In their current Applied Optics paper, Pershin et al. investigate the capability of the Raman Lidar technique to measure the thickness of transparent bulk samples floating in water in laboratory conditions. Precise measurement of sample thickness results from accurate identification of air–transparent sample–water interfaces. The transparent bulk samples were ice and poly methyl methacrylate (PMMA). The Raman Lidar technique is based on sending light pulses and detecting shifts in backscattered light wavelength (called Raman shift). Specific molecule structures have noticeable signatures in the Raman spectrum, and thus, analysis of these spectra together with elastic backscattering signal (i.e. unchanged) is suggested to improve identification accuracy of interfaces between different transparent materials.
The results of the laboratory experiments show that interfaces between air–PMMA–water could be detected solely from elastic backscattering signal peaks. However, once an optical defect is present in the PMMA brick, reliable identification of the sample–water interface requires additional investigation of the OH Raman spectra originating from water. Comparable to the PMMA sample, the interface between air and ice is identified at the elastic backscattering signal maximum. However, reliable detection of the ice–water interface is more challenging and requires advanced analysis of measured OH Raman spectra. An analysis technique already applied in seawater temperature remote measurements with Raman Lidar is adopted successfully here.
The laboratory results presented in this article verify that this Raman Lidar technique is capable of accurate thickness measurements of the studied transparent bulk materials. The journal readership will be looking forward to further field applications, especially of floating ice location and thickness studies, employing this Raman Lidar technique.
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