ESA ENVISAT Advanced Along Track Scanning Radiometer (AATSR)

1994 - 1995

Project overview

The Advanced Along Track Scanning Radiometer (AATSR) instrument is a seven channel visible/infrared radiometer due to be launched on the European Space Agency (ESA) satellite ENVISAT-1. The instrument is an improved version of the very successful ATSR flown on ESA’s first Remote Sensing Satellite (ERS-1) in 1991 and its successor ATSR-2, launched in April 1995 on ERS-2. The instrument views the same area of sea both through a near-vertical (nadir) atmospheric path and through an inclined path of different length some distance along the satellite track, permitting accurate determination of the atmospheric correction. The infrared channels described here are used for the measurement of global sea surface temperatures averaged over a 50km square area with an accuracy of 0.25°C between adjacent 1km square areas. The instrument builds up images of the sea surface pixel by pixel by means of a scanning telescope that focuses radiation onto a field stop in the focal plane assembly. The thermal infrared channels which are the subject of this paper are centred at approximately 11 and 12µm. The disposition of the coatings in the 11 and 12µm channels is novel insofar that the dichroic beamsplitter which splits the 11 and 12µm channels simultaneously defines both the entirety of the transmitted 11µm band and the short wavelength side of the 12µm band.

The University of Reading are responsible for the spectral design and fabrication of the mid and long wavelength infrared entrance windows and the dichroic beamsplitters filters.

Delivered hardware

Description	Filter Type	Quantity	Wavelength Region	Substrate Material	Dimensions
Beamsplitters	Longwave-pass edge filters	2 channels	9.0 - 11.0 µm	Germanium (Ge)	11.0 mm Dia x 1.0 mm T
Filters	Narrow Bandpass filters	3 channels	3.7 - 12.0 µm	Germanium (Ge), Sapphire (Al203)	8.5 mm Dia x 2.0 mm T