Current models used in marine biology for studying population growth, species interaction, and nutrient exchange in the ocean are extremely data limited. An understanding of how different species are distributed throughout the water column and their life cycle development would significantly improve our predictive capability and basic knowledge of the complexities of sea life interdependence. One cogent example is in forecasting red tide blooms based on the, as yet unknown, oceanic condition factors.

To address the need for high resolution images of plankton species, we are developing a digital holographic camera that could be used in underwater environment with low-power deployment vehicles. Holograms are recorded using an inline configuration in a lens-less setup onto a CCD sensor. Image slices through the recorded hologram are reconstructed by a computer and processed for automated species identification routines developed in collaboration with researchers at Woods Hole Oceanographic. Resolutions down to 3 microns have been achieved through small volumes using one setup, while another version offers 9 micron resolution throughout a 500 milliliter sampling volume.

Research has focused on understanding and expanding the limits of digital holographic imaging as it applies specifically to mixed optical media and small target objects. A number of arrangements have been tested using copepod cultures and samples from local docks. Recently, the camera system was used to image plankton and diatoms in the Caribbean and mid-Atlantic during a research cruise, producing excellent images. The same system was used to track algae along three-dimensional trajectories using a new technique for recording digital holograms several times faster than the sensor’s frame rate. Current and future work centers on producing multi-scale imagery (2 microns to 2 cm), extracting additional velocity information from specially-recorded holograms, improving our processing methods, reducing power consumption, and designating an optimized design for use on an automated underwater vehicle.