TRMM Realtime System

trmm jaxa near real time image

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Data Access Overview

 

The GPM Near Realtime data is available after completing the registration requirement from our "jsimpson" archive.  Note: Your registered Email address is used for both your User name and Password.

Historically, the TRMM NRT data was retained for 3 days only. After this time, the standard TRMM products would be available from our 'arthurhou' production data archive or the GES DISC.

 

TRMM Near Realtime Information

Data is divided into 3 subdirectories on the ftp server. One contains PR data; another contains the TMI data and the third contains the VIRS data. Generally, new data is available every 3 hours or so. Users are encouraged to write automated ftp scripts that check the location periodically for the arrival of new data.

Each TRMM real-time granule (approximately an orbit) is compressed. While sizes may vary, the average compressed sizes per granule are:

 

TMI 1B11RT- brightness temperature 10.70 MB
TMI 2A12RT - surface rain rate 8.82 MB
PR 2A23RT -rain type 4.71 MB
PR 2A25R1-near surface rain rate 5.61 MB
PR 2A25R2- 20 vertical levels of rain rate 20.12 MB
VIRS 1B01- radiances 145.23 MB (this is really the full TRMM product)

 

The Latest TRMM Realtime 3 Hourly and 7 Day Rainfall Images can be viewed on the TRMM Web site.

Latest 3 hourly Global Rainfall

 

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TRMM Realtime, GPM Documentation and External Links

 

Realtime documentation icon

 

TRMM File Specification Real Time System Version 7P3

TRMM 3B4X Version 7 Documentation

TRMM 3B4XRT Readme notes

TRMM Realtime Merged Products Software (FORTRAN / C/ IDL)

PPS/GPM Documentation

PPS/GPM ATBD (Algorithm Theoretical BAsis Document)

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TRMM World Wide Web Page

TRMM 2A12 TMI Quick Looks Page

NRL Site

 

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Data Tools

THOR data viewer -screen shot- for TRMM and GPM data

 

STORM (Data Search, Custom Subsets and Subscriptions)

TRMM Science Algorithm Toolkit

GPM Science Algorithm Toolkit

PPS Data Viewer - THOR (Tool for High-Resolution Observation Review)

VIRS L1B Radiance Converter

TRMM Overflight finder

 

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Realtime Background Information (TRMM)

 

All TRMM data became available to the general science community on September 01, 1998.   Standard TRMM products are available after the mandatory registration from our PPS data archive, or the EOS Goddard Data and Information Services Center (DISC) within 72 hours of their collection.   Any user can visit our public ftp archives or choose to establish an account with the DISC to receive the standard TRMM products.

In order to support users who want more timely TRMM data to determine its usefulness in areas such as modeling, weather monitoring, disaster monitoring, etc., the TRMM science team authorized the establishment of a real-time processing and distribution of TRMM data. The goal is to have data available for retrieval within 3 hours of collection of the oldest byte in the orbit. This system is obviously "near real-time" rather than "real-time", as the data is recorded on the spacecraft and downloaded only once every 90 minutes or so. This means that the oldest data in any download stream is already 90 minutes old before any processing is performed. An additional 90 minutes is allocated to complete all levels of processing. Generally, processing is completed well before the 90 minute requirement.

The products produced by the real-time system are actually parameter subsets of the standard TRMM products. Generally, only surface rain parameters were retained from the standard TRMM products. To achieve the time requirements the predictive ephemeris rather than the definitive ephemeris must be used in geolocating the data. This sometimes leads to slight geolocation errors. The specification and descriptions of the real-time products can be obtained from other areas of this document. Each product contains data for roughly a TRMM orbit.

A major effort was made to reduce the size of near real-time products so that the data could be electronically retrieved more quickly. TRMM real-time data is only available via ftp from the TRMM real-time server. All products are stored in compressed format. These are compressed using gzip.

 

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How to become a GPM Near Realtime Data User

 

Users desiring access to the GPM Realtime system need to register with PPS. Please consult the following document for complete details:

How to get Access to GPM NRT Data

It is also important to note that when you fill out or update your contact information and areas of Interest that you check "Near-Realtime Products"  besides the "FTP Access in additon to Standard Research Products" option.

 

 

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TRMM Instrument Information

 

TRMM Instruments and swath patterns

 

See the following PPS Web Page for details on the GPM Instrumentation

General TRMM Overview

TRMM is a joint NASA/JAXA space mission. NASA provided the satellite, TMI, VIRS and the ground system including a Precipitation Processing System (PPS).  Japan's JAXA provided the H-II launch vehicle, launch facility at Tanegashima Space Facility in Japan and the Precipitation Radar instrument. PR was jointed designed by JAXA and Japan's Communications Research Laboratory (CRL). It was launched on November 27, 1997 (November 28, 1997 in Japan).

The TRMM orbit is a circular orbit at an altitude of 402.5 km. It has an inclination of 35 degrees to the Equator. The coverage area is 35 degrees south latitude to 35 degrees north latitude. This orbit yields extensive coverage of the tropics and allows extraction of rainfall data over a 24 hour period. The low altitude also ensures that TRMM instruments are able to resolve cloud radiances over small areas. This permits more accurate translation of those signals to the average rain over the area than if the sensing area were larger.

The TRMM observatory weighs approximately 3620 kg and provides approximately 1100 watts of power from a gallium arsenide solar array/nickel cadmium battery subsystem. The observatory has a three-axis attitude control subsystem that keeps instruments pointed to within 0.2 degrees. Transmission of data and command telemetry is done through NASA's Tracking Data Satellite System (TDRSS). A hydrazine reaction control subsystem maintains the orbit at 402.5 km ( +- 1.25 km).

TRMM hosts five instruments; The TRMM Microwave Imager (TMI), the Visible Infrared Scanner (VIRS) and the Precipitation Radar (PR) comprise the rainfall measurement package.  These instruments are the primary mission payload.  The remaining two instruments, CERES and LIS, are part of the Earth Observing System program (EOS). Additional information is provided on this page for the rainfall measurement instruments.  No information is included here for the two EOS instruments (CERES and LIS). Additional information about these can be obtained directly from the EOS.

The core TRMM science mission objectives are:

  • To obtain and study multi-year science data sets of tropical and subtropical rainfall measurements
  • To understand how interactions between the sea, air and land masses produce changes in global rainfall and climate
  • To help improve modeling of tropical rainfall processes and their influence on global circulation in order to predict rainfall and variability at various time scale intervals
  • To test, evaluate, and improve the performance of satellite rainfall estimates measurements and techniques.

 

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TRMM Microwave Imager -- TMI

TMI is similar to the SSM/I instrument flown on the DMSP satellite series. There are some key differences. These are:

  • the addition of vertically and horizontally polarized channels at 10GHz
  • the scan geometry is the same for every scan rather than alternating between an A scan and a B scan
  • TMI has about twice as many pixels per scan
  • the water vapor channel was moved from 22.235 GHz to 21.3 GHz to avoid saturation in the tropics

The TMI is a 9 channel, 5 frequency, linearly polarized, passive microwave radiometric system. The instrument measures atmospheric and surface brightness temperatures at: 10.7, 19.4, 21.3, 37.0 and 85.5 GHz. Each frequency has one vertically and one horizontally polarized channel except for the 21.3 GHz that has only vertical polarization.

The 10.7, 19.4, 21.3 and 37.0 GHz channels are considered low resolution and the 85.5 GHz channels are considered high resolution. TMI has a conical scanning geometry, rotating continuously about a vertical axis. It receives upwelling radiation from 49 degree off nadir. Scene radiation is recorded from left to right (looking in the +X flight direction) over an annular sector of 130 degrees about the sub-satellite track. The separation between successive scans is 13.85 km along the X which is nearly equal to the resolution of the 85 GHz beams. The swath width is 758.5km. This swath is covered by 104 low resolution pixels or 208 high resolution pixels.

 

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Visible Infrared Scanner

The VIRS instrument is similar to the AVHRR instrument flown on the NOAA satellite series. VIRS has a swath width of 720 km and a horizontal resolution of 2 km at nadir. VIRS measures radiance values in the following channels:

Channel

Spectral Region

Wavelength (mm)

1

Visible

0.63

2

Near Infrared

1.6

3

Near Infrared

3.75

4

Infrared

10.8

5

Infrared

12.0

 

All five channels are in operation day and night. VIRS is a cross-track scanning system and records scene radiation from right to left looking in the +X direction over a scan angle of +- 45 degrees from the nadir. The swath width is covered by 261 pixels and every scan line has the same geometry.

 

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Precipitation Radar

PR is a Japanese instrument jointly developed by JAXA and CRL. PR is an active 13.8 GHz radar, recording energy reflected from atmospheric and surface targets. The PR electronically scans from right to left looking in the +X direction across the ground track of the satellite every 0.6 seconds with a swath width of 215 km.

Each PR scan contains 49 rays sampled over an angular sector of 34 degrees. For any given ray, the instrument begins recording samples at a fixed distance from the satellite and records a certain number of samples every 125 km along the ray. The starting distance and the number of samples are different for each ray. Assuming the satellite altitude is 350 km, the sampling begins about 23 km above mean sea level and extends for a certain distance along the ray. This distance along the ray is 33.5 km at the two rays farthest from nadir, monotonically declining to 30.25 km at the two rays adjacent to nadir and jumping to 34.75 km at the single nadir ray. The extra data in the nadir ray is known as "the mirror" because it records energy reflected not once from a target, but three times (ground to target to ground). Rays other than the nadir ray also sample "below" the surface. The purpose of this extension "to see" below the surface is to detect clearly the location of the surface.

 

See the following PPS Web Page for details on the GPM Instrumentation

 

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