About the project
Regional product calibration
Two major limitations are found in remote sensing of algal blooms: optically complex coastal waters and the variety of species of algae with very different pigments and concentrations.
To build regional algorithms, more accurate data for optically complex coastal waters is necessary to fit the standard products provided by space agencies. In-situ and laboratory measurements allow regional parameterization of apparent and inherent optical properties, improving the precision of satellite products.
The hypotheses considered in this project are the following:
- That the optical properties of Chilean coastal waters are particular and, through their influence on surface reflectance, ultimately determine the extent to which HAB species can be remotely detected.
- That the high spectral resolution scattering and absorption optical properties of key HAB species (including A. catenella) are spectrally separable to allow custom tuning of remote sensing algorithms.
- That the optical properties of Chilean coastal waters, combined with knowledge of the optical properties of key HAB species, can be used to tailor specific HAB algorithms suitable for both in situ and remote sensing HAB detection .
In situ bio-optical measurements and surface water sampling
The first step in improving the accuracy of satellite HAB detection is a greater and better understanding of the optical complexities of the waters of relevant regions through in situ measurements.
4 measurement campaigns were carried out in the regions of Los Lagos, Aysén, and Magallanes. The staff was trained in the use of the measurement instruments and protocols, including the use of the software. Radiance and irradiance measurements were taken with the TriOS radiometric instrument, funded by the IT17F1012 project, showing positive results from both the protocol and the training of IFOP staff, ensuring the permanence and usability of the measurements:
Illustration 1: Radiance measured with the TriOS radiometric instrument in the Chiloé campaign.
Illustration 2 Irradiance measured with the TriOS radiometric instrument in the Chiloé campaign
The HPLC and PABS samples taken were analyzed at CSIRO’s laboratories in Hobart, Australia.
Optical characterization of target species, including pigments
To address the need to know the optical properties of all species that form blooms, and thus to improve the ability to detect them through satellite observations, laboratory measurements were performed on cultures of key species isolated from samples from the region, especially those that are considered harmful. The species that were successfully cluttered are:
- Heterosigma akashiwo
- Protoceratium reticulatum
- Pseudochatonella sp.
- Alexandrium minutum (Australian version)
Specific absorption curves
Improved algorithm test design
Spectral modeling of apparent optical properties (AOP) such as reflectance to determine the sensitivity of reflectance to different algal species that cause flowering, different concentration levels, and other optical properties present in water such as Colored Dissolved Organic Matter ( CDOM) and suspended sediments.
Inherent Optical Properties (IOPs) such as absorption and scattering of both phases will be used to parameterize a radiative transfer model (eg HydrolightTM), to solve the radiative transfer equation by forward modeling for reflectance spectra Of surface. The agreement of the calculated reflectance with the in situ reflectance measured specifically at selected stations (optical closure) will allow confirmation of the accuracy of the fit.