Minimize Atmospheric Monitoring

Three essential data can be extracted from OLCI observations related to atmosphere:

  • the atmospheric composition (mainly aerosols and water vapour): essential information for climate studies and weather forecasting
  • illumination condition (fraction of available natural light) of the observed area: a key input for biological studies
  • downwelling solar radiation (long- and short-wave) at the Earth's surface and top-of-atmosphere: critical information in estimating and monitoring the Earth Surface Radiation Budget (SRB).

Atmospheric Composition

Water vapour is both radiatively and chemically active, and so plays a key role in the atmosphere. It is the strongest greenhouse gas (GHGs), even if it is influenced more indirectly than directly by anthropogenic activity. It is an essential indicator for convection and radiative forcing in the Upper Troposphere (UT) and Lower Troposphere (LT). In addition, in the stratosphere, water vapour is a source gas for hydroxide, a chemically active gas in the ozone budget.

Scientific evidence confirms that the ascending branch of Brewer Dobson Circulation, controlling the balance of water vapour in the UT and in the LS, is modifying because of climate change. Using OLCI, scientists and weather forecasters have access to the integrated water vapour column measured over land and ocean.

envisat water vapour map

Figure 1: Total Column of Water Vapour (annual product 2003) (image courtesy of ACRI-ST)

By mass, atmospheric aerosols are minor components of the atmosphere, however, they are a crucial constituent of climate and particularly of climate change. Global radiation is impacted by aerosol which directly scatters solar radiation and indirectly influences cloud reflectivity, cloud cover and cloud life time.

Tropospheric aerosols can be formed in two different ways: either directly from the surface, e.g. sea salt from oceans or dust, smoke and soot from continents, or in the atmosphere through complex (photo-) chemical processes and reactions between gaseous components. These gaseous constituents came themselves from the surface, for example dimethyl sulphide (DMS) over oceans or sulphur and nitrogen oxides over continents. Most stratospheric aerosols originate in volcanic eruptions, powerful enough to inject Sulphur Dioxide (SO2) into this layer. Apart from volcanic eruptions, stratospheric aerosols can arise from Oceanic Carbonyl Sulphide (OCS), from low SO2 emissions (from Kilauea-type volcanoes) and other anthropogenic sources (industrial and aircraft operations). Climate is also affected by radiative effects induced by changes in cirrus cloud amounts, particle size and/or lifetime.

OLCI provides aerosol optical thickness and Angstrom exponents to scientists and weather forecasters.

Illumination Condition

Photosynthetically Active Radiation (PAR) is defined as the spectral range of solar radiation (in terms of wave band, from 400 to 700 nm) which photosynthetic organisms can use in the process of photosynthesis.

Agriculture, forestry and oceanography represent the main scientific fields using PAR measurements, to compute the euphotic depth in the ocean, for instance. OLCI products include PAR measurements for both land and ocean applications. Over land, this parameter ensures a link between plant status and available radiation. Over ocean, its value is necessary to compute primary production.

An essential component of surface energy budget is the Surface Radiation Budget (SRB). It is important to almost all aspects of climate and, therefore, required to be monitored systematically. SRB is composed of upward and downward solar and thermal infra-red irradiances. To be used in climate applications, these components require complex strategies of measurement due to their high fluctuation over the electromagnetic spectrum, over time and position.

In order to be a relevant part of climate research and assessment, it is essential to have well-analysed and planned measurement approaches of surface irradiance observations.

Radiation quantities are possibly responsible for forcing climate change, however these climate variations will alternately change observable radiation fields. As a consequence, it is required to proceed to a complex analysis of radiation observations for application to climate. Information on surface radiation budget is available from OLCI product.

For further information about atmospheric applications and services available, see: Copernicus website.