Ace fts instrument after 7 5 years on orbit
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ACE-FTS instrument: after 7.5 years on-orbit. Henry Buijs ABB Ryan Hughes U. Of Waterloo. Balloon borne solar occultation (1975-1980) To elucidate Stratospheric chemistry related to ozone depletion Successful commercialization of very high resolution FTS

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ACE-FTS instrument: after 7.5 years on-orbit

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ACE-FTS instrument: after 7.5 years on-orbit

Henry Buijs


Ryan Hughes

U. Of Waterloo

Balloon borne solar occultation (1975-1980)

To elucidate Stratospheric chemistry related to ozone depletion

Successful commercialization of very high resolution FTS

DA8 series with 0.0026 cm-1 resolution (1980-2005)

Dynamic alignment flat mirror interferometer

Technology used for Cris

Used in many labs to contribute to HITRAN data base

Successful commercialization of a rugged industrial FTS

MB100 series 1986-present

“Wishbone” scan arm with cube corner mirrors

No alignment required

Technology used for most ABB satellite FTS projects

FTS heritage ABB Bomem formerly Bomem Inc.

Ground based Hyper-spectral sounder

Measures down-welling spectral radiance

Permits Temperature and moisture profiling from ground

Good vertical resolution in boundary layer

Joint development project with U of Wisconsin

FTS heritage ABB Bomem formerly Bomem Inc.

Autonomous operating 3rd gen


  • Atmospheric Chemistry Experiment (ACE) development started early 1999 (Phase B contract award) under Canadian Space Agency’s Space Science program.

  • Mission objectives: better understanding of atmospheric chemistry of ozone

    • The instrument suite includes an FTS, two 128x128 sun imagers and an active sun-tracker

  • Prime contractor is ABB Bomem Inc., with main subcontractors

    • Ball Aerospace and EMS Technologies.

    • Many persons have contributed to the ACE-FTS development, including universities and research labs.

  • The FTS design is based on the classical Michelson interferometer with a double-pass optical layout.

    • It is tilt and shear compensated and requires no active alignment.

  • The ACE-FTS Instrument was launched August 12th, 2003

Main Design and Programmatic Requirements

  • ACE science objectives require

    • High spectral resolution (0.02 cm-1),

    • High SNR (> 100)

    • Widespectral coverage (750-4100 cm-1)

  • Combination of these three requirements resulted in a challenging instrument design.

    • Jacquinot merit factor W is >3x107

      • Highest merit factor ever targeted for a space-borne spectrometer operating in the infrared.

  • Instrument design is also constrained by low mass (40 kg), power (40 W) and volume allocations from the spacecraft bus.

    • Scisat-1 mission is a small satellite mission concept

  • Program required to design and manufacture a low cost, quickly-developed instrument while keeping risks as low as possible.

Scisat-1 spacecraft

ACE-FTS Optical Layout

ACE interferometer

The ACE-FTS Instrument

Input Optics-side


ACE-FTS Interferometer Sub-System

  • ACE-FTS still operating on the primary redundancy side at full resolution

  • Metrology laser power shows a decrease of less than 2% observed over 7.5 years

  • Excellent reliability of the ACE-FTS (more than three original mission lifetime requirement)

Integration to spacecraft bus

SciSat Inside the Pegasus Fairing

ACE in orbit

Circular orbit

Altitude 650 km,

Orbital period 98 min.

Inclination 74°

Selected to provide high latitude occultations

Solar occultation mission

Approximately 15 occultations /day (~5400/year)

Orbit Characteristics

Tangent height

Coverage characteristics

Coverage characteristics

Exo-atmospheric spectra

Do not contain any atmospheric features

Provide instrument response to solar spectrum

Atmospheric spectra include above + atmospheric absorptions

Ratio atmospheric/exo-atmospheric provides precise atmospheric transmission

Subtracting transmission loss of higher layers provides transmittance at tangent height only

Optical beam at tangent height is ~ 3 km

Limits vertical resolving power

Scan time is 2 s.

Rate of change during scan depends on beta angle

Spectral analysis method

Ace spectra NO2 region

Many weak lines of NO2

B3M compared with ACE data CFC12 region



B3M compared with ACE HCl region


B3M compared with ACE and DA8





ACE profiles

Very good absolute concentration determination

Limited by HITRAN issues

Calibration cannot change over time

Does not rely on blackbody calibration sources

Exo-atmosphere/atmosphere ratio

Vertical resolution ~ 3 km

Vertical sampling < 1km

Lower limit of profile

Limited by cloud

Limited by spectral saturation

Upper limit of profile

Limited by sensitivity

Profile performance

Example result, CO2 study (P.Y. Foucher et al)

On-orbit SNR comparison mid-march 2004 (ss3171) and mid-march 2008 (ss24754)





Source: ACE Science Team (Ryan Hughes, UofWaterloo)

Frequency of occultations with ice 2004 to 2007





On-orbit FTS temperature (interferometer beamspliter) 2004-2008

Increase of temperature of ~1deg/year observed

S/C anomaly

Source: ACE Science Team (Ryan Hughes, UoWaterloo)

In date of June 2008, the temperature of the instrument is 25 degrees Celcius in average; there is still room for further temperature increase as the instrument was qualified during TVAC for temperatures from 0 to 40 degrees Celcius.

Level 2 data

Concentration profiles of molecules

Official data processing soon in 5th version

Data processing

ACE-FTS is the first instrument on-orbit to measure the following molecules:




COCl2 (phosgene)

formic acid






PAN (peroxyaceylnitrate)

Molecules measured for the first time

Improved vertical resolution

Image slicing

Maintain basic throughput

With <1 km vertical resolution

Improved solar tracking

Account for distortion due to refraction

Cloud discrimination

Future trends

Future trends

Lower cost missions

To increase number of sensors

Some reduction of spectral resolution

Since ACE has shown the detailed spectrum

Good retrievals are possible at lower resolution

Smaller instrument

Faster scanning

Higher SNR

Include shorter wavelength

To avoid saturation of spectra at lowest altitudes

Using weaker overtone Near IR bands

Future trends

Scientific papers

About 130 publications identified so far (July 2008)

More than 104 with review committees

ACE-FTS on Scisat-1 has significantly exceeded its 2 years mission

7th anniversary on August 12, 2010

Very good in-flight performances

Excellent scientific returns


Thanks to all ACE/SciSat-1 team !

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