Abstract : The Dewan optical turbulence parameterization has been the Air Force Research Laboratory optical turbulence model of choice for various research efforts involving optical turbulence during the past several years. The Dewan parameterization was developed to convert standard radiosonde data into vertical profiles of Cr2, the refractive index structure constant, which is the critical parameter for describing optical turbulence. The Dewan parameterization provides useful vertical profiles of Cr2 in the upper troposphere and stratosphere, though there is certainly a need for improvement at these altitudes. The statistical relationships relating Dewan's Y parameter to wind shear, which form the basis of the Dewan parameterization, are often not found in atmospheric measurement data, thus this is an area to explore in developing improved optical turbulence parameterization for the troposphere and stratosphere. Several modified-Dewan optical turbulence parameterization are developed and tested for the lower troposphere, the troposphere, the stratosphere and the combined tropospherelstratosphere.