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Radiative transfer

Brightness temperature spectra measured by ARIES and IASI. The lower plot shows differences between observed and modelled spectra.

We maintain, develop and evaluate models of atmospheric radiative transfer which underpin the operational use of satellite observations.

Increasingly, a large number of observations about the Earth's weather are derived from satellites. Measurements of radiation, spanning wavelengths of light from the microwave to the visible and ultraviolet parts of the spectrum, can be interpreted to give information about the atmosphere. For NWP this information is primarily about how the temperature and humidity varies with location and height. To make good use of satellite data we need accurate models of how radiation propagates through the atmosphere.

A number of different gases (such as carbon dioxide, water vapour and ozone) absorb and emit radiation in the atmosphere. The spectroscopy of these species describes in detail how their absorption properties vary with wavelength. It is important to include the latest spectroscopic parameters, such as those published by HITRAN, in radiative transfer models.

A new generation of satellite sounding instruments now possess hundreds if not thousands of channels, each measuring a different wavelength of light. The Infra-Red Atmospheric Sounding Interferometer (IASI) instrument on the European MetOp satellite is a good example, with over 8000 infra-red channels. The ongoing challenge is to describe the atmospheric absorption properties adequately so that these hyperspectral measurements can be put to best use.

Key Aims

  • Validation and testing of atmospheric radiative transfer codes, such as LBLRTM
  • Use of field campaign data sets to establish baseline accuracies of state-of-the-art radiation models.
  • Collaboration with colleagues involved in satellite data assimilation to optimise the use of radiative transfer codes in operational weather forecasting.

Current Projects

  • SALSTICE - a campaign to diagnose the sources of errors in the Unified Model representation of Land Surface Temperature (LST) and evaluation of the IASI-B instrument on MetOp-B.
  • JAIVEx - a UK/US collaboration for calibration and validation of IASI.
  • CAVIAR - a NERC consortium involving the Met Office investigating the causes and radiative impact of the water vapour continuum, the pervasive underlying absorption feature attributed to atmospheric H2O.

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