John Potyondy & Larry Schmidt
Stream Systems Technology Center
Fort Collins, Colorado
The advent of laser levels and surveying instruments makes surveying easier than
ever allowing one person to do simple surveys such as stream channel cross-sections
and channel slope measurements. Laser levels project a beam in a circular plane through
a rotating prism. A special leveling rod with a detector is moved up or down until
the beam intersects it. The use of laser levels is deceptively simple - set the instrument
up, turn it on, watch the laser spin, get out the rod, wait for the magical beeping
sound, record the data and you're done.
New technology offers many advantages. At the same time surveyors need to remember
that basic surveying principles are unaltered by the new equipment. This is especially
true regarding error trapping and equipment checking. Even with a laser level it
is wise to run a closed level loop to verify that the data is within accepted standards.
Some additional things we learned includes:
1. Check the calibration of the instrument each time you use it. Do the standard
two peg test or set the laser up, take a reading on a fixed point, rotate the instrument
90 degrees and take a second reading on the fixed point repeating this procedure
as you rotate the instrument 180 and 270 degrees. All of the reading should be identical.
If they are not, the instrument needs to be calibrated.
During our last outing with a laser level, we were told that the laser is always
in calibration as long as it spins. If the laser is no longer level, it simply won't
run. We found out the hard way that this is not true. Our laser appeared to work
fine but yielded a closure error of about one meter at the end of the day.
Check the calibration each time you use it and especially if it is bumped, dropped,
or otherwise jolted.
2. Never run two crews with two lasers in an area at one time to increase productivity.
The sensor on the rod doesn't discriminate between the laser beams sent out by each
instrument. By projecting two laser light planes at one time, you may inadvertently
switch from reading one laser to the other. If you don't catch it, the result is
garbage data.
3. Avoid shooting excessively long distances. Even though the laser is capable of
shooting elevations 3,000 feet away, this is not a good idea. Remember, the earth
is not flat! Try to keep the distance between the laser and the point you are shooting
for elevation to distances of less than 300 feet. If you need the elevation of a
point 3,000 feet away, move the instrument several times by establishing a number
of turning points.
4. If you are working in brushy terrain (like riparian areas with heavy willow vegetation),
a traditional level often "sees" through the bushes better than a laser.
Don't throw away your old equipment. In some cases, it's better than the new.
5. Keep good notes. If you have two laser levels, record the serial number in the
field notes at the beginning of each day so that if one instrument malfunctions,
you can salvage some of the day's work . Always close each survey in the field and
do the computations before you take down the instrument and depart for the office.
