Assorted particles of diverse shapes and sizes, including suspended sediments, marine snow, and microscopic plankton, are found in all water bodies of the world. Characterizing these particles and plankton (e.g., their size, shape, abundance, etc.) and their interactions with the local environment is critical to different research areas in the ocean sciences including, but not limited to, sediment transport, remote sensing/ocean optics, ecological studies of marine food webs and carbon sequestration. Thus, there is a significant need to develop novel in situ instrumentation that can directly quantify particle characteristics, distribution, and concentration in diverse aquatic environments.

This project revolved around the development of an autonomous digital holographic imaging system (“AUTOHOLO”) for the in situ characterization of marine particles and plankton. Digital holography is an ideal tool to study particles, providing 3-D information within free stream sampling volumes that vastly exceed the 2-D cross sections sampled by conventional imaging instruments. The instrument was successfully developed and tested over a wide range of turbidities in diverse environments, including lakes, estuaries, and the coastal ocean. The modular optical design made deployment possible in a lens-less configuration as well as with a microscope objective, allowing for characterization of particles and plankton over a size range of a few microns to a few centimetres. A high-resolution camera, acquiring data at a sampling rate of up to 3.2 Hz, can sample ~ 15 L of water per minute. The instrument is equipped with a battery pack which allows for remote deployment for several days to weeks. The AUTOHOLO is currently being used in different scientific projects, including in the characterization of harmful algal blooms and sensitive larval species in freshwater and marine environments.

Broader Impacts: Three postdoctoral researchers, one graduate student, and four undergraduate students were trained in various aspects of this project. A special issue, consisting of 24 peer-reviewed articles related to small scale spatial and temporal patterns in marine plankton and organisms, conceived and developed over the course of this project was published in the journal Frontiers in Marine Science. This project also inspired a series of talks focused on small scale patterns in particles and plankton at the 2019 Aquatic Sciences Meeting of the Association for the Sciences of Limnology and Oceanography (ASLO, session SS027). The data collected from a previous generation holographic imaging system as well as the current one, consisting of several million holograms, has been used to create and maintain a continuously updated, labelled database of different planktonic species. A portion of this dataset has been used for training and validating machine learning algorithms which allow for automated and rapid identification of different planktonic species from holographic datasets. This expanding database is also available to the general public and scientific community on request.

Last Modified: 12/29/2021
Modified by: Aditya R Nayak