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TRMM Level 1B Product Precipitation Radar (PR) Reflectivities 1C21

Data Access:

1C21: http://disc.sci.gsfc.nasa.gov/data/datapool/TRMM_DP/01_Data_Products/01_Orbital/04_Pr_Ref_1C_21/

Contents:

Summary

This document provides basic information on 1C21, the TRMM Preciptation Radar (PR) Reflectivities data product.

The TRMM 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 reflectivity algorithm (1C21) converts the power and noise estimates from 1B21 to radar reflectivity factors (Z-factors). In order to reduce output data volume, only pixels with power that exceeds the minimum echo detected in 1B-21 are converted and stored.

Data Flow Description

PR Level 1A ==> 1B21 PR Power ==> 1C21 PR Reflectivities

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

Data Set Description

Data Characteristics

TRMM 1C21 (PR) 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: ~44 MB
Original: ~157 MB		 Compressed: ~45 MB
Original: ~159 MB
File Type HDF HDF

Data Format Structure

Further information on the contents and structure of the 1C21, PR Reflectivities product can be found in Volume 3 of the "File Specifications for TSDIS Products - Level 1" .

Data Format Structure for 1C21, PR Reflectivities
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
PR Cal Coef Vdata Table 4  18 - - - Calibration coefficients for the PR. The records consist of: Transmission coefficient (unitless, 1 record),
Reception coefficient (unitless, 1 record), and
FCIF I/O Characteristics (unitless, 16 records).
Descriptions are TBD by NASDA.
Ray Header Vdata Table 60  49 - - - Information about each ray (angle bin) that is constant for every scan. The record number represents the angle bin number. Each record describes one ray and is defined in Ray Header Table.
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 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 - - - Status of each scan.
Navigation Vdata Table 88  nscan - - - Spacecraft geocentric information
Powers Vdata Table 6  nscan - - - Powers: Radar Transmission Power and Transmitted Pulse Width.
System Noise Integer SDS 2  nray*nscan 100 -120 ~ -20 dBm System Noise (dBm) is an average of the 4 measured system noise values. Missing data are given the value of -32,734.
System Noise Warning Flag Integer SDS 1  nray*nscan - - - System Noise Warning Flag indicates possible contamination of lower window noise by high towers of rain.
1 means possible contamination;
0 means no possible contamination.
Minimum Echo Flag Integer SDS 1  nray*nscan - - - Minimum Echo Flag indicates the presence of rain in the ray (angle bin).
Bin Storm Height Integer SDS 2  2*nray*nscan - - - Bin Storm Height is Range Bin Number of the storm top.
Satellite Local Zenith Angle Float SDS 4  nray*nscan - - - Angle, in degrees, between the local zenith and the beam's center line. The local (geodetic) zenith at the intersection of the ray and the earth ellipsoid is used.
Spacecraft Range Integer SDS 4  nray*nscan - - m Distance (m) between the spacecraft and the center of the footprint of the beam on the earth ellipsoid.
Bin Start of Oversample Integer SDS 2  2*29*nscan - - - Bin Start of Oversample is the starting range bin number of the oversample (either surface or rain) data, counting from the top down.
Land/Ocean Flag Integer SDS 2  nray*nscan - - - Land or ocean information. The values of the flag are:
0 = Water, 1 = Land, 2 = Coast.
Surface Detect Warning Flag Integer SDS 2  nray*nscan - - - Definition TBD by NASDA.
Bin Surface Peak Integer SDS 2  nray*nscan - - - Range bin number of the peak surface echo. This peak is determined by the post observation ground processing, not by the on board surface detection. The range bin number is defined in this volume in the section on Precipitation Radar, Instrument and Scan Geometry.
Bin Ellipsoid Float SDS 2  nray*nscan - - - Range bin number of the earth ellipsoid. The range bin number is defined in this volume in the section on Precipitation Radar, Instrument and Scan Geometry. This field will not be used until product version #4 products are available. Until that time this field contains zero (0) and should be ignored.
Bin Clutter Free Bottom Integer SDS 2  2*nray*nscan - - - Range bin number of the lowest clutter free bin. Clutter free bin numbers are given for clutter free certain and possible, respectively. The clutter free certain bin is always less than or equal to the clutter free possible bin number. This field will not be used until product version #4 products are available. Until that time this field contains zero (0) and should be ignored.
Bin DID Average Inetger SDS 2  nray*nscan - - - Mean range bin number of the DID surface elevation in a 5 km x 5 km box centered on the IFOV. The range bin number is defined in this volume in the section on Precipitation Radar, Instrument and Scan Geometry. This field will not be used until product version #4 products are available. Until that time this field contains zero (0) and should be ignored.
Bin DID Top Integer SDS 2  2*nray*nscan - - - Range bin number of the maximum DID surface elevation in a box centered on the IFOV. The first dimension is the box size, with sizes of 5 km x 5 km and 11 km x 11 km. The range bin number is defined in this volume in the section on Precipitation Radar, Instrument and Scan Geometry. This field will not be used until product version #4 products are available. Until that time this field contains zero (0) and should be ignored.
Bin DID Bottom Integer SDS 2  2*nray*nscan - - - Range bin number of the minimum DID surface elevation in a box centered on the IFOV. The first dimension is the box size, with sizes of 5 km x 5 km and 11 km x 11 km. The range bin number is defined in this volume in the section on Precipitation Radar, Instrument and Scan Geometry. This field will not be used until product version #4 products are available. Until that time this field contains zero (0) and should be ignored.
Normal Sample Inetger SDS 2  140*nray*nscan 100 -20 ~ 80 dBz PR Reflectivities (dbZ) of the normal sample. Since each ray has a different size, the elements after the end of each ray are filled with a value of -32700. Other bins where data is not written due to a transmission, calibration, or other problem, including an entire scan of missing bins, have the value of -32700. The size of each ray is specified in Ray Header, with an accuracy of 1.0 dBz.
Surface Oversample Integer SDS 2  5*29*nscan 100 -20 ~ 80 dBz PR Reflectivities (dBZ) of the surface echo oversample for the central 29 rays (rays #11-39), with an accuracy of 1.0 dBz. Bins where data is not written due to a transmission, calibration, or other problem, including an entire scan of missing bins, have the value of -32700. In the CrossTrack dimension, Offset = -10 and Increment = 1.
Rain Oversample Integer SDS 2  28*11*nscan 100 -20 ~ 80 dBz PR Reflectivities (dBz) of the rain echo oversample for the central 11 rays (rays #20-30), with an accuracy of 1.0 dBz. Bins where data is not written due to a transmission, calibration, or other problem, including an entire scan of missing bins, have the value of -32700. In the CrossTrack dimension, Offset = -19 and Increment = 1.
TRMM 1C21 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/04_Pr_Ref_1C_21/.

Appendix

   
PR Power Ray Header
Name Format Description
Ray Start 2-byte integer Starting range bin number of Normal sample
Ray Size 2-byte integer Number of Normal samples in the ray
Angle 4-byte float Angle (degrees) of the ray from nadir. The sign of the angle is consistent with the sensor y-axis, i.e., the angle is positive to the right of the direction of travel if the spacecraft is in normal mode.
Starting Bin Distance 4-byte float Distance (m) between the satellite and the starting bin number of the Normal sample for the ray
Rain Threshold 1 4-byte float Threshold used in minimum echo test (unitless). Value set by NASDA
Rain Threshold 2 4-byte float Threshold used in minimum echo test (unitless). Value set by NASDA
Transmitter Antenna Gain 4-byte float Transmitted radar antenna effectiveness (dB)
Receiver Antenna Gain 4-byte float Received radar antenna effectiveness (dB)
One-way 3dB Along-track Beamwidth 4-byte float Radar beamwidth (radians) at the point transmitted power reaches one half of peak power in the along-track direction.
One-way 3dB Cross-track Beamwidth 4-byte float Radar beamwidth (radians) at the point transmitted power reaches one half of peak power along the cross-track.
Equivalent wavelength 4-byte float Equivalent wavelength (m).
Radar Constant 4-byte float Radar constant dC (units are dB), which relates Received Power to Radar Reflectivity. dC depends on angle.
PR Internal delayed time 4-byte float The time (seconds) between when echo returns at antenna and when echo is recorded in onboard processor.
Range Bin Size 4-byte float The vertical resolution of Normal sample bin (250 m).
Logarithmic Averaging Offset 4-byte float The offset value (dB) between logarithmic average and normal average (+2.507dB).
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] 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.

PR Powers
Name Format Description
Radar Transmission Power 2-byte integer The total (sum) power of 128 SSPA elements corrected with SSPA temperature in orbit, based on temperature test data of SSPA transmission power. The units are dBm * 100. For this variable, the TSDIS Toolkit does not provide scaling.
Transmitted Pulse Width 4-byte float Transmitted pulse width (s) corrected with FCIF temperature in orbit, based on temperature test data of FCIF.

Minimum Echo Flag
Value Mean
0 no rain
10 rain possible
11 rain possible (Echo greater than rain threshold #1 in clutter range)
12 rain possible (Echo greater than rain threshold #2 in clutter range)
20 rain certain

1C21 Bin Storm Height Description 
Bin Storm Height is Range Bin Number of the storm top.
The first dimension is threshold, with values of possible rain threshold and 
certain rain threshold in that order. The Bin Storm Heights are generated in 
the procedure to determine the Minimum Echo Flag. The Bin Storm Height is the
top range bin of the portion of consecutive range bins that flagged the ray as 
rain possible or rain certain. The range bin number is defined in this volume 
in the section on Precipitation Radar, Instrument and Scan Geometry.

1C21 Bin Start of Oversample Description 
The first dimension is the Bin Start of Oversample and Surface Tracker Status. 
The second dimension is the ray. The number of rays is 29 because this 
information only applies to the rays that have oversample data (rays #11 to #39). 
The third dimension is the scan. 
The Surface Tracker Status has the value of 0 (Lock) or 1 (Unlock), where Lock 
means that 
(1) the on board surface detection detected the surface and 
(2) the surface detected later by processing on the ground fell within the 
oversample bins. 
Unlock means that Lock was not achieved. The range bin number is defined in 
this volume in the section on Precipitation Radar, Instrument and Scan Geometry.
 
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  • Last updated: Sep 18, 2009 10:32 AM ET