Measurements With Lasers

Measurements With Lasers

Lasers can be of great value in night rescue or military operations, when fording of shallow streams and rivers becomes necessary.  If the water is relatively clear, lasers enable a quick assessment of comparative depths at various places in the body of water.  In nighttime operations, night vision equipment, even Generation 3 goggles, are of little help when there is a need to determine where to cross a creek or shallow river.  This is because present night vision equipment can see only the surface of the water, and not what is beneath it. 

The laser depth measurement method, although crude and inaccurate, can be helpful in determining where the shallowest water is and what underwater obstructions might be present.

 The technique works best if the water is clear or only slightly murky, although it can work in very shallow muddy water.  The beauty of the technique is that it can be used before reaching the stream or river.  For instance, looking down from a ridge, it may be possible to quickly scan the waterway in the valley below and determine where would be the logical place to ford.  It is important that the laser used for depth finding have a collimated beam, and it is preferable that it be a powerful red laser, such as the Pulsar or Red Spyder II.  Green lasers can be used, but the brightness of the beam (before it hits the water) can make it difficult to see subtle changes in water depth.  Often, it will be helpful to use binoculars or night vision goggles when depth finding, particularly if you are far from the body of water.  In combination with night vision equipment, low powered laser pointers can also be used for depth finding, but they do not provide nearly as much useful information as the higher power lasers.

This depth measurement method works because as the laser beam travels down through the water, the beam is diffused by particulate matter in the water.  Each microscopic particle reflects light back toward the surface and so a luminescent glow develops around the beam.  In most situations, the further down into the water the beam travels, the greater in diameter this luminescent glow becomes.  By moving the beam around, it is often possible to ascertain where the water is most shallow, or where holes and rocks are..  It takes much experience to be able to quickly and accurately determine depth using this technique because the size of the luminescent circle will be different from one body of water to another, primarily because of differences in water clarity.  How well it works depends on how far the laser is from the water, the angle at which the beam enters the water, water clarity, and a number of other factors.  It is certainly not a good way to determine where to ford, but it is sometimes the most practical way.

Fishermen and other outdoorsmen can use this technique to determine the best areas for night fishing, or to locate underwater obstructions such as logs, rocks, sunken boats, etc. 

Because many aquatic species are attracted to bright light, a laser might be used to attract fish to a given area, or to determine what manner of life lives beneath the surface.  It should be noted, however, that some species of fish are scared off by the bright beam of a laser, as are certain creature which live above the water.

If water is relatively clear, a laser can also be used as a tool to illuminate underwater terrain and make it visible to those looking into the water from above.  This method is not as good as placing a powerful light under water, but it can be done from a distance, and without getting into the water.  In some situations, particularly when using low powered lasers, night vision goggles will enable a better view of the underwater terrain.

In covert ops, if night vision equipment is available, an infrared pocket laser can be used for depth measurement.  The laser is used as previously described, and the beam and resultant illumination viewed with night vision goggles.  Should an infrared laser and night vision equipment not be available for the covert operation, use a red laser rather than a green one.  The red beam will be far less visible than a green beam and the operation less likely to be detected by the enemy.

When using lasers for depth finding, laser goggles obviously can’t be used, so extreme caution must be taken not to direct the beam into anyone’s eyes.

Poor Man’s Radar

At night, if night vision isn’t available, one can often use a laser to get an idea of what the terrain far ahead looks like.  By waving the laser back and forth, trees, vehicles, utility poles, buildings, small hills, and other objects are made visible in a crude but colorful way.  This technique is no substitute for high-grade night vision, but it’s certainly better and safer than “being in the dark” about what lies ahead.  This technique is best done with a low powered laser pointer, so that no danger will be posed to people, animals, or aircraft in the distance - or your own eyes.  The reason to consider your own eyes is because when flashing a laser around in the dark, you will eventually hit a highly reflective object and have the beam reflected back at you.  This is one those situations in which wearing laser goggles is not wise because moving around in the dark, with your vision impaired by light-limiting eyewear, is not a smart thing to do.  When using high powered lasers, such as those sold by Warn Laser, the beam intensity should be attenuated down to a safe level, as previously described.  Any color laser can be used for this crude “radar” technique, but red is probably best because the dot (where the beam impacts against an object) is less obscured by the brightness of the beam itself.  Plus, in covert operations, a red beam is much less likely to be spotted by the enemy than a green beam - unless, of course, the enemy is equipped with night vision.