The lidar ratio is found to be sensitive in three distinct regions in a space defined by index of refraction and particle size. This implies that inversion of the lidar equation will be complicated if the parameters of the aerosol under study fall into one of these sensitive regions. The model used to explore this space covers the complex plane of refractive index bounded by real part 1-2 and imaginary part 0-infinity and mode particle size parameter bounded by 0.03-3000. Furthermore, the model is compared to a literature survey of lidar ratios.
A semiempirical approximation to the extinction efficiency Q(ext) for randomly oriented spheroids, based on an extension of the anomalous diffraction formula, is given and compared to the extended boundary condition method or T-matrix method. Using this formula, Q(ext) can be evaluated over 10(4) times faster than by previous methods. This approximation has been verified for complex refractive indices m = n - ik, where 1.01 = n >/= 2.00 and 0 = k >/= 1 and aspect ratios from 0.5 to 4. We believe the approximation is uniformly valid over all size parameters and aspect ratios. It has the correct Rayleigh and large particle asymptotic behavior. The accuracy and limitations to this formula are extensively discussed.
A semiempirical approximation to the extinction efficiency based on a modification to the anomalous diffraction formula is given and compared to the exact Mie computation. This approximation has been verified for complex refractive indices m = n-ikappa, where 1.01 = n = 2.00 and 0 = kappa = 10. The approximation is uniformly valid over all size parameters and has the correct Rayleigh and large particle asymptotic behavior. The accuracy of this formula is discussed as well as its computational advantages. The formula is also applied to some of the LOWTRAN aerosol models.
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