The Atmospheric Transmission Measurement system measures absolute spectral transmission values with system accuracy of few percent. The spectral measurements are taken in the range of 0.4 – 14.0 μm at distance of up to 6km. The system can measure very absorbing atmosphere (fog, haze, low visibility, etc.,). The Atmospheric Transmission Measurement system is field useable, has simple deployment and is designed to work 24/7.
The Atmospheric Transmission Measurement System is based on a chopped source located at the far end of the path with measurement instrument (SR-5000N) at the near end. The spectroradiometer is locked onto the chopped signal produced by the source and a method known as synchronous detection (or lock-in amplification) is employed.The synchronous detection method is used so that, although the chopped signal may be small relative to the absolute signal entering the collecting aperture of the radiometer, only the signal from the desired source is measured and all other radiation is ignored. This method provides the highest possible SNR for long-path atmospheric transmission measurements.The source is typically chopped at frequencies of 500 Hz and the spectroradiometer is locked in frequency and in phase with it. Any signal that is not in the exact frequency and phase of the source is cancelled out by the synchronous detection circuitry implemented in the SR-5000N.