FTIR ground-based reference data - Reference profile data collected from the NDACC FTIR network - 15 to 20 stations from pole to pole - Most data available within 2 months to one year after acquisition - Typically 300 km, 3 h co-locations, to be fine-tuned - Application of generic data harmonization protocol (e.g., for vertical regridding and smoothing) Recent example: Validation of MIPAS data product evolution (including newest version) - Vertical CH4 profile and subcolumn comparisons - Bias and spread w.r.t. MIPAS ex-ante uncertainties - Error budget closure via OSSSMOSE simulations - Dependence on influence quantities, long-term trends - Delta-validation of algorithm improvements and of data evolution (here, 3 consecutive MIPAS data versions) Multi-TASTE versatile QA/validation system Methane profile validation for ALTIUS using the Multi-TASTE versatile QA/Validation system A. Keppens ([email protected]), D. Hubert, J. Granville, and J.-C. Lambert (Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium) MIPAS vs NDACC FTIR MIPAS 1σ SYST, DAY Station Lat. Long. Inst. Eureka 80.0 -86.4 U.Tor. Ny-Ålesund 78.9 11.9 IFE/IUP Thule 76.5 291.2 NCAR Kiruna 67.8 20.4 KIT Bremen 53.1 8.8 IFE/IUP Zugspitze 47.4 11.0 KIT Jungfraujoch 46.5 8.0 ULg Toronto 43.6 -79.4 U.Tor. Izaña 28.3 -16.5 KIT Mauna Loa 19.5 -155.6 NCAR Altzomoni 19.1 -98.7 UNAM Paramaribo 5.8 -55.2 IFE/IUP St Denis -20.9 55.5 IASB Mt. Maido -21.1 55.4 IASB Wollongong -34.4 150.9 UWo. Lauder -45.0 169.7 NIWA Arrival Heights -77.8 166.7 NIWA ALTIUS methane profile data - Stratospheric methane (CH4) is an increasingly abundant greenhouse gas, and a major source of stratospheric water vapour through its oxidation, which also produces carbon dioxide (CO2). - ALTIUS will contribute valuable observations of methane concentration in the UT/LS and above, needed for assessments of global changes in atmospheric composition, transport and climate: vert. range 15-45 km, vert. resol. 1 km, uncertainty 2-5 %, global coverage in 3 days - Evaluation of the fitness for purpose of ALTIUS data requires independent data quality assessment and production of appropriate quality indicators use of established Multi-TASTE system ALTIUS vertical range De Mazière et al. (2008)
Transcript
FTIR ground-based reference data - Reference profile data collected from the NDACC FTIR network - 15 to 20 stations from pole to pole - Most data available within 2 months to one year after acquisition - Typically 300 km, 3 h co-locations, to be fine-tuned - Application of generic data harmonization protocol
(e.g., for vertical regridding and smoothing)
Recent example: Validation of MIPAS data product evolution (including newest version) - Vertical CH4 profile and subcolumn comparisons - Bias and spread w.r.t. MIPAS ex-ante uncertainties - Error budget closure via OSSSMOSE simulations - Dependence on influence quantities, long-term trends - Delta-validation of algorithm improvements and of data
evolution (here, 3 consecutive MIPAS data versions)
Multi-TASTE versatile QA/validation system
Methane profile validation for ALTIUS using the Multi-TASTE versatile QA/Validation system
A. Keppens ([email protected]), D. Hubert, J. Granville, and J.-C. Lambert (Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium)
ALTIUS methane profile data - Stratospheric methane (CH4) is an increasingly abundant greenhouse gas, and a major source of
stratospheric water vapour through its oxidation, which also produces carbon dioxide (CO2). - ALTIUS will contribute valuable observations of methane concentration in the UT/LS and above,
needed for assessments of global changes in atmospheric composition, transport and climate: vert. range 15-45 km, vert. resol. 1 km, uncertainty 2-5 %, global coverage in 3 days
- Evaluation of the fitness for purpose of ALTIUS data requires independent data quality assessment and production of appropriate quality indicators use of established Multi-TASTE system
On the validation of ALTIUS stratospheric water vapour profiles with ground-based and in-situ reference data T. Verhoelst, D. Hubert, A. Keppens, and J.-C. Lambert Royal Belgian Institute for Space Aeronomy, BIRA-IASB
2. Application of generic validation protocol 1. Water vapour profile data from ALTIUS (Füssen et al., AMTD, 2016)
4. Horizontal smoothing and co-location mismatch errors
First A
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IUS
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ALTIUS
3. Comparison with reference measurements
Generic validation protocol implemented in BIRA-IASB’s Multi-TASTE versatile satellite QA/Validation system and in FP7 QA4ECV Atmospheric ECV Validation Server (see also Keppens et al., AMT, 2015, and Compernolle et al., EC 2016):
• Data content study: QA/QC diagnostics on data, ex-ante quality indicators and filtering, and identification of spatio-temporal domain of assessment
• Information content study: Analysis of ALTIUS averaging kernels to derive DFS, true vertical resolution, altitude registration error…
• Comparison with ground-based and in-situ reference measurements: deriving differences after co-location and harmonization, determination of bias, spread, drift, dependence on key influence quantities…
Reference data (in 15-30km altitude range, i.e. dry stratospheric air): • Frost-point hygrometers (FPH) with controlled descent: surface – 27km, 10m
vertical sampling (but averaged over 250m), 4% random uncertainty, 10% systematic uncertainty; 3 launch sites operated by NOAA
• Campaign data when available, e.g. aircraft MWR or LIDAR measurements, other in situ sensors such as fluorescence hygrometers,…(e.g. Milz et al., AMT, 2009)
Co-location criteria: spatio-temporal constraints such as 3-12 hours time difference, a few hundred km max. separation, or separate latitude and longitude constraints, complemented with dynamical constraints such as a limit on the equivalent-latitude difference. To be fine-tuned as a compromise between sufficient comparison pairs and minimal impact of atmospheric variability.
Harmonization: smoothing of the high-res data with several techniques. One is with the vertical AK and prior of the low-res data: e.g. smoothed FPH vs. ALTIUS or MWR vs. smoothed ALTIUS. In the latter case, also the a priori can be harmonized.
Post
er b
y K
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et a
l.
Horizontal resolution: • Across track: determined by FOV and scanning sequence. • Along track, i.e. along the line-of-sight (LOS): governed
by atmospheric radiative transfer and by measurement/retrieval sensitivity → Best evaluated by constructing horizontal averaging kernels.
Most limb-viewing instruments (occultation, scattered light, IR limb emission) have horizontal resolutions of the order of 100km and worse along the LOS (e.g. von Clarmann et al., AMT, 2009). Co-location mismatch: 1) Differences in spatio-temporal smoothing between
ALTIUS and reference measurements, 2) sampling mismatch related to the co-location criteria
that were used to construct the comparison pairs. both need to be addressed in the error budget of the data comparisons. They can be estimated with the OSSSMOSE metrology simulator (Verhoelst et al., AMT, 2015, being further extended to several ECVs in H2020 project GAIA-CLIM), as illustrated in the right-hand figure. Measurements and their comparison are simulated by applying multi-D observation operators on high-res gridded fields such as reanalyses.
Scientific target SR6: Measuring trends in UT/LS water vapour, with a focus on the tropical tape recorder and vortex dehydration. Product requirements: • 15-30km altitude range • Global coverage in 3 days • 1km vertical resolution • 25km horizontal resolution • 5% target accuracy, 20% threshold Performance prospects: observations in “bright limb”, “solar occultation”, and “stellar occultation” modes. 20% accuracy reached in occultation mode, BL performance still to be characterized.
Simulation of the error budget of the comparison between MIPAS and balloon-based in-situ H2O VMR measurements in Antarctica (from Lambert et al., ISSI, 2012)
Conclusion: Paucity of reference measurements, high atmospheric variability and
significant differences in horizontal resolution require dedicated efforts to optimize validation strategies and to quantify irreducible co-location mismatch errors, e.g. using the OSSSMOSE simulator.
This study has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640276 (project GAIA-CLIM).
ALTIUS Validation Methodology
Jean-Christopher Lambert, Daan Hubert,
Arno Keppens, Steven Compernolle, Bart Dils,
Bavo Langerock, and Tijl Verhoelst
Royal Belgian Institute for Space Aeronomy (IASB-BIRA)
Total Ozone Validation Protocol (ACC-9, Feb. 2013)
Limb validation heritage
2
NOW
SOUNDER MISSION
S AM II Nimbus 7
S AGE I AE M -B
S AGE II E RBS
HALOE UARS
ORA E URE CA
P OAM II S P OT 3
ILAS ADE OS
P OAM III S P OT 4
S AGE III M eteor-3M
GOM OS E nvisat
S CIAM ACHY E nvisat
ILAS - II ADE OS - II
ACE FT S S CIS AT -1
ACE M AE S T RO S CIS AT -1
S AGE III IS S
AIUS Gaofen-5
LIM S Nimbus 7
S AM S Nimbus 7
UV / V IS / IR S M E
LAS Ohzora
IS AM S UARS
CLAE S UARS
M LS UARS
S M R Odin
OS IRIS Odin
S AGE III M eteor-3M
S ABE R T IM E D
S CIAM ACHY E nvisat
M IP AS E nvisat
HIRDLS E OS Aura
M LS E OS Aura
S M ILE S Kibo JE M /IS S
OM P S Limb S uomi-NP P
S AGE III IS S
ALT IUS E S A E W P
OM P S Limb JP S S -2
2000s 2010s1970sOCCULTATION
LIMB
1980s 1990s 2020s
Spectral range: UV / V IS UV to NIR V IS/ IR IR M W
Domain of application Co-location processing, analysis and documentation
Analysis of co-locations Domain of validity of the validation and statistics
Ozonesonde network co-locations with
GOMOS bright limb (see poster by D. Hubert et al.)
14
Resampling, unit conversions etc.
Different data manipulations and validation processes can provide different results, sometimes with complementary perspectives. It is often valuable (and more scientific) to apply and combine several methods rather than select only one !
Keppens et al., AMT 2015
Resampling, smoothing,
unit conversions…… Resampling, smoothing,
unit conversions…
15
Data comparisons Quality Indicators and their statistics
Data comparisons Quality Indicators and their statistics
influence quantities
16 Illustrations from poster by D. Hubert et al.
Total Ozone Validation Protocol (ACC-9, Feb. 2013)
Earth Watch Element specific
Facilitate EO data delivery to operational services:
1. Harmonized calculation and reporting of uncertainties
• FP7 QA4ECV, H2020 GAIA-CLIM
• SPARC LOTUS, OCTAVE, TUNER
2. Harmonized reporting of validation and quality information
3. Operational QA/geophysical validation facility
4. QA/geophysical validation of Level-3/4 data products
17
Validation of higher level data How really ‘global’ are global networks ?
Verhoelst et al., CCI PM8, 2013; Coldewey-Egbers et al., AMT 2015
Need for objective identification of grid
cells/zones/months where ground-based L3/L4 validation
makes sense (see also poster by Verhoelst et al.)
cci ozone
18
CAMS NDACC Validation Server
19
FP7 QA4ECV Atmospheric
ECV Validation Server
S-5p TROPOMI Mission Performance Centre
Validation Data Analysis Facility
Sentinel-5p and its validation facility to be launched in August !
21
Why validate ALTIUS ?
Geophysical validation is a cross-cutting scientific activity,
contributing to data product development and evolution, and
producing innovative and exciting scientific research !
Without independent, reference-based, user-oriented validation,
we risk:
• Misinterpretation of fictitious patterns and variability
• Wrong (or uncertain) trend assessments
• Too noisy => too many years needed to detect trends
• Erroneous interpretation/non detection of unusual events
• Erroneous conclusions on climate-atmosphere links
• Poorer constraint of NWP, DA, services…
• More hazardous decision making (Montreal Protocol…)
• And many others…
22
THANK YOU !
Use of ALTIUS for exploratory studies in the NIR region and synergies with other instruments
Sébastien Payan1, Claude Camy-Peyret2, Laurence Croizé3
1 - LATMOS - Tour 45, couloir 45-46, 3ème et 4ème étage, Boite 102 , UPMC, 4 Place Jussieu, 75252 Paris Cedex 052 – IPSL (UPMC/UVSQ), Paris, France
3 - ONERA / DOTA / MPSO - Chemin de la Hunière, BP 80100, 91123 Palaiseau Cedex
Figure 1 : Lightening related TLEs - Pasko, 2003
Abstract
References
Objective and Method
Outlook
Atmospheric physics and chemistryIn the troposphere, lightening are important sources of NOx which then influencequantities of O3 and of OH. TLEs might have the same effects in the middleatmosphere.The HALESIS (High Altitude Luminous Events Studied by Infrared Spectro-imagery)project aims to accommodate a spectro-imager aboard a stratospheric balloon in orderto measure disturbed atmospheric radiances in the minutes following a TLE.
Table 1 : Altitudes and duration of TLEs - Pasko, 2010
Transient Luminous Events (TLEs) are electrical and optical events which occurs above thunderstorms. According to their altitude, duration (table 1), size,shape and color we can distinguish four different types (figure 1). The energy deposition of a TLE disturbs the atmospheric composition, which modifiesatmospheric radiances. The interest is dual.
Good ALTIUS coverage of low latitude were TLE occurs frequently : we will exploreexpected quasi-coincidences with TARANIS.We will propose a selection of spectral intervals in the NIR where potentialsignatures of TLE are expected and use/elaborate models for estimating themagnitude of the expected signals
Name Altitude Duration
Blue Jets 10-40 km A few 100 ms
Gigantic Jets 10-90 km A few 100 ms
Sprites 50-90 km 10 ms
Elves or Halos 70-90 km 1 ms
• L. Croizé, S. Payan, J. Bureau, F. Duruisseau, R. Thieblemont, and N.Huret, « Effect of Blue Jets on Atmospheric Composition: Feasibility ofMeasurement From a Stratospheric Balloon », IEEE J. Sel. Top. Appl.Earth Obs. Remote Sens., vol. 8, no 6, p. 3183-3192, June 2015.
• V. P. Pasko, « Atmospheric physics: Electric jets », Nature, vol. 423, no
6943, p. 927-929, June 2003.• V. P. Pasko, Y. Yair, and C.-L. Kuo, « Lightning related transient
luminous events at high altitude in the Earth’s atmosphere:phenomenology, mechanisms and effects », Space Sci. Rev., vol. 168,no 1-4, p. 475-516, 2012.
HALESIS purpose is to study the perturbed atmosphere in the seconds/minutes following the events from stratospheric balloon :• To measure the effect of these events on stratospheric chemistry by retrieving the concentration of species potentially produced or perturbed (NOx,
NO+, O3, OH, ...)• To monitor the vibrationally excited chemical species associated with TLEs;
The main scientific objectives of ALTIUS will mainly be covered by the UV and Vis regions. But the potential afforded by the instrument for spectrally resolvedlimb imaging in the near infrared (NIR) is interesting both in the bright limb geometry and during the night when the limb geometry will be primary used for darkcurrent measurements. Depending on the mission timelines and on the ability to store and download the recorded data, we propose in cooperation with theinstrument team to explore the possibility to extract useful information from spectrally resolved limb images acquired during the night in the NIR spectral regioni.e. 0.9 to 2 µm (5000 to 11000 cm-1). The objectives would be
1) to devise a strategy for selecting specific narrow intervals and for generating average images to lower the detection limit for weak spectral features in thisspectral region,
2) to assign the observed spectral signatures to known species and processes, and
3) to complement the information obtained with the data collected with other instruments and to compare with model results.
One specific example would be HALESIS, a balloon-borne experiment that should document transient luminous effects (TLE)by limb imagery and that should be available in the lifetime of ALTIUS.
Spectral range of the ALTI1US channels and maximum spectral resolution
Context
Complementary approach can be used:- Balloon campaign: a spectro-imager is used to monitor the atmospheric effect of
a TLE after its detection using a high sensitivity panchromatic imager- Satellite approach: Look for quasi-coincidence in time and space (match-up)
between TARANIS (detection) and ALTIUS (limb measurements) for diagnosingthe TLE effects on atmospheric composition
Balloon campaign approach:The chosen strategy is to identify some TLE occurrences from a stratospheric balloon and to infer the local atmospheric composition in the following minutes with an acquisition frequency of about a few hyperspectral cubes every 10 s. This acquisition frequency should make it possible to monitor NO2 but also NO, NO+, and O3 concentration time evolution. To do that, we are currently:- Developing a kinetic model to simulate TLEs impact on atmospheric
vibrational chemistry;- Working on the next generation of hyperspectral imager (see poster 84);- Working on faster radiative transfer model (see poster 83)
Satellite approach:- Identify narrow spectral intervals where TLE should affect significantly
NIR ALTIUS radiances- Design a strategy in cooperation with the mission/instrument team for
combining ALTIUS measurements having internal calibration objectives(dark current) with potentially interesting atmospheric measurements inthe limb during the night
- Prepare dedicated timelines for the specific objective of match-upsbetween ALTIUS and TARANIS
- O3 Wulf band / O2 bands / N2+ (0.92 and 1.105 µm) / N2 (1.04 µm)
ALTIUS wavelength selections foroccultation simulations in the NIRband (nominal mission).
Abstract Altius will be flying in a high-inclination low Earth orbit, offering a vantage point for both
nadir and limb viewing of the atmosphere. At the same time, this provides an interesting
coverage of the upper atmosphere, and in particular the ionosphere, in situ. We propose
to augment Altius by having it carry small scientific instruments as piggyback payloads. In
particular, a Sweeping Langmuir Probe instrument (Altius/SLP) would be appropriate,
since this requires little investments as the instrument exists in a launch-ready cubesat
version (PICASSO/SLP) and as it requires very few resources (limited mass, power,
volume, telemetry, no constraints on spacecraft attitude), making it ideally suited as a
mission add-on. The scientific and partly operational goals would be to provide frequent
coverage of the ionosphere/plasmasphere transition at low magnetic latitudes and an
assessment of the presence of auroras, the size of the polar caps, and thus the energy
input into the magnetosphere from the dayside/nightside reconnection balance, from
monitoring the electron density and ion and electron temperatures along the orbit. A
bonus would be the knowledge of the spacecraft potential, which is an important
diagnostic for understanding the spacecraft environment. Mutual comparison of the
different Altius/SLP Langmuir probes, and comparison with PICASSO/SLP, could provide
unique information regarding the sheath that forms as the spacecraft moves through the
upper ionosphere.
J. De Keyser (1,2), S. Ranvier (1), M. Anciaux (1), E. Gamby (1), H. Lamy (1)
Piggybacking a small Langmuir probe instrument on Altius :
Altius/SLP
Langmuir probe operating principle The basic idea of a Langmuir probe is
straightforward: apply an electric potential
difference between the spacecraft ground (which
corresponds to the potential of the electrically
conducting spacecraft hull) and an electrically
conducting probe that is positioned in the plasma
environment at some distance from the
spacecraft, and then measure the electric current
that flows in response to this potential difference.
This current is due to the collection of ions or
electrons on the probe surface. In a sweeping
Langmuir probe, the applied potential is varied
over a certain range, so that the current-voltage
characteristic is obtained, from which one can
determine
• the electron density and temperature, as well
as the ion temperature (making certain
assumptions about the plasma velocity
distributions).
• the spacecraft potential relative to the ambient
plasma.
Accommodation We propose to use the SLP sweeping Langmuir probe instrument
developed by BIRA-IASB for the PICASSO cubesat on Altius. We will
operate the Langmuir probes also in antenna mode, that is, letting the
probes float at the ambient potential, so that it performs an electric field
measurement. This will require minor changes to the design.
The major issue for accommodating SLP on Altius are the booms. Ideally, 2
deployable booms of >1.5 m length would be needed. Such booms would
keep the probes far enough from the spacecraft, and would prevent (most
of the time) that one of the probes is in the plasma wake. If such booms are
not available, one can opt for installation of several probes on small
deployable masts near the corners of the spacecraft. The longer the
booms, the more accurate the electric field values.
We might envisage a combination of cylindrical and spherical Langmuir
probes. That would offer different means to determine the physical
parameters so as to be able to check the underlying hypotheses. Another
option is to use different coatings on different probes, since there have
been some concerns about the influence of surface processes on the aging
of Langmuir probes, especially in LEO where atomic oxygen is prevalent.
Conclusion The SLP Langmuir probes are ideal instruments for piggy-backing: As they have been designed for a CubeSat platform,
they demand limited mass, power, and volume resources. Using rather short booms, they can be mounted on the
spacecraft body or on the deployable solar panel. The instrument does not demand a specific attitude. If used in a
“monitoring” mode, it would not require much telemetry bandwidth either. Nevertheless, the science case is compelling:
as the Altius satellite will fly in a polar orbit at an altitude of ~600 km, it would provide an ideal platform to scan ion and
electron density and electron temperature in the upper ionospheric F-region, providing information on the base of the
plasmasphere (at low magnetic latitude) and about the location of auroras and the size of the magnetic polar cap (at high
magnetic latitude), which represent quantities that are important from a space physics point of view. Knowledge of
spacecraft potential may be interesting for Altius from an engineering standpoint to monitor spacecraft charging.
Science case The instrument would be operated in a monitoring mode that permits
the continuous study of the plasmasphere, the auroral region, and
the polar caps. The regular coverage of all latitudes and all magnetic
local times would facilitate finding (magnetic) conjunctions with other
spacecraft. It would be particularly interesting to combine these data
with those of EISCAT or its successor EISCAT-3D in the context of
the study of the auroral ionosphere. Depending on the number of
booms, the plasma sheath surrounding Altius could be examined.
The instrument would be suited to cover the typical densities and
temperatures encountered in the regions of interest.
Acquisition rate of spectra: 8 HzResponse time: 1 to 3 seconds, depending on altitudeVertical resolution on stratospheric balloon: 5m at 1sOperation range : from ground to >35 kmMaterials adapted to sticky molecules : electropolishedstainless steel, PFA or amorphous silicon coatingSmall sample volume: < 100 cm3
Measurement dynamic range : 104 to 105
Patrick JACQUET, Valéry CATOIRE, Michel CHARTIER, Claude ROBERT, Gisèle KRYSZTOFIAK, Nathalie HURET Laboratoire de Physique et Chimie de l’Environnement et de l’Espace (LPC2E), UMR CNRS-Université Orléans, France
Daniele ROMANINILaboratoire interdisciplinaire de Physique (LIPHY), UMR CNRS-Université Grenoble Alpes, France
SPECIES: a multi-channel infrared laser spectrometer with optical-feedback cavity-
enhanced absorption (OF-CEAS) for in situ balloon-borne and airborne measurements
Over the last decades, thanks to significant technological advances in measurement techniques, our understanding of the chemistry and dynamics of the upper
troposphere and stratosphere has progressed significantly. However some key questions remain unsolved and new ones arise in the climate change context. The full recoveryof the ozone layer in a period of halogens decrease and N2O increase (and the delay of this recovery), the impact of the climate change on the stratosphere and the role ofthis one as a feedback are very uncertain. To address these challenges, one needs instruments able to measure a wide variety of trace gases simultaneously with a widevertical range, combined to chemical and dynamical modelling at different scales.LPC2E and LIPHY laboratories are developing a new balloon-borne and airborne instrument:SPECIES (SPECtromètre Infrarouge à lasErs in Situ). Based on the Optical Feedback Cavity Enhanced Spectroscopy (OF-CEAS) technique combined with mid-infrared quantumor interband cascade lasers (QCLs or ICLs), this instrument will offer unprecedented performances in terms of vertical extent of the measurements, from ground to themiddle stratosphere, and number of molecular species simultaneously measured with sub-ppb detection limits (e.g. O3, N2O, HNO3, NH3, H2O2, HCl, HOCl,CF2O, CH4, CH2O,CO, CO2, OCS, SO2). Due to high frequency measurement (>0.5 Hz) it shall offer very high spatial resolution (a few meters).
Context
SpeciesTheoritical LOD(1s averaging,
5 km absorption path)Species
Theoritical LOD(1s averaging,
5 km absorption path)
N2O 30 pptv HCl 50 pptv
NO 400 pptv O3 6 ppbv
NO2 50 pptv H2O2 100 pptv
HNO3 100 pptv HCHO 300 pptv
NH3 800 pptv HCOOH 400 pptv
OCS 25 pptv CO 3 ppbv
SO2 200 pptv CO2 400 ppbv
COF2 200 pptv CH4 500 pptv
HOCl 200 pptv
Performances SPECIES mechanical design
* Other measurable species : HCN, CH3CN, HONO, CH3Cl, ClONO2, HF…
< 20 kg
OF-CEAS principle applied to SPECIES
Without Optical-Feedback With Optical-Feedback (laser and cavity in phase)
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OF-CEAS* Optical scheme
Falcon-20 (SAFIRE, CNRS – Météo France)
Acknowledgements: This work was funded by the French space agency CNES, the LabexVOLTAIRE (ANR-10-LABX-100-01), and the PIVOTS project from the Région Centre – Val de Loire (ARD 2020 program and CPER 2015-20).
Example of spectrum obtained for the optical bench of the OCS channel (@4.87µm) :- 104 scanned modes (0.5 cm-1)- Ring-down of 17 microseconds Equivalent optical absorption length for low absorptions of 10 km- Signal/Noise at the top of modes: about 10000- Precision on the ring down: better than 1/1000- Search and locking time of the piezo on a mode of the cavity: a few seconds- Rejection of the deformations of the optical bench: from 0 to about 20 Hz
𝑥 −𝑡𝜏
time
Laser interruption
Ring down measurement
- Modular design: 3 to 6 modules (19” racks)
- Each individually measuring 2 species or more
- Measured species can be easily selected depending on scientific objectives
* Optical Feedback Cavity Enhanced Spectroscopy (Morvilleet al., Appl. Phys. B 2005; Romanini et al., Appl. Phys. B 2006)
OF-CEAS advantages:• Absolute measurement (no
calibration gases required)• Frequency self-calibrated spectra
(without frequency reference)• Effective path length of several km
retrieved with a single ring-down measurement
• Extended dynamic range compared to direct absorption spectrometry
• Optimized mode injection high signal output, especially important considering the lowering of detection sensitivity in mid-IR
• Does not require expensive optical component such as optical isolators, optical switch or large area photodetectors
• Negligible apparel width : at resonance laser width is about 10 kHz
