Optical remote sensing of subsurface water temperature and salinity
Abstract
The significant problem addressed by this project is that there is no standard method for remotely and actively measuring, monitorin,g or mapping the subsurface water temperature and salinity in oceans and coastal waterways. Nor are there methods for determining th,ese parameters simultaneously. Correspondingly, there is a gap in our knowledge about the temperature and salinity of water below th,e surface, such knowledge being highly desirable and potentially very powerful in a range of sectors that include defence. Specific,applications include monitoring and surveillance, validating hydrologic models, and predicting the underwater propagation of sound.,Previous work by our group has culminated in the construction and testing of multi-channel Raman spectrometers which were found to b,e effective in determining the temperature of natural water samples from Sydney Harbour with accuracies between 0.2 - 0.5C. These s,pectrometers are LIDAR-compatible, in that they use pulsed laser excitationat either green or blue wavelengths, and fast sensitive d,etection. This compatibility with LIDAR (Light Detection and Ranging) enables depth-resolved temperature and salinity measurements t,o be made. Our apparatus is broadly similar to the airborne LIDAR-based bathymetry that is used routinely to measure water depth in,coastal environments, but with additional channels to detect inelastically-scattered signals. The research proposed here is strongly, focussed on transitioning our apparatus and methodologies to the field, identifying the parameter space in which accurate informati,on about temperature and salinity can be obtained, and identifying the limitations outside of that space. We will do this through a,combination of numerical modelling (Monte Carlo simulations), lab-based experimentation, and field studies. Our target specification,s are 0.2 C for temperature, 0.2 psu for salinity, 0.5 m for depth resolution, and 10-100m for range, depending on the turbidity,of the water. The three project outcomes we anticipate are:1. A modelling capability that a) includes the prediction of Raman return,s, b) predicts signal to noise ratios as a function of depth, and c) informs the design of field apparatus. 2. Lab-based studies tha,t demonstrate a) demonstrate the potential to measure temperature and salinity, independently and simultaneously and b) quantifies t,he signal to noise ratios required to achieve the target accuracies.3. Field implementation of methods and apparatus to measure temp,erature and salinity.A final report documenting key findings, with critical evaluation of the capabilities for multi-channel spectro,meter to measure the water column will be provided at the conclusion of the project.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 08, 2022
- Source ID
- N629092212012
Entities
People
- Helen M. Pask
Organizations
- Macquarie University
- Office of Naval Research
- United States Navy