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TRMM Product Level 2A Precipitation Radar (PR) Rain Characteristics (2A23)

Data Access for

2A23: http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/07_Rain_Type_2A_23/

Contents of the TRMM Precipitation Radar Rain Characteristics

Summary

This document provides basic information on 2A23, TRMM PR Rain Characteristics 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 PR qualitative algorithm (2A23) inputs PR reflectivities (1C21) and returns a rain/no rain decision based on echo structure. When rain is present, a storm height is calculated. If a bright band is detected, the height of the bright band is also given.

Data Flow Description

PR Level 1A ==> 1B21 PR Power ==> 1C21 PR Reflectivities ==> 2A23 PR Rain Characteristics

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

Data Set Description

Data Characteristics

TRMM 2A23 Data Characteristics
  Pre-boost (before 2001-08-07) Post-boost (after 2001-08-24)
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: ~6.2 MB
Original: ~13.6 MB		 Compressed: ~6.3 MB
Original: ~13.8 MB
File Type HDF HDF

Data Format Structure

Further information on the contents and structure of the 2A23 product can be found in Volume 4 of the "File Specifications for TSDIS Products - Level 2 and Level3" .

Data Format Structure for 2A23, PR Rain Characteristics
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  - - - - The specification of the swath geometry
Scan Time Vdata Table 8  nscan - - - The time associated with the scan, expressed as 8-byte float UTC second of the day.
Geolocation Float SDS 4  2*nray*nscan - - degree 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.
Scan Status Vdata Table 15  nscan - - - The status of each scan.
Navigation Vdata Table 88  nscan - - - Spacecraft geocentric information
Rain Flag Integer SDS 1  nray*nscan - - - The rain flag is identical to the Minimum Echo Flag of 1C21.
0: no rain
10: rain possible
11: rain possible (echo greater than rain threshold #1 in clutter region)
12: rain possible (echo greater than rain threshold #2 in clutter region)
13: rain possible
15: rain possible
20: rain certain
Rain Type Integer SDS 2  nray*nscan - - - The Rain Type Flag.
Shallow Rain Flag Integer SDS 1  nray*nscan - - - The Warm Rain Flag is set as follows:
= 10:  maybe shallow, isolated
= 11:  shallow isolated (with confidence)
= 20:  maybe shallow but not isolated
= 21:  shallow but not isolated (with confidence)
= 0:    when not shallow
< 0:    when not rain certain or data missing
Status Flag Integer SDS 1  nray*nscan - - - The Status Flag indicates whether the data are obtained over sea or land and the confidence.
Height of Bright Band Integer SDS 2  nray*nscan - - - A positive Height of Bright Band is defined in meters above mean sea level. Negative values are defined as follows:
-1111: No bright band
-8888: No rain
-9999: Data missing.
Bright Band Intensity Integer SDS 4  nray*nscan - - - The maximum value of the bright band (dBZ) obtained from normal samples. The range is from 0.00 to 100.0 dBZ. Negative values are defined as:
-1111: No bright band
-8888: No rain
-9999: Data missing.
Bright Band Peak Bin Integer SDS 2  nray*nscan - - - A positive range bin number that corresponds to the peak of the bright band. This bin number is in the Level-1 bin numbering scheme (125m, see Level-1 PR description). Negative values are defined as:
-1111: No bright band
-8888: No rain
Bright Band Boundary Integer SDS 2  2*nray*nscan - - - Positive bin number of the boundary of the bright band. The first index indicates the bottom. This bin number are in the Level-1 bin numbering scheme (125m, see Level-1 PR description). Negative values are defined as:
-1111: No bright band
-8888: No rain
Bright Band Width Integer SDS 2  nray*nscan - - - The width of the bright band in meters.Negative values are defined as:
-1111: No bright band
-8888: No rain
Bright Band Status Integer SDS 2  nray*nscan - - - Indicates the status of the bright band detection. This flag is a composite of three internal status flags: BB_status[j] = BB_detection_status * 16
                     + BB_boundary_status[j] * 4
                     + BB_width_status[j]
where each status on the right hand side takes the following values: 1: poor, 2: fair, 3: good.
Height of Freezing Level Integer SDS 2  nray*nscan - - - 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
Height of Storm Integer SDS 2  nray*nscan - - m A positive Height of Storm is the height of the storm top above mean sea level in meters. A positive Height of Storm is given only when rain is present with a high degree of confidence in 1C21 (i.e., the Minimum Echo Flag in 1C21 has the value of 2 [rain certain]). Negative values are defined as:
-1111: Height of Storm not calculated because rain is not present with a high level of confidence in 1C21
-8888: No rain
-9999: Data missing
Spare Float SDS 2  nray*nscan - - - Spare will characterize the width of the bright band. Since this characterization requires much research, the meaning is not disclosed.
TRMM 2A23 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/07_Rain_Type_2A_23/ .

Appendix

   
TRMM 2A23 Rain Type Flag
Value Meaning Conditions
100 Stratiform certain When R_type_V = T_stra; (BB exists)
and R_type_H = T_stra;
110 Stratiform certain When R_type_V = T_stra; (BB exists)
and R_type_H = T_others;
120 Probably stratiform When R_type_V = T_others;
and R_type_H = T_stra;
130 Maybe stratiform When R_type_V = T_stra; (BB detection certain)
and R_type_H = T_conv;
140 Maybe stratiform
or maybe transition
or something else		 When R_type_V = T_others; (BB hardly expected)
and R_type_H = T_stra;
152 Maybe stratiform Shallow isolated (type of warm rain) is detected
When R_type_V = T_others;
R_type_H = T_stra;
and shallowRain = 20 or 21;
160 Maybe stratiform, but rain hardly expected near surface BB may exist but is not detected
When R_type_V = T_others;
R_type_H = T_stra;
170 Maybe stratiform, but rain hardly expected near surface BB hardly expected. Maybe cloud only
When R_type_V = T_others;
R_type_H = T_stra;
200 Convective certain When R_type_V = T_conv; (no BB)
and R_type_H = T_conv;
210 Convective certain When R_type_V = T_others;
and R_type_H = T_conv;
220 Convective certain When R_type_V = T_conv; and R_type_H = T_others;
230 Probably convective When R_type_V = T_conv; (BB exists)
and R_type_H = T_conv;
240 Maybe convective When R_type_V = T_conv;
and R_type_H = T_stra;
251 Convective Shallow isolated is detected
When R_type_V = T_conv, R_type_H = T_conv
and shallowRain = 10 or 11;
252 Convective Shallow rain (non-isolated) is detected
When R_type_V = T_conv, R_type_H = T_conv
and shallowRain = 20 or 21;
261 Convective Shallow isolated is detected
When R_type_V = T_conv;
R_type_H = T_others;
and shallowRain = 10 or 11;
262 Convective Shallow rain (non-isolated) is detected.
When R_type_V[i] = T_conv,
R_type_H[i] = T_others;
and shallowRain[i] = 20 or 21;
271 Convective Shallow isolated is detected
When R_type_V = T_others;
R_type_H = T_conv;
and shallowRain = 10 or 11;
272 Convective Shallow isolated is detected
When R_type_V = T_others;
R_type_H = T_conv;
and shallowRain = 20 or 21;
281 Convective Shallow isolated is detected
When R_type_V = T_conv;
R_type_H = T_stra;
and shallowRain = 10 or 11;
282 Convective Shallow rain (non-isolated) is detected.
When R_type_V[i] = T_conv,
R_type_H[i] = T_stra;
and shallowRain[i] = 20 or 21;
291 Convective Shallow isolated is detected
When R_type_V = T_others;
R_type_H = T_stra;
and shallowRain = 10 or 11;
300 Others When R_type_V = T_others;
and R_type_H = T_others;
312 Others Shallow rain (non-isolated) is detected
When R_type_V = T_others,
R_type_H = T_others;
and shallowRain = 20 or 21;
313 Others If sidelobe clutter were not rejected, shallow isolated would be detected
When R_type_V = T_others,
R_type_H = T_others;
and shallowRain = 20 or 21;		 
where
      R_type_V: rain type classified by the V-profile method,
      R_type_H: rain type classified by the H-pattern method,
                which is based on SHY95 developed by Prof. 
                Houze and his group.

The above assignment of numbers has the following meaning:
      (merged) Rain Type / 100 = 1: stratiform,
                                 2: convective,
                                 3: others.

      (merged) Rain Type Flag % 100 = Sub-category,

      (merged) Rain Type Flag % 10 = 0: usual,
                                     1: shallow isolated,
                                     2: shallow non-isolated,
                                     3: sidelobe clutter only (once shallow isolated 
                                        overwritten as sidelobe clutter only). 
                                        rainTytpe % 10 = 3 occurs for type 313 only.

where Rain Type Flag % 10 means MOD (Rain Type, 10) in FORTRAN.

Though rainType is changed to int16, no rain and missing values remain the same, that is
                      -88: no rain
                      -99: data missing

TRMM 2A23 Status Flag
Value Meaning Where
0 good over ocean
10 BB detection may be good over ocean
20 R-type classification may be good
(BB detection is good or BB does not exist)		 over ocean
30 Both BB detection and R-type classification may be good over ocean
50 not good (because of warnings) over ocean
100 bad (possible data corruption) over ocean
1 good over land
11 BB detection may be good over land
21 R-type classification may be good
(BB detection is good or BB does not exist)		 over land
31 Both BB detection and R-type classification may be good over land
51 not good (because of warnings) over land
101 bad (possible data corruption) over land
2 good over coastline
12 BB detection may be good over coastline
22 R-type classification may be good
(BB detection is good or BB does not exist)		 over coastline
32 Both BB detection and R-type classification may be good over coastline
52 not good (because of warnings) over coastline
102 bad (possible data corruption) over coastline
4 good over inland lake
14 BB detection may be good over inland lake
24 R-type classification may be good
(BB detection is good or BB does not exist)		 over inland lake
34 Both BB detection and R-type classification may be good over inland lake
54 not good (because of warnings) over inland lake
104 bad (possible data corruption) over inland lake
9 may be good land/sea unknown
19 BB detection may be good land/sea unknown
29 R-type classification may be good (BB detection is good or BB does not exist) land/sea unknown
39 Both BB detection and R-type classification may be good land/sea unknown
59 not good (because of warnings) land/sea unknown
109 bad (possible data corruption) land/sea unknown 
When it is "no rain" or "data missing", Status Flag contains the following values:
           -88: no rain
           -99: data missing

Assignment of the above numbers are based on the following rules:
    
  When Status >= 0
        Status/100 = 0: good, may be good, or not good
                     1: doubtful
  (Status/10) % 10 = 0: good, may be good when status < 100,
                        and not good when status >= 100
                     1: BB detection not so confident
                     2: R-type classification not so confident
                        (but BB detection is good, or when BB does not exist)
                     3: BB detection is not so confident and R-type 
                        classification not so confident
                     5: Over-all quality of the processed data for the j-th 
                        scan angle is not good (but may not be too bad to be 
                        classified as bad data)
       Status % 10 = 0: over ocean
                     1: over land
                     2: over coastline
                     4: over inland lake
                     9: land/sea unknown

In other words, we can check the confidence level of 2A-23 by the following way:

        Status Flag >= 100 : bad (untrustworthy because of possible data corruption)
  100 > Status Flag >=  10 : result not so confident (warning)
        Status Flag  =   9 : may be good
    9 > Status Flag >=   0 : good

The last digit of Status Flag indicates over ocean, land, etc.
 
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  • Last updated: Sep 18, 2009 10:32 AM ET