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Simulation of Laser-Induced Light Emissions from Water and Extraction of Raman Signal

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  • 1 Naval Research Laboratory, Washington, D.C.
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Abstract

A simulation of the laser-induced Raman and fluorescence spectra produced by laser irradiation of the water column is described as well as a method of extracting the Raman signal from the fluorescence spectra using multiple laser excitation wavelengths. The simulation includes Gelbstoff fluorescence at 440 and 580 nm, chlorophyll-a fluorescence at 685 nm, Raman signal, and noise sources. Water temperature, relative intensities of the fluorescence signals, sky noise, water clarity, and depth of the return can be varied as well as system optical parameters such as collector size or sea surface range to test system design specifications. A simple method to extract the Raman signal from the fluorescent background signal is developed that uses five laser excitation wavelengths within the range of 510–570 nm. An average fluorescence signal is calculated and subtracted from the raw signal at one of the laser excitation wavelengths to obtain the Raman signal. A two-component Gaussian fit is made to the extracted Raman curve in the wavenumber domain, and a ratio of the Gaussian amplitude at Δν of 3434 cm−1 to the amplitude at Δν of 3198 cm−1 is calculated and used to determine the water column temperature.

Corresponding author address: Jeffrey E. James, Naval Research Laboratory, Code 7221 Remote Sensing Division, 4555 Overlook Avenue, Washington, DC 20375-5000.

Email: jjames@ccf.nrl.navy.mil

Abstract

A simulation of the laser-induced Raman and fluorescence spectra produced by laser irradiation of the water column is described as well as a method of extracting the Raman signal from the fluorescence spectra using multiple laser excitation wavelengths. The simulation includes Gelbstoff fluorescence at 440 and 580 nm, chlorophyll-a fluorescence at 685 nm, Raman signal, and noise sources. Water temperature, relative intensities of the fluorescence signals, sky noise, water clarity, and depth of the return can be varied as well as system optical parameters such as collector size or sea surface range to test system design specifications. A simple method to extract the Raman signal from the fluorescent background signal is developed that uses five laser excitation wavelengths within the range of 510–570 nm. An average fluorescence signal is calculated and subtracted from the raw signal at one of the laser excitation wavelengths to obtain the Raman signal. A two-component Gaussian fit is made to the extracted Raman curve in the wavenumber domain, and a ratio of the Gaussian amplitude at Δν of 3434 cm−1 to the amplitude at Δν of 3198 cm−1 is calculated and used to determine the water column temperature.

Corresponding author address: Jeffrey E. James, Naval Research Laboratory, Code 7221 Remote Sensing Division, 4555 Overlook Avenue, Washington, DC 20375-5000.

Email: jjames@ccf.nrl.navy.mil

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