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Between July and August each year, the US National Oceanic and Atmospheric Administration (NOAA) Fisheries Service conducts surveys to determine the abundance and size distribution of deep-sea scallops in areas between Cape Hatteras, NC, and Georges Bank (a large elevated area of thesea floor that separates the Gulf of Maine from the Atlantic Ocean, situated between Cape Cod, MA, and Cape Sable Island, Nova Scotia, Canada). To do this, sample height measurements from 125,000 scallops are taken from approximately 500 randomly selected locations using an 8-ft scallop dredge towed at 3.5 knots for 15 min. To increase the accuracy and speed of these measurements over current methods, William Kramer, an IT specialist at the NOAA Woods Hole Laboratory on Cape Cod, obtained a Pioneer Funding grant from the Chesapeake Bay Trust to develop a prototype machine-vision system.

System specifications required measuring scallops from 25 to 200 mm at speeds of 1800 scallops per hour (2 s/scallop). The design of the conveyor-based system had to incorporate a washing system to remove much of the debris from the catch before the scallops could be measured. The stand-alone system was also required to log readings to the PC-based vision system and the ship’s onboard computer system, which is used to log additional data about the catch.

Depending on their age and environment, scallops may be covered in barnacles or other organic material, making them appear dark in reflected light. Scallops are typically much lighter on the bottom than the top, except for “albino” scallops that are white on both sides. Because the system was required to handle scallops loaded with either side facing up, a backlight system provided a high-contrast silhouette of each scallop regardless of its shell color and texture.

Seeing scallops

Designed and developed by Compass Technical Consulting, the prototype vision system consists of a standard Series 2200 conveyor from Dorner Manufacturing modified to include a stainless-steel idler roller, an electroluminescent backlight, and a translucent belt (see Fig. 1). An aluminum shroud was fabricated over the conveyor to house the camera and laptop PC. To capture images of the scallops as they traverse the conveyor, an IEEE 1394-compatible Lightwise 1.3 monochrome camera from Imaging Solutions Group with an 8-mm-focal-length lens was positioned 35 cm over the conveyor. Running at 30 frames/s at 1280 × 1024, the camera provides 1/4-mm/pixel resolution and is compatible with LabView software from National Instruments.

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To increase the accuracy and speed of scallop measurements, Compass Technical Consulting built a prototype vision system that uses a conveyor to load scallops under a shrouded imaging system, which determines scallop height based on diameter.

Acknowledgements go to Steve Tomanovich, Compass Technical Consulting, Vision Systems Design and Imaging Solutions Group.

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