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Multi-band optical/IR transmissometry during the VAMPIRA trials, spring 2004

Author: Jong, A.N. de · Cohen, L.H. · Moerman, M.M.
Type:article
Date:2004
Source:Gonglewski J.D.Stein K., Optics in Atmospheric Propagation and Adaptive Systems VII, 13-14 September 2004, Maspalomas, Conference code: 64485, 5572, 151-162
series:
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 238140
Article number: 46
Keywords: Electronics · Aerosols · Atmospheric transmission · Multi-band · Optical/IR transmissometer · Atmospheric aerosols · Backscattering · Electromagnetic waves · Infrared radiation · Measurement errors · Meteorology · Particle size analysis · Refraction · Temperature distribution · Atmospheric transmission · Infrared sensors · Optical/IR transmissometers · Atmospheric optics

Abstract

Scattering by atmospheric aerosols is one of the environmental parameters determining the range performance of optical and infrared sensors. Extinction of the target contrast along the path due to scattering is difficult to estimate in real operational conditions due to uncertainties in the size distribution of the particles, their constitution and concentration along the path. Knowledge on their behaviour allows calculation of the atmospheric transmission by means of standard scattering formulae. In-situ measurement of the characteristics of the particles by means of counters provides data of limited value due to the possible impact of the direct environment. The data may also be not representative for the particles at other locations along the path. Similarly the measurement of the particle characteristics by means of LIDAR provide an asymmetric view, while the backscatter by the particles is difficult to translate into extinction coefficients in forward direction. Multi-band transmissometry along the path of interest provides however direct information on the real atmospheric propagation characteristics. Furthermore the multi-band data allow the validation of the aerosol model, to be used in transmission models such as MODTRAN. The VAMPIRA trials, organised in March/April 2004 by Germany in the Baltic Sea near Eckernförde, provided an opportunity to test the usefulness of a 7-channel optical/IR transmissometer, developed at TNO-FEL. In this paper the set-up of the system is described and samples of data are presented. The multiband transmission data, collected over an 8.6 km path over water, are compared with extinction values obtained from in-situ particle measurements. The data show clearly that the aerosols have rural characteristics during most of the time.