An atmospheric limb sounder proposed by the Belgian Institute for Space Aeronomy ALTIUS Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere Didier Fussen, Emmanuel Dekemper, Didier Pieroux, Jurgen Vanhamel, Bert Van Opstal, Filip Vanhellemont, Nina Mateshvili, Ghislain Franssens 7th Limb Conference @ Bremen / Jun-2013 / E-Mail: [email protected] Courtesy of Dr J-C Lambert There was a dramatic decrease in the number of vertical atmospheric sounders: during the 2005-2006 period, 4 missions were interrupted: SAGE II , HALOE, SAGE III, POAM III April 2012: ENVISAT died … ENVISAT (2002-2012) Important progresses have emerged to perform atmospheric remote sounding with high vertical resolution. PAST FUTURE SOUNDER SOUNDER Limb sounding allows for a global coverage in 1-3 days !!! PAST FUTURE Limb scan Full 2-D limb imaging Filter or grating spectrometers Acousto-optical filters ALTIUS uses the simple concept of a spectral camera, i.e., a combination of an AOTF filter with a 2-D imager HYPERSPECTRAL CUBE (wavelength x space) x space = wavelength x (space x space) Altitude registration of ALTIUS FOV Limb imaging is a powerful tool! VIS image 10 20 30 40 50 60 10 20 30 40 50 60 NIR image 10 20 30 40 50 60 10 20 30 40 50 60 PSC’s with mono- or bimodal ...from cirrus or convective clouds structure can be distinguished... II.2 Sun shape analysis Due to the diffraction by the atmosphere, the Sun appears higher than its actual position. Its shape is also flattened. By solving the inverse ray-tracing problem, atmospheric density profile can be retrieved. By studying the Sun apparent shape, the presence of clouds/PSC/PMC can be detected. II.2 Profile retrieval Assuming hydrostatic equilibrium, T profiles can be retrieved using the Zernike moments of the successive images of the refracted Sun disk. Acousto-optic cell of an AOTF on base of TeO2 or KDP a = 1.5 cm crystal Diffracted light L = 2.8 cm Incident light Spectral imaging with AOTF Acousto‐Optical Tunable Filters have a number of advantages for remote sensing from space instruments: ‐ robust, light and compact device (a few hundred g and cm3) ‐ small power consumption (0.1‐3W) ‐ quick wavelength selection (ms) ‐ up to 100% efficiency (TeO2) ‐ moderate bandwidth (0.5‐3 nm, λ‐dependent) Spectral imaging with AOTF Illustration of spectral capabilities with the ALTIUS visible channel breabdoard. Spectral picture taken with ALTIUS vis. ch. BB NO2 detection by DOAS at 645 nm. Spectral imaging with AOTF: easy DOAS implementation Dekemper et al., Appl. Opt. 51 (25), 2012 Spectral imaging with AOTF in the UV: a more challenging issue… TeO2 KDP crystals The collabo..) Preliminary results: it works! AOTF. O3 Chappuis band UV spectral images Ozone Chappuis band Importance of UV-channel for ozone retrieval error λ (nm) 312.5 318.5 575.1 604.5 759.9 I.T. (s) 4.5 4.5 3 3 3 H. bin. 20 20 20 20 20 Altitude range (km) Total error (%) Horizontal resolution (km) Vertical resolution (km) 10 – 50 < 5 10 0.5 ALTIUS multimode observations Global coverage can easily be achieved in three days… Star occultations... Unlike GOMOS, ALTIUS would not need a sophisticated star tracker... Transmission spectra From static forward/side mode to dynamic tomography... Get access to the 3D-ozone field... Full 3-D global coverage by a tandem of micro-satellites: a dream ? Scientific requirements Total Spatial res. Atmosph. Spectral Occulta- Priority Species error Limb (∆z,∆y,∆x) region range (nm) tion (%) (km) O3 UT/LS 5 550-650,1020 x x 500,10,1 300-350/550- O3 US 5 x x 500,10,1 A 650 250-300, O3 MS 20 x500,NA,1 1260-1280 NO 2 LS/US 30 450-550 x x 500,50,2 CH 4 UT/LS 20 1600-1800 x x 500,50,2 B H2O UT/LS 20 900-1800 x x 500,50,2 CO 2 UT/LS 2 1550-1600 x x 500,50,2 BrO UT/LS 20 320-360 x 500,50,1 OClO UT/LS/US 25 320-400 x 500,NA,1 NO 3 LS/US 25 662 x 500,NA,1 aerosol/PSC UT/LS 25 250-1800 x x 500,20,1 C 1260- O2 MS 30 x500,NA,5 1270/1530 PMC MS 50 250-1800 x x 500,20,1 Reminder ALTIUS is a limb sounder spectrometer, capable of a 0.5 km vertical sampling. It consists of three independent spectral camera’s (optics+AOTF+2-D imager) in the UV- Vis-NIR range (250-1800 nm). The instrument, on board a heliosynchronous micro- satellite, is operated in a multi-mode approach (limb, solar occ, stellar occ) using nominal and campaign/calibration scenarios. It allows for 3-D atmospheric tomography. The main geophysical targets are strato/mesospheric ozone profiles and minor trace gases (NO2,H2O, BrO, CH4, aerosols, temperature..). PROBA Introduction Key figures • Mass : 100 – 130 kg (25 – 40 % P/L) • Launch : October 22th 2001 by PSLV • LEO, Sun Synchronous orbit, ~600 km • Volume : 80cm x 60cm x 60cm • Originally 1 year of mission • Power : 30 to 50 W average platform, • Succesfully in more then 3,5 year 120 W peak •PROBA 2 launch: 2007, Rockot • Compatible with PSLV /DNEPR/ ASAP5/ Rockot • High pointing accuracy (0.015° 2sigma) • Powerfull computer (up to 100 MIPS) Spacecraft: External Accomodation 670 mm (Z) x 670 mm (X) x 860 mm (Y). Spacecraft Accomodation: Internal Payload accomodation • Initial Volume constraint (H x L x W ) : 260 x 500 x 547 mm3 • End of phase B0 : 320 x 500 x 547 mm3 Preliminary design VIS channel AOTF and polarizers CMOS detector Limb/Solar/Stellar aperture Mechanism Pointing Proven pointing accuracy from PROBA 2 data SWAP reported in this review: - an absolute pointing error of 10 pixels was observed, this relates to 30 arcsec (->150 microrad = 400 m). - relative pointing error (most important for ALTIUS) is < 3 arcsec (15 microrad) over 5 seconds PARAMETER OPTIMIZED with margins size 320 x 500 x 547 mm3 weight 56.2 kg power 32.7 W science data 3.7 Gigabits / orbit downlink 30 min /day The ALTIUS story so far…. • 2005: preliminary ideas (thanks to SAGE III and OSIRIS limb success) • Jan 2006 – Nov 2006: phase 0 study / CDF review • Oct 2007: phase A preliminary review • Jun 2009: phase A final review • Feb 2011: phase B0 review • Oct 2011: First ASAG meeting • Jun 2012: phase B1 RFQ sent to industry • Dec 2012: Industry proposals rejected • Spring 2013: re-issue of RFQ’s for platform/payload Phasing… B0 B1 B2 C0 C1 D0 ... 8m 2m 2m 6m 6m 12 m PFM MAIT General I/F Concept to STM PFM Completion of P layout P /L definition STM design MAIT design KOCoDR PDRPre - CDR PFM AR FAR CDR Preliminary design Detailed design BB testing STM MAIT ELM design ELM MAIT P/L PFM MAIT Eval PFM PFS MAIT Eval FPS P /F STM design P /F STM MAIT P /F PFM design P /F PFM MAIT P/F P /F system engineering / mission analysis SDR CDR OIP task P /L and P /F interaction VE task Why to propose the ALTIUS mission? A summary: 1. Monitoring of global changes is impossible without stratospheric measurements. 2. Dramatic decrease of available (and, in particular, European) instruments capable of a vertical remote sounding of the atmosphere. 3. New and promising technologies are emerging. 4. Many potential communities to use data and to promote the ALTIUS concepts from a scientific level to an operational capacity. Spare slides Mass budget: Payload Budget: Mass and volume • Total mass: 168 kg (incl margin 5%) • Payload : 56,2 kg (incl margin 20%) • Launch volume of the box: 670 mm (Z) x 730 mm (X) x 860 mm (Y). Payload Power consumption • Initial power consumption: 54 W (45W + 20% margin) which includes: UV detector FPA 0.29 UV detector FEE 1.14 VIS detector FPA 0.29 VIS detector FEE 1.14 TEC cooler for UV 5 TEC cooler for VIS 5 SWIR FPA 0.29 Detector FEE 1.14 Stirling cooler 7.14 UV AOTF RF Amplifier 4.29 Vis AOTF RF Amplifier 2.14 NIR AOTF RF Amplifier 4.29 Provision for Power needed for the mechanism stepper motor Power needed for the pin puller for fail safe mechanism Provision for baseplate heating Power consumption of the main electronics including: o Central control board with FPGA o DDS based RF generator (low power) o HSK board o Image handling board o Mechanisms control logic o TM/TC interface with S/C 12.86 TOTAL 45.01 20% Margin 9.002 TOTAL with margin 54.012 Payload power consumption But • Duty cycle of the instrument (16% during the limb + SO, 30% during the stellar occultation) • Decrease of the TEC power consumption (for a lower P/L temperature) => 2.5 W in place of 5W (UV and VIS) • NIR channel in stand by mode during stellar occultation Total Power consumption Power budget • Worst case (EoL, worst case solar flux, 10% system margin,…) Nominal Scenario ( Backward pointing in the limb + solar occultation + stellar occultation) : positive ( +0,17 W over 24 h) Left looking scenario : positive ( with a sunbathing orbit) Tomography mode : positive (with a sunbathing orbit) Thermal budget • No active cooling of the Payload except for – NIR detector with a Stirling cooler – VIS and UV detector with a TEC • Passive thermal cooling Payload Straps Radiator Dark space • Goal : Thermal design should guarantee errors due to thermal effect will be less than ½ pixel Data Volume • Based on the characteristics of the – NIR channel: SOFRADIR NEPTUNE detector – UV and VIS channels: CMOS sensor from Caeleste • Windowing during stellar and solar occultation for all channels • Compression (0.7 for limb, 0.4 for SO and StO) Science data volume : 3.63 Gbit/orbit Housekeeping : 01Gbit/orbit Ground Station Redu (Belgium) – 1704 ground‐contacts per year – 4.7 passes per day (average) – 34.5 minutes per day contact (average) – 7.4 minutes per pass contact (average) – 705 minutes worst‐case gap time between 2 contacts Link budget • Downlinking : – 2 X‐Band Antennas (one for the redundancy).