18 Nov How Do We Know? – Part 2
In the previous “How Do We Know…” post, we talked about how we used surface features, in particular sewer manholes, to validate our results. In this post, I want to talk about how we use stuff we can’t see to validate ASTlive!’s performance. In this case, we need to get data from other sources to compare with, and we’ll talk about two ways we have done this.
In one instance, we were surveying inside a water treatment facility to help the owners understand if they could build another gravity thickener where they wanted. They knew of some features but were concerned about things they didn’t know about. We deployed ASTlive! and mapped out the area (about 1/3 of an acre). Our map showed the structures they knew about in the correct places at the depths they had; it also showed depths for structures they knew where, but not how deep. And finally, we had acoustic returns from areas that they didn’t know about, and the client said they had confidence in our new structures because of the very good correlation with what they knew.
The second example comes from a small survey we did in a back yard to locate a power conduit and water line. The only surface indications were where the power line emerged from the garage into the ground and we knew it went to the bard, 150 yards away. We deployed our acoustic equipment and found both the conduit and the water line. After we finished the acoustic analysis, we went back to the site with an inductive probe, as both structures were shallow enough (4-5 feet) and both were conducting. The position and depth measured with that equipment matched with our acoustic measurements. Boo-ya!
Next, we’ll talk about more indirect validation, and then we’ll wrap up with a real validation based on excavations…