A stratospheric remote sounding experiment on a microsatellite: ALTIUS Atmospheric Limb Tracker for

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A stratospheric remote sounding experiment on a
micro-satelliteALTIUSAtmospheric Limb
Tracker for Investigation of the Upcoming
Stratosphere
Dr. Didier FUSSEN didier_at_oma.be
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Motivations

• More and more attention is paid to the
  troposphere because of direct environmental
  effects. HOWEVER, the stratosphere remains the
  most fragile component of the atmospheric system.
  It is impossible to monitor and to model the
  climatic changes without long term stratospheric
  data!

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Scientifically speaking, we cannot afford to
restrict the domain covered by past experiences
like those onboard ENVISAT
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Courtesy of J-C Lambert (BIRA-IASB)
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• There is a dramatic decrease in the number of
  vertical atmospheric sounders
• Virtually, no European instrument available from
  2008 till ?

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A non-exhaustive list of scientific questions to
address. Some are old topics, none is unimportant!

• Recovery process of global ozone, especially the
  changes in the vertical distribution
• Investigation of natural cycles of ozone
• Detailed investigation of the Antarctic and
  Arctic ozone distribution, also during the polar
  night
• Investigation of mesospheric ozone and its
  diurnal variation
• Investigation of the climatology of mesospheric
  and stratospheric clouds
• Investigation of the global vertical distribution
  of NO2 and its diurnal cycle
• Investigation of the global vertical distribution
  of NO3
• Investigation of the global vertical distribution
  of water vapor
• Impact of chlorine and bromine species
• etc

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3. Very important technological progresses are
presently emerging in the field of vertical
atmospheric remote sounding.
SOUNDER
SOUNDER
Limb sounding allows for a global coverage in 1-3
days !!!
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ENVISATAt about 800 km 14 11/35 revolutions /
day Global coverage in 3 days
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How to perform a fast global coverage?
Limb scan (perpendicular/forward) allows for a
one day full coverage. This will make the optical
design more complicated
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Limb scan Filter or grating spectrometers No
gradients
Full 2-D limb imaging Acousto-optical
filters Horizontal gradients
ALTIUS SPECTRAL CAMERA AOTF IMAGER !
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Limb imaging is a powerful tool!
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PSCs with mono- or bimodal structure can be
distinguished...
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...from cirrus clouds
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A simple concept...
ALTIUS SPECTRAL CAMERA AOTF IMAGER !
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ALTIUS working modes...
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Ozone Chappuis band
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Convolved Modtran radiances (??/?20.0125)
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Stars can be used for altitude registration
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Technical questions and scientific strategy to
address... Field of view and internal optics.
Straylight. Can we foresee a star occultation
mode during dark limb periods (polar night)? Can
we solve star scintillation effects by numerical
techniques? Can we observe limb emissions? Which
signal-to-noise ratio and which dynamical range?
My first guess spectral radiance (in
photons/sec/cm2/nanometer/steradian) goes from
3e10 at 70 km to 3e13 at 10 km for lambda450 nm
and should vary as lambda(-4) in a first
approximation (a factor 250 between lambda250 nm
and lambda1000 nm). Ideally, acquisition time
should be lt 0.1 sec Robustness of saturated
pixels. How many different acquisition modes
full spectral selected windows occultation
mode dark charge measurement? We need a
pre-study for the spectral information content.
Is a preprocessing on board needed? Is AOTF the
most suited spectrometer wrt filter and grating
design? According to technical info from DN, full
spectral range would require 4 different detector
technologies (UV, VIS, NIR and IR). Feasability
on a small platform? Which data rate can we
afford? Which computing power do we need to
compress data? Ground support equipment? Do we
need cooling if we limit the range to the NIR? If
we try to capture the full Sciamachy range, is
efficient and light cooling possible? Do we want
(some) nadir measurements? Which freedom for the
user-controlled Proba-type satellite? Absolute
calibration mode Do we foresee a testing
activity ground based and a balloon campaign? .
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• Who will be interested in the ALTIUS project?

scientific community to monitor longterm
evolution of the ozone layer
scientific community to understand the
stratospheric chemistry
scientific community to inter-compare and
validate data with remaining instruments
meteorological community daily ozone and/or
radiative field maps to be assimilated in weather
forecast systems.
GMES and successors
the Belgian Science Policy in demonstrating the
usefulness of the micro-satellite program and the
scientific added value with respect to the
technological goal
international space agencies to promote global
troposperic/stratospheric monitoring by
micro-satellites
space industry to evaluate the potentialities of
such instruments and to propose
hardware/software improvement for future
missions.
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PROBA Introduction

• Key figures
• Mass 100 130 kg (25 40 P/L)
• Volume 80cm x 60cm x 60cm
• Power 30 to 50 W average platform,
• 120 W peak
• Compatible with PSLV /DNEPR/ ASAP5/
• Rockot
• High pointing accuracy (0.015 2sigma)
• Powerfull computer (up to 100 MIPS)

• Launch October 22th 2001 by PSLV
• LEO, Sun Synchronous orbit, 600 km
• Originally 1 year of mission
• Succesfully in more then 3,5 year
• PROBA 2 launch 2007, Rockot

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PROBA Value

• Autonomous Operation
• Onboard Autonomy (orbit attitude determination,
  FDIR)
• Ground Segment Automation (low operational cost)
• Simple commanding 1 image 1 command
  (coordinates)
• Performant on-board computer (ADPMS)
• Fine Pointing Stability
• Agile platform (3-axis stabilized)
• High pointing accuracy
• High pointing Stability (point stare snapshot
  imaging)
• Complex manoeuvring (motion compensation
• - push broom imaging - multiple backward /
  forward scanning)
• Modularity and flexibility in design
• PA Approach Esa Quality Label

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Why to propose the ALTIUS project?A summary

• Monitoring global changes impossible without
  stratospheric measurements.
• Dramatic decrease of available (and, in
  particular, European) instruments capable of
  vertical remote sounding of the atmosphere.
• New and promising technologies are emerging.
• Many potential communities to use data and to
  promote the ALTIUS concepts.

Interested people please contact
Didier.Fussen_at_oma.be