The Instruments:

Advanced Synthetic Aperture Radar (ASAR)

As a high-resolution, wide-swath imaging radar, this is the largest Envisat instrument and produces high quality colour images of the oceans, coastal zones, polar ice and land regions irrespective of weather conditions, cloud coverage or night/daytime. It works by bouncing microwaves off the Earth’s surface and measuring the reflected radiation. ASAR also has five different modes of operation, allowing a variety of image types.

ASAR will collect information on:

• Ocean wave characteristics
• snow and ice extent
• sea ice extent and motion
• land and surface properties
• surface topography
• deforestation and extent of desert areas
• surface soil moisture and wetland extent
• disaster monitoring, e.g floods, earthquakes, landslides

Medium Resolution Imaging Spectrometer (MERIS)

MERIS measures solar radiation reflected from the earth’s surface and clouds in the visible and infra-red parts of the spectrum. MERIS will detect biophysical properties (e.g chlorophyll concentration) of the oceans and coastal water composition which are especially important in understanding the impact of human activities on the coastal environment. The Meris data can also be interpreted as large scale maps, showing vegetation distribution, clouds and water vapour.

Advanced Along-Track Scanning Radiometer (AATSR)

AATSR will continue the work of similar instruments on the ERS satellites, ensuring a near-continuous bank of information on sea surface temperatures over a 15 year period. Measurement of sea temperatures is one of the most reliable geographical indicators of changing climate. The AATSR is so accurate it will be able to record temperatures within 0.3 C.

Radar Altimeter (RA-2)

RA-2 is an enhanced version of an ERS instrument and will provide weekly measurements of ocean surface levels, wave height and wind speed. It will provide improved mapping of icecap and sea-ice as well as land elevation and lake levels.

Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS)

DORIS is a highly accurate microwave tracking system which allows the positioning of Envisat in space to be fixed to within a few centimetres.

Microwave Radiometer (MWR)

MWR is a passive radiometer which measures the total atmospheric water vapour and cloud liquid water content to provide real-time atmospheric correction for RA-2 timings.

Laser Retro-Reflector (LRR)

LRR is identical to instruments flown on ERS-1 and ERS-2. It will support the functions of DORIS and the RA-2 instrument in determining the precise orbit of the satellite by reflecting high powered pulsating lasers to ground-based stations.

Global Ozone Monitoring by Occulation of Stars (GOMOS)

GOMOS will measure starlight occulation (the brightness or spectrum of light surrounding a star) through the atmosphere, detecting ozone and other trace gases and high altitude chemical reactions. These measurements are vital to our understanding of ozone depletion.

Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

MIPAS is an infrared Fourier spectrometer – a sophisticated instrument designed to measure the concentration of various atmospheric constituents. It has a high spectral resolution and range, allowing global measurement of more than 20 trace gases during all seasons, atmospheric pressure, and temperature. MIPAS can operate equally well during daylight and dark.

Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY)

SCIAMACHY observes reflected and scattered sunlight to measure trace gas and aerosol concentrations. The measurements obtained will enable the investigation of a wide range of phenomena which have a direct influence on atmospheric conditions including forest fires, dust storms, industrial pollution, volcanic activity and events associated with the Sun.