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

The ALTIUS mission Status and expected performance of O 3 , NO 2 and aerosols limb measurements E. Dekemper 1 , D. Fussen 1 , D. Pieroux 1 , F. Vanhellemont 1 , J. Thoemel 1 , N. Mateshvili 1 , G. Franssens 1 , Q. Errera 1 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 observations...”

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 O 3 limb mission based on 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 grating (horizontal slit) vertical scans occult. SAGE-III solar occult. + limb grating (horizontal slit) vertical scans scattering OMPS-LP limb scattering prism (vertical slit) stare ALTIUS limb scattering + solar AOTF spectral image occult. + stellar occult.

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) O 3 (but also NO 2 and aerosols f.i.) can be retrieved from a small number of 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) 650km LEO, 10:30 LTDN, 3±0.2 orbit days revisit time pointing jitter: < 25µrad (2σ, over 5sec)

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

Current ALTIUS design

ALTIUS scientific objectives (all three measurement modes) Horizontal Horizontal Total Photo- Vertical Vertical res. along res. along Priority Observable error Coverage chemistry range res. [km] parallels meridians [%] [day/night] [km] [km] A O 3 UT-LS 1 10 500 5 global d/n A O 3 US 1 10 500 5 global d/n A O 3 MS 1 50 500 20 polar n B NO 2 LS-US 2 50 500 30 global d/n B H 2 O UT-LS 2 50 500 20 global d/n B CH 4 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 NO 3 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 operational 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 operational 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 λ s : 300 nm Doublet 1 35-60 km 65 km OSIRIS λ w : 351 nm λ s : 315 nm Doublet 2 30-50 km 55 km OSIRIS λ w : 351 nm λ w1 : 525 nm Triplet λ s : 600 nm 10-40 km 45 km SOLSE/LORE λ w2 : 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 Error 15km 20km 25km 30km 35km 40km 45km 50km 55km source Type 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% 8.6% 7.8% 2.7% 2.8% 2.8% 4.3% 5.7% 5.1% 7.3% Total (5.4) (5.1) (1.4) (2.2) (2.2) (3.7) (5.1) (4.4) (5.7)

O3 L2-data performance How does ALTIUS O3 L-2 product compare with OPEROZ requirements? Vertical Along-track Vertical Update Horizontal Uncertainty coverage Sampling resolution Frequency coverage B/T (%) (km) B/T (km) B/T (km) B/T (h) Global, incl. LS 100 200 1 2 12 24 8 16 polar night Global, incl. MS 100 200 1 2 12 24 4 8 polar night Global, incl. US 200 400 2 4 Daily Weekly 4 8 polar night 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 occultation event predictor) - O3 profiles at each ALTIUS measurement location were kept as synthetic observations - no bias was assumed, but typical ALTIUS error bars (dependent on observation 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: