Data Access for 2B31:
http://mirador.gsfc.nasa.gov/cgi-bin/mirador/presentNavigation.pl?tree=project&project=TRMM&dataGroup=Orbital&dataset=2B31%20(Version%20007):%20Combined%20Rainfall%20Profile%20(PR,%20TMI)&version=007
Contents: 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. 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 PPS 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. | TRMM 2B31 can be accessed and ordered using the Goddard DAAC's TRMM Data Search and Order System at http://mirador.gsfc.nasa.gov/cgi-bin/mirador/presentNavigation.pl?tree=project&project=TRMM&dataGroup=Orbital&dataset=2B31%20(Version%20007):%20Combined%20Rainfall%20Profile%20(PR,%20TMI)&version=007 .
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). | |
