3 - TRMM -Tropical Rainfall Measuring Mission

    3.1 Project Overview

    The Tropical Rainfall Measuring Mission (TRMM) is a joint mission between NASA and the National Space
Development Agency (NASDA) of Japan designed to monitor and study tropical rainfall and the associated release of energy that helps to power the global atmospheric circulation shaping both weather and climate around the globe. The TRMM Observatory carries five instruments. It includes the first spaceborne Precipitation Radar (PR), the TRMM Microwave Imager (TMI), a Visible and Infrared Scanner (VIRS), a Cloud and Earth Radiant Energy System (CERES), and a Lightning Imaging Sensor (LIS).
 
 
 

SENSOR	CHANNELS	PRODUCTS
Precipitation Radar	13.8 GHz	Three-dimensional storm structure
Microwave Imager (TMI)	10.7, 19.4, 21.3, 37, 85.5 GHz	Rainfall Rate
Visible and Infrared Scanner (VIRS)	0.63 to 12 micrometers	Cloud Brightness and Temperature
Cloud and Earth Radiant Energy System (CERES)	Visible and IR Spectra	Solar and IR Flux / Cloud properties
Lightning Imaging Sensor (LIS)	Spaceborne Camera	Location and detection of lightning

Precipitation Radar (PR):

• Horizontal ground resolution of 4 km
• Swath width of 220.5 km
• Vertical profiles of rain and snow from the surface to a height of 19.3 km
• Has good resolution and high quality images because radar frequency is about 3 times that of typical ground-based radars.

• Gets quantitative rainfall information over a wide swath width of 784 km
• Based on the design of the SSM/I with the addition of an extra frequency of 10.7 GHz
• Measures minute amounts of microwave energy emitted by the Earth and atmosphere
• Can quantify water vapor, cloud water and rain intensity in the atmosphere
• Calculations of rainfall are based on Planck's radiation law - how much energy a body radiates given its temperature
• Water surfaces emit half of the microwave energy specified by Planck and appear colder to passive microwave radiometer
• Raindrops emit 100% of their actual temperature so they appear to be warmer than the water surfaces
• Land emits 90% of its real temperature. The high frequency microwaves are strongly scattered by ice particles in the rain clouds.  Therefore, this reduces the amount of microwave signal at the satellite and contrasts with the warmer land.

• Indirect indicator of rainfall
• Ability to delineate rainfall
• Senses radiation coming up from the Earth's surface in 5 spectral regions ranging from visible to infrared
• Intensity of radiation in the bands determines the brightness and temperature of the source
• Colder temperatures have greater intensities at shorter wavelength bands while warmer temperatures have greater intensities at longer wavelength bands
• Since colder clouds occur at higher altitudes, measured temperature is an indicator of cloud height, where the higher cloud tops are positively correlated with precipitation from convective clouds
• To distinguish between the high cirrus clouds that flow out of thunderstorms and the convective clouds, it compares two infrared channels at 10.8 and 12 micrometers
• Uses a rotating mirror and looks straight down

• Based on NASA Langley's ERBE which used three satellites to provide global energy budget measurements from 1984-1993.
• Measures energy at the top of the atmosphere and estimates energy in the levels of the atmosphere and at the surface
• Uses very high resolution cloud imaging instruments to determine cloud properties

• Detects and locates lightning from staring imagers
• The field of view allows the sensor to observe for 80 seconds. This is sufficient time to estimate flashing rate which tells the researcher whether the storm is growing or decaying
• Optical lens system removes background signal enabling detection of 90% of all lightning strikes

    3.2 LBA - Calibration Field Experiment

    Under support from NASA/TRMM, a major ground validation program, known as TRMM/Brazil, was carried out in Amazonia from January 1999 to 28 February 1999. This program focuses on the dynamical, microphysical, electrical and diabatic heating characteristics of tropical convection in this region. Data collected in the program have been used in part to validate products from the TRMM satellite as it repeatedly overflies this region. TRMM/Brazil was conducted in parallel with the wet season component of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA).This experiment is an international research initiative led by Brazil. LBA is designed to create the new knowledge needed to understand the climatological, ecological, biogeochemical, and hydrological functioning of Amazonia, the impact of land use change on these functions, and the interactions between Amazonia and the Earth system.

    3.3 Satellite Radar vs Ground Radar Validation

    TRMM-LBA Satellite Overpass Visual Calendars
 

    Based in the Satellite Overpass Visual Calendar we compared the Satellite Radar precipitation with ground radar for January and February of 1999 such that, the overpass overlapped the ground radar with an area greater than 50%.

    January 99
    From the Overpass Visual Calendar we evaluated days 11/17/18/19/20/23/25/27
 

DAY	Evaluation
11	Convective area located to the south of the radar sites. Precise correlation of location and intensity between the Satellite Radar Precipiation and the Ground Radar Precipitation.
17	Agreement between both radars of small scattered echoes. GOES indicated that there was scattered high clouds over the area.
18	A small convective system was aligned to the north of the radar sites. Both radars captured the similar location and intensity of the system.
19	Relatively few scattered echoes on both radars. GOES water vapor image verified few cirrus over the region.
20	A small convective system was located to the southwest of the radar sites. There was an accurate representation by both radars of this system's location.
23	The Ground radar indicated a large convective system to the northwest of the radar site. However, the swath of the Satellite radar did not cover this area. There was good representation between the two radars for the area covered.
25	A large convective system of strong intensity was located to the northwest of the radar sites that was well rapresented by both radars.
27	Day with relatively few clouds, as indicated by GOES. Minimal activity on both radars.

    February 99
    From the Overpass Visual Calendar we evaluated days 01/03/08/10/17/24/25.
 

DAY	Evaluation
01	Analisis of the cloud system matches very well between the Satellite Radar Precipitation and the Ground Radar Precipitation. Several convective systems ligned nortwest-southeast are represented in both radar with similar shape and intensity.
03	Several convective systems at the west sector are well represented in both radars satellite and ground.
08	Day with few clouds. Small system ligned north-south at -61.5 long and -11.0 lat matches well in both sensors.
10	Large system at north well represented. Includes details of the small systems nearby.
17	Large system at northeast well represented.
24	Systems located at south and southeast well represented.
25	Several mesoscale systems very weel represented by the two sensors.  For example the family of aligned clouds at southeast area.

 

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