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    Instrument   Product of the measurement
Remote sensing
  MIPAS-STR Michelson Interferometer for Passive
Atmospheric Sounding/STRatospheric
  Profiles and vertical column of the
atmospheric constituents
  SAFIRE-A Spectroscopy of the Atmosphere using
Far-InfraRed Emission/Airborne
  Profiles and vertical column of the
atmospheric constituents
  GASCOD-A Gas Absorpion Spectrometer Correlating
Optical Differences/Airborne
  Profiles and vertical column of the
atmospheric constituents
In situ
  ACH Airborne Condensation Hygrometer   Water vapour (from 0 to 8 km)
  ECOC ElectroChemical Ozone Cell   Ozone
  FISH Fast In-Situ Stratospheric Hygrometer   Water vapour
  FLASH FLuorescent Aircraft Stratospheric Hygrometer   Water vapour (from 8 to 20 km)
  FOZAN Fast OZone ANalyser   Ozone
  HAGAR High Altitude Gas chromatograph for
Atmospheric Research
  CFC-11, CFC-12, N2O and SF6
In situ
  FSSP-300 Forward Scattering Spectrometer Probe   Particle dimensions (23-0.4 mm)
  MAS Multi-wavelength Aerosol Spectrometer   Density and optical properties of the
  mini-COPAS COndensation Particle System   Density of small particles (<0.4 mm)
Remote sensing
  ABLE AirBorne Lidar Experiment   Density and optical properties of the
particles (2-15 km from the aircraft)
  MAL Microjoule Airborne Lidar   Particle density (0-2 km from the
Two basic criteria guided the choice of the scientific payload for the APE-GAIA campaign:
  • the priority assigned to chemistry observations;
  • and the subsequent the decision to optimise the observation strategy for remote sensing measurements.

The core of the scientific payload of the APE-GAIA campaign consists, therefore, of remote sensing devices for chemical species. The combination of two Fourier transform spectrometers, SAFIRE-A and MIPAS-STR, operating in the Far and Medium Infrared respectively, is particularly important.
The two instruments perform emission measurements by using the limb sounding technique, and are capable of observing simultaneously a large number of constituents involved in the ozone depletion processes.
MIPAS-STR measures almost all the compounds of the NOy family, and together with SAFIRE-A, covers Cly species (i.e. HCl and ClONO2). SAFIRE-A has its strength in the observation of HOx compounds and Bry species (HBr and HOBr), which are also observed by the GASCOD-A Visible-Ultraviolet spectrometer (BrO). The latter completes the group of the remote sensing chemistry payload, and measures columns and vertical profiles of several other trace species (O3, OClO, NO2, NO3, SO2, O4).
In situ measurements of ozone (ECOC, FOZAN), water vapour (FISH, FLASH, ACH), and other tracers (HAGAR) will provide independent values for these specific compounds. Furthermore, the higher spatial resolution, and the possibility provided by these sensors of measuring the horizontal variability of the atmospheric composition, will provide an important synergy with the limb sounding observations.
Finally, another important feature of the M55 scientific payload is the possibility of studying heterogeneous chemistry by combining the composition measurements from the chemical sensors with the measurements of aerosols and polar stratospheric cloud particles obtained by in situ devices (FSSP-300, MAS, and mini-COPAS) and lidars (ABLE and MAL).

Researchers carry out last set-up
operations on the scientific payload
on board the M55-Geophysica
before its departure on a
new flight mission.