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SEMPAS
SEMPAS is an ultraviolet/visible and infrared spectrometer, designed to detect emissions from ships, such as CO₂, SO₂ and NOx.
The instrument is equipped with a tracking system that “picks up” ships when they enter their fairway in front of the Belgian coast and follows them until they leave the corridor. During that time the spectrometer monitors the ship’s emissions.
MECHANICAL DESIGN
Salty sea air accelerates corrosion, making material selection and proper design crucial for the SEMPAS instrument, which is intended to operate on the North Sea. Its housing is made from a highly corrosion-resistant stainless steel alloy, while the optical head, constructed from lightweight aluminium, is protected by specialised surface treatments.
To minimise galvanic corrosion, similar materials were used whenever possible, and in critical cases, certain components were deliberately oversized to allow controlled corrosion without compromising structural integrity.
Watertightness posed another challenge. To ensure a reliable seal, all mechanical components were meticulously welded, and double O-rings were used for extra protection.
ELECTRONIC DESIGN
The electronic design of SEMPAS builds on technology inherited from an earlier built sun tracker system. However, instead of tracking the Sun, SEMPAS is designed to track boats at the horizon. This is achieved using an electronically driven motorized pan-tilt optical head, carrying a tracking camera operated in the visible wavelength range. The movable optical head includes also a UV/visible optical fiber that redirects the incoming signal to the spectrometer. So far, no infrared detection has been implemented yet.
Since the instrument operates offshore year-round and requires stable temperatures for accurate measurements, a robust temperature control system is essential. All electronics, including a computer and a power distribution unit, are housed inside a well-insulated, thermally regulated enclosure using high-performance thermo-electric Peltier elements.
The spectrometer itself is placed inside an additional thermal box for even more precise thermal control. Additionally, moisture-resistant insulation was used to minimize temperature fluctuations and improve cooling efficiency.
The instrument’s computer can be accessed via Wi-Fi or 4G. Also included in the SEMPAS electronics are a GPS antenna and a radio transponder that receives the ship’s broadcasted initial locations. In the event of a main power failure, the incorporated uninterruptable power supply (UPS) and battery guarantee a power autonomy up to several hours.
SEMPAS demonstrates how innovative engineering, smart material choices and robust component selection combine to create a reliable and durable instrument, capable of withstanding harsh marine conditions – including salty air, splashing water, high wind speeds, and varying temperatures.
Read more
Development of the SEMPAS instrument for monitoring pollutant emissions from ships over the North Sea (News 26/07/2023)
