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TRMM Product Level 2A Precipitation Radar (PR) Rainfall Rate and Profile

Data Access for

2A25: http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/08_Pr_Prof_2A_25/"

Summary

This document provides basic information on 2A25, TRMM PR Rainfall Rate and Profile Product.

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.

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  2*nray*nscan - - 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  80*nray*nscan 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  80*nray*nscan - 0 ~ 255 - For estimated rain rates at the radar range gates from 0 to 20km. ( Bit and Meaning )
Corrected Z-factor Integer SDS 2  80*nray*nscan 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  5*nray*nscan - 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  5*nray*nscan 1000000 0.00010 ~ 0.00200 - It relates the attenuation coefficient, k (dB/km) to the Z-factor: k = αβ. 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*Zβ. β is computed for each ray.
Z-R Parameter a Integer SDS 2  5*nray*nscan 100000 0.0050 ~ 0.2000 - Parameter a for Z-R relationship (R=aZb) 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  5*nray*nscan 10000 0.500 ~ 1.000 - Parameter a for Z-R relationship (R=aZb) 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  5*nray*nscan - - - Parameter A in the M = AZ^B relationship.
Precipitation Water Parameter B Integer SDS 2  5*nray*nscan - - - 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  5*nray*nscan - 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  2*nray*nscan 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  2*nray*nscan - 0.0 ~ 100.0 - Roughly represents the rain rate integrated along the ray using two different methods.
Zeta_mn Float SDS 4  2*nray*nscan - 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  2*nray*nscan - 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  2*nray*nscan - 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  2*nray*nscan - 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  2*nray*nscan - - - 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.
 
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/ .

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
     
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  • Last updated: Sep 18, 2009 10:32 AM ET