Sunday, December 30, 2012

Researching With Google Earth – Part Two

Researching With Google Earth – Part Two
Looking for a  clear visual sense of the places you’re writing about (and can’t afford to visit in person)?  This series of Finding Stuff posts shows you how to use Google Earth for effective location visualizations (download the free program here

The Task At Hand

For the purposes of these posts, the terrain we’re exploring is Flanders, Belgium, the site of some of the heaviest fighting between German and Allied forces during World War I. Specifically, we’re trying to find, and define, a line of nineteen huge mines dug by the British Army, which they filled with nearly a million pounds of high explosives, and simultaneously detonated under German positions on June 7, 1917. 

Please review the text and screen shots of Part One for techniques on creating a general Google Earth overview of a region, using user uploaded photos, pinning a placemark, and driving around with Google Street View.

We had gotten up to the three at Kruisstraat, so that leaves just five more to plot: Ontario Farm, Trench 127 (#1 and #2) and Factory Farm (#1 and #2). Now all nineteen are placemarked and ready to be linked.

Measuring Distances

Have you ever needed to know the distance between two points? Google Earth’s measuring tool makes this a snap, and the results are available in eleven different units of measurement: Centimeters, Kilometers, Inches, Feet, Yards, Miles, Nautical Miles, Degrees, Arcseconds, and Smoots (a unit created as a practical joke by MIT students in 1958, who used the height of freshman Oliver Smoot to measure the length of the Harvard Bridge. Google reckons a smoot is 67 inches (1.7018 meters).

As you’ll recall from the last post, we located a mine crater at a place called Spanbroekmolen. You may also recall that the British Army “moles” (as the tunnelers called themselves) dug a 1,700 foot tunnel to reach the spot they reckoned was right below a fortified German bunker. The question begs: where was the entrance to the tunnel? We’re going to run a digital tape measure to look at the possibilities.

On Google Earth’s menu bar you’ll find a ruler icon. Click on that and the Ruler window pops up. Choose “Line,” and choose “Feet.” Place the cursor at the center of the mine crater and run a line out 1,700 feet to the south. Keeping the left mouse button held down, swing an arc and you’ll get a good visual sense of the spots the moles might have picked to start their tunnel. The little copse of trees to the south-southwest is as good a place as any to release the mouse button. Due to the obliteration of the countryside by three years of war, there is little likelihood that anything remotely resembling a tree stood there in 1917. But you get the idea.

Not happy with your line? Just click on “Clear” and run it again. Happy? Click on “Save.” This brings up another window that, among other things, lets you choose the color and thickness of the line, and give the feature a name. When you’re done, click “OK” and your line is fixed in place.

In the last post we spent a little time at the Kruisstraat craters. You can use the Ruler tool to measure their widths. The larger is pretty big—228 by 217 feet. In this case, there’s really no point in saving the line, so just close the Ruler window. We can do the same thing to measure the distance from Spanbroekmolen to Kruisstraat. Center to center it comes up at 632 yards (or 339.42 smoots).

The explosion of the nineteen mines was so loud that it was reported to have been heard by British Prime Minister David Lloyd George, who that morning was at his house south of London, near Walton Heath, Surrey. A quick Google Earth measurement from the heath to the mine line tells us that the distance is 140 air miles. It must have been one very loud bang.

As a side note, the firing of the mines was the largest manmade explosion in the history of the world, until the Trinity A-Bomb test in 1945.

Marking Pathways

By using the Ruler tool you can also trace continuous freehand paths on the map imagery. The picture below shows a freehand rendition of the Allied (turquoise) and German (orange) front lines in 1917 (data for these came from a WWI British trench map). This sort of drawing is not 100% accurate, but consider it a fair graphic representation of the situation on the ground. Run a ruler and you can see that in some places the trench lines were within a hundred yards of each other.

You can also use Add Path to run graphic lines. That’s the icon at the top Menu Bar with two lines and three dots. This is the measuring tool we’ll use to connect the nineteen mines.
Left click on the starting point (Hill 60 #1 and #2) and release. Cursor down to St Eloi, left click and release. A line from point A to point B appears. Move to Hollandsches Farm and do the same. A line from B to C appears. Repeat all the way around until you reach the Factory Farm mine craters. You should now have a continuous path that touches on each of the mines. Before naming and saving, check the distance. It ought to be 8.07 miles. And now we're accomplished our mission: plotting the arc of mines.

The Add Path tool can be very useful for making all sorts of graphic depictions—tracing abandoned railway lines, creek beds, otherwise faint trails. You can even use it to trace the placement of a long gone building.

Determining Altitudes/Elevations

Google Earth is pretty good about measuring altitudes, and hence, topographic elevations. Going back again to Spanbroekmolen, we want to know difference in height between the German bunker and the British tunnel entrance. You’ll notice at the bottom center of the screen strings of numbers that move whenever you move the cursor. The one on the right is elevation. The center of the old mine crater is at an altitude of 239 feet. The tunnel entrance that we guessed at earlier, is 152—a difference of 87 feet (high ground always gives the defender a tactical advantage).

Flanders is famous for its scenic rolling landscape. But even the slightest elevation could be hell in battle. After the mines exploded on June 7, British Army troops had to storm up the hill, past the smoking Spanbroekmolen crater, down another slope, across a flat barely 400 yards wide, and back up yet another hill to reach their objective, the village of Wytschaete. As Google Earth tells us, the change in elevation for troops in that sector was about 70 feet.
You can also use the elevation tool to measure the depth of bodies of water (works best with oceans and seas).

One of the features missing from Google Earth is elevation contours. If you’re familiar with USGS-type topographic maps, you know that they have wavy lines that signify gradients. These can be really helpful for getting a sense of the overall terrain. In Earth you have to roll the cursor all over the image and watch the elevation number change to get a less clear sense of the lay of the land. Street View, if available, can be a useful tool for seeing how the terrain is laid out. And to a lesser extent, so can the 2D Ground View. (n.b.: a beta-test feature is being added to Google Maps that will let you see contours, but it’s availability is currently very limited).

Locating Places Using Latitude and Longitude

What if you only have a site’s latitude and longitude? Google Earth is beautifully set up to handle this. And it’s a feature especially useful when measuring over bodies of water.
Let’s track the positions of an American submarine wolf pack in the Luzon Strait (the "Devil's Sea") off the northern coast of the Philippines in May 1944. They were stalking a Japanese merchant convoy, MI-11, that had sailed from Japan, headed for Brunei.

All we know about the subs’ locations at any given time was their latitude and longitude as noted in their after action reports. From recently declassified intelligence reports we also know the estimated noon positions of the convoy. These documents were acquired at National Archives II in College Park, Maryland.

The first sub to spot the convoy was USS Hammerhead, at 5:31am on May 30th, at location 20° 52’ North, 120° 47’ East. 

Move over to the Fly To search box on the far upper left. Enter the position like this: 20 52N 120 47E (you don’t need symbols like degrees, minutes, or periods). Click go and the cursor will move to the spot. Drop a placemark and name it. As for Hammerhead’s track after this, we know she left the area, so we’ve drawn in a path line to represent her course.

There are no other useful entries for Hammerhead, so we move on to Parche, Steelhead, and the ships of convoy MI-11. Here’s the finished image:

Accurately plotting courses, particularly in one of the most famous submarine actions of WWII, is painstaking work. The chart in the screen capture above took about 12 hours to create, with lots of checking and double-checking. But when it was finished it gave a complete picture of the battle, and helped to clear up decades of confusion over who was where, when.

Tip: If you need to be really precise, you can add seconds to the values you input: 20 52 19.07N 120 47 12.6E.

In a future post we’ll discuss how to use Google Maps and Bing Maps for Finding Stuff. But the next post will explore how to take advantage of the proliferation of historical digital archival repositories since the advent of the Internet.
If this post was helpful or interesting to you, please let me know. I’m always looking for ways to improve the blog.

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