Lidar Game Changing Tool for Research and Metal Detecting

How did you first get acquainted with Lidar?

A friend of mine who has been metal detecting for over 50 years told me for some time, he’s been using this newer technique to uncover cellar holes in the northeast and that it often helped him to find untouched colonial sites. So, one evening we set up a Zoom conference call, and he shared the basics of using the tool, and from then on, I was hooked on the possibilities. I noticed that at a detector meeting, when I asked about using Lidar to find places to metal detect, with some of the more experienced members, I was told that it was a best kept secret and not to mention it too loud in public or some people might get upset.

So what is this mysterious tool Lidar?

Lidar is an acronym for “light detection and ranging.” It is sometimes called “laser scanning” or “3D scanning.”

Light Detection and Ranging (lidar) is a technology used to create high-resolution models of ground elevation with a vertical accuracy of 10 centimeters (4 inches). Lidar equipment, which includes a laser scanner, a Global Positioning System (GPS), and an Inertial Navigation System (INS), is typically mounted on a small aircraft. The laser scanner transmits brief pulses of light to the ground surface. Those pulses are reflected or scattered back, and their travel time is used to calculate the distance between the laser scanner and the ground.   

Lidar data is initially collected as a “point cloud” of individual points reflected from everything on the surface, including structures and vegetation. To produce a “bare earth” Digital Elevation Model (DEM), structures and vegetation are stripped away.  

Lidar applications can be divided into airborne and terrestrial types. I primarily use the airborne software applications which create detailed topographic maps of the surface of the ground which can be viewed in layers. I typically use just two layers. The Elevation Viewer includes a statewide digital elevation model (DEM) that can be displayed as hillshade, shaded relief, slope or aspect.The gps coordinates of the location are easy to find in the Elevation Viewer using the coordinates tool.

Airborne lidar (also airborne laser scanning) is when a laser scanner, while attached to an aircraft during flight, creates a 3-D point cloud model of the landscape. This is currently the most detailed and accurate method of creating digital elevation models, replacing photogrammetry. One major advantage in comparison with photogrammetry is the ability to filter out reflections from vegetation from the point cloud model to create a digital terrain model which represents ground surfaces such as rivers, paths, cultural heritage sites, etc., which are concealed by trees. Within the category of airborne lidar, there is sometimes a distinction made between high-altitude and low-altitude applications, but the main difference is a reduction in both accuracy and point density of data acquired at higher altitudes.

Airborne lidar can also be used to create bathymetric models in shallow water. I personally have not used this technique, but I know people can find structures and look at the bottom. It is limited based on clarity of the water.

Bathymetric lidar is most useful in the 0–10 m (0–33 ft) depth range in coastal mapping.^[50]

On average in fairly clear coastal seawater lidar can penetrate to about 7 m (23 ft), and in turbid water up to about 3 m (10 ft)

Another type of lidar I have not used but have explored is called terrestrial lidar.

Terrestrial applications of lidar (also terrestrial laser scanning) happen on the Earth’s surface and can be either stationary or mobile. Stationary terrestrial scanning is most common as a survey method, for example in conventional topography, monitoring, cultural heritage documentation and forensics.^[45] 

The 3-D point clouds acquired from these types of scanners can be matched with digital images taken of the scanned area from the scanner’s location to create realistic looking 3-D models in a relatively short time when compared to other technologies

What are some of the uses of lidar in relation to metal detecting?

The applications really depend on your location. In southern New England, lidar was used to reveal stone walls, building foundations, abandoned roads, and other landscape features obscured in aerial photography by the region’s dense forest canopy.

Here in the northeast my main use is to scan forested areas for evidence of colonial cellar holes. Its amazing how the mapping tool can visualize under a forested area to show irregularities in the ground. Once you learn how to interpret the data, you can see that cellar holes have a distinct appearance as do wagon roads, well-worn trails and stone walls. My friend and mentor is so good at using this tool that he can often tell where the first and early sites that did not use stonework for the foundations were occupied These areas were often inhabited while the permanent structures were being built and can be very productive because they are often neglected when people focus on just the obvious cellar hole.

Lidar has many uses in archaeology, including planning of field campaigns, mapping features under forest canopy, and overview of broad, continuous features indistinguishable from the ground. I have heard stories of ancient ruins being found under a forested canopy and even unknown pyramids being located. In CT a lost and forgotten mineshaft was found using the technique.

Fort Cumberland National Historic Site, Canada, lidar discovered archaeological features related to the siege of the Fort in 1755. Features that could not be distinguished on the ground or through aerial photography were identified by overlaying hill shades of the DEM created with artificial illumination from various angles.

Lidar was used to search for the legendary city of La Ciudad Blanca or “City of the Monkey God” in the La Mosquitia region of the Honduran jungle. During a seven-day mapping period, evidence was found of man-made structures in the jungle thatwee hidden from aerial views.

Why do many detectorists not like people talking about it or for you to teach it?

The obvious answer is that many people using these techniques have established honey holes that have been very productive, and they want to keep them secret. I can often see who use these techniques at the monthly meetings even though they never mention it. These people consistently are winning find of the month with colonial artifacts and I believe many times this technique and possibly some other special tools like Historic mapworks and historic aerial photography have been used.

Is it difficult to learn?

Like anything there is a learning curve. After a couple of hours with my friend I was able to get enough of the basics to get started…

Not surprising but You tube has relatively little information about it except a few descriptions from the UK where is has been used more extensively. As time goes on more and more people are hearing about it. TV shows have even featured it in crime scene investigations. A few sites have offered formal training. A link is below for a three-hour course.

Training website

https://coast.noaa.gov/digitalcoast/training/intro-lidar.html

Is it available everywhere?

Unfortunately, although the mapping continues there are still some states that do not have the technology in place. In CT a lot of work has been done through the university system.

There are some states that may have partial access.,.

 I recommend researching your location and checking if a lidar database exists for your area.

The USGS hopes to complete collection of lidar data for all of the U.S. and its territories by 2022 (status map). Due to high cloud cover and remote locations, Interferometric Synthetic Aperture Radar (IfSAR)—rather than lidar—is being used in Alaska. 

The National Map is the primary repository for USGS base geospatial data. Access lidar data using: 

• 3DEP LidarExplorer – Point cloud data and lidar-derived DEMs 
• The National Map Download Client 
• The National Map Services  

Do you need special hardware or software?

Yes, you will need an elevation viewer software package which is specific for each state. They are usually free of charge. However, I have found it frustrating when consulting and trying to help people around the country and finding that the software and elevation viewer often does not use a common platform. It’s like learning it all over again. For hardware, I have used my apple tablet, a pc, laptop and even my phone. However, in general the bigger the screen the better and easier it is to view the lidar maps. I also like to print the maps to study later.

Have you found any drawbacks to using lidar?

Yes, it is just a tool and a start in the research process. When I find a potential location, I mark the GPS coordinates and the need to research if it is on public or private land and whether permission will be needed. I will also walk to the site to confirm it has potential and have found that sometimes natural stone formations can be misleading and look like cellar holes. I once found over 50 cellar holes to later be disappointed that they were all on private land and detection was not allowed when I asked permission. I strongly urge and warn you to always seek permissions. There are lots of stories of people getting arrested or fined for being on protected sites.

Can it be used in water?

I personally have not used it in the water, but it does have potential applications for shallow and clear water. It can show where there were structures. It is called bathymetric lidar.

What is the best way to get started?

My suggestion is to first research whether the tool is available in your area. Often you can just google lidar and your location may give you some leads. Then you must find the viewer and start looking at maps. In the viewer there are usually multiple layers of maps you can view. Personally, I like to use the hill shade and base maps the most, but it is a matter of preference.

Be patient and don’t give up. There is a learning curve but for some people the rewards can be obvious to find new sites. But remember this is only one research tool. There are many out there. I have a Youtube presentation on this and other techniques if you are interested. It’s long, so make sure to make a strong cup of coffee.

Good luck and happy hunting. LMK if you try it and how you make out. A link to my game changer Facebook group is below.