Validation and sensitivity of a simulated-photograph technique for visibility modeling

The Los Alamos Scientific Laboratory (LASL) visibility model is capable of producing simulated “before and after” pictures that illustrate visual effects of smoke plumes. Although the model has been under development for a few years, until recently there had been very little testing of the model against field experience or testing of sensitivity of the model results to numerical approximations used in the model.Further validation and sensitivity testing of the LASL model began in late 1979. The work focused on three areas: (1) comparison of the LASL model results with plumes encountered in the field, (2) comparison of LASL background-atmosphere model results with measured sky intensities and (3) examination of the variation of model results with changes in the numerical approximations.The field study took place during August of 1979 in the vicinity of coal-fired power plants in northwestern New Mexico and northern Arizona. Telephotometer, NO_x plume measurements and aerosol size distribution measurements of aerosols were made in the plumes of three different coal-fired power plants. Photographs were taken of the plumes and simulated photographs were prepared by the model.Light intensities calculated by the background radiative transfer model were compared to measured light intensities in a very clean atmosphere and in a moderately hazy atmosphere. The measured intensities were derived from photographic densities, or from telephotometer measurements.In addition to the field measurements, differences resulting from increased numbers of wavelengths in the color representation were examined. We also examined other changes in the numerical approximations. This paper describes the results of these studies.