<title>Wide-spectral-range transmissometer used for fog measurements</title>

Abstract

A wide spectral range transmissometor has been developed at the Phillips Laboratory for long path atmospheric measurements. It was designed to provide narrow band spectral coverage in three bands between 0.4 and 14 micrometers by programmed scanning with circular variable filters. The system uses three detectors so that three spectral regions can be sampled simultaneously. Two sources, a black body and a ribbon filament lamp are combined in a single beam. A two way path is provided by use of cat's-eye retro-reflectors. Transmitter and receiver are combined in the same unit and by using multiple retroreflectors located at different positions the path length can be readily changed by realignment of the unit. This increases the dynamic range of the system and makes possible measurement of rapidly changing atmospheric conditions. The transmissometer was recently used to provide transmission measurements as part of the FLAPIR (Forward looking infrared and Lidar Atmospheric Propagation in the InfraRed) field measurement program at Brunswick Naval Air Station, which had the purpose of determining the feasibility ofusing lidars to predict the effectiveness ofinfrared imaging devices. Measurements were made primarily in fog and rain conditions.

<title>Blurring effect of aerosols on imaging systems</title>

“…The state of the atmosphere was continuously monitored with two forward-scatter point visibility meters located at the receiver site and at 500 m down range, with a wide spectral range transmissometer [13] aligned along the same axis as our imaging system, and with aerosol particle and rain drop size spectrometers operating near our receiver.…”

<title>Forward-looking IR and lidar atmospheric propagation in the infrared field program</title>

“…This was accomplished by surrounding the targets with sanded blue styrofoam insulation panels. 3. It is assumed that equation 1 1 is a predictor of the DUWIR performance.…”