I will be writing a series of blogs for GLOBE to share the scientific experiences that were part of a 145 day, 1555 mile (2502 km) hike around the largest freshwater lake in the world.  Note that it is measured by area, not depth or volume, two very significant measurements, but with less importance to our hike since area would determine the actual distance that we would cover.

Map of Lake Superior; from midwestweekends.com

My wife, Kate Crowley, and I chose to do this hike after my retirement from an environmental education center in Minnesota.  We are both in our sixties and  were the first couple to follow the shoreline of this magnificent lake.  We did it for many reasons – to promote healthy living, to get people to care about freshwater, and to challenge people to take action on their values and concerns.

Freshwater is one of the most important issues in the world. Living in Minnesota, which is known as the land of 10,000 lakes and is the headwaters for both the Great Lakes and the Great River (Mississippi), we feel we have an opportunity to share our concern with the world.

As a college instructor in science and environmental education, as well as director of the Audubon Center, education was a very important part of my career and I love to combine education and science.  The walk allowed us a chance to continue our focus on environmental education.

This blog is not about the hiking for 4 ½ months, but about the science we did as part of the effort.  Perhaps you can see how you might duplicate some of the research in places where you live.

Mike Link and Kate Crowley begin their journey around Lake Superior; photo courtesy of Mike Link

Part 1 Point samples

Our first commitment was to take photos every three miles along the shore with GPS locations and notes. The photos were taken in the four cardinal directions and serve as a visual record. We ended up doing 300 points. At first we thought we would do them regardless of whether we could see the shoreline or not, but eventually we questioned this and eliminated stops where the lake was not in sight.   We hope that these records will become available through GLOBE.

What this did was to cause us to take note of a variety of things that enriched our experience. For one thing, we were able to actually register the way the vegetation changes around the lake. On the south shore we found hemlock and beech and there was a nice mix of forest types with a substantial amount of deciduous trees. We found beautiful, healthy old white pines; very popular with bald eagles.

The large sand beaches that dominated this shoreline were usually backed up with a beach grass and beach pea community with pines, fir, and spruce behind them. Paper birch, aspen, yellow birch and maple were common deciduous trees in this region. I also found it fascinating how the mountain ash grows to tree size here. Because of Minnesota’s shoreline, I am used to thinking that the mountain ash is a shrub, but these were tall tree with high canopies mixed with the other native species.

Mike Link and Kate Crowley stopping for a rest on their hike around Lake Superior; photo courtesy of Mike Link

Moving north into Canada we transitioned from the white pine/birch/cedar forest to the boreal black spruce forest between Lake Superior Provincial Park and Pukaskwa National Park. Spruce became dominant and would stay with us across the northern reach of the lake. Sandy bays still had beach grass and beach pea, but the large areas of bedrock shoreline meant that lichens, mosses, butterwort, and sundew patches were common.

Traveling from Nipigon, Ontario, Canada to the south, the vegetation began to include more pines again. On the Sibley Peninsula, we felt the forest became what we expected, with the exception that on the exposed rocks and islands Arctic disjuncts (a species from the last ice age) still reproduce and flower. There are a few of these on the Susie Islands in Minnesota, near the border and some species on the shore, but nothing like the Canadian flora and its gorgeous array of plants like crusted saxifrage, Artic bramble, and alpine bistort. This area of Lake Superior supports many of these species that are globally rare.

As we walked down the Minnesota coastline we moved into second and third growth forests with lots of birch and aspen. Second and third growth forests are forests which have re-grown after a major disturbance, such as a fire, insect infestation or timber harvest.  In these forests, the birch was often in poor shape and there were no young white cedar because of the voracious white tail deer. The mountain maple is browsed extensively by the deer, but seems able to withstand the onslaught, while species like mountain ash are nipped back to the ground almost as soon as they have a season of growth. We found the Encampment Forest Reserve to be one of the last vestiges of the original shoreline vegetation.

HOW WILL THIS BE USED?

You may hear people say – “It wasn’t like that when I was a kid.”  People will talk about change and say that things were different, but that is what we call anecdotal evidence.  It is based on memory and inconsistent reporting.  So how do we answer the question of how has the lake shore changed over the years and not use anecdotal evidence?

Our point samples become a baseline.  We know the day, the year, and the GPS points and those will remain a consistent reference point.  In other years people can use GPS to go back to the same place and observe and measure the changes according to our records.  This can be replicated in your backyard, school yard, or any place you want to create a permanent baseline record for others in future years.

From the first part of the series, you can see how important GPS is to Earth System Science research.  We would love to hear how you have used GPS protocols in your research!  Leave us  a comment or email us at science@globe.gov.

Exact location becomes less important for many things, so one GPS reading would be enough. A few months ago, GLOBE and the National Optical Astronomy Observatory had a Web-based field campaign called GLOBE@Night to measure light pollution. This was done by looking for stars visible in the constellation Orion. The more stars you could see, the less light pollution there was. In this case, the observers didn’t need as precise GPS readings, because light pollution wouldn’t change much in 10 meters. Similarly, clouds will look similar to two observers 100 meters apart. I always take GPS measurements as carefully as I can, however — because sometimes I need better accuracy than I originally thought. In fact GLOBE@Night asks you to record all the decimal places for latitude and longitude on your GPS unit.

Let’s go back to my earlier question, “Why were we able to use GPS elevation to determine how a rock formation sloped horizontally?” Look again at the elevation plot (below). On a given day, it looks like individual elevations could be off (relative to the line) by five meters, either due to GPS error, or due to our not being exactly at the top of the reddish-black rock layer. However, the elevation of the rock layer changed by over 30 meters in the kilometer over which we took measurements on 23 September. Also, we took about 20 measurements along that kilometer, which is in some sense like using four averages of five points. Similarly, the elevation change was about 20 meters over a kilometer along the line we walked on 24 September, and we took 15 measurements (3 sets of five). Finally, all of our measurements on both days were taken in about two hours. Over a longer period, we would expect the average to change, much as it does from day to day in the elevation graphs and table.

Some hints in taking GPS measurements:

1. Nearby terrain can block satellites and make GPS readings less accurate. That could be why there is more scatter for the Western Point elevation graph, which was closer to the mountains than the Eastern point graph.
2. Your body also blocks the satellites. It’s best to hold it over your head or away from your body. If you are holding the GPS in front of you, it’s best to face the Equator, since the GPS satellite orbits keep them in the lower latitudes longer. During my tests, I think this might have also led to greater scatter at the Western Point, because I was holding the GPS unit waist-high and was facing north. At the Eastern Point, I faced east. (Of course the GPS was on the ground when we took the rock layer elevation measurements.)
3. Averaging seems to improve precision and accuracy. However, the average on a given day can still be too high or too low.
4. You should take measurements to five decimal places if they appear on your GPS unit. 37.35000 degrees North is five meters south of 37.35005 degrees North. If you follow a careful procedure to get 37.35005 degrees North, you don’t want to add error by missing the last decimal place!

Just for fun, why not take some GPS measurements at exactly the same location and see how they change from day to day?

Figure 5 shows the GPS elevation for the five periods, for the Western Point on the circuit, and for the Eastern Point on the circuit. Let’s look at the Eastern Point graph first. This graph is called a bar graph or histogram. The measurements for the different days are in different colors. The numbers along the bottom are the elevations in meters. Not all the elevation numbers are on the graph, but you can guess what the missing numbers should be. For example, halfway between 1643 and 1647 is 1645. The bars represent observations between the numbers at their edges — a range of two meters.

• One just above where “1645″ meters should be on the graph (meaning there is one measurement between 1644 and 1646 meters).
• One at 1647 meters (one measurement between 1646 and 1648 meters).
• Two at 1649 meters (that is, two measurements between 1648 and 1650 meters). Here the squares “run together”)
• One at 1653 meters (one measurement between 1652 and 1654 meters).

So the elevations varied from as low as 1644 meters to as high as 1654 meters — up to 10 meters — on 1 November. We would need the actual numbers of course to know the range exactly.

It looks like the average Eastern Point elevation for 1 November is the lowest of the 5 days on the graph, since the blue squares are mostly above the lower numbers. Similarly, the brown squares are mostly above the highest numbers, so it looks like the average measured elevation is highest on 3 November in the afternoon. This is just what we see on the table below.

Now the Western Point. Again, it looks like the blue squares are mostly near the low numbers, which suggests that the average elevation is the lowest on 1 November. The table shows that the average elevation measurement on this day is the lowest of the five days — but not by much! 3 November a.m. (1649.7 or pink in the figure) is almost as low. The range of values at the Western Point on 1 November is between as low as 1644 meters and as high as 1648 meters — up to 14 meters! When is the highest elevation measured at the Western Point? In the table the highest elevation is measured on 5 November. Does this look right from the Figure?

The actual elevation of the Western Point, from a topographic map, is between 1646 and 1652 meters, so the average value in the table — 1654 meters — is a little too high. If we take 1649 meters as the true elevation, the highest single value, between 1662 and 1664 meters, from the figure, is up to 15 meters too high. The highest daily average in the Table, 1659 meters on 5 November, is 10 meters too high. The five-day average, 1654 meters, is only five meters too high. Thus averaging the observations on a given day give a better answer than the single points. And averaging measurements over more than one day makes the estimated elevation even better, but most people don’t have the time to do this!!

In tracking the rock layer (see last blog), we didn’t stay in one place very long, and we averaged two hurried measurements at each location. So why were we so successful in tracking the rock layer? To find out more about the accuracy of the GPS elevation, I did an experiment, which I will now describe.

We live on the top of a mesa, inside an oval formed by the street and sidewalks. One trip (circuit) around the oval on the sidewalk is about 500 meters. I picked a point at the west end of the oval (the Western Point), where there was an oil stain just large enough for me to put both feet on). I picked a second point at the east end of the oval (the Eastern Point, where there was a distinctive set of cracks in the surface). Thus I could repeat measurements at exactly the same two points.

To do the rock layer observations, we walked and stopped only long enough to get the two GPS readings. So I decided I would do the same thing in the oval. The next three mornings, I got up early and walked around the oval six times. I stopped at the Eastern Point and the Western Point, just long enough to take two GPS readings of latitude, longitude, and elevation. On the third day, I took the same measurements in the afternoon. Two days after that, I stayed at the Eastern Point and took position measurements using the GLOBE protocol (except with six measurements instead of five, to have the same number as the other days). Then I went to the Western point to obtain six positions and elevations the same way.

How did I do with GPS position?

Notice that the positions on the last two days (white and yellow) changed by over 10 meters if you use only one point to define your position.

The second figure shows the average for each day at the Eastern Point. the “+” marks the average position for all the days. Three points — for two of the “morning” circuits (black triangles) and for the GLOBE averages (white triangle, upside down so that you can see the black triangle underneath), were close to the average position. The farthest point from the average is only about 3 meters away. This is about as good as I think I can do with my GPS unit.

I recently had the chance to help survey a rock layer about 300 kilometers southeast of Boulder, Colorado. We were there to see whether a reddish-brown rock layer was level or tilted (sloped) in some direction. Since I study weather and climate rather than geology, I was there as a citizen scientist — a volunteer, rather than a professional. We took GPS readings of latitude, longitude, and elevation at the top of the reddish-brown layer. The top was fairly easy to see if the layers were visible, since the rock layer above it was white. You can easily see where the layers meet in the cliffs in Figure 1. We call where the layers meet the “contact.”

Figure 3 shows the results of our measurements. Combining the measurements for the two days, we found that the top of the reddish-brown layer sloped downward toward the north with about a 3% slope (if you go north 100 meters, the top of the rock layer will be three meters lower). Two other groups were following the rock layer a few kilometers away. Both groups found that the rock layer sloped toward the north, by about the same amount.

Figure 3. GPS elevations along the east side of the canyon (23 September) and the west side (24 September). North is to the right of the graph, so the rock layer is lower to the north.

We were surprised that the GPS elevations worked so well:

• First, the elevations varied rapidly on our GPS units.
• Second, GPS experts tell me the elevation is less accurate than the location.
• Third, we only took one reading at a location (though I would try to average the GPS elevation when it varied).
• Finally, while our GPS elevations agreed well with the elevation of the rock layer from a topographic map on second day, the two elevations differed by slightly more than 20 meters the first day.

In the next few entries, I will describe why we were so successful.