Satellite derived bathymetry and benthic mapping

My main focus in this area is to put capability for the latest physics-based methods into the hands of practitioners. This is provided by the software IDA. Typically I also work closely with clients to ensure the tools are used to their full potential. For example: suggesting efficient workflow practices, quality assurance, and understanding the benefits and limitations of processing options. This can be done through training courses (either online or in person) or by partnering on projects.

In addition NOL does undertake a limited amount of production work of bathymetric and bottom cover maps. If you are in need of satellite derived maps of shallow water areas, but do not want to develop in-house capability for production, please get in touch to discuss the requirements. At the very least I can offer some free advice.

Radiative transfer modelling

On various projects I have provided unique capabilities for the modelling of light in natural environments. In-house models include a GPU-accelerated 3-dimensional geometric optics model, an FDTD particle scattering model (see below), and fast vectorial Monte-Carlo models for atmospheric and surface applications.

Light propagation visualisations from the 3D geometric optical model:

• Animation 1 - Wave focusing over dome shaped corals.
• Animation 2 - 360° rotation around branching corals.
• Animation 3 - Wave focusing on sand.
• Animation 4 - Seagrass canopies illuminated under wave motion.

These models have been used in remote sensing and photobiolgy applications, see references below. In addition to innovative development I have 20 years' experience in 'traditional' plane-parallel radiative transfer modelling of the atmosphere and water column, such as provided by the model HydroLight which I maintain and develop. I work on projects as an advisory expert, or directly provide deliverables such as sensitivity analyses, error propagations, lookup tables and other analyses that require using or developing radiative transfer models.

If you are looking for this kind of expertise, please feel free to send me an email.

Particle scattering

In addition to geometric optics I also work on the propagation of Maxwell's equations to deduce scattering properties of particles of arbitrary shape and composition. I have an in-house GPU-accelarated FDTD (Finite Difference Time Domain) model which makes performing 1000's of runs for orientation and particle variations computationally efficient. The following example is from Zhai et al. 2020.

• Animation - Slice through Microcystis phytoplankton colony with vacuoles.

I am particularly interested in projects that might assist in the support and release this code.

References

Selected publications giving further details and examples of collaborative work.

Most are open access, otherwise request a pdf reprint.

Satellite derived bathymetry and benthic mapping

Casal G, et al. (2020) Satellite-derived bathymetry in optically complex waters using a model inversion approach and Sentinel-2 data. Estuarine, Coastal and Shelf Science 32: 173–182.

Hedley J, et al. (2018) Coral reef applications of Sentinel-2: Coverage, characteristics, bathymetry and benthic mapping with comparison to Landsat 8. Remote Sensing of Environment 216: 598-614.

Hedley J, et al. (2017) Remote sensing of seagrass leaf area index and species: The capability of a model inversion method assessed by sensitivity analysis and hyperspectral data of Florida Bay. Frontiers in Marine Science 4:362.

Radiative transfer modelling

Hedley J, McMahon K, Fearns P (2014) Seagrass canopy photosynthetic response is a function of canopy density and light environment: A model for Amphibolis griffithii. PLoS ONE 9(10): e111454.

Hedley J & Enriquez S (2010) Optical properties of canopies of the tropical seagrass Thalassia testudinum estimated by a three-dimensional radiative transfer model. Limnology and Oceanography 55: 1537-1550.

Hedley J (2008) A three-dimensional radiative transfer model for shallow water environments. Optics Express 16: 21887-21902.

Particle scattering (FDTD)

Zhai S, et al. (2020) Optical backscattering and linear polarization properties of the colony forming cyanobacterium Microcystis. Optics Express 28: 37149-37166.

Hedley J (2012) Modelling the optical properties of suspended particulate matter of coral reef environments using the finite difference time domain (FDTD) method. Geo-Marine Letters 32: 173–182.