan mid-Time. |
Spacecraft
Attitude [3] |
3 X 4-byte float |
The satellite attitude Euler angles at the Scan mid-Time. The order
of the components in the file is roll, pitch, and yaw. However, the
angles are computed using a 3-2-1 Euler rotation sequence representing
the rotation order yaw, pitch, and roll for the rotation from Orbital
Coordinates to the spacecraft body coordinates. Orbital Coordinates
represent an orthogonal triad in Geocentric Inertial Coordinates where
the Z-axis is toward the geocentric nadir, the Y-axis is perpendicular
to the spacecraft velocity opposite the orbit normal direction, and the
X-axis is approximately in the velocity direction for a near circular
orbit.
Note this is geocentric, not geodetic, referenced, so that pitch and
roll will have twice orbital frequency components due to the onboard
control system following the oblate geodetic Earth horizon. Note also
that the yaw value will show an orbital frequency component relative to
the Earth fixed ground track due to the Earth rotation relative to
inertial coordinates. |
Sensor Orientation
Matrix [3 X 3] |
3 X 3 X 4-byte float |
The rotation matrix from the instrument coordinate frame to
Geocentric Inertial Coordinates at the Scan mid-Time. |
Greenwich
Hour Angle |
4-byte float |
The rotation angle (degrees) from Geocentric Inertial Coordinates
to Earth Fixed Coordinates. |
| TRMM PR Scan Status
|
| Name |
Format |
Values |
Description |
| Missing |
1-byte integer |
Value and meaning |
Indicates whether information is contained in the scan. |
| Validity |
1-byte integer |
Bit and meaning |
A summary of status modes. |
| QAC |
1-byte integer |
0: No decoding error occurred. |
The Quality and Accounting Capsule of the Science packet as it
appears in Level-0 data. |
Geolocation
Quality |
1-byte integer |
Bit and Meaning |
A summary of geolocation quality in the scan. |
| Data Quality |
1-byte integer |
Bit and Meaning |
A summary of data quality in the scan. |
Current Spacecraft
Orientation |
1-byte integer |
Value and Meaning |
Current spacecraft orientation. |
| Current ACS Mode |
1-byte integer |
Value and Meaning |
Current ACS mode. |
| Yaw Update Status |
1-byte integer |
0: Inaccurate
1: Indeterminate
2: Accurate |
Yaw update status. |
| PR Mode |
1-byte integer |
1: Observation Mode
2: Other Mode |
PR mode. |
| PR Status 1 |
1-byte integer |
0: Normal
1: A little questionable |
A warning for scan data.
This field is used only for NASDA's data analysis. |
| PR Status 2 |
1-byte integer |
0: Not initialized
1: Initialized |
Initialization in Onboard Surface Algorithm. |
Fractional
Orbital Number |
4-byte float |
|
The orbit number and fractional part of the orbit at Scan Time.
The orbit fraction part is calculated as:
(Time-Orbit Start Time)/(Orbit End Time-Orbit Start Time) |
| Value
and Meaning of Missing |
| Value |
Meaning |
| 0 |
Scan data elements contains information |
| 1 |
Scan was missing in the telemetry data |
| 2 |
Scan data contains no elements with rain |
| Bit
and Meaning of Validity
|
| Bit |
Meaning if bit=1 |
| 0 |
Spare (always 0) |
| 1 |
Non routine spacecraft orientation (2 or 3) |
| 2 |
Non routine ACS mode (other than 4) |
| 3 |
Non routine yaw update status (0 or 1) |
| 4 |
Non routine instrument status (other than 1) |
| 5 |
Non routine QAC (non-zero) |
| 6 |
Spare (always 0) |
| 7 |
Spare (always 0) |
| Bit and Meaning of
Geolocation Quality
|
| Bit |
Meaning if bit=1 for Non-routine Situation |
Routine Situation |
| 0 |
Latitude limit error |
If all status modes are routine, all bits in
Validity = 0. Routine means that scan data has
been measured in the normal operational situation
as far as the status modes are concerned. Validity
does not assess data or geolocation quality. Validity
is broken into 8 bit flags. Each bit=0 if the status
is routine but the bit = 1 if the status is not routine.
Bit 0 is the least significant bit (i.e., if bit i=1 and
other bits = 0, the unsigned integer value is 2**i). |
| 1 |
Geolocation discontinuity |
| 2 |
Attitude change rate limit error |
| 3 |
Attitude limit error |
| 4 |
Satellite undergoing maneuvers |
| 5 |
Using predictive orbit data |
| 6 |
Geolocation calculation error |
| 7 |
not used |
| Bit and Meaning of
Data Quality
|
| Bit |
Meaning if bit=1 |
Note |
| 0 |
Missing |
Unless this is 0 (normal), the scan data is
meaningless to higher processing. Bit 0 is the
least significant bit (i.e., if bit i=1 and other
bit = 0, the unsigned integer value is 2**i). |
| 5 |
Geolocation quality is not normal |
| 6 |
Validity is not normal |
Value
and Meaning of
Current ACS Mode
|
| Value |
Meaning |
| 0 |
Standby |
| 1 |
Sun Acquire |
| 2 |
Earth Acquire |
| 3 |
Yaw Acquire |
| 4 |
Nominal |
| 5 |
Yaw Maneuver |
| 6 |
Delta-H (Thruster) |
| 7 |
Delta-V (Thruster) |
| 8 |
CERES Calibration |
TRMM Frequency Analysis Result*
(Number of visits for a 30-day period) |
| Radar Site |
Latitude (°) |
PR (~215 km) |
VIRS (~720 km) |
TMI (~760 km) |
| Kwajalein Atoll |
8.72 |
9 |
29 |
31 |
| Darwin, Australia |
-12.45 |
10 |
31 |
32 |
| Guam |
13.50 |
9 |
32 |
32 |
| Om Koi, Thailand |
17.80 |
9 |
31 |
33 |
| Kauai, HI |
22.17 |
13 |
36 |
38 |
| Sao Paolo, Brazil |
-23.58 |
12 |
41 |
42 |
| Taiwan |
23.92 |
11 |
40 |
42 |
| Key West, FL |
24.67 |
13 |
41 |
42 |
| Miami, FL |
25.75 |
13 |
45 |
45 |
| Brownsville, TX |
25.97 |
13 |
43 |
47 |
| Corpus Christi, TX |
27.85 |
15 |
49 |
51 |
| Tampa, FL |
28.03 |
13 |
51 |
52 |
| Melbourne, FL |
28.10 |
15 |
49 |
53 |
| San Antonio, TX |
29.53 |
16 |
57 |
59 |
| Jacksonville, FL |
30.33 |
19 |
63 |
65 |
| Texas A&M, TX |
30.58 |
18 |
67 |
68 |
| Jerusalem, Israel |
31.87 |
20 |
92 |
102 |
PR:
Precipitation Radar
VIRS: Visible/InfraRed Scanner
TMI: TRMM Microwave Imager
* This analysis result was derived based on TRMM
pre-boost orbital information.
The revisit frequency should be slightly higher after TRMM boost
(August 24, 2001).
If you have questions regarding this table, please send email to:
helpdesk@tsdis02.nascom.nasa.gov. |
|
Atmos Composition
