After accidentally finding Russian tanks in Polish forests I was curious to see if there was something else hiding under the forest canopy. Remember, I randomly picked a 500 by 500 meter LiDAR tile as example data to introduce a group of forestry students to LiDAR processing with LAStools during the ForseenPOMERANIA camp. After extracting ground points with „lasground.exe„, strange bumps appeared in the bare-earth hillshades generated with „las2dem.exe“ for terrain that was supposed to be completely flat … they turned out to be Russian WW-II positions.
I met Achim when returning to teach the next two groups of students. His hobby is a mix between geo-caching and conflict-archaeology: locating old German bunkers based on approximate coordinates available in historic records and tourist maps and then mapping them precisely with GPS. Achim had a list of longitude/latitude positions as KML files where he was planning to search for known bunkers. I used „lasboundary.exe“ to create polygonal outlines in KML format for all areas where we had LiDAR from the forestry project. With Google Earth it was easy to find overlaps between his target areas and our LiDAR coverage.
Comparing our LiDAR coverage computed with lasboundary.exe with the approximate location of bunkers.
Zooming in on the area of overlap between our LiDAR coverage and the bunker locations.
A hillshaded DSM derived from all first returns using a pipeline of lastile, las2dem, and blast2dem.
A hillshaded bare-earth DTM derived from the ground returns using a pipeline of lastile, lasground, las2dem, and blast2dem.
Amazing! A network of trenches becomes clearly visible by the laser which easily penetrates through the canopy.
In contrast – nothing to see in the corresponding aerial image of the same area.
At first glance it looks like a maze of little creeks that are running alongside the ridges of the hillsides but we know that water flows downhill and not „along-hill“. What we see is a network of WW-II trenches that are connecting the bunkers Achim is looking for. A closer look also reveals the likely location of those bunkers.
Each disturbance in the ground was either a bunker or an artillery position connected by a network of trenches.
In comparison – the aerial view is revealing very little.
We were able to pin-point all bunkers in the hillshaded DTM and found an additional artillery position on top of the hill.
In comparison – the aerial view is again revealing very little.
In red the GPS track of our hike including the wet loop through the swamp … (-:
The suspected position of ru 17/18 (in blue) based on old maps was about 60 meters off. Also the position on top of the hill … unmistakable.
I placed a pin on each of them and exported their longitude and latitude coordinates for upload into Achim’s GPS device. The next day we set out to verify our LiDAR findings on the ground.
Achim and me preparing for the field trip.
Driving along muddy roads to the spot closest to the target GPS locations.
The target area is surrounded by managed mono-culture forests that have been planted some 30 to 50 years ago.
Heading for the first GPS point … (-;
Still dry after walking past the swamp.
Muddy after a loop into the swamps … but I did not spill any coffee.
One of the bunkers we saw in the hillshade. This side was „blown“ up after the war.
Achim at the entrance to the bunker.
This is the emergency exit. It used to be filled with loose sand all the way to the top.
The emergency exit („Notausgang“) from the inside of the bunker. Opening the thick steel door and shoveling the sand into the bunker created the escape route.
Spooky … the old German writings are still visible. This says „Sprachrrohr“ meaning „speak tube“.
This is the „inner defense“ and the writing says „
When the bunker was „in use“ there were no trees and it was over-looking this open field from above.
These gigantic steel screws were holding a thick steel plate in place behind which the machine gun was installed.
This is the „entrance defense“ (Eingangsverteidigung) of the bunker.
Looking out of the „entrance defense“ (Eingangsverteidigung). Notice the location of my coffee cup.
Here you see my coffee cup in the same spot. The „entrance defense“ made sure that unfriendly folks did not linger at the entrance to the bunker.
Taking a picture of mushrooms.
Pretty mushrooms are growing in the ruins of the bunker.
The moss-covered bunker in the quiet forest is almost beautiful.
If you look careful you can make out the old camouflage paint on the walls of the bunker.
Achim walking through remains of the 70 year old trenches that were dug by young boys of the Hitler youth as the Russian front was crumbling.
A junction connecting trenches leading to different bunkers.
Although the trenches are quite overgrown they show up very clear in the hillshaded DTM.
The back entrance to another bunker. The front side that is pointing East was destroyed.
A mushroom growing in the trenches with the shadow of a bunker in the background on the left.
A concrete podest in the center of a position at the top of a hill.
You can see this postion marked as „Stellung“ in the hillshaded DTM.
Discussing our findings during the following workshop for forestry students.
It was a rainy day. Walking through this maze of green and overgrown trenches from one moss-covered bunker ruin to the next felt oddly quiet and peaceful. Achim explained that these bunkers were originally built to defend the border with Poland – long before the Second World War broke out. Only when Russian soldiers were advancing on Germany after the collapse of the Eastern front, the young boys of the Hitler Youth were commanded to dig this network of trenches in order to fortify the bunker and stop enemy lines from gaining ground. After the war the Russians blew up all bunkers that were facing East so that their troops would not ever have to face them again.
0 Kommentare zu „locating German bunkers concealed by canopy“
Must have been terrifying to face these bunkers and even more so if hand-to-hand combat broke out inside the bunkers/trenches