The advancement of science usually depends on new measurement technologies. The invention of telescope enables physicists to find the expansion of the universe. The presence of microscope makes possible for biologists to discover cells. In our lab, we focus on the development of three-dimensional (3D) imaging technologies, and apply them in the areas of fluid mechanics, animal ecology, and environmental and life sciences. We mostly use two imaging methods: the single-camera holographic imaging and the multi-camera stereo-imaging.
Digital Holographic Imaging
Different from regular imaging, the Digital Holographic Imaging (DHI) uses a coherent light source (e.g. laser). It records an interference pattern that contains both intensity and phase informations of an object. When combined with a microscope objective and a high speed camera, this technology provides real-time 3D data at the micro/nano scales. One challenge with DHI is the relatively low accuracy in the depth direction. We are developing better particle re-focusing methods to overcome this problem. We are applying the DHI in turbulent flows to resolve the smallest length scale flow structures. We are also implementing the DHI in environmental and life sciences, for example, to monitor the locomotions of micron planktons, bacteria, and living cells.
Another method to obtain the 3D information is to record an object from different directions using multiple cameras, namely the stereo-imaging. This method typically requires two steps: the camera calibration and the 3D reconstruction. For laboratory and small-scale experiments, the calibration can be done easily by imaging a fixed target. But for field and large-scale (~100 m) applications, using a fixed target is not possible. We are developing novel calibration procedures based on moving targets to overcome this problem. A second challenge is the optical occlusion problem when the imaged field has high number densities. We are testing novel stereo-matching methods to solve this problem. With these new improvements, we are using stereo-imaging to track the movement of animals in the natural and ecological environments.
- Ling H, McIvor GE, Nagy G, MohaimenianPour S, Vaughan RT, Thornton A, Ouellette NT (2018) Simultaneous measurements of three-dimensional trajectories and wingbeat frequencies of birds in the field. J. R. Soc. Interface. 15, 20180653.
- Ling H, Katz J (2014) Separating twin images and locating the center of a microparticle in dense suspensions using correlations among reconstructed fields of two parallel holograms. Appl. Opt.53(27), G1-G11.