A LIDAR-compatible, multichannel raman spectrometer for remote sensing of water temperature

The design and operation of a custom-built LIDAR-compatible, four-channel Raman spectrometer integrated to a 532 nm pulsed laser is presented. The multichannel design allowed for simultaneous collection of Raman photons at two spectral regions identified as highly sensitive to changes in water temperature. For each of these spectral bands, the signals having polarization parallel to (‖) and perpendicular to (⊥), the excitation polarization were collected. Four independent temperature markers were calculated from the Raman signals: two-colour(‖), two-colour(⊥), depolarization(A) and depolarization(B). A total of sixteen datasets were analysed for one ultrapure (Milli-Q) and three samples of natural water. Temperature accuracies of ±0.4^◦ C–±0.8^◦ C were achieved using the two-colour(||) marker. When multiple linear regression models were constructed (linear combination) utilizing all simultaneously acquired temperature markers, improved accuracies of ±0.3^◦ C–±0.7^◦ C were achieved.