TRMM Precipitation Radar Rain Characteristics

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 objectives of 2A25 is to correct for the rain attenuation in measured radar reflectivity and to estimate the instantaneous three-dimensional distribution of rain from the TRMM Precipitation Radar (PR) data. The estimates of attenuation-corrected radar reflectivity factor and rainfall rate are given at each resolution cell (4 km x 4 km x 250 m) of the PR. The estimated near-surface rainfall rate and average rainfall rate between the two pre-defined altitudes (2 and 4 km) are also calculated for each beam position.

TRMM Satellite Operating Altitude Change

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.

Sponsor and Acknowledgement

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.

Future Updates

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.

Data Flow Description

PR Level 1A ==> 1B21 PR Power ==> 1C21 PR Reflectivities ==> 2A25 PR Rainfall Rate and Profile

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

Data Set Description

Data Characteristics

TRMM 2A25 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: ~16 MB Original: ~253	Compressed: ~16 MB Original: ~256 MB
File Type	HDF	HDF

Data Format Structure

Further information on the contents and structure of the 2A25 product can be found in Volume 4 of the "File Specifications for TSDIS Products - Level 2 and Level3"

Data Format Structure for 2A25, PR Rainfall Rate and 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.
Clutter Flag	Vdata Table	4	49	-	-	-	Mainlobe Clutter Edge and Sidelobe Clutter Range. ( detail )
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	2nraynscan	-	-	degree	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.
scLocalZenith	Float SDS	4	nray*nscan	-	-	degree	Spacecraft local zenith angle.
Scan Status	Vdata Table	15	nscan	-	-	-	Status of each scan.
Navigation	Vdata Table	88	nscan	-	-	-	Spacecraft geocentric information.
Rain Rate	Integer SDS	2	80nraynscan	100	0.0 ~ 300.0	mm/h	Estimate of rain rate at the radar range gates from 0 to 20 km along the slant range. A value of -88.88 mm/hr (stored as -889) means ground clutter.
Reliability	Integer SDS	1	80nraynscan	-	0 ~ 255	-	For estimated rain rates at the radar range gates from 0 to 20km. ( Bit and Meaning )
Corrected Z-factor	Integer SDS	2	80nraynscan	100	0.0 ~ 80.0	dBZ	Attenuation corrected reflectivity factor (Z) at the radar range gates from 0 to 20 km along the slant range. Values of reflectivity less than 0.0 dBZ are set to 0.0 dBZ. A value of -88.88 dB (stored as -8888) is a ground clutter flag.
Parameter Node	Integer SDS	2	5nraynscan	-	0 ~ 79	-	Range bin numbers of the nodes at which the values of Attenuation and Z-R Parameters are given (see below). The values of the parameters between the nodes are linearly interpolated.
Attenuation Parameter Alpha	Integer SDS	2	5nraynscan	1000000	0.00010 ~ 0.00200	-	It relates the attenuation coefficient, k (dB/km) to the Z-factor: k = α^β. α is computed at ncell2(5) radar range gates for each ray.
Attenuation Parameter Beta	Integer SDS	2	nray*nscan	1000	0.5 ~ 2.0	-	It relates the attenuation coefficient, k (dB/km) to the Z-factor: k = α*Z^β. β is computed for each ray.
Z-R Parameter a	Integer SDS	2	5nraynscan	100000	0.0050 ~ 0.2000	-	Parameter a for Z-R relationship (R=aZ^b) is determined from the rain type and the height relative to the freezing level, the non-uniformity parameter (ζ) and the correction factor (ε) for the surface reference technique.
Z-R Parameter b	Integer SDS	2	5nraynscan	10000	0.500 ~ 1.000	-	Parameter a for Z-R relationship (R=aZ^b) is determined from the rain type and the height relative to the freezing level, the non-uniformity parameter (ζ) and the correction factor (ε) for the surface reference technique.
Precipitation Water Parameter A	Integer SDS	2	5nraynscan	-	-	-	Parameter A in the M = AZ^B relationship.
Precipitation Water Parameter B	Integer SDS	2	5nraynscan	-	-	-	Parameter B in the M = AZ^B relationship.
Precipitation Water Parameter Sum	Float SDS	4	nray*nscan	-	-	-	Sum of PWC from rain top to surface.
Maximum Z	Float SDS	4	nray*nscan	-	0.0 ~ 100.0	dBZ	Maximum value of measured reflectivity factor at each IFOV.
Rain Flag	Integer SDS	2	nray*nscan	-	-	-	Rain Flag indicates rain or no rain status and the rain type assumed in rain rate retrieval. The default value is 0 (no rain). Bit 0 is the least significant bit (i.e., if bit i=1 and other bits =0, the unsigned integer value is 2**i).
Rain Type	Integer SDS	2	nray*nscan	-	-	-	A copy of the 2A23 Rain Type field. See 2A23 description.
Range Bin Numbers	Integer SDS	2	5nraynscan	-	0 ~ 79	-	Range Bin Number of various quantities for each ray in every scan. The Range Bin Numbers in this algorithm are different from the NASDA definition of Range Bin Number described in the ICS, Volume 3. The Range Bin Numbers in the algorithm range from 0 to 79 and have an interval of 250m. The earth ellipsoid is defined as range bin 79.
Averaged Rain Rate	Integer SDS	2	2nraynscan	100	(1)0.0 ~ 3000.0 (2)0.0 ~ 300.0	mm/h	There are two kinds of Average Rain Rate. The first one is the average rain rate for each ray between the two predefined heights of 2 and 4 km. The second one is the integral of rain rate from rain top to rain bottom.
Precipitable Water Sum	Integer SDS	2	nray*nscan	-	-	-	The sum of precipitable water from the top range bin to the bottom range bin (see Range Bin Numbers above).
Method Flag	Integer SDS	2	nray*nscan	-	-	-	Method Flag indicates which method is used to derive the rain rate. The default value is 0 (including no rain case). Bit 0 is the least significant bit (i.e., if bit i =1 and other bits =0, the unsigned integer value is 2**i).
Epsilon	Float SDS	4	nray*nscan	-	0.0 ~ 100.0	-	Correction factor for the surface reference.
Epsilon_0	Float SDS	4	nray*nscan	-	0.0 ~ 100.0	-	The adjustment parameter computed from the filtered surface reference PIA (2A21 algorithm).
Zeta	Float SDS	4	2nraynscan	-	0.0 ~ 100.0	-	Roughly represents the rain rate integrated along the ray using two different methods.
Zeta_mn	Float SDS	4	2nraynscan	-	0.0 ~ 100.0	-	Average of zeta in the vicinity of each beam position (average over three scans and three IFOVs). It is calculated using two methods.
Zeta_sd	Float SDS	4	2nraynscan	-	0.0 ~ 100.0	-	Standard deviation of zeta in the vicinity of each beam position (using three scans and three IFOVs). It is calculated using two methods.
Xi	Float SDS	4	2nraynscan	-	0.0 ~ 99.0	-	Normalized standard deviation defined as Zeta_sd/Zeta_mn. When Zeta_mn takes on small values (or zero) Xi is set to 99.0. It is calculated using two methods.
NUBF Correction Factor	Float SDS	4	2nraynscan	-	K-Z: 1.0 ~ 3.0 Z-R: 0.8 ~ 1.0	-	Non-Uniform Beam Filling (NUBF) Correction Factor is used as a correction to reflectivity and attenuation calculations. The two NUBF Correction Factors are given for the k-Z and Z-R relations. The ranges are 1.0 to 3.0 and 0.8 to 1.0, respectively.
Quality Flag	Integer SDS	2	nray*nscan	-	0 ~ 255	-	It gives the overall error that affects the entire angle bin data, such as the error associated with the non-uniform beam filling effect and the surface reference reliability. If data are missing, the reliability will be set as 10000000 in binary. The default value is 0 (normal). ( Bit and Mean )
Near Surface Rain	Float SDS	4	nray*nscan	-	0 ~ 3000	mm/hr	Rainfall rate near the surface. A value of -99.99 mm/hr is a missing flag.
Near Surface Z	Float SDS	4	nray*nscan	-	0.0 ~ 100.0	dBZ	Reflectivity near the surface. A value of -99.99 dBZ is a missing flag.
Estimated Surface Rain	Float SDS	4	nray*nscan	-	0 ~ 3000	mm/hr	Reflectivity near the surface. A value of -99.99 mm/hr is a missing flag.
PIA	Float SDS	4	3nray*nscan	-	-	-	Path Integrated Attenuation (PIA)[two-way] estimates for three cases: (1) The final adjusted PIA estimate (2) The difference between the PIA at the surface and near surface range bins (3) The PIA estimate from 2A21
Error Rain	Float SDS	4	nray*nscan	-	-	dB	Error in Near Surface Rain Rate.
Error Z	Float SDS	4	nray*nscan	-	0.0 ~ 100.0	dBZ	Error in Near Surface Z.
Spares	Float SDS	4	2nraynscan	-	-	-	Contents and ranges are not public.
Height of Freezing Level	Float SDS	4	nray*nscan	-	-	m	A positive Height of Freezing Level is the height of the 0°C isotherm above mean sea level in meters. estimated from climatological surface temperature data. Negative values are defined as: -5555: When error occurred in the estimation of Height of Freezing Level -8888: No rain -9999: Data missing
Sigma-zero	Float SDS	4	nray*nscan	-	-50.00 ~ 20.00	dB	The normalized surface cross section. This field is copied from the 2A21 product file.

Tools for Visualizing Data

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.

Sample Software

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.

Data Access Information

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 2A25 can be accessed and ordered using the Goddard DISC's TRMM Data Search and Order System at http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/08_Pr_Prof_2A_25/ .

Points of Contact

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)

References

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 PR 2A25 Clutter Flags
Name	Format	Description
Mainlobe Clutter Edge	1-byte integer	Absolute value of the difference in Range bin Numbers between the detected surface and the edge of the clutter from the mainlobe.
Sidelobe Clutter Range	3 x 1-byte integer	Absolute value of the difference in Range Bin Numbers between the detected surface and the clutter position from the sidelobe. A zero means no clutter indicated in this field since less than 3 bins contained significant clutter.

TRMM 2A25 Reliability
Bit	Meaning if bit=1
0	rain possible
1	rain certain
2	bright band
3	large attenuation
4	weak return (Zm < 20 dBZ)
5	estimated Z < 0 dBZ
6	main-lobe clutter or below surface
7	missing data

TRMM 2A25 Rain Flag
Bit	Meaning if bit=1
0	rain possible
1	rain certain
2	Zeta^ Beta > 0.5 [Path Integrated Attenuation (PIA) larger than 3 dB]
3	large attenuation (PIA larger than 10 dB)
4	stratiform
5	convective
6	bright band exists
7	warm rain
8	rain bottom above 2 km
9	rain bottom above 4 km
10	not used
11	not used
12	not used
13	not used
14	data missing between rain top and bottom
15	not used

TRMM 2A25 Method Flag
	If all bits 0: no rain. Otherwise:
Bit	Meaning when set (except bit 1)
1	0: over ocean 1: over land
2	over coast, river, etc.
3	OIA from constant-Z-near-surface assumption
4	spatial reference
5	temporal reference
6	global reference
7	hybrid reference
8	good to take statistics of epsilon
9	HB method used, SRT totally ignored
10	very large pia_srt for given zeta
11	very small pia_srt for given zeta
12	no ZR adjustment by epsilon
13	no NUBF correction because NSD unreliable
14	surface attenuation > 60 dB
15	data partly missing between rain top and bottom

TRMM 2A25 Quality Flag
Bit	Meaning if bit=1
0	unusual situation in rain average
1	NSD of zeta (xi) calculated from less than 6 points
2	NSD of PIA calculated from less than 6 points
3	NUBF for Z-R below lower bound
4	NUBF for Z-R above upper bound
5	epsilon not reliable (epsi_sig <=0.0)
6	2A21 input data not reliable
7	2A23 input data not reliable
8	range bin error
9	sidelobe clutter removal
10	probability=0 for all tau
11	pia_surf_ex <=0.0
12	const Z is invalid
13	reliabFactor in 2A21 is NaN
14	data missing
15	not used
Bit 0 is the least significant bit (i.e., if bit i =1 and other bits =0, the unsigned integer value is 2**i). Meanings are assigned to each bit in the 16-bit integer if the bit = 1.

TRMM 2A25 Range Bin Number Definitions
- top range bin number of the interval that is processed as meaningful data in 2A-25
- bottom range bin number of the interval that is processed as meaningful data in 2A-25
- actual surface range bin number
- range bin number of the bright band if it exits
- range bin number at which the path-integrated Z-factor first exceeds the given threshold
- range bin number at which the measured Z-factor is maximum
- range bin number of near surface bin

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 Spacecraft Orientation
Value	Meaning
0	+x forward
1	-x forward
2	-y forward
3	Inertial -- CERES Calibration
4	Unknown Orientation

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.

NASA Official: Steve Kempler
Website Curator: Stephen W Berrick

Last updated: August 25, 2008 15:25:23 GMT