To conduct the measurements, Hou needed a self-illuminating optical target as part of a visibility test. One of the factors affecting undersea visibility is the background, or path radiance, of light. A target that is active -- or self-illuminating, like an iPad -- will help to reduce or remove the impacts of path radiance, which helps isolate a specific visibility factor researchers want to zero in on.
Hou decided on the iPad for use in the experiment after exploring other options, which were either too expensive or would take too long to deliver, according to the NRL. The iPad’s compact size and weight, as well as its brightness, low power consumption, and low heat emissivity were other design factors that made it useful. However, since it’s not waterproof, a colleague of Hou’s designed a waterproof case to protect the device.
To conduct the experiment, researchers attached the iPad to a rigid frame called the image Measurement Assembly for Subsurface Turbulence, or iMAST. Onboard the boat, researchers used the device to display active targets, such as resolution charts and image patterns, before lowering it into the water.
Once submerged, the iPad allowed control of the brightness of the patterns and charts for the purpose of the experiments, which in the end confirmed researchers’ theory that optical turbulence interferes with visibility under the water, according to the NRL.
Researchers plan to conduct future experiments to further quantify and lessen the effects of optical turbulence to aid in the design of the Navy’s next-generation electro-optical systems.