Relative spectral attenuation coefficients of water

Area of Science:

• Optical Oceanography
• Spectroscopy
• Water Optics

Background:

• The attenuation of light in water is crucial for understanding underwater visibility and remote sensing.
• Previous studies have suggested potential fine spectral structures in water's attenuation properties.

Purpose of the Study:

• To precisely measure the relative variation of the attenuation coefficient with wavelength in distilled and seawater.
• To identify any subtle, fine spectral structures within the attenuation versus wavelength curve.

Main Methods:

• Laboratory experiments were conducted using distilled and seawater samples.
• Spectral measurements were performed in the 3750 Å to 6850 Å range with a high resolution of 0.2 Å.
• Longer water paths (9.7 m and 19.5 m) were utilized to enhance sensitivity.

Main Results:

• Microphotometer trace analysis revealed no discernible fine spectral structure in either distilled or seawater.
• The detection limit for variations in the attenuation coefficient was determined to be 0.1 x 10⁻⁴ cm⁻¹, limited by plate grain.
• Broad, unstructured peaks were observed in the relative coefficient versus wavelength curves around 4700 Å, 5150 Å, and 5500 Å, with approximate widths of 50 Å.

Conclusions:

• The study found no evidence of significant fine spectral structure in the attenuation coefficient of water within the investigated spectral region and resolution.
• The observed broad peaks are likely artifacts or broad absorption features rather than fine spectral details.
• These findings contribute to a better understanding of the optical properties of water for various applications.