Advances in Satellite Methane Measurement: Implications for Fossil Fuel Industry Emissions Detection and Climate Policy
April 1, 2022
Advances in Satellite Methane Measurement: Implications for
Fossil Fuel Industry Emissions Detection and Climate Policy
On November 15, 2021, under the authority of Section 111
achieving climate change mitigation and public health
of the Clean Air Act, the U.S. Environmental Protection
goals. Measuring methane emissions on a large scale is
Agency (EPA) published a rulemaking that “proposes
difficult, and the measurement technologies continue to
comprehensive standards of performance for GHG
evolve (see CRS In Focus IF10752, Methane Emissions: A
[greenhouse gas] emissions (in the form of methane
Primer, by Richard K. Lattanzio).
limitations) ... for new, modified, and reconstructed sources
in the Crude Oil and Natural Gas source category, including
Advances in remote sensing of methane from satellites may
the production, processing, transmission and storage
improve monitoring and detection of emissions from oil,
segments” (86 Federal Register 63110, November 15,
coal, and natural gas operations. Improving the
2021). Lessening unintended emissions known as fugitive
measurement of these methane emissions can contribute to
emissions is one set of actions in this proposal to constrain
the U.S. effort to meet treaty obligations under the United
large emissions sources known as super-emitters. The
Nations Framework Convention on Climate Change
rulemaking requests both information and comments on
(UNFCCC). These obligations include emissions reporting
alternative measurement technologies for methane
requirements as well as scientific and technical cooperation
emissions, especially those attributed to super-emitters. The
(see CRS Report R40001, A U.S.-Centric Chronology of the
EPA is seeking input on technologies that could distinguish
United Nations Framework Convention on Climate
large emission events and a definitional emissions level for
Change).
designating an event as “large.” It is specified in the
rulemaking that “any emissions visible by satellites should
Methane Monitoring Strategies
qualify as large emission events” (86 Federal Register
There are two general categories for methane monitoring.
63110, November 15, 2021). The role of evolving satellite
One method, sometimes referred to as “bottom up” (BU),
technologies that have the ability to monitor methane and
extrapolates measurements from individual components.
contribute to the identification of “large emission events” is
BU methods rely on averaging numerous leak test
discussed here.
measurements of industry components to develop
“emissions factors” that are aggregated and used to estimate
Background on Methane Emissions
emissions, based on the number of facilities and the levels
Fossil-fuel-related industries emit methane into the
of production. However, because emissions factors are
atmosphere. Methane has a global warming potential 28
based primarily on leakage measured under normal
times greater than carbon dioxide over a 100-year period. It
conditions, they may not fully account for abnormal super-
is second only to carbon dioxide in contributions to global
emitter events. As a result, BU methods may understate
temperature increases from human emissions of greenhouse
total emissions.
gases. It has been estimated for the United States that
approximately 30% of methane emissions from onshore oil
Emerging technologies may enhance the second type of
and gas production arise from fugitive emissions, while
monitoring strategy. Referred to as “top down” (TD), these
such emissions are approximately 1.8 times greater than
methods provide direct empirical measurements of
emissions from venting for pipelines and liquefied natural
methane, not estimates based on emissions factors, at
gas facilities.
specific locations. Using either ground-based instruments or
those on aircraft or satellites, methane emissions may be
Fugitive emissions are generally described as leaks from
measured directly. The downsides of TD are relative cost,
pressure containment systems, which can include leaks
and coverage limitations. Satellites and aircraft
from valves or flanges, in fossil fuel facilities. Fugitive
measurements cost more than computer model estimates
emissions also include methane that escapes to the
extrapolated from limited sampling during normal
atmosphere from incomplete combustion during flaring
operation. Also, some of these TD methods typically occur
(burning of excess gas). A small number of fugitive
only at infrequent intervals, and may miss detection of
emission events, known as super-emitters, account for
sporadic emission events. As technologies mature, costs
approximately 50% of fugitive emissions in the fossil fuel
may drop. Increasing satellite sampling frequency offers an
sector and are sourced from approximately 5% of fugitive
opportunity to improve accuracy and precision.
emission events. Locating, identifying, and attributing these
events to specific sources is critical to reducing methane
Satellite Measurement of Methane
emissions overall.
Emissions
Satellite detection methods can involve tradeoffs that may
Reducing fugitive methane emissions, including super-
allow some fugitive emissions to go undetected. These may
emitter events, is believed by some to be important for
be addressed as technical capabilities improve and datasets
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Advances in Satellite Methane Measurement: Implications for Fossil Fuel Industry Emissions Detection and Climate Policy
from satellites with complementary capabilities are
with NASA), and ZY-1 02D (Chinese satellite launched in
combined. As satellites pass overhead, they scan a
2019) combine this ability to measure methane with a
continuous strip of the Earth’s surface known as a swath.
spatial resolution better than 50 m x 50 m, which is likely
The swath width is the horizontal width of this strip. There
sufficient to allow fugitive emissions attribution to a
is a tradeoff between the swath width and the resolution of
specific facility. Making use of the data from these satellites
the image. A satellite such as the European Space Agency
for fugitive emissions detection could add to current
instrument TROPOMI has a swath width of 2,600
attribution capabilities. Data from some of these satellites
kilometers (km) and spatial resolution of 7 km x 5.5 km
are already publicly available at no cost to users.
(across x along track). Such a wide swath scans a large area
but typically lacks the resolution to distinguish individual
Survey capacity may be enhanced by MethaneSAT, a joint
features such as specific oil or gas facilities. A satellite such
project of the Environmental Defense Fund (a U.S.
as the Italian Space Agency instrument PRISMA—with a
nonprofit) and the New Zealand Space Agency. Its
swath width of 30 km and a spatial resolution of 30 meters
specifications include a swath width greater than 200 km, a
(m), with a high-resolution sensor—may be able to
spatial resolution of 0.1 km x 0.4 km, and a detection
distinguish such facilities. Such a narrow swath width
threshold of approximately 2 parts per billion (ppb) of
restricts the area that can be sampled on any given
methane. If successful, MethaneSAT would be able to
overpass. This tradeoff means that a wide-survey satellite
survey large areas and detect methane emissions with some
may detect an area of high emissions but lack the resolution
spatial specificity, although its ability to attribute an
to attribute it to a specific facility, whereas a high-
emission event to a specific facility would be limited.
resolution satellite may miss a sporadic emission event
altogether if it is outside the narrower swath being sampled.
Alone or in combination, satellite platforms such as
MethaneSAT, TROPOMI, the GHGSat satellites, and the
There are strategies to address these tradeoff issues and
methane measurement capabilities of an increasing number
improve the detection, quantification, and attribution of
of hyperspectral satellites could provide an increase in the
fugitive methane emissions. These strategies include
detection, measurement, and attribution of super-emitter
increasing satellite survey capacity to detect elevated
fugitive methane emission events, with a corresponding
regional methane concentrations suggesting emission
increase in researchers’ ability to detect such events
events, increasing satellite capacity for direct location
systematically.
attribution of such events, and using satellites with
complementary capabilities in tandem.
Improving Greenhouse Gas Inventories
Enhanced satellite attribution capabilities may also improve
Enhanced attribution capability may be obtained by having
U.S. efforts to develop a more accurate greenhouse gas
more high-resolution satellites available for observations.
inventory. EPA prepares an annual Greenhouse Gas
Three high-resolution Canadian GHGSat satellites with
Inventory (GHGI; EPA 430-R-21-005, Inventory of U.S.
spatial resolution of at least 50 m x 50 m are currently
Greenhouse Gas Emissions and Sinks: 1990-2021), which
operational. These systems are able to discern individual
is submitted to the United Nations as part of the U.S.
point sources of fugitive emissions at the facility level,
commitment under the UNFCCC. The GHGI has been the
allowing specific attribution in some cases. These satellites
subject of some criticism, as studies have found that the
have a narrow 12 km x 12 km field of view and are capable
GHGI may underestimate U.S. methane emissions from the
of sampling locations of high emissions, identified by
oil and natural gas sectors. Some studies suggest that part of
survey satellites such as the MethaneSAT (American-New
this underestimation may be due to the underrepresentation
Zealand space mission currently scheduled for launch in
of emissions from large emission events or super-emitters.
October 2022) or the European Space Agency TROPOMI
Satellite sensors have a demonstrated ability to detect large
instrument on board the Copernicus Sentinel-5 Precursor
methane emission events. If this capacity is further
satellite launched in 2017. The launch of additional
developed and then systematically applied in oil- and gas-
GHGSat satellites is planned for mid-2022.
producing areas of the United States, it might provide
information that could increase the accuracy of the GHGI
Recent scientific advances in hyperspectral sensing may
by providing information on large emission events that
also increase attribution capability. Experiments have
might otherwise go undetected.
shown that hyperspectral sensors can be used to measure
atmospheric methane. Satellites such as PRISMA (launched
Jonathan D. Haskett, Analyst in Environmental Policy
in 2019 by the Italian Space Agency), Copernicus
Hyperspectral Imaging Mission for the Environment
IF12072
(CHIME; European Space Agency mission in collaboration
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Advances in Satellite Methane Measurement: Implications for Fossil Fuel Industry Emissions Detection and Climate Policy
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https://crsreports.congress.gov | IF12072 · VERSION 1 · NEW