Borehole
Video Cameras
Borehole
video cameras are specialized equipment that have
evolved over the last seventy years to fill an indispensible niche for their
users. Originally they were used by well drillers to inspect casing, help
retrieve tools, and view other problems with wells. Over the years, the
borehole camera market has expanded to include users in many professions such
as geologists, public health workers, construction, mining, dam inspection, and
tank and pipe inspectors,
Although
borehole cameras are being used more frequently today than ever before, they
are not mass production items. One is not likely to find a borehole camera in a
garage sale or on e-bay, since once a person has owned a borehole camera, he or
she will only reluctantly give it up. A user often discovers how helpful they
are on the first well or borehole.
What
Are Borehole Cameras?
In its
simplest form, it is a water proof camera with some type of lights either built
in or attached to the camera or cable. The camera is connected to a cable that
allows it to be lowered into a hole or pushed past a constriction. The cable
will have one of more conductors that allow a signal to be sent to the system
operator to view an image on a monitor and sometimes to a recording device. In
practice, most professionals use borehole cameras with additional features that
provide more capabilities. The basic camera system may not be useful in all
situations so the industry has developed borehole cameras to produce videos in
a wide variety of situations. Some of these cases are discussed in this
article.
Borehole
Videos
Videos of
boreholes provide a continuous stream of still images commonly referred to as a
video or movie. A video is much better than a single image at providing
information of the borehole, as a continuous stream of images helps us perceive
the subject better. For purposes of showing the differences in lighting
techniques, we have used several single frames that were "captured"
from borehole videos. While these images are not as helpful in studying the
borehole as a video, they are useful in comparing different lighting methods.
Limitations
of Video Photography in Boreholes
Unlike most
nature photography which uses natural light, borehole video camera systems must
supply their own light. This is true in boreholes, shafts, mines, caves, and
other voids. By supplying the only light, the photographer has a great deal of
creative control -- literally painting the scene with light; however, the small
size of most boreholes severely limits light placement. Most borehole camera
manufactures settle for placement of camera lights, usually LEDs,
around the camera lens. While this location is the most economical, when
it is the only light source, it produces flat images and videos with no shadows
and little texture, making the video less clear than videos with off camera
lighting. Main lights next to the lens may also cause glare when particles are
suspended in the water in front of the lens as the light bounces off these
particles directly back into the camera.
Primary and
Supplemental Off Camera Lights
The best
photographic or video images are obtained when there is a primary light to the
side or at a substantial angle to the direction the camera is viewing. Any
professional photographer can easily explain the advantages of early morning or
late afternoon photography and using indirect lighting and off camera flashes.
If the
subject is illuminated only by the on camera LEDs
around the camera lens, the borehole or mine shaft will appear two-dimensional
and features closer to the camera will be much brighter than those farther
away. By moving the primary light source away from the camera, shapes and forms
are better revealed and the video or picture is more likely to show depth.
Moving the
primary light source to the side is not possible in most boreholes, however
when the primary light is attached above the camera or on the cable, its light
bounces off the borehole walls and has the effect of indirect lighting. This
indirect light usually improves the videos. When bright off camera lights are
used as the primary light, the on camera light provides fill light that reduces
the harsh shadows and gives the appearance of a more natural image. This is
similar to the way we see our environment with the sun serving as the primary
light and the sunlight bouncing off objects to provide fill light. Indoor
photography is similar lamps and flashes providing the primary light and in
direct light bouncing off the walls and ceilings.
Lighting In
Poor Quality Water
Sometimes
the fill light is not needed, for example, when suspended particles are in the
water. Light from the LEDs around the camera bounces
off these particles and goes directly back into the camera. This is a type of
glare that reduces the quality of the image in several ways. Some camera
systems have circuitry that allows the on camera lights to be turned off and
use only the off camera lights. Most borehole cameras have an automatic
electronic shutter with no moving parts that adjust the light sensitivity of
the camera.
The next to
the lens camera lights provide fill when used with brighter off camera primary
lights. This arrangement usually produces the best videos; however, when the
water has many suspended particles, the on camera light may reflect directly
back into the lens causing glare. In this situation, using only the off
camera lights as the primary light source will usually improve the video
substantially.
(Two
pictures comparing glare)
Panning and
Tilting Cameras
A
motorized pan and tilt function allows one to turn the camera left and right
and tilt the camera up and down by remote control using a joy stick. This
design allows one camera to do more than two cameras can do in the dual camera
systems. It also provides significant savings over multi-camera designs. The
pan and tilt option provides the operator with a quick and easy means to view
in any direction.
In relatively shallow boreholes, the manual
tilting mechanism is effective when using a pipe string. This method becomes
increasingly difficult at greater depths. As a general rule, the deeper and
larger the borehole, the more useful the motorized pan and tilt becomes. The
flexibility afforded by the pan and tilt option allows the user to do close up
detailed inspection of areas of interest in one pass down the borehole saving
the need for repeated passes that sometimes decrease visibility by increase the
amount of suspended material in the water. The pan and tilt camera mimics the
method a person uses to study a subject intently, this is looking at an object
from several directions. Viewing of an important subject from various angles
gives more detail and leads to a better understanding of critical subjects in
boreholes and voids.
Large
voids, shafts, irrigation wells, mines
(Picture of Super Eight Adjustable
Light with pan tilt)
Viewing
large and distant objects presents a special problem that can be greatly
improved with three techniques. Combining all three methods will yield the best
videos of distant objects.
Supplement
bright lights will be the most important factor in improving videos of
irrigation wells, shafts, and mines. Some manufactures have adjustable lights
that have multiple attachment options. Generally, taping flash lights to the
camera or cable is not very successful.
Some
manufactures offer ultra low light cameras that can view in much lower light
than other cameras. These units may sacrifice color to achieve the ability to
view at greater distances.
All
professional grade camera manufactures offer a camera system that can view to
the side, either by using two cameras, in one case, with one permanently set
pointing down and the other one pointing straight to the side with 360 degree
rotation. The other alternative is the pan and tilt camera that allows the
operator to aim the camera in any direction with a joy stick. Using tape to
point a camera to the side is difficult and only marginally effective.
Small
Holes, Past Pumps and Obstructions – Small is Good
Videoing
in boreholes requires small cameras, or at least skinny ones. Most cameras are
two inches or less in diameter. A few are about 1 to 1 ½ inches and diameter
and one manufacture has a ¾ inch diameter camera. These smaller cameras usually
have a tapered top to allow it to slip past objects on the way out. There are times when one may need to view
past a pump to go past a protrusion. In these situations, the smaller the
camera diameter, the better.
(Picture
of a nano going in a tight place) (Picture of the tapered end of a nano)
Focal
length, lens selection, and zoom
Most
borehole cameras have a fixed focus lens that view close-up subjects with very
good clarity. The disadvantage of a close up lens is that distant objects can
be slightly out of focus. This may not matter since most boreholes are a foot
or less in diameter. For larger
borehole and voids, a few manufactures offer lenses with different focal ranges
to accommodate users who video distant objects.
A few very expensive cameras have zoom focus.
Camera
Resolution and Good Images
Improving image resolution can be
accomplished three ways.
The
simplest method is to move the camera closer to the subject. In shallow boreholes
this can be done with a pipe string attached to the camera. This method is
especially effective with a tilting camera and at depths of less than 100 feet.
The side view in a duel camera is closer to the borehole wall then the down
viewing camera, thus the side view will have slightly better resolution than
the down view. The pan and tilt camera can be placed even closer to a subject
since the camera when tilted extends an inch or two closer to the borehole
wall. Thus the tilting camera has a small advantage over duel cameras in term
of resolution and distance to subject.
Another
method to improve resolution is to increase the lines of resolution of the
camera and all the capability of all the other parts of the system to handle a
higher resolution image. This includes the cable, monitor and other electronic
processing. At this time there are no high definition borehole camera systems
available in the general borehole camera market. There are modest differences
in camera resolution between manufactures. Considering lines of resolution of
the camera is not sufficient to compare different systems as all system factors
should be considered to determine effective resolution.
The
third method to improve resolution applies in situations where there is
insufficient light. Some borehole and voids have dark surfaces and absorb much
of the light. Others are too large for the lights next to the lens. A grainy
image results in low light. The solution
in these situations is to use an ultra low light camera, more supplemental
light, or both.
(Diagram)
(Side
bar case history)