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MicroMAPs
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A
Low-Cost
Nadir-Viewing
Remote
Sensor
for Detection of CO and N2O in the
Troposphere
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Background
Carbon
Monoxide
(CO)
is
a
product of incomplete combustion of fossil fuels and
natural organic materials. Large quantities of CO are produced
hourly from the operation of vehicles, slash and burn agriculture,
power plants and forest fires. Increasing levels of atmospheric
CO are changing the chemical balance in the troposphere and contribute
to changes in the earth's climate.
As
MicroMAPS
views
the
earth
from an airborne or orbital platform, it
produces “snapshots” of the distribution of CO and Nitrous Oxide (N2O)
through the technique of non-dispersive correlation spectroscopy.
This data is reduced to three-dimensional pictures of percentages of
atmospheric CO in the earth’s troposphere.
N2O
is
a
background
gas
thought to be only slightly affected by man's
activities. This gas is used to provide a comparison standard for the
measurement of CO above the cloud ceiling. CO is a
“greenhouse gas” in its own right, but is equally important as an
indicator of the sources of the primary greenhouse gas carbon dioxide
(CO2), which results from combustion. A map of CO in the
atmosphere can more easily point to the anthropogenic sources of CO2
than a map of CO2 levels. This is because remote sensing CO2
directly is difficult due to its high background level which washes out
the relatively small changes due to combustion plumes. This data
can then be used in conjunction with other scientific observations to
assess the global impact of fossil fuel burning on air quality and
climate.
MicroMAPS
was
developed
in
the
1990s for launch in 1998 on the Clark Spacecraft
as part of NASA’s Small Satellite Technology Initiative (SSTI).
It is the successor to the earlier instrument MAPS, which successfully
flew on the Shuttle in 1982 and 1994, pioneering the use of remote
sensing as a tool for tropospheric exploration. When the
program was cancelled the instrument was put into storage for later use
in an orbital or aircraft mission.
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Airborne at Last!!!
In
2003
an
opportunity
arose
to fly MicroMAPS on the Proteus
high altitude aircraft developed by Burt Rutan’s company, Scaled
Composites.
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Proteus
at
NASA
Langley-MicroMAPS
is
housed in the landing gear housing to the
left
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Proteus
on
a
test
flight
over the Western US.
MicroMAPS
is
in the right hand faring.
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The
first
missions
were
flown
by the Proteus pilot, Mike Melvill, in the
summer of 2004. Mike recently made aviation history as the first
civilian to fly a spaceship out of the atmosphere into low Earth sub
orbit. Melvill flew SpaceShipOne to a record-breaking altitude of
approximately 62 miles, making him the first private pilot to become an
astronaut.
MicroMAPS
was
flown
under
the
auspices of NASA Langley and a Virginia
Space
Grant
Consortium (VSGC) team made up of three Virginia
Universities
(Old Dominion University, Virginia Polytechnic Institute and University of Virginia) – MicroMAPS is also on
Proteus supporting INTEX-NA. INTEX-NA is an
integrated atmospheric field experiment with a threefold mission: to
identify the quantity of polluting gases and aerosols that flow from
North America to the Atlantic Ocean, to understand the transport and
chemical changes of these gases over the ocean, and to assess the
global impact of this flow on air quality and climate. Dr. Vickie
Connors of NASA Langley heads the project.
INTEX-NA is a component of the International Consortium for Atmospheric
Research on Transport and Transformation (ICARTT), which takes
advantage of the fact that several groups in North America and Europe will conduct concurrent field campaigns
this summer with common goals.
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TEST FLIGHT OF A
MicroMAPS BREADBOARD (DETAILS)
In
October
1994
a
breadboard
model of MicroMAPS was flown on the NASA
Ames DC-8 research aircraft
in an under flight of the MAPS which
flew on STS68. Approximately 40,000 line km of CO and N2O measurements
were made over a 10 day period over the US and southern
Canada.
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Description of the
MicroMAPS Hardware
MicroMAPS is a
gas filter correlation radiometer capable of detecting trace
atmospheric gasses by remotely sensing their infrared (IR) absorption
characteristics. MicroMAPS is based on a commercial instrument
called GASCOFIL developed by
Resonance for pollution monitoring. While the method can be used to
detect a number of trace species (including CH4, SO2, and NO2), the
current version of MicroMAPS detects CO and N2O from a nadir viewing
airborne or orbital platform. To do this, the instrument is equipped
with CO and N2O gas cells and configured to observe the earth's IR
radiance in a band centered at 4.67 microns. It has been demonstrated
that the synchronous detection of alternatively chopped signals through
CO, vacuum and N2O view cells can produce a quantitative measure of CO
in three tropospheric layers. The simplicity of the method affords a
low cost technique for generating global maps of these important
atmospheric species when viewing from space.
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Photo
of
MicroMAPS
at
NASA
Langley
prior to Proteus integration
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MicroMAPS
uses
the
same
method
of detection of trace CO (gas cell correlation
spectroscopy) as an older instrument called MAPS. MAPS (The
Measurement of Air Pollution from Satellites) has heritage from
Shuttle missions in 1982, 1984 and 1994 (STS-2, STS-41G and STS-68) See
Reichle et al,
[1986] for a description of MAPS over
flights.
MicroMAPS
differs
from
MAPS
in that it has only one optical path with a rotating chopper containing
up to eight gas cells instead of three optical paths with two gas cells
one clear cell and three detectors. Incoming IR spectral energy from
the atmospheric target and ground is collected by a telescope and
modulated by gas cell chopper wheel. A PbSe detector converts the
optical signals to electronic waveforms which are digitized by a 12 bit
A to D converter and processed a digital format by an on board
microprocessor.
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MicroMAPS Optical
Design Specifications
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Telescope
Aperture
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0.8
inches
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Telescope
field
of
view
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2.4
degrees
(Square)
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Number
of
elements
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5
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Element
Material/Coating
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Ge/AR
Coated
gt
99
%
T at 4.67m
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Etendu
(A
Omega)
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7.2
x
10-3
(cm2
steradian)
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Gas
Cell
Clear
Aperture
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0.8
inches
circular
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Beam
Size
at
Gas
Cell
Chopper
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0.2
inches
(approx.
square)
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MicroMAPS
Interface Specifications
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Size
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25.4
x
17.2
x
15
cm (excluding lens tube)
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Mass
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(6.5
kg
max)
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Power
Consumption
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16
Watts
max
orbital
average
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Input
Voltages
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15,
-15,
5
Volts
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Interface
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Serial
RS
422
standard
with
XMODEM protocol
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