Characteristics of laser-induced inelastic-scattering signals from coastal waters

Abstract

This paper describes laser-induced fluorescence and Raman signal measurements from coastal waters. These measurements collect laser-induced signals as a function of laser wavelengths and water temperatures. For each laser wavelength, the laser energies simultaneously induce dissolved organic material (DOM) fluorescence, alga fluorescence, and Raman signals. For the water samples used, these measurements show that DOM and Raman signal amplitudes are insensitive to water temperatures. However, alga fluorescence signals increases slowly with increases in water temperatures. The wavelength-dependent measurements show that Raman signal amplitudes decrease with increases in excitation laser wavelengths between 490 and 535 nm, the wavelength range used in these measurements. The alga fluorescence signal amplitudes also decrease with increase in excitation laser wavelengths. However, these decreases are insignificant compared to that of Raman signals. Within the excitation laser wavelength range studied, the DOM fluorescence does not show significant spectral structures that depend on laser wavelengths. The measurement results suggest optimum laser wavelengths for studying laser-induced inelastic scattering in coastal waters. These data also suggest that for both active and passive coastal water remote sensing, Raman signals may bias alga fluorescence measurement results depending on relative alga fluorescence and Raman signal intensity.