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Case Study

Alternative to Infra-Red Spectroscopy

The Client

A European consortium of fishermen, fish processors and biologists.

They came to us about a particular fishing issue. Read the brief for more information

The Issue

Crustacean, in particular crab, grow by casting off their existing shell, growing a new, larger one and filling the excess space within the shell with seawater. This makes it difficult when fishing to differentiate between large, meat filled crab and recently moulted crabs full of seawater. This results in inefficient crab fishing, transporting poor quality crab far from their habitat.

Infra-red spectroscopy was able to differentiate between crabs full of meat and full of water but these were large, expensive (c£100k) and contained high speed rotating optics. Once detected it is not permitted to returning the crab to the sea near the harbour.

The project aim was to develop a cost-effective, boat transportable crustacean grading unit for objective grading of species into different qualities based on meat content in order to improve fishing sustainability and efficiency.

Our approach

We visited the Oslo based manufacturer of in-line spectroscopy equipment to better understand how the equipment currently worked and to see what opportunities there were for miniaturisation and cost reduction. Considering the requirement for mounting on a boat operating in harsh conditions out at sea it was clear that another approach was required as the current method was too expensive and delicate.

Reviewing the spectroscopy data from scanning crabs full of meat and full of water there were four key wavelengths of light which appeared to provide enough information to be able to determine their approximate composition. This would allow the scanning system to be reduced to four separate wavelength LED (light emitting diode) sources, fixed frequency band pass optical filters and four optical receivers.

Prototype electronics and firmware were produced which allowed for adjustments and optimisation through experimentation. The LED brightness and durations and the gain of each optical receiver were software configurable to allow experimental tuning without having to re-spin printed circuit boards.

The Results

After thorough testing and optimisation the results were compared with the those from the full spectroscopy units.

The prototype scanner was confirmed to be correctly separating crab full of water from those full of meat, surprisingly due to female crabs containing roe the prototype was also able to differentiate between male and female crabs reasonably well.

The prototype contained no moving parts other than a simple shutter used to exclude light for calibration, no mirrors which could corrode and had a production cost estimate of less than £200.

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