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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


3/27

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


4/27

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)


5/27

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


6/27

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


7/27

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


Swath Width:+ 80 degrees


8/27

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


Swath Width:600 km


9/27

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


10/27

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


11/27

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


12/27

PrecipitationRadar


13/27

TRMM Precipitation Radar Algorithm

Level 1

IB21

IC21

Level 2

2A21

2A23

2A25

Level 3

3A25

3A26


14/27


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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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


16/27


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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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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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.


19/27

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


20/27

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


21/27

Ave Rain: Digital Array Viewer


22/27

Sigma 0: Digital Array viewer


23/27

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.


24/27

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


25/27

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.


26/27

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


27/27

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/

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