November 2024: we come across an interesting request about repairing or replacing a pair of 20+ year-old Impulse laser measurement devices that have been out in the field helping an Anthropology professor accomplish archaeological site mapping tasks:
“Aloha–I’m writing to inquire about having one or both of my 2 LTI Impulse lasers repaired. These were purchased back in 2001 and/or 2002. I have been using both regularly for the past 20+ years in archaeological fieldwork in China and more recently South Africa.”
The message comes from Christian E. Peterson, PhD, Department of Anthropology Professor and Graduate Chair at the University of Hawai’i at Manoa. Along with the service request, he also describes how the Impulse rangefinders help with plane table mapping processes. Novatr describes plane table mapping, or plane table survey, as “the simultaneous observation and plotting of field conditions on paper by a surveyor. The plane table is a flat, leveled board mounted on a tripod that serves as the drawing surface. This eliminates the need for intermediate calculations and allows surveyors to visualize and map the area in real-time.”
Attendee at the 2022 Oregon Logging Conference poses with their trusty Laser Tech Impulse rangefinder, a discontinued Laser Tech product known for its ruggedness and longevity.
As we help Dr. Peterson find the best path forward, we can’t resist asking if he might share more about himself and the type of archaeological site mapping fieldwork his Impulse units have seen. To our delight, he agrees, giving us a look into the history of some classic and well-traveled Laser Tech gear.
The original LTI Impusle was released in 1995 as a 2nd generation version of the Criterion 400. The Impulse kept most of the Criterion 400’s capabilities while introducing a more compact design and providing a more affordable price tag. Both of these early Laser Tech ruggedized rangefinders were exceptionally popular with forestry professionals thanks to their accurate measurements, robust nature, and long lifespans. You may recall another Impulse appearance on our Professional Measurement blog, which told the story of our team somehow finding a way to fix up a 26 year-old Impulse 200. The big takeaway is that it’s not uncommon for Impulse units to get 20+ years of field use under their belt.
Christian E. Peterson, PhD, prepares a plane survey table in the field.
Since the beginning, I’ve found that using my Impulse rangefinders for plane table mapping is an easy and effective option. My advisor introduced me to Laser Tech rangefinders in graduate school. Since then, I have used them continuously in my archaeological field research.
At this time, I’m still using a pair of Impulse units manufactured back in 2001 and 2002! These units are only now approaching the end of their impressively long use lives. It hasn’t been easy for them either.
Both have experienced sustained use in a variety of different locations, often under less-than-ideal conditions. They’ve traveled with me to places like northeastern China, Hawai’i, and South Africa. When I finally retire them, I’ll be upgrading to the TruPulse 200X.
I use my Impulse rangefinders to record the spatial extents and distributions of ancient remains across the surfaces of archaeological sites. Once a staple of archaeological fieldwork, plane table mapping has been largely supplanted in recent decades.
Christian E. Peterson, PhD, looks through his Impulse rangefinder.
Nowadays, you’re far more likely to see expensive, overengineered, and unduly complicated Total Station and DGPS mapping solutions. I find this trend to be unfortunate for a few reasons. For starters, setting up a rangefinder-assisted plane table mapping is a much less laborious option.
The same goes for moving your setup to a new location. It’s also a far simpler and faster method for collecting data of a sufficient resolution. On top of that, it’s much less expensive than a Total Station or the combination of a DGPS receiver and rover. In my opinion, both of those options are overkill for most archaeological purposes.
With my typical setup, an Impulse rangefinder functions as an ersatz alidade. The vertical bracket that came with the unit mounts to a flat aluminum bar to form the base of an inverted “T”. Knurled knobs are installed at either end to aid with tabletop positioning. Most local machine shops can build a setup like this for you.
I like to use compact, lightweight, wooden plane tables with a sturdy tripod. Vintage ones, produced for the U.S. Geological Survey, are my favorite. I place a large sheet of metric graph paper on top of that plane table, then grab my architect’s ruler and a pencil, and I’m ready to go.
Using rugged rangefinders instead of a traditional alidade helps speed up my data collection process. It eliminates any need for me to use a rodman or perform trigonometry. It also greatly improves the accuracy of my horizontal and vertical measurements, especially over longer distances.
I’ve found the Impulse rangefinder excellent for contour mapping and plotting within a local grid of a few hundred meters or less. I like that there’s no data to download or backup daily. Plus, the paper maps can be quickly and easily digitized once fieldwork is done.
South Africa’s Kruger National Park is the most challenging environment in which I’ve used my Laser Tech rangefinders. The archaeological site mapping projects we’re currently working on are littered with Iron Age artifacts and other remains, which is great. However, the mopane trees that have since colonized the area pose serious line-of-sight problems. This requires frequent movement of the plane table to map everything.
Complicating matters further is the need to stay close to my teammates and our game guards. This is because of the numerous elephants, giraffes, buffalo, zebra, antelope, lions, and other wild animals that freely roam the park. Sometimes they even like to visit us on-site! It makes for a fluid situation where we often pack up and quickly move the station to another location. Fortunately, my rugged rangefinders make it easy to acquire and reacquire occupation points that we can continue mapping near.
Christian E. Peterson, PhD, maps an archaeological site with his rugged Impulse rangefinders and plane survey table.
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