Seeing fine distinctions

Since the primary sense used by humans is sight, operating a vessel in the darkness of night is an activity many boat owners are finding daunting. The availability of night vision devices in the 1990s certainly emboldened some mariners. Now a different type of night vision unit, with its own advantages, is becoming more affordable. Companies like FLIR Systems, Neraida Vision Systems and Hoteye are offering new infrared sensors for marine use.

Many of us associate night vision with the soft, green images produced by night vision units that come in the form of handheld binocular or monoculars. Also in this category are military-type night vision goggles from various sources and of varying levels of quality. These units became popular in the 1990s as military-based night vision technology was released for civilian use. This type of night vision uses photo multiplier tubes to multiply the small amount of visible light available at night and produce a visible scene.

The other type of night vision device senses infrared (IR) radiation, a different slice of the electromagnetic spectrum with slightly lower frequency and longer wavelengths than visible light. Infrared cameras for the marine market have been available for several years. The difference in the sensors being offered now is increased sensitivity at a lower price.

Infrared sensors use a solid state chip that detects the longer wavelengths of infrared light. The IR units now being offered by Neraida, FLIR and others sense “far infrared” (“near infrared” is just outside the range of visible light). Far IR is also called thermal IR. These units can sense heat, such as the heat given off by the human body. If the only images these units picked up were from objects making their own heat via oxidation, like people and engines, then IR cameras might not be tremendously useful. What makes them so effective for seeing at night, however, is their ability to sense the differences in temperature down to, in the case of the unit from Neraida, -67° F. These units can sense differences in temperature to 0.075 of a degree. These fine gradations are displayed on a monitor to present a picture of your surroundings. “An IR unit just notices the absolute difference,” explained Clay Wild, director of business development for maritime systems for FLIR Systems. “We don’t care how hot or cold an object is, we just want to see temperature difference so we can avoid an object in the water.”

The IR energy these thermal sensors pick up comes from physical processes. For example, the concrete piers of a bridge will absorb heat from sunlight all day and then after sunset, the concrete will retransmit that heat into its surroundings.

But even those materials that don’t absorb and retransmit to a significant degree will still show up on IR sensors because all materials warmer than absolute zero emit some amount of IR energy – even objects you might not expect, such as ice.

A thermal IR night vision unit provides an impressively detailed picture of the situation around your boat at night, even through light fog and haze. They are also excellent in the area of man-overboard recovery. A person in the water shows up bright white against the water background.

According to Robert McNealy, president of Neraida Vision Systems, that is where his Nerin3R unit particularly shines. “We have a 53° by 40° field of view,” McNealy said. “That’s the widest field of view on the market.” A wide field of view allows one to find a person in the water more easily with less panning and tilting of the camera. The Nerin3R is priced at $79,000 and is aimed at the luxury power yacht market.

FLIR Systems sells a similar unit called the ThermoVision Mariner. Like the Nerin3R, the ThermoVision Mariner is an IR camera on a motorized mount that allows the camera to pan and tilt. The FLIR unit is produced by a company that is one of the largest producers of IR gear. Due to FLIR’s volume advantages, according to Wild, the company can offer the ThermoVision Mariner for less than $10,000 installed.

IR cameras are still expensive for most voyagers, but they seem on the verge of becoming a more common installation aboard voyaging boats.

By Ocean Navigator