Friday, January 24, 2014

LIDAR Resolution

     All these images were created using LAS files downloaded from  These are massive files of LIDAR datapoints, with no accompanying geo-referenced  images.  I created all the  images  by sorting out the ground surface points using Fusion software, which was designed for analyzing forests.

Here is the Fusion interface, running  a project of the Copicut area east of Fall River, MA.  Fusion can generate its own reference images from the LIDAR data.  The red area to the right is Copicut reservoir, and is colored red due to low datapoint density.  The topo lines were created from groundpoint data. The white area denotes the area being sampled for imaging.  It helps to have a real topo map or satellite imagery open in another window for reference while working.

The commands for processing data are entered  at the C-prompt.  I hadn't done this since the 1980s, and found that it is not as hard as it looks. The screen shows part of the shoreline of South Watuppa Pond. 
      While working with data from different sites, I noted differences in image quality. This was explained in the Fusion user's manual as follows:

" In open, flat areas, ground contours can be recorded from an aircraft flying overhead providing accuracy within 6 inches of actual elevation. In steep, forested areas accuracy is typically in the range of 1 to 2 feet and depends on many factors, including density of canopy cover and the spacing of laser shots."

     The type of forest also seems to affect resolution in LIDAR.  This is a deciduous second-growth forest along a lake in RI. The false color indicates tree height.

The ground surface image of the same area shows boulders along the shore, a farm road, walls, and a cellar hole with an outcrop directly north.

     There are low cairns at this site, but they are not visible.  Presumably the resolution is too low to detect structures only 1 or 2 feet tall. LIDAR can detect taller cairns, such as those at Parker Woodland.

      LIDAR imaging of areas in dense pine forests produces impressive results. Here's the satellite imagery of part of the Copicut area with a house at lower right, and a field at bottom center. There is nothing visible through the dense pine forest.

This is the same area in LIDAR data.  Taller trees are yellow or red, and the field is deep blue.

Here is the ground surface image of the same area, with the house at lower right. The walls of an old farmstead form a neat grid.  There is a farm road that  runs through the fields at the top of the image, and exits at the upper right corner.  I have never been to this area, and had no idea what was there.

Here is another view further north in the same site, with a road and houses in the upper left corner.

The conical objects  are too large to be  boulders. They may be artifacts from very dense stands of  pine trees. They don't appear in images from deciduous forests, even if there are numerous large boulders present. There is a Filter command to remove such artifacts.
     All these images were taken from Fusion's viewer (LDV), which is only practical when working with smaller areas.  Fusion can export surface image files as JPEG files.  Depending on file size and image quality, it may be possible to create LIDAR atlases of forested areas.  Of course, nothing replaces actual visits to a site, but  LIDAR images can help in selection of sites.

Saturday, January 18, 2014

LiDAR Works!

A rainy Saturday, with plenty of time to examine LiDAR images. LiDAR is laser scanning of the ground from aircraft.  This has recently been suggested as a tool for mapping stone walls and other features hidden by the forests of New England.  LiDAR images are being incorporated into the topographic maps at Google Maps and Google Earth, but as far as I know, pure LiDAR images are not available.  Luckily, LiDAR data and software for filtering it are available online, and are free!  The LiDAR data files are free for download at    The software is Fusion, which was developed for use by the US Forestry service.  It has plenty of functions for analyzing forest canopy coverage and tree size, and can  pull out the ground points to make a 3-D surface.  Fusion is available at, along with  a tutorial and  data examples.
     Fusion is easy to install, but is not the most user-friendly software to run.  The commands for making the ground point images are entered at DOS level.  There are examples of these commands in the tutorial Exercise 7, Part 2.  I got them to work by copying and pasting into a text file, and rewriting  the file paths as needed. All the images here were generated using the default values given in the tutorial.

Here is a transmitter on top of Neutaconkanut Hill in Johnston, RI.  This view shows all the LiDAR data.  The false color spectrum shifts from blue to red with increased height.  Trees are clearly visible.

Here is the ground surface for the same area, tilted and enlarged.  Houses are clearly visible, as are the two concrete pads for transmitters in the center of the open space.

Here are the cliffs at Snake Den State Park in Johnston, RI. This three-dimensional view will be invaluable in painting reconstructions of sites.
      LiDAR images did show stone walls, but they were faint.  It will probably take some serious tweaking to get the resolution of the images in the Journal of Archaeological Science article.

 This is the same group of walls ending at a cliff that I showed 3/7/2012. The wide walls show up well; the thin connecting wall is barely visible. The diagram below shows the walls.  The cairns merely represent approximate locations of cairns.  Many are quite low and do not show up in the scan.


LiDAR produced a very clear image of the tall, conical cairns at Parker Woodland.  Unfortunately, the corners of four data files met in the cairn field, but most of the cairns were on one corner.  North is at the top of the scan.  I see the trail at upper right. Note the organization of the cairns at the center into two long lines.  There may be a depression between them, which was either a trail or a cart path.

This is definitely a work in progress.  These scans give far more detail than points on a topo map and make it easier to visualize the layout of a site.  I think LiDAR would be very useful for investigating a suspected site before visiting it.

Wednesday, January 15, 2014


Sunday I returned to the hilltop  from 3/18/2012.  This is the first group of propped boulders that I noticed formed a "corner".  Heading uphill, the first propped boulder I visit  is this huge one, with a cavity  8 feet long, 4 feet high, and 3 feet deep.  With a sloping roof and side, the useful space would be about 24 cubic feet.  This cavity  could have been used as a shelter.

The cavity floor has a couple of rocks.  The flat one is too close to the boulder roof  to be practical as a work surface.

The granite in this area is foliated, and breaks into neat slabs.  A side view of the boulder shows two such slabs, which have slipped off. There are no tool marks visible along the edges of these slabs.  Presumably, the cavity was formed by chipping away  the lower layer of rock.

    If this was  a home or a women's food processing area, there would be some grinding slicks around.  They are not easy to find since they are often covered with dirt or moss or leaves. Sometimes the little bowl is filled with leaves or pine needles, highlighting it on top of a rock. Here is the most likely grinding slick, in a broken rock a few steps from the propped boulder.

I couldn't find any grinding slicks at the other propped boulders in the corner.  Instead, I found evidence of quartz quarrying near the hilltop site with the large pedestal boulder.

Note the propped boulder in the left foreground.  It split vertically, producing the flat slab my knapsack is resting on.  About 140 feet from this site is this boulder.

A careful look inside reveals this large chunk of quartz, left from a vein.

In front of this little quartz mine.

Maybe the table site was the men's stone work area and meeting place.  Even though the granite rocks seem permanent, they are slowly splitting, breaking, and shifting. These sites are only shadows of their original structure, and are vanishing. 

Sunday, January 12, 2014

Water Flowing Across a Landscape, Revisited.

Once in a while I am lucky to see water running down this "staircase" of flat rocks. Usually it is dry, since the water only runs after heavy rain or snow melt.  The water disappears into a large pile of rocks, leaving the ground  dry.  I have described it before (5/29/2013). This afternoon I was out for a walk, and I heard the water running.

The stream is visible as a bright little waterfall just below the top of the staircase, and drips off larger rocks near the bottom.  It is easier to see in this  video.

Wednesday, January 8, 2014

Work Tables

In recent posts, I have shown that propped boulders are arranged  in "corners" of three, with one in the center, and the other two roughly equidistant from it, forming a right or obtuse angle. The two large adjacent enclosures I showed in September 2013 may actually be several "corners".  These  boulders were chosen by Natives for alteration  from among the many strewn across the landscape.   Creating these structures would have been very labor intensive, and the purpose is mysterious. Were they memorials, shrines, or markers for trails or territories?
      Recently, I read Connecticut's Indigenous Peoples by Lucianne Lavin and Paul Grant-Costa. Archaeological digs of old campsites show that there were different work areas within a campsite.  The tasks were assigned by gender, with each gender having its own work area some distance from the residential area.  The men would make stone tools and arrowheads at their work site, thereby keeping stone chips and debris from being scattered about the residential area.  The women would process food at a separate site. Therefore, a campsite could contain three smaller sites with different purposes. Then I realized that the "corner" could have  been a campsite, and the propped boulders markers for the different sites. Some of the propped boulders may have been used as task-specific work tables.

     I showed this propped boulder as part of a corner last week. It has a square shape and a flat top, and  may have become tilted over the centuries.   Historical documents such as the accounts of Verazzano describe the Natives as tall, often  nearly 6 feet in height.  I'm about the same height, and find this stone is at waist level, and  easy to walk up to. (That's my gloved finger to the left.)

Here is another possible work table from the large enclosures I showed  earlier (9/11/2013).

The other side.

The top is shown below. The slope may look uncomfortably steep for people standing around the table, but this slope was probably excavated for  the  farm road directly downhill, and eroded over time.

These two boulders  look like they were shaped into squares with flat tops.  The table above is next to this propped boulder.

Unfortunately, there is no way to get a good photo of this large boulder resting on smaller rocks. Perhaps this site was used by the men for tool production.
     I have shown another propped boulder with a grinding slick ( 9/18/2013 ).  Presumably, this would have been used by women for food production.  Here is another propped boulder at a site about 20 miles from this one, with a large grinding slick.

Similarly, the large flat pedestal boulder that Larry Harrop found could have been a table (3/14/2012).  One can easily imagine people clustered around the table at this site.  On the day I took the photo, someone  had left a beverage can on top of  the table.

    While it's easy to claim that any flat rock was a work surface, these tables  have been altered by being propped or perched, and are at  the "corners" of a campsite.    If these flat propped boulders were used as work tables, the ground around them would contain large amounts of stone chips or food waste.  An archaeological dig could  identify and date the use of the table.
     Why prop a boulder for use as a work table?  There may have been practical purposes, such as under-table storage or  toe room for the user.  There may have also been a spiritual component, such as opening a portal to the spirit world for such important functions as food and tool production. Of course, most of the propped boulders I have seen are too large and rounded to be tables.  There must have been  some other purpose for creating them.

Monday, January 6, 2014

New Tool

Check out this article at National Geographic here. The resolution of these LiDAR scans is greater than that of satellite imagery, and they aren't blocked by trees.  The LiDAR scan of the farmstead shows some rounded structures that could be rock piles.
I can't wait until these scans are available online!

Wednesday, January 1, 2014

Finding the Corner

There is an old saying that whatever you do on New Year's Day, you do all year.  I sure hope it is true, because I had a very pleasant afternoon at one of my favorite sites.  A few weeks ago,  I was looking over some old pictures, and noticed this propped boulder (waypoint 61).

It rests  on two supporting stones, and has a commanding position on a rocky outcrop. Looking at other propped boulders in the area, I found this one 450 feet to the west (waypoint 42).

It is also on two supporting stones, and overlooks a swamp from a jumble of huge boulders.

If it is true that Natives chose which boulders  to prop in order to form a three-sided "corner", there should be another propped boulder site.  Figuring that the sides are roughly equal in length, I made waypoints for some possible locations.

Luckily, this afternoon's weather was very pleasant, and I got out and visited these locations.
Possible  5 was in a swamp, and the area for 2 had been bulldozed for development years ago. There was nothing convincing at possibles 1 and 3, but at possible 4...Bingo!

Here is a view from the side.

Also close by is this larger propped boulder. It looks like stone has been chipped away from underneath.

If this looks familiar, it is because it is near this shelter which was shown 6/5/2013.  It was probably built into this old quarry by campers or deer hunters.   

With the addition of this site, the propped boulder corner is this:

These propped boulders are on bedrock or on top of outcrops, places that were not cleared for farming.  They may have had some Native significance as boundary markers, memorials, or personal worship sites.