The ALTIUS mission Status and expected performance of O 3 , NO 2 and - - PowerPoint PPT Presentation

The ALTIUS mission

Status and expected performance of O3, NO2 and aerosols limb measurements

• E. Dekemper1, D. Fussen1, D. Pieroux1, F. Vanhellemont1, J. Thoemel1, N.

Mateshvili1, G. Franssens1, Q. Errera1

1 BIRA-IASB, Brussels, Belgium

The limb gap ALTIUS’ inception dates back to 2006, just after the golden age of limb sounding. (from NDACC/satellite working group, 2006 assessment)

The limb gap GCOS 2010 implementation plan: Action A26: “Establish long-term limb-scanning satellite measurement of profiles of water vapour, ozone and other important species from the UT/LS up to 50 km.” ATMOS 2012 (Brugge, Belgium): R11: “To understand better interaction between the troposphere and the stratosphere a satellite mission providing limb measurements with high vertical resolution in the UT/LS region is required.” ATMOS 2015 (Heraklion, Greece): (GHG and future missions panel) R8: “It is again recommended to perform altitude-resolved atmospheric composition observations (≥ UTLS), i.e., actions need to be taken to close the limb gap.” O3 symposium 2016 (Gothenburg, Scotland):

• N. Livesey: “The looming chasm in spaceborne limb sounding
• bservations...”

The limb gap Status today: Limb instruments beyond their nominal lifetime: OSIRIS: +13 years (launched in 2001, 2 years lifetime) ACE: +11 years (launched in 2003, 2 years lifetime) MLS: +7 years (launched in 2004, 5 years lifetime) Limb instruments aging: OMPS-LP: +0 years (launched in 2011, 5 years lifetime) Limb instruments foreseen: SAGE-III: 2016, 5 years ALTIUS: 2020, 5 years OMPS-LP: 2022, 7 years

ALTIUS origin In 2006, D. Fussen saw an opportunity for starting an O3 limb mission based

• n national funding scheme.

Known political constraints:

• small mission fitting within Belgium’s ressources
• based on the PROBA micro-satellite platform

=> ALTIUS would be a UV-VIS-NIR instrument

ALTIUS origin Limb scattering technique provides the largest coverage, but no nighttime measurement => no polar night measurements (Heritage: OSIRIS, SCIAMACHY, SAGE-III, OMPS-LP)

ALTIUS origin All limb scattering instruments have experienced serious issues with the determination of the line of sight tangent altitude. 20% error for 500m bias!

ALTIUS origin Solar occultation yields the largest SNR => best precision, but only two measurements/orbit and still no polar night measurements (Heritage: SAGE-II, SAGE-III, SCIAMACHY)

ALTIUS origin Stellar/planetary occultations offer nighttime sounding, but a sparse coverage. (Heritage: GOMOS)

ALTIUS origin Most past and present UV-VIS-NIR limb sounders were based on grating spectrometers requiring mechanical scanning or tracking systems.

Measurement mode spectrometer technology method for covering the limb SAGE II solar occult. filters sun tracker GOMOS stellar occult. grating (horizontal slit) strack tracker OSIRIS limb scattering grating (horizontal slit) vertical scans SCIAMACHY limb scattering + solar

• ccult.

grating (horizontal slit) vertical scans SAGE-III solar occult. + limb scattering grating (horizontal slit) vertical scans OMPS-LP limb scattering prism (vertical slit) stare ALTIUS limb scattering + solar

• ccult. + stellar occult.

AOTF spectral image

ALTIUS origin Most past and present UV-VIS-NIR limb sounders were based on grating spectrometers requiring mechanical scanning or tracking systems. Advantages:

• broad spectral range sampled
• all species measured at the same time

Drawbacks:

• mechanisms can fail...
• tangent altitude determination not easy
• scanning time

ALTIUS origin Decision chain that led to the ALTIUS mission concept: 1) mechanisms should be avoided (add risk and complexity) => a true imager captures the atmosphere at once 2) O3 (but also NO2 and aerosols f.i.) can be retrieved from a small number

• f wavelengths

=> dispersive elements not mandatory for atmospheric remote sensing => filters can do the job (SAGE-II) 3) imaging + filtering => spectral imaging Advantages:

• simpler and various pointing calibration schemes
• higher vertical sampling
• occultations performed without complex tracking mechanisms

4) PROBA platform agility offers all three measurement modes: =>ALTIUS will perform day and night measurements: limb scattering + Solar occultation + stellar occultations

Current ALTIUS design

mass P/L: 57kg, S/C: 174kg power P/L + S/C on duty: 122W (avg)

• rbit

650km LEO, 10:30 LTDN, 3±0.2 days revisit time pointing jitter: < 25µrad (2σ, over 5sec)

Current ALTIUS design

UV VIS NIR UV VIS NIR spectral range 250-400 440-800 900-1800 field of view 2°x2° 2°x2° 2°x2° filter type Fabry-Perot AOTF (TeO2) AOTF (TeO2) image sampling 171x171 512x512 256x256 detector type CMOS CMOS HgCdTe spatial sampling 600 m 200 m 400 m spectral res. 2-2.5 nm 2-9 nm 2-9 nm scene size 100x100 km 100x100 km 100x100 km

Current ALTIUS design

ALTIUS scientific objectives (all three measurement modes)

Priority Observable Vertical range Vertical

• res. [km]

Horizontal

• res. along

parallels [km] Horizontal

• res. along

meridians [km] Total error [%] Coverage Photo- chemistry [day/night] A O3 UT-LS 1 10 500 5 global d/n A O3 US 1 10 500 5 global d/n A O3 MS 1 50 500 20 polar n B NO2 LS-US 2 50 500 30 global d/n B H2O UT-LS 2 50 500 20 global d/n B CH4 UT-LS 2 50 500 20 global d/n B aerosol UT-LS 1 20 500 25 global d/n B PSC UT-LS 1 20 500 25 polar d/n C PMC MS 1 20 500 50 polar d/n C OClO LS-US 1 50 500 25 global n C BrO UT-LS 1 50 500 20 global d C NO3 LS-US 1 50 500 25 global n C T° LS-MS 2 2 C gradients LS-US 1 10 10 30 global d/n

Current status of the mission In December 2015, ALTIUS passed two critical reviews organised by ESA:

• OPEROZ: operational ozone capabilities
• science added value

In December 2016, ALTIUS will officially become an element of the Earth Watch programme (ESA/EO). Scientific developments never stopped (PRODEX programme). Industrial phases will resume in 2017.

Current status of the mission The agreement between BELSPO and ESA is that ALTIUS will satisfy

• perational requirements for the O3 profiles product.

Lead author:

• M. Van Weele

Current status of the mission The agreement between BELSPO and ESA is that ALTIUS will satisfy

• perational requirements for the O3 profiles product.

The aim is to meet the OPEROZ minimum mission requirements to fullfill the needs of two user communities:

• U1: operational users (atmosphere monitoring, NWP, air quality,...)
• U2: long-term monitoring (Montreal Protocol)

O3 L2-data performance Typical O3 measurement scheme:

Ratio Wavelengths

• Alt. Range
• Norm. Alt.

Heritage Doublet 1 λs : 300 nm 35-60 km 65 km OSIRIS λw : 351 nm Doublet 2 λs : 315 nm 30-50 km 55 km OSIRIS λw : 351 nm Triplet λw1 : 525 nm 10-40 km 45 km SOLSE/LORE λs : 600 nm λw2 : 675 nm

O3 L2-data performance Sensitivity of the limb measurements to the O3 concentration:

O3 L2-data performance Sensitivity of the retrieved O3 profile to the actual O3 state: (averaging kernels + vertical resolution)

O3 L2-data performance Retrieval error based on measurement error (MAP solution, black line follows minimum SNR requirements, red assumes current performance):

O3 L2-data performance Retrieval error based on measurement error (MAP solution, black line follows minimum SNR requirements, red assumes current performance):

Error source Error Type 15km 20km 25km 30km 35km 40km 45km 50km 55km SNR random 7%(2) 6%(1) 2.5%(1) 2%(1) 2%(1) 3%(2) 4%(3) 4%(3) 6%(4) Pointing bias 5% 5% 1% 2% 2% 3% 4% 3% 4% Spectral bias 0% 0% 0% 0% 0% 0.5% 1% 1% 1% Total 8.6% (5.4) 7.8% (5.1) 2.7% (1.4) 2.8% (2.2) 2.8% (2.2) 4.3% (3.7) 5.7% (5.1) 5.1% (4.4) 7.3% (5.7)

O3 L2-data performance How does ALTIUS O3 L-2 product compare with OPEROZ requirements?

Vertical coverage (km) Along-track Sampling B/T (km) Horizontal coverage Vertical resolution B/T (km) Update Frequency B/T (h) Uncertainty B/T (%) LS 100 200 Global, incl. polar night 1 2 12 24 8 16 MS 100 200 Global, incl. polar night 1 2 12 24 4 8 US 200 400 Global, incl. polar night 2 4 Daily Weekly 4 8

Timeliness < 3 hours Stability B/T 1 / 3 %/decade

Importance of occultations Does the relatively small number of occultations in polar night suffices to constraint the polar O3 field? An OSSE was performed with BASCOE to assess the value of ALTIUS O3 data compared to MLS O3 data. Methodology:

• BASCOE generated a global O3 field from July to October 2008.
• orbits of ALTIUS were generated with the orbital model (including an
• ccultation event predictor)
• O3 profiles at each ALTIUS measurement location were kept as synthetic
• bservations
• no bias was assumed, but typical ALTIUS error bars (dependent on
• bservation mode) were associated to the synthetic observations
• different assimilation runs were performed with BASCOE
• a free model run
• assimilation of the full MLS data set
• assimilation of different combinations of ALTIUS measurements

Importance of occultations

Importance of occultations Comparison of free run, MLS, and all ALTIUS measurements assimilation at 55hPa:

Importance of occultations Capability of the different ALTIUS measurement modes to constrain the model.

NO2 measurements OMPS-LP is not capable of measuring NO2 because of a poor spectral

• resolution. ALTIUS could be the only instrument delivering NO2 profiles

after 2020, with potential synergies with the Sentinels to get the tropospheric column. Typical total uncertainty: 10-20%

Ratio Wavelengths

• Alt. Range
• Norm. Alt.

Heritage Doublet λs: 439.6 nm 10-40 km 45 km POAM III λw: 442.2 nm

Proof of concept with the NO2 camera A lab prototype of the visible channel is now the first NO2 camera. (Dekemper et al.: “The AOTF-based NO2 camera”, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-237.)

Proof of concept with the NO2 camera The instrument was pointed to a coal-fired power plant in Romania to measure the NO2 content in the flue gas.

Proof of concept with the NO2 camera The instrument was pointed to a coal-fired power plant in Romania to measure the NO2 content in the flue gas.

Aerosol measurements Simulations for the retrieval of the aerosol extinction coefficient along the limb line of sight showed good results, with the driving error being the tangent altitude determination. Typical uncertainty on the extinction coefficient: 10%.

Ratio Wavelengths

• Alt. Range
• Norm. Alt.

Heritage Doublet λ1: 470 nm 12-35 km 8 km OSIRIS, SAGE II λ2: 1020 nm

Open questions Not everything is frozen at the moment. There may be room for adjustments at the level of both the instrument, and the mission. Here are a few questions worth considering before going futher in EarthWatch with ALTIUS. 1) What if ALTIUS was looking side track instead of along track in limb mode? Benefit: unprecedent horizontal resolution capturing latitudinal gradients. 2) What is the desired ground sampling for O3, NO2 and aerosols? 3) What are the needs in terms of aerosol profiles? Which parameters? (extinction, angström coef., PSD, mode radius, number density,...) 4) Do you see any potential synergy with another instrument that we didn’t identified so far? 5) ...