Bache-Wurdemann Baseline Measuring Apparatus: Not so Modern Surveying Techniques

Try saying that 10 times over. Are we even speaking English? I have recently been playing around with shooting LiDAR on my iPhone and trying to determine how precise and accurate it is. It could be a useful tool for some approximate measurements on the flood studies I work on. It is not going to replace traditional surveying, but that doesn't mean it isn't a useful tool. Let's roll back the clock a little and take a look at some of the original surveying techniques. Specifically, some of the original mapping of Mobile Bay and the surrounding areas.

Before total stations, LiDAR, drones, and other advanced surveying tools there was the Bache-Wurdemann Baseline Measuring Apparatus. This was in essence a 6 meter long metal bar that was laid end to end with another 6 meter long metal bar. The metals thermal expansion was known, temperature was measured, and this was repeated tirelessly for great stretches. A baseline was formed, often several miles long, and triangulation was used to precisely map the area. The apparatus this post will focus on was designed by AD Bache, and constructed by William Wurdemann, a talented German instrument maker. AD Bache was the 2nd Director of the US Coast Survey, and devised plans for the above mentioned apparatus in 1845. Some facts from the report that contained the Dauphin Island, Alabama baseline survey:

• Party was on the ground for 6 weeks

• only managed 17 working days

• Greatest day they managed 183 tubes or ~0.7 miles

• With some remeasurement, the greatest supposable error for the entire base was computed to be less than 6/10ths of an inch!

The Bache-Wurdemann Baseline Measuring Apparatus was a tool used in geodetic surveys in the mid-nineteenth century. It consisted of 2 rods or bars of iron and brass at different diameters, coated in tar, connected to a fixed end, and rack and pinion that terminated into a blunt knife edge and polished agate plate on the other end. The idea being that the thermal expansion difference could be noted, and precise measurements could be achieved. This whole device was encased in aluminum, and was considered a technological advancement at that time (circa 1850s).

This is how our coastlines were originally surveyed. Brilliant and precise men like A.D. Bache led that charge. The device described above was used from 1846 through 1873 to measure numerous baselines. If you ever travel to Dauphin Island, consider traveling to the east end of the island and wandering around Fort Gaines. Base No. 1, a stone monument from the DI baseline, part of the Eastern Oblique Arc surveyed in 1847, can be found there. A link to a useful wayfinding site can be found here, where I sourced this picture. By the way, did I mention AD Bache was a great-grandson of Benjamin Franklin?

Ooo, and if you want to do some sluething, Base No. 5 was classified as destroyed. It gradually was either taken by the sea, or bulldozed from human activity. The highlights from the NGS datasheet are shown below, or linked here.

• 1917-documented as in water at high tide but still there

• 1950-still there but still underwater

• 1956-bulldozer dumped 3' of sand, dozer operator contacted with no luck, NGS did a thorough search....LOST

• 1958-1 hr search, no results

• 1970-found base of granite block with triangulation, dug around underwater with face mask but no copper bolt marking center found; classified as destroyed

30°14'56.9"N 88°08'14.8"W