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THE
AQUA SATELLITE-VITAL STATISTICS
- Click this link for information on Aqua's vital statistics
A
NEW PLATFORM FOR OLD QUESTIONS
Aqua
will make measurements of the Earth at the same time, all
the time. This is because the satellite will orbit the planet
on a nearly polar route, passing over different points on
the ground at approximately 1:30 pm and 1:30 am. By maintaining
a consistent time for taking readings, the integrated suite
of sensors on Aqua will facilitate sophisticated measurements
of planetary processes that until now have been challenging
to collect and calibrate. Working in concert or independently,
Aqua's scientific hardware will be used to study climate change,
vegetation, water vapor in the atmosphere, clouds, precipitation,
soil moisture, sea ice, land ice, snow cover and more.
It's a broadly defined mission overall, specifically composed
of both narrowly and widely tailored objectives. The processes
targeted for study directly affect life on Earth; they describe
the tangible world: rainfall that waters crops, snow and ice
that reflect heat back into space, and changes in vegetation
that describe how our planet's biosphere may be shifting due
to human induced climate pressures.
FLIGHT
HARDWARE: AQUA'S RESEARCH PAYLOAD
MODIS
First,
a review: color is a description of light. Light is electromagnetic
radiation. Therefore, color, at least in the visible sense,
is a description of electromagnetic radiation. Even beyond
the realm of what's visible to the human eye, the specific
characteristics of a particular color can tell a great deal
about the material that's reflecting or emitting it.
From this simple axiom comes the development of a sensor that's
designed specifically to capture the subtleties of color.
It's called MODIS, the Moderate-resolution Imaging Spectroradiometer,
and by many estimations, this is the future of color. Aqua's
MODIS will measure visible and infrared light in 36 distinct
bands-it will view the world in 36 colors, in other words.
MODIS will not be helpless at night, either. The dramatic
reduction in visible light when the planet turns away from
the Sun does not curtail the instrument's ability to collect
data of other wavelengths.
These measurements will be used to generate scientific products
about land surface cover, vegetation, phytoplankton in the
oceans, fires on land, sea ice cover, snow cover on land,
and properties of clouds and aerosols in the atmosphere.
CERES
CERES
stands for Clouds and the Earth's Radiant Energy System. As
the name suggests, the instrument looks at clouds and the
Earth's radiation balance. More specifically, CERES studies
how much heat is emitted and reflected by the Earth on a broad
scale. CERES scientists will also deliver detailed information
about clouds by analyzing the data in concert with the data
from the MODIS instrument. By studying how clouds function
in relation to the larger planet, scientists can develop new
predictive models about weather systems and how the Earth
maintains its delicate temperature balance.
The first CERES instrument went into space aboard the TRMM
satellite, launched in 1997. Designed to study rainfall in
the tropics, TRMM successfully showed how a device of this
kind could provide valuable data for weather and climate related
research. The second and third CERES instruments launched
onboard the Terra platform in 1999; Aqua will enable the fourth
and fifth of these to fly above the Earth.
AMSR-E
The
water cycle propels the Earth's climate. Not only is water
vapor the most important greenhouse gas, but its circulation
through the Earth's many parts also distributes energy. The
water cycle is an extremely complex process, and a better
understanding of its subtleties can provide valuable information
to scientists. One of the key instruments on the Aqua satellite
to explore these questions and more is AMSR-E, the Advanced
Microwave Scanning Radiometer for the Earth Observing System.
By collecting emitted radiation in the microwave range of
the spectrum, AMSR-E will study precipitation, near-surface
wind speeds, sea surface temperature, soil moisture, snow
cover, and more.
Compared to the other instruments onboard Aqua, AMSR-E is
also distinctive for its appearance. Rising like a golden
sail above the bow of the vehicle, the instrument spins 40
times a minute. It will gather data from an 867-mile (1445
km) swath of the planet as it orbits.
HSB
The
Humidity Sounder for Brazil (HSB) is Brazil's latest foray
into space. Charged with the task of deriving water vapor
readings in the lower atmosphere, this instrument will be
used largely to provide humidity measurements beneath overcast
conditions and help make readings by its collaborating instrument
AIRS more accurate. HSB will be able to make humidity measurements
even if clouds or thick haze heavily covers the sky beneath
it. HSB measurements will also be used to measure the intensity
of rain over given areas, as well as provide supplemental
information about clouds, both valuable on an orbiting observatory
designed to study the Earth's climate.
AMSU
The
two completely separate sensor units that make up AMSU, the
Advanced Microwave Sounding Unit, collect data in 15 spectral
bands. That means its sensors read information by measuring
emitted light from observed surface features in 15 distinct
"colors", although these microwave "colors"
are not visible to the human eye. Scientists will treat the
data collected by the two AMSU units as if they came from
a single piece of hardware. Onboard Aqua the twin sensors
are designed to operate in synchrony; back on the ground the
data processing system will combine the measurements. AMSU
will make measurements of atmospheric temperature, with particular
attention paid to the stratosphere (the upper atmosphere),
and a secondary goal of providing temperature observations
in the troposphere (the lower atmosphere). When it looks at
lower altitude parts of the sky, AMSU will be able to filter
out data signatures from low lying clouds. The instrument
sees the Earth in a swath of 1014 miles (1690 km).
AIRS:
A NEW SATELLITE, A NEW INSTRUMENT
While
the other five instruments on Aqua are all highly sophisticated
pieces of technology, the Atmospheric Infrared Sounder, or
AIRS, breaks new ground. It's designed to collect data about
the Earth using 2378 distinct spectral channels in the infrared
range, plus four more channels in the visible and near-infrared
part of the spectrum. Where AIRS makes its most compelling
statement of purpose is in its synergy with two other instruments
onboard Aqua. By using microwave data from AMSU and HSB to
take into account the effects of clouds, AIRS will be able
to make unprecedented measurements of temperature through
vertical columns of the atmosphere, as well as making temperature
measurement for the planet's surface. By fusing data about
water vapor, temperature, and clouds, powerful new tools become
available for research and analysis into the Earth's climate
at a systemic, process-oriented level.
THE
AIRS TRIO: MEASURING MORE THAN AIR TEMPERATURE
AIRS
may be the headliner, but in conjunction with AMSU and HSB,
this is one trio worthy of lofty high notes. This is the most
advanced atmospheric sounding system ever put into space.
Scientists are eager to put it to the test.
The idea is that each instrument will be able to make measurements
that complement data gathered by the other two. The AIRS instrument
itself has the major role of looking at infrared light, taking
measurements that the scientist's data processing system can
use to derive highly sensitive temperature information.
In this visualization we get a better sense of what the trio
will be trying to see. We're looking at a simulated three-dimensional
section of the atmosphere, using data from NASA's advanced
NSIPP (NASA's Seasonal to Interannual Prediction Project)
climate model to illustrate the point. NSIPP simulates the
Earth's climate inside a powerful supercomputer, enabling
experts to conduct virtual "experiments" on the
natural world. By looking through the total volume of atmosphere,
AIRS, AMSU, and HSB are able to quantify water vapor, cloud
density, and temperature simultaneously. This co-incident
data acquisition is vital if experts are to better understand
their interrelationship.
The visualization also emphasizes the three-dimensionality
of the measurements themselves. Just as the atmosphere is
not a flat component of the total planet, neither are its
features. They vary over distance: as you climb a mountain,
the air not only gets colder but also drier. With the AIRS
trio, experts can compile accurate profiles of vast regions
of the atmosphere.
Listed specifically, some of the products AIRS will provide
include temperature and humidity profiles, a quantified value
for how much a particular region is covered by clouds, cloud-top
height, and cloud-top temperature. It will also be able to
precisely measure the differences in day-night surface temperatures
and provide a reliable measurement of total atmospheric water
in a given region.
This kind of data will likely have a major influence in our
ability to forecast weather and help us better understand
the nature of Earth's climate system.
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