The ALTIUS mission. Status and expected performance of O 3, NO 2 and aerosols limb measurements

Transcription

1 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

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

3 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...

4 The limb gap Status today: Limb instruments beyond their nominal lifetime: OSIRIS: ACE: MLS: +13 years (launched in 2001, 2 years lifetime) +11 years (launched in 2003, 2 years lifetime) +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

5 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

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

7 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!

8 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)

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

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

11 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

12 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

13 Current ALTIUS design mass power orbit pointing P/L: 57kg, S/C: 174kg P/L + S/C on duty: 122W (avg) 650km LEO, 10:30 LTDN, 3±0.2 days revisit time jitter: < 25µrad (2σ, over 5sec)

14 Current ALTIUS design UV VIS NIR UV VIS NIR spectral range filter type detector type spectral res Fabry-Perot AOTF (TeO2) AOTF (TeO2) CMOS CMOS HgCdTe field of view image sampling spatial sampling nm 2-9 nm 2-9 nm scene size 2 x2 2 x2 2 x2 171x x x m 200 m 400 m 100x100 km 100x100 km 100x100 km

15 Current ALTIUS design

16 Priority ALTIUS scientific objectives (all three measurement modes) Observable Vertical range Vertical res. [km] Horizontal res. along parallels [km] Horizontal res. along meridians [km] Total error [%] Coverage Photochemistry [day/night] A O 3 UT-LS global d/n A O 3 US global d/n A O 3 MS polar n B NO 2 LS-US global d/n B H 2 O UT-LS global d/n B CH 4 UT-LS global d/n B aerosol UT-LS global d/n B PSC UT-LS polar d/n C PMC MS polar d/n C OClO LS-US global n C BrO UT-LS global d C NO 3 LS-US global n C T LS-MS 2 2 C gradients LS-US global d/n

17 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.

18 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

19 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)

20 O3 L2-data performance Typical O3 measurement scheme: Ratio Wavelengths Alt. Range Norm. Alt. Heritage Doublet 1 λ s : 300 nm λ w : 351 nm km 65 km OSIRIS Doublet 2 λ s : 315 nm λ w : 351 nm km 55 km OSIRIS λ w1 : 525 nm Triplet λ s : 600 nm km 45 km SOLSE/LORE λ w2 : 675 nm

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

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

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

24 O3 L2-data performance Retrieval error based on measurement error (MAP solution, black line follows minimum SNR requirements, red assumes current performance): Error Error source 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% 7.8% 2.7% 2.8% 2.8% 4.3% 5.7% 5.1% 7.3% (5.4) (5.1) (1.4) (2.2) (2.2) (3.7) (5.1) (4.4) (5.7)

25 O3 L2-data performance How does ALTIUS O3 L-2 product compare with OPEROZ requirements? Vertical coverage (km) Along-track Sampling B/T (km) LS MS US Horizontal coverage Global, incl. polar night Global, incl. polar night Global, incl. polar night Vertical resolution B/T (km) Update Frequency B/T (h) Uncertainty B/T (%) Daily Weekly 4 8 Timeliness Stability B/T < 3 hours 1 / 3 %/decade

26 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 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

27 Importance of occultations

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

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

30 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. Ratio Wavelengths Alt. Range Norm. Alt. Heritage Doublet λ s : nm λ w : nm km 45 km POAM III Typical total uncertainty: 10-20%

31 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: /amt )

32 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.

33 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.

34 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. Ratio Wavelengths Alt. Range Norm. Alt. Heritage Doublet λ 1 : 470 nm λ 2 : 1020 nm km 8 km OSIRIS, SAGE II Typical uncertainty on the extinction coefficient: 10%.

35 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)...