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An Introduction to TRMM and
its Precipitation Radar (PR)Arash Mashayekhi
CASA REU Program
Sandra Cruz-Pol, Assoc. Prof. ECE UPRM
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The Big Picture
Why TRMM?
Tropical Rain Measurement Mission
tropical rainfall Drives the Climate Machine
Need to understand the Water Cycle TRMM: the first space-borne rain radar (PR)
and microwave radiometric data
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About TRMM:Launched:
November 28, 1997
Circular Orbit altitude:
350 km
Inclination:approx. 35 deg.
Orbit Duration:
91 minutes (16 Orbits a day)
Time Spent over Puerto Rico during
each orbit:1.14 minutes
Total Time spent over Puerto Rico
Each Day:
18.2 minutes
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TRMM Primary Instruments for
Measuring Precipitation:
1. Precipitation Radar (PR)
2. TRMM Microwave Imager (TMI) radiometer
3. Visible and Infrared Scanner (VIRS)
Two Addi t ional Ins truments:
1. Cloud and Earth Radiant Energy Sensor
(CERES)
2. Lightning Imaging Sensor (LIS)
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Microwave Imager
Introduction:
passive microwave sensor designed to
provide quantitative rainfall information
Provides Valuable Information on:
Quantity of the water vapor, Quantity of the cloud water
Intensity of the rainfall in the
atmosphere.
Specifications:Frequency:10.65 to 85.5 GHz
Horizontal Resolution:6 to 50 km
Swath Width:760 km
TMI
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Visible and Infrared Scanner
Introduction:
senses radiation coming up from the Earth in
five spectral regions, ranging from visible to
infrared
It is used to:
Delineate rainfall
Determine the brightness
(visible and near infrared) or
temperature (infrared) of the
source emitting radiation
Specifications:
Wavelength:.63 to 12 um
Horizontal Resolution:2 km
Swath Width:720 km
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Cloud and Earth Radiant
Energy Sensoro Introduction
o The data from the CERES instrument will be used to study the
energy exchanged between the Sun; the Earths atmosphere,
surface and clouds; and space.
Gathers information on:
Cloud propertiesCloud
Effects
cloud-amount,
altitude, thickness, and
the size of the cloud
particles
Specifications:
Wavelength:.5 to 50 um
Horizontal Resolution:10 km
Swath Width:+ 80 degrees
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Lightning Imaging Sensor
Introduction: The Lightning Imaging Sensor is a
small, highly sophisticated instrument
that will detect and locate lightningover the tropical region of the globe.
the sensor will provide
information that could lead tofuture advanced lightning
sensors capable of significantly
improving weather
"nowcasting."
Specifications:
Wavelength:.77765 m
Horizontal Resolution:4 km
Swath Width:600 km
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Precipitation Radar
Introduction: The Precipitation Radar is the first active space borne radar
designed to provide three-dimensional maps of storm structure
PR will provide valuable information on:
Rain size, speed, and altitude
Intensity and distribution of the rain
Rain type
Storm depth
Melting layer altitude: The height at which
snow melts into rain
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Precipitation Radar
Specifications:
o Frequency :13.8 GHz (Ku-band)
o More than four times higher than that of a typical ground basedradar (NEXTRAD ~ 3 GHz, S-band)
o Horizontal Resolution:4.3 km
o Swath Width:215 km
o Vertical Profile of Rain and Snow:19.3 kmo Able to detect rainfall rate down to .7 millimeters/hr
o Able to separate vertical rain echo samples of 250 meters
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Precipitation Radar
Specifications (Contd):
Power Consumption:224 W
Solid state power amplifiers (128) are used to conserve power
Target Area:
phased array antenna that steers the beam electronically
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PrecipitationRadar
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TRMM Precipitation Radar Algorithm
Level 1
IB21
IC21
Level 2
2A21
2A23
2A25
Level 3
3A25
3A26
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TRMM Precipitation Radar Algorithm
Level 1 (IB21, IC21)
IB21
Calculates received power by performing extensive
internal calibrations
Data in IB21 include:
Location of Earth surface and surface clutter
System noise level
Land/Ocean Flag
And many more
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TRMM Precipitation Radar Algorithm
Some Examples of IB21 Data: Navigation
X, Y, Z Components of Space Craft Velocity and Position
Latitude
Longitude
Altitude
Sensor Orientation
Min. Echo Flag
0 : No Rain
10: Rain possible but maybe noise
20: Rain Certain
Land / Ocean Flag 0: Water
1: Land
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TRMM Precipitation Radar Algorithm
Level 1 (IB21, IC21)Output: Radar Reflectivity Factor
Almost same file format as that of IB21: Power replaced by Radar Reflectivity Factor
Noise replaced by Dummy Variable
Level 2 (2A21, 2A23, 2A25)Primary Objective:
Compute Path Integrated Attenuation (PIA) using theSurface Reference Techniques (SRT).
Input Data: IB21
Output used by: 2A25, 3A25, and 3A26
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TRMM Precipitation Radar Algorithm
Level 2 (2A21, 2A23, 2A25) Main Objectives:
Classification of Rain Types
Output of Rain / No Rain Flag
Computation of estimated height of freezing level
Output of the height of storm top Input Data: IC21
Output used by: 2A25, 2B31, 3A25, 3A26
Level 2 (Contd)(2A21, 2A23, 2A25)
Main Objectives: Input Data: IC21, 2A21, 2A23
Output used by: 3A25, 3A26
Correct for the Rain Attenuation in measured Radar Reflectivity
Estimate instantaneous 3-D distribution of rain
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TRMM Precipitation Radar Algorithm
Level 3 (3A25, 3A26) Objective:
calculate various statistics over a month from the level 2
Four types of statistics are calculated:1. probabilities of occurrence
2. means and standard deviations
3. histograms
4. correlation coefficients
Level 3 (3A25, 3A26) Objective:
Compute rain rate statistics
Compared to 3A25 statistics produced from 3A25 are conditioned either on the presence of
rain or on the presence of a particular type of rain but statistics from 3A26are unconditioned.
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Data for Rain event
We requested data for a strong rain event
that occurred in Puerto Rico last May
2004.
Dates May 14, 15, 21
We have corresponding data for NWS
NEXRAD in Cayey, PR and rain gauges
around the island.
Our goal is to compare these data sets
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How does the data look like?
Data files are huge: 30MB for each 1.1minute. Total of over 1GB for the event.
There are several (~20) products
Ave rain Near surface rain
Sigma zero
Rain flag Zeta
PIA
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Ave Rain: Digital Array Viewer
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Sigma 0: Digital Array viewer
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Need to Filter
We only need
Near surf rain
Quality flag
?
And of course Latitude/Longitude, Date,
Time to map over Puerto Rico
This filtering should considerably reduce
the data file sizes.
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Rain algorithm
Once we filter the data
Need to develop code in IDL to convert to
arrays in text
Compare actual rain algorithm being used byNWS. The Rosenfelt tropical convective
2.1
250RZ
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PR Rain Characterization
Look at different algorithms per region
Elsner & Carter, 2000; Vasquez & Roche,
1997suggest that the island be divided into
~6 rain regions each with a differentalgorithm for 3 seasons.
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Tropical Environment
Tropical weather is especiallydifficult to forecast due toseveral factors including:
Easterly trade winds causedforced convection
Complex topography of theisland
In the fall, we plan to use CSUdisdrometer to help furthercharacterize rainfall in PR.
C dit
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Credits TRMM Official Website
TRMM Education and Outreach Scientist :
Dr Jeffrey B. Halverson
Responsible NASA Official:Dr.Robert Adler
http://trmm.gsfc.nasa.gov/
NASA Official Website
Editor: Jim Wilson
NASA Official: Brian DunbarLast Updated: July 6, 2004
http://www.nasa.gov/home/index.html
Japan Aerospace Exploration Agency (JAXA) Official Website
http://www.jaxa.jp/index_e.html
National Space Development Agency of Japan (NASDA) Official Website
http://www.nasda.go.jp/index_e.html
Tropical Rainfall Measuring Mission
TRMMPrecipitation Radar Algorithm Instruction Manual For Version 6
http://trmm.gsfc.nasa.gov/http://www.nasa.gov/home/index.htmlhttp://www.jaxa.jp/index_e.htmlhttp://www.nasda.go.jp/index_e.htmlhttp://www.nasa.gov/home/index.htmlhttp://www.nasda.go.jp/index_e.htmlhttp://www.jaxa.jp/index_e.htmlhttp://www.nasa.gov/home/index.htmlhttp://trmm.gsfc.nasa.gov/