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Why Study Tropical Rainfall?
The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.-Japan
satellite mission to monitor tropical and subtropical precipitation and
to estimate its associated latent heating. Motivations include:
- The tropics play an important role in the global hydrological cycle,
and tropical rainfall is the critical component of this role.
Three-fourth of the atmosphere's heat energy derives from the release of
latent heat of condensation in the process of precipitation. Two-thirds of the global
precipitation occurs in the tropics.
- The variability of tropical rainfall affects the lives and economics
of more than half of the world's population.
- The large spatial and temporal variability of rainfall systems poses
a major challenge to estimating global rainfall.
TRMM provides systematic, multi-year, visible, infrared, and
microwave measurements of rainfall in the tropics as key inputs to
weather and climate research. The satellite observations are
complemented by ground radar and rain gauge measurements to validate
the satellite rain estimation techniques.
- To obtain and study multi-year science data sets of tropical and
subtropical rainfall measurements.
- To understand how interactions between the ocean, air, and land
masses produce changes in global rainfall and climate.
- To improve modelling of tropical rainfall processes and their
influence on global circulation in order to predict rainfall and its
variability at various space and time scales.
- To test, evaluate, and improve satellite rainfall measurement
techniques.
Tropical Rainfall Data at the Goddard DAAC
The Tropical Rainfall Measuring Mission (TRMM) satellite was
launched on November 27, 1997 (EST). Data from TRMM are
archived and distributed by the Goddard DAAC and can be accessed from the
DAAC's TRMM Data Search and Order Web Interface.
The TRMM satellite carries three rain measuring instruments. NASA
GSFC provided the TRMM Microwave Imager (TMI), the Visible Infrared
Scanner (VIRS), and the observatory, and operates the TRMM
satellite via the Tracking and Data Relay Satellite System (TDRSS).
The The Japan Aerospace Exploration Agency (JAXA) of
Japan provided the Precipitation Radar (PR), the first space-borne
precipitation radar, and launched the TRMM observatory.
The TRMM orbit is circular, non-sun-synchronous, at an altitude of
350 km and an inclination of 35 degrees to the Equator. This orbit
provides extensive coverage in the tropics and allows each location to
be covered at a different local time each day. This kind of sampling
enables the analysis of the diurnal cycle of precipitation.
The VIRS (of NOAA AVHRR heritage) is a five-channel,
cross-track scanning radiometer operating at 0.63, 1.6, 3.75, 10.8, and
12 um, which provides high resolution observations on cloud
coverage, cloud type, and cloud top temperatures.
The TMI (of DMSP SSM/I heritage) is a multichannel
passive microwave radiometer operating at five frequencies: 10.65,
19.35, 37.0, and 85.5 GHz at dual polarization and 22.235 GHz at single
polarization. The TMI provides information on the integrated
column precipitation content, cloud liquid water, cloud ice, rain
intensity, and rainfall types (e.g., stratiform or convective).
The 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 define the
layer depth of the precipitation.
There are two other TRMM instruments whose data are
not archived at the Goddard DAAC. The Lightning Imaging Sensor
(LIS), already tested in space, is a calibrated optical sensor
operating at 0.7774 um, and it observes the distribution and
variability of lightning over Earth. The Clouds and Earth's Radiant
Energy System (CERES), of NASA's Earth Radiation Budget Experiment (ERBE)
heritage, is a broadband scanning
radiometer with a total spectral range of 0.3 to 50 um; it measures
emitted and reflected radiative energy from Earth's surface and the
atmosphere and its constituents (e.g., clouds, aerosols).
The instrument characteristics for the VIRS, TMI,
and PR are shown in the following table:
TRMM Instrument Characteristics
| Characteristic | Visible Infrared Scanner | TRMM
Microwave Imager | Precipitation Radar |
|---|
| Frequency/Wavelength | 0.63,
1.6, 3.75, 10.8, 12 um | 10.65, 19.35, 37.0, 85.5
GHz dual polarization, 22.235 GHz vertical polarization |
13.8 GHz horizontal polarization |
| Scanning Mode | Cross
track | Conical | Cross track
|
| Ground Resolution | 2.1
km | Ranges from 5 km at 85.5 GHz to 45 km at 10.65
GHz | 4.3 km at nadir |
| Swath Width | 720 km |
760 km | 220 km |
Ground Validation (GV) radar sites provide surface radar
measurements to support the validation of the satellite-derived
products. Validation sites include Darwin, Australia; Melbourne,
Florida; Houston, Texas; Kwajalein Atoll, Republic of Marshall Islands;
Tel Aviv, Israel; Sao Paolo, Brazil; Guam, Marianas Islands; Kaohsiung,
Taiwan; Om Koi, Thailand; and two multi-radar sites at Florida and Texas.
Additional information can be obtained from the TRMM
Office.
TRMM satellite data for each orbit are stored on board and
transmitted to the ground via the TDRSS. The TRMM science data are
processed by the TRMM Science Data
and Information System (TSDIS) into standard products. These
products are transferred to the Goddard DAAC for archival and
distribution.
The table below summarizes the TRMM standard products
available at the Goddard DAAC.
Level 1 products are the VIRS calibrated radiances,
the TMI brightness temperatures, and the PR return power and
reflectivity measurements. Level 2 products are derived geophysical
parameters at the same resolution and location as those of the Level 1
source data. Level 3 products are the time-averaged parameters mapped onto a
uniform space-time grid.
TRMM Products at the Goddard DAAC
| Level | Visible Infrared Scanner | TRMM
Microwave Imager | Precipitation
Radar | Combined Products | Ground Validation
(GV) |
|---|
| Level 1 | Visible & IR
radiances | Microwave brightness temperatures |
Radar return power & reflectivity |
NA | Cal. radar reflectivity at each
GV site |
| Level 2 | NA |
TMI profile for CLW, prec. water, cloud ice, prec. ice,
latent heat, & surface rain | PR surface cross-section
& path attenuation, rain type, storm, & freezing height; PR profile for
rain rate, reflec., attenuation, & rain top/bottom height |
Rain rate, drop size dist. parameters, path integrated
attenuation | Rain existence, rain map, rain type, 3-D
reflectivity, rain gauge, disdrometer |
| Level 3 | NA |
TMI monthly rainfall, rain rate, rain frequency, &
freezing height | PR monthly surface rain total, rain
profile at 2, 4, 6, 10 & 15 km, fractional rain, storm height
histogram, snow ice layer, surface rain rate, & path
attenuation | Monthly surface rainfall, CLW, rain
water, cloud ice, & grauples; combined instruments calibration, global
gridded rainfall | Rain map, 3-D map |
TRMM standard products can be ordered from the Goddard DAAC, via the
TRMM Data Search and Order
Web Interface.
In addition to the standard products, the Goddard DAAC also provides,
as part of its value-added TRMM support to facilitate analysis and processing
by users, certain special products, including:
- Orbital gridded products, e.g., for the TMI Hydrometeor Profile standard
product, a 0.5 degree by 0.5 degree resolution special product.
- Geographical subsets of the orbital gridded products.
- Parameter subsets of selected standard products.
- Satellite and ground radar coincidence subset products for the Ground
Validation sites.
- Geographical Information System (GIS)-compatible TRMM products.
Data sets are distributed via FTP. Potential TRMM data users,
especially those with specific needs, are urged to contact the
Hydrology Data Support Team:
hydrology-disc@listserv.gsfc.nasa.gov
.
Please send us your name and email so we can keep you informed.
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Atmos Composition
