Range-resolved water temperature measurement using Raman LiDAR with multiplexed excitation

Area of Science:

• Optics and Photonics
• Environmental Sensing
• Spectroscopy

Background:

• Accurate temperature profiling is crucial for understanding aquatic environments.
• Traditional methods for underwater temperature measurement can be invasive or limited in scope.

Purpose of the Study:

• To develop and validate a remote sensing technique for measuring temperature profiles in water.
• To assess the accuracy and depth resolution of the proposed method.

Main Methods:

• Utilizing time-multiplexed blue gallium-nitride laser diodes with separated wavelengths as the excitation source.
• Collecting elastic and Raman scattering returns using a dual-channel detector system.
• Calibrating the ratio of Raman measurements for temperature retrieval and elastic measurements for attenuation correction.

Main Results:

• Successfully achieved remote temperature measurements in clear water up to 50 meters.
• Demonstrated temperature accuracy better than 0.5 °C at 10 meters and 1 °C at 50 meters.
• Achieved depth resolution ranging from 0.5 to 4 meters using 5 ns excitation pulses.

Conclusions:

• The developed Raman spectroscopy technique offers a viable non-contact method for underwater temperature profiling.
• The system shows promise for applications requiring precise monitoring of thermal gradients in aquatic systems.
• Further optimization could enhance accuracy and depth resolution for broader environmental applications.