Airbus Defence and Space

GOMOS looks to the stars for ozone profiling

Monitoring long-term ozone trends and other trace gases

GOMOS (Global Ozone Monitoring by Occultations of Stars) is one of the instruments on an Earth Observation satellite, so it would be logical to assume it was pointed towards the Earth, but in fact GOMOS prefers to focus on the stars. This apparent contradiction stems from GOMOS’s use of a method known as ‘stellar occultation’ – employed here for the first time – to accurately measure and monitor the Earth’s ozone layer.

The heart of GOMOS (OMC)

As well as acting as a protective shield against harmful solar UV radiation, ozone also plays a role in the temperature structure of the Earth’s atmosphere, so careful monitoring of global ozone distribution over the long term is essential.

The GOMOS instrument, which was built and developed in France for the Envisat satellite, can measure and monitor even minor changes in the concentration of ozone and other atmospheric gases. This data provides scientists with important clues that help them to understand the chemical processes going on in the atmosphere.

 GOMOS, Envisat instrument built by Airbus Defence and Space

GOMOS uses the method of stellar occultation to record and monitor ozone levels. This method involves orienting the instrument’s line of sight towards a pre-selected star and maintaining this until the star disappears behind the Earth’s atmosphere observed on the horizon. During this process, the ultraviolet, visible, and near-infrared spectra of the star are continuously recorded. The further the star sets behind the atmosphere, the more its radiation is absorbed by the gases in the atmosphere. The absorption spectra recorded by GOMOS can be used to determine the concentration of the gases in the atmosphere.

Comprising some 400 stellar occultations a day, the data supplied by GOMOS is tremendously useful for applications in ozone and atmospheric research. For example, the data captured by GOMOS is used to create models of how the distribution of ozone will develop over the long term, enabling scientists to draw conclusions on how our atmosphere will evolve over the coming years and decades. For example, in 2004 – and again in 2011 – GOMOS observed a sharp increase in the concentration of nitrogen dioxide at an altitude of 65 kilometres. Monitoring the concentration of nitrogen dioxide in the atmosphere is of particular importance because this gas can deplete ozone levels. Over the subsequent two months, GOMOS monitored this layer as it sank to an altitude of 45 kilometres and destroyed ozone in its path – providing us with yet another missing piece of the ozone puzzle.

For 10 years, GOMOS has been contributing to our understanding of the processes that determine the physical photochemical behaviour of the atmosphere. GOMOS has so far carried out spectral tracking on stars more than one million times.


SCIAMACHY MIPAS GOMOS Advanced Synthetic Aperture Radar ASAR AATSR
      SCIAMACHY           MIPAS          GOMOS           ASAR           AATSR


Earth ObservationEnvironmentEnvisat