. Atmospheric remote sounding from satellites is an essential component of the observational strategy deployed to monitor atmospheric pollution and changing composition. The IASI nadir looking thermal infrared sounder onboard MetOp will provide 15 years of global scale observations for a series of key atmospheric species, with unprecedented spatial sampling and coverage. This paper gives an overview of the instrument's capability for measuring atmospheric composition in the perspective of chemistry and air quality. The assessment is made in terms of species, accuracy and vertical information. Global distributions are presented for CO, CH4, O3 (total and tropospheric), HNO3, NH3, and volcanic SO2. Local distributions of organic species measured during fire events, such as C2H4, CH3OH, HCOOH, and PAN are also shown. For each species or process, the link is made to specialized papers in this issue.

/pdf/monitoring-of-atmospheric-composition-using-the-thermal-2ktxqf7uy7.pdf

Monitoring of atmospheric composition using the thermal infrared IASI/METOP sounder

Abstract. Atmospheric remote sounding from satellites is an essential component of the observational strategy deployed to monitor atmospheric pollution and changing composition. The IASI nadir looking thermal infrared sounder onboard MetOp will provide 15 years of global scale observations for a series of key atmospheric species, with unprecedented spatial sampling and coverage. This paper gives an overview of the instrument's capability for measuring atmospheric composition in the perspective of chemistry and air quality. The assessment is made in terms of species, accuracy and vertical information. Global distributions are presented for CO, CH4, O3 (total and tropospheric), HNO3, NH3, and volcanic SO2. Local distributions of organic species measured during fire events, such as C2H4, CH3OH, HCOOH, and PAN are also shown. For each species or process, the link is made to specialized papers in this issue.

http://systemarchitect.mit.edu/docs/selva12b.pdf

A survey and assessment of the capabilities of Cubesats for Earth observation

Requirements for the GMES Atmosphere Service and ESA's implementation concept: Sentinels-4/-5 and -5p

. The Orbiting Carbon Observatory-3 (OCO-3) is NASA's next instrument dedicated to extending the record of
the dry-air mole fraction of column carbon dioxide ( XCO2 ) and solar-induced fluorescence (SIF) measurements from space.
The current schedule calls for a launch from the Kennedy Space Center no earlier than April 2019 via a Space-X Falcon 9 and Dragon capsule.
The instrument will be installed as an external payload on the Japanese Experimental Module Exposed Facility (JEM-EF)
of the International Space Station (ISS) with a nominal mission lifetime of 3 years.
The precessing orbit of the ISS will allow for viewing of the Earth at all latitudes less than approximately 52 ∘ ,
with a ground repeat cycle that is much more complicated than the polar-orbiting satellites
that so far have carried all of the instruments capable of measuring carbon dioxide from space. The grating spectrometer at the core of OCO-3 is a direct copy of the OCO-2 spectrometer,
which was launched into a polar orbit in July 2014.
As such, OCO-3 is expected to have similar instrument sensitivity and performance characteristics to OCO-2,
which provides measurements of XCO2 with precision better than 1 ppm
at 3 Hz, with each viewing frame containing eight footprints approximately 1.6 km by 2.2 km in size.
However, the physical configuration of the instrument aboard the ISS, as well as the use of a new pointing mirror assembly (PMA),
will alter some of the characteristics of the OCO-3 data compared to OCO-2.
Specifically, there will be significant differences from day to day in the sampling locations and time of day.
In addition, the flexible PMA system allows for a much more dynamic observation-mode schedule. This paper outlines the science objectives of the OCO-3 mission and, using a simulation of 1 year of global observations,
characterizes the spatial sampling, time-of-day coverage, and anticipated data quality of the simulated L1b.
After application of cloud and aerosol prescreening, the L1b radiances are run through the operational L2 full physics retrieval algorithm,
as well as post-retrieval filtering and bias correction,
to examine the expected coverage and quality of the retrieved XCO2 and to show how the measurement objectives are met.
In addition, results of the SIF from the IMAP–DOAS algorithm are analyzed.
This paper focuses only on the nominal nadir–land and glint–water observation modes,
although on-orbit measurements will also be made in transition and target modes, similar to OCO-2,
as well as the new snapshot area mapping (SAM) mode.

/pdf/the-oco-3-mission-measurement-objectives-and-expected-2y84ruilw5.pdf

The OCO-3 mission: measurement objectives and expected performance based on 1 year of simulated data

The Infrared Atmospheric Sounding Interferometer (IASI) is a key payload element of the METOP series of European meteorological polar-orbit satellites. IASI will provide very accurate data about the atmosphere, land and oceans for application to weather predictions and climate studies. The IASI measurement technique is based on passive IR remote sensing using an accurately calibrated Fourier Transform Spectrometer operating in the 3.7 - 15.5 μm spectral range and an associated infrared imager operating in the 10.3-12.5 μm spectral range. The optical configuration of the sounder is based on a Michelson interferometer. Interferograms are processed by the on-board digital processing subsystem which performs the inverse Fourier Transform and the radiometric calibration. The integrated infrared imager allows the co registration of the IASI sounder with AVHRR imager on-board METOP.
The first model (proto-flight) of IASI has successfully completed a verification program conducted at ALCATEL SPACE premises in Cannes. This paper provides a brief overview of the IASI mission, instrument architecture and key performances results. A companion paper1 by Alcatel provides more information on instrument design and development.

IASI instrument: technical overview and measured performances

New types of sounders dedicated to selected species could be used on small satellites to monitor atmospheric chemistry
with simpler instruments. A new kind of Fourier transform spectrometer has been patented by CNES a few years ago.
Based on a static configuration, two projects are being studied at CNES with laboratory breadboards. One is dedicated to
CO2 concentration monitoring in near infrared. The other one works in thermal infrared to study CO and O3 atmospheric
profiles. MoLI breadboard, with a new highly integrated interferometric core, will be used for a long time measurement
of CO2 concentration. MOPI is another breadboard under development to transpose this concept in thermal infrared
during the SIFTI phase A study. These new generation spectrometers consist in a Michelson interferometer with
staircase mirrors assembled by molecular adhesion. They are adapted to narrow spectra sounding from space and could
lead to totally static and highly stabilized instruments.

Static Fourier transform spectroscopy breadboards for atmospheric chemistry and climate

IASI is an infrared atmospheric sounder. It will provide meteorologist and scientific community with atmospheric spectra. The IASI system includes 3 instruments that will be mounted on the Metop satellite series, a data processing software integrated in the EPS (EUMETSAT Polar System) ground segment and a technical expertise centre implemented in CNES Toulouse. The instrument is composed of a Fourier transform spectrometer and an associated infrared imager. The optical configuration is based on a Michelson interferometer and the interferograms are processed by an on-board digital processing subsystem, which performs the inverse Fourier transforms and the radiometric calibration. The infrared imager co-registers the IASI soundings with AVHRR imager (AVHRR is another instrument on the Metop satellite). The presentation will focus on the architectures of the instrument, the description of the implemented technologies and the measured performance of the first flight model. CNES is leading the IASI program in association with EUMETSAT. The instrument Prime is ALCATEL SPACE.

/pdf/iasi-instrument-technical-description-and-measured-1tfpntsdt4.pdf

IASI instrument: technical description and measured performances

Measuring the concentration of greenhouse gases from space is a topical challenge. They are measured via a precise
analysis of the signature of chemical gaseous species (CO 2 , CH 4 , CO, etc.) in the spectrum of the Earth's atmosphere.
Two types of spectrometer are commonly used. The first is based on the interference between two radiation waves. The
Infrared Atmospheric Sounding Interferometer (IASI) aboard the METOP satellite is a good example of a fullyoperational
instrument of this kind. The second is based on the use of dispersive optical components. These instruments
must have high radiometric and spectral resolutions in narrow spectral bands to be able to discriminate absorption lines
from various atmospheric chemical species and to quantify their concentration. This is the case, for example, of the
instrument aboard NASA's Orbiting Carbon Observatory (OCO).
Our analysis led us to define a new instrument concept, based on a dispersive grating spectrometer, offering similar
performance in a more compact and therefore less expensive instrument.
After describing this instrument, which uses a specific grating component, a preliminary assessment of performances
will be presented, including the theoretical calculations and formulae. A mock-up version of this specific grating
demonstrated the feasibility of this concept and its capabilities. This preliminary design is encouraging and shows that
such a spectrometer may be compatible with a microsatellite bus. Some prospects for improvement are also considered.

A new space instrumental concept for the measurement of CO 2 concentration in the atmosphere

This paper concerns an original design for a spectro-imager, in which spectral analysis is performed by interferometry, with the necessary path difference being obtained as a direct result of the apparent displacement of the source as seen from the satellite while orbiting. Descriptions will be given of the bread-board model used to determine the feasibility of the project, and of the transportable spectro-imager (SIT) currently being produced at Aerospatiale Cannes (France).

Christian Buil

Papers

IASI instrument: technical overview and measured performances

Static Fourier transform spectroscopy breadboards for atmospheric chemistry and climate

IASI instrument: technical description and measured performances

A new space instrumental concept for the measurement of CO 2 concentration in the atmosphere

Interferometric Spectro-Imager System (ISIS)