Considerations in the Accuracy of a Long-Path Transmissometer

A recently developed long-path (≊ 15 km) transmissometer (LPT) was configured with a design criteria of measuring transmission independent of atmospheric turbulence accurately enough to determine ambient aerosol extinction coefficients with better than 10% error. To assess the ability of the LPT to measure atmospheric extinction accurately and to assess its response to atmospheric turbulence, a series of field programs was initiated to compare it to other measures of extinction as well as to itself using different path lengths. Relative accuracy of the transmissometer-derived extinction is calculated by comparing it to other measurements of extinction when it is expected that those measurements would be unperturbed by meteorological conditions and/or relative humidity. For instance, integrating nephelometers can accurately measure near-Rayleigh extinction, and teleradiometer contrast measurements of artificial black targets under standard meteorological conditions eliminate the errors associated with the ...