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Learning from previous experiments to better prepare future missions

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The GOMOS experiment flew on board the ENVISAT satellite and measured the composition of the atmosphere from 2002 until 2012. This might seem far back in time, but this instrument, a pioneer in terms of its measuring technique (stellar occultation), still poses a challenge to those who want to explore its data. Despite offering more opportunities for observation than just looking at the one Sun in the solar system, stars produce such weak signals that it questions quite a few principles of data processing methods. It would be best to solve this in preparation of future missions.
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Not one star, but three hundred

GOMOS is an instrument that flew onboard ENVISAT and sounded the Earth’s limb using the occultation technique between 2002 and 2012. Instead of using the Sun as light source as usual, what provides two measurements opportunities per orbit (one sunset and one sunrise), GOMOS pointed to about 300 stars, providing a large dataset of atmospheric composition measurements.

A drawback of this spectacular increase is the weakness of the measured signal and its sensitivity to scintillation. In addition, the large diversity of spectral characteristics offered by stars with various temperature and magnitude makes the data retrieval challenging.

A world of challenges and opportunities

For this reason, this past experiment remains a very interesting topic of studies. Not only it provides a unique dataset for this particular period marked by increasing signatures of human activities and by the occurrence of several large tropical volcanic eruptions that gradually loaded the stratosphere in aerosols, both of them affecting the climate in a significant way.  

Also on a technical point of view, it obliges to reconsider the retrieval methods used so far and the way to extract the information from the measurements, using the most recent status of our knowledge to obtain the accurate and reliable data needed to quantify the atmospheric composition.

Learning from the past to better prepare for the future

Such challenge is not limited to the processing and the analysis of the GOMOS dataset: the stellar occultation technique used in this pioneering experiment will be used in other innovative experiments like ALTIUS, where the use of imaging capabilities will increase even more the complexity of the data retrieval.

Therefore, it is of utmost importance to solve and understand as good as possible the problems and science questions addressed by this first stellar occultation. Learning from past experiments to prepare for the future is a key message!

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Figure 2 caption (legend)
The occultation technique is a particular way to observe the limb of the planet: the satellite (here: with the GOMOS instrument) points to the light source (sun, star or planet) during its set or rise, scanning the whole atmosphere above a given location indicated by the longitude and latitude of the tangent point.