Abstract
Multiwavelength Raman/high spectral resolution lidars that measure backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm can be used for the retrieval of particle microphysical parameters, such as effective and mean radius, number, surface-area and volume concentrations, and complex refractive index, from inversion algorithms. In this study, we carry out a correlation analysis in order to investigate the degree of dependence that may exist between the optical data taken with lidar and the underlying microphysical parameters. We also investigate if the correlation properties identified in our study can be used as a priori or a posteriori constraints for our inversion scheme so that the inversion results can be improved. We made the simplifying assumption of error-free optical data in order to find out what correlations exist in the best case situation. Clearly, for practical applications, erroneous data need to be considered too. On the basis of simulations with synthetic optical data, we find the following results, which hold true for arbitrary particle size distributions, i.e., regardless of the modality or the shape of the size distribution function: surface-area concentrations and extinction coefficients are linearly correlated with a correlation coefficient above 0.99. We also find a correlation coefficient above 0.99 for the extinction coefficient versus (1) the ratio of the volume concentration to effective radius and (2) the product of the number concentration times the sum of the squares of the mean radius and standard deviation of the investigated particle size distributions. Besides that, we find that for particles of any mode fraction of the particle size distribution, the complex refractive index is uniquely defined by extinction- and backscatter-related Ångström exponents, lidar ratios at two wavelengths, and an effective radius.
Highlights
Several approaches for the retrieval of particle microphysical parameters from multiwavelength lidar measurements were developed in the past two decades [1,2,3,4,5]
Sets, and several algorithms of particle microphysical parameters (PMP) retrievals provide us with an effective radius, see Ref. [1,2,3,4,5]. Taking into account such products as lidar ratios (LRs), backscatterrelated Ångström exponent (BAE), and EAE measured with lidar and an effective radius retrieved with these available algorithms, we can put these values into our synthetic OD (SOD) bank and find the respective
We find that the linear correlation between particle surface-area concentration and the extinction coefficient at 355 nm is approximately
Summary
Several approaches for the retrieval of particle microphysical parameters from multiwavelength lidar measurements were developed in the past two decades [1,2,3,4,5]. [12], the surface-area and volume concentrations of mineral dust were retrieved from lidar measurements taken during the Saharan Mineral Dust Experiment (SAMUM) These parameters were subsequently analyzed in the context of a correlation study that involved extinction and backscatter coefficients. It was shown [13] that the number concentration has only a low correlation with the measured extinction and backscatter coefficients In this contribution, we investigate in a systematic manner and on the basis of a special look-up table, which correlations between the lidar OD and PMPs exist, and if these correlations can be used in our inversion methodology for improving the retrieval quality of the microphysical data products.
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