Satellite Instruments

Our satellite retrievals focus on two main areas:

Retrievals Using High Resolution Infrared Spectral Measurements (e.g. MIPAS)

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a Fourier transform spectrometer for the measurement of high-resolution gaseous emission spectra at the Earth's limb. MIPAS was launched on the ESA platform ENVISAT in 2002. The MIPAS instrument operates in the near to mid-infrared (4.15 - 14.6 µm) where many of the atmospheric trace gases that play a major role in atmospheric chemistry have important emission features.

Several students and post-docs are engaged in MIPAS projects within AOPP, and there are frequent visits to other European institutes engaged in related work.

AOPP has been involved in the development of the operational processor which is run by ESA to retrieve profiles of temperature and six major species (CH4, H2O,HNO3, N2O, NO2 and O3) in near real time, and has a continued role as an ‘Expert Support Laboratory’ in order to monitor these results and suggest improvements. In addition, we have developed our own retrieval software with the aim of retrieving the ESA species with improved accuracy (without the constraint of near-real-time processing) and many other species (e.g. SF6, SO2, OCS and NH3) with infrared signatures within the MIPAS spectra. The practical analysis of the large data rate MIPAS signal (approximately 40000 points per spectrum, 17 tangent height spectra per profile) has been achieved by devising the algorithms and creating the software to select spectral microwindows (continuous spectral regions typically less than 1 cm-1 in width). Microwindows are chosen to optimise the information they contain on an atmospheric trace gas for a range of altitudes. A combination of these microwindows are used to determine the entire trace gas profile. This technique reduces the number of data points that need to be processed by a factor of ~100 without significant loss of information (relative to processing all spectra at all measurement altitudes). We also aim to retrieve atmospheric continuum information associated with cloud and aerosols, and use MIPAS data to validate HIRDLS measurements.

Retrievals Using Nadir Imager Radiometers (e.g. ATSR series)

The ATSR (Along Track Scanning Radiometer) instruments produce infrared images of the Earth at a spatial resolution of one kilometre. The first ATSR instrument, ATSR-1, was launched on board the European Space Agency's (ESA) European Remote Sensing Satellite (ERS-1) in July 1991, as part of their Earth Observation Programme. An enhanced version of ATSR, ATSR-2, was successfully launched on board ESA's ERS-2 spacecraft on 21st April 1995. ATSR-2 is equipped with additional visible channels for vegetation monitoring. The AATSR (Advanced Along Track Scanning Radiometer) instrument has been successfully launched on board the ENVISAT spacecraft on 1st March 2002 at 01:07 GMT from the Kourou spaceport in French Guiana.

Satellite measurements of the surface of the Earth are inevitably affected by the passage of radiation through the atmosphere. The dual view design of ATSR makes it possible to estimate and correct for such atmospheric effects. The two views result from the instrument's conical scanning mechanism. Each scan takes readings from the nadir position and then sweeps round to take measurements from a point about 900 km along the satellite's track. A few minutes after acquiring the forward view, the satellite passes over the same spot and takes readings for the nadir view. As the two views of the same scene are taken through different atmospheric path lengths, it is possible to estimate both the surface and the atmospheric contribution to the measured radiance.

EODG uses data from ATSR-2 and AATSR as input to the ORAC retrieval scheme to determine the microphysical properties of clouds and aerosols. Results from this work are vital for estimating long-term trends in atmospheric behaviour and so to better understand anthropogenic influence on the atmosphere.

EODG research is mainly focussed on using data gathered by the following satellite instruments: