Full text: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

Outline of the algorithm The AVHRR scene is 
treated block by block. The algorithm starts by 
calculating the gaseous transmittance values on 
the basis of the geometry of the scene and the 
entries in the appropriate tables. It then goes 
on to index the sun and satellite angle look-up 
tables. It then calculates, for both channels, 
the Rayleigh optical thickness over the block, 
and finally, pixel-by-pixel, it calculates the 
ground reflectance. 
"Thermal" channels: channel 4 and 5. Surface 
brightness temperature are calculated using the 
conventional split window technique, which is 
designed to take account of the water vapour 
content of the atmosphere. 
The calibration and atmospheric correction 
modules form an integral part of the pre 
processing software, which includes cloud 
detection and a two-step automatic geometric 
correction module. Clouds are detected by their 
radiometric properties. The algorithm is based 
on the cascade philosophy used in the APOLLO 
algorithm (Saunders 1986), in which a series of 
tests take place, the most powerful first. 
Thresholds are set dynamically in small blocks of 
the imagery. During the geometric correction, an 
elliptical orbital model is used to navigate the 
data, after which they are registered accurately 
using GCPs detected automatically along the 
coastlines of Europe. 
When installed, this software will enable clients 
to order AVHRR data pre-processed to a known 
standard. Rather than, as at present, spending 
large amounts of time, effort and money on pre 
processing the data, the thematic user will then 
be able to start immediately to work on the 
aspects of the data which directly concern him. 
E S R I N (1986) European Utilisation of TIROS-N 
Data. Proposal for a Co-Ordinated Service. 
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Scientific and Industrial Research for ESA/ESRIN. 
Contract 6296/86/HGE- 1 
Kaufman Y.J. and B.N. Holben ( in press) Calibration 
of the AVHRR visible and near-IR bands by 
atmospheric scattering, ocean glint and desert 
reflection. J. Appl. Met. 
Lauritson L.. G.J. Nelson. and F.W. Porto ( 198 9) 
Data extraction and calibration of TIROS-N/NOAA 
radiometers. N 0A A Technical Memorandum NESS-107. 
National Environmental Satellite Service, US Dept 
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Saunders R.W. (1986) An automated scheme for the 
removal of cloud contamination from AVHRR radiances 
over western Europe. IJRS. 7_:867. 
Smith G. R . . R.H. Levin. P. Abel and H. Jacobowitz 
(1988) Calibration of the solar channels of the 
NOAA-9 AVHRR using high altitude aircraft 
measurements. J. Atmos. Ocean. Technol. 5_( 5 ) : 6 31 - 
Stavlor W.F. ( 1989) Degradation rates of the AVHRR 
visible channel for the NOAA 6, 7 and 9 spacecraft. 
J. Atmos. Ocean. Technol. In press. 
Tanré D.. Deroo C.. Duhaut P.. Herman M.. Morcrette 
J.J.. Perbos J. et P-Y. Peschamps ( 1986) Simulation 
of the Satellite Signal in the Solar Spectrum (5S). 
Laboratoire d'Optique Atmosphérique, Université des 
Sciences/Techniques de Lille, 59655 Villeneuve d'Asq 
Cedex, France 
Teillet P . M. . P , N . Slater, Y. Mao. Y. Ding. R.J. 
Bartel l , S.F. Biggar. R.P. Santer, R , D , Jackson and 
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of the NOAA AVHRR sensors. SPIE conf . , Orlando 

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