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| Titel |
A Compact, Low Resource Instrument to Measure Atmospheric Methane and Carbon Dioxide From Orbit |
| VerfasserIn |
Scot Rafkin, Michael Davis, Ruth Varner, Sourish Basu, Lori Bruhwiler, Adrienn Luspay-Kuti, Kathy Mandt, Pete Roming, Alejandro Soto, Mark Tapley |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141792
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| Publikation (Nr.) |
 EGU/EGU2017-5336.pdf |
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| Zusammenfassung |
| Methane is the second most important radiatively active trace gas forcing anthropogenic
climate change. Methane has ∼28 times more warming potential than carbon dioxide on a
100-year time horizon, and the background atmospheric concentration of methane has
increased by more than 150% compared to pre-industrial levels. The increase in methane
abundance is driven by a combination of direct human activity, such as fossil fuel extraction
and agriculture, and natural feedback processes that respond to human-induced climate
change, such as increased wetland production. Accurate accounting of the exchange between
the atmosphere and the natural and anthropogenic methane reservoirs is necessary to predict
how methane concentration will increase going forward, how that increase will modulate the
natural methane cycle, and how effective policy decisions might be at mitigating
methane-induced climate change. Monitoring and quantifying methane source intensity
and spatial-temporal variability has proven challenging; there are unresolved and
scientifically significant discrepancies between flux estimates based on limited surface
measurements (the so-called “bottom-up” method) and the values derived from
limited, remotely-sensed estimates from orbit and modeling (the so-called “top-down”
method).
A major source of the discrepancy between bottom-up and top-down estimates is likely a
result of insufficient accuracy and resolution of space-based instrumentation. Methane
releases, especially anthropogenic sources, are often at kilometer-scale (or less), whereas past
remote sensing instruments have at least an order of magnitude greater footprint areas.
Natural sources may be larger in areal extent, but the enhancement over background levels
can be just a few percent, which demands high spectral resolution and signal-to-noise ratios
from monitoring instrumentation.
In response to the need for higher performance space-based methane monitoring, we have
developed a novel, compact, low-resource instrument that meets the accuracy and spatial
resolution challenges demanded by methane exchange processes. The baseline instrument
uses reflected sunlight 0.7591-0.7646 μm and 1.6058-1.6761 μm, permitting individual
spectral identification of CH4, O2, CO2 and H2O. By combining spectral information, the
complicating effects of aerosol and clouds can be reduced. A spectral resolving
power of R∼20,000 is achieved by utilizing a novel matching off-axis parabolic
(OAP) mirror system to send a collimated beam to an Echelle grating, which then
picks off the high orders of interest and sends them back to one of the OAPs for
final focus. A beamsplitter before the focus separates the near-visible O2 signal
from the ∼1.6 μm CH4, CO2, and H2O signals, creating two separate imaging
channels. A high-heritage H1RG detector is used in both channels. The instrument
images a 0.03∘× 5∘ field-of-view, with a point-source resolution of 0.03∘. These
specifications produce a 33 km wide instantaneous image at the nominal altitude
of 380 km, with 200 m point-source resolution. Higher altitudes yield increased
instantaneous coverage at the cost of wider point-source resolution. The 200 m pixels can
be averaged to produce higher signal-to-noise while still maintaining km-scale
resolution.
The entire instrument consumes 55 W with a mass of 20 kg and total volume of 0.07 m3.
Thus, the instrument provides performance similar to or better than existing hardware in a
much smaller package. The small resource footprint provides the opportunity to fly as
payload on one or multiple small satellite payloads or on the International Space
Station. |
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