By Noor Ghouse
My coworker, Jen and I spent three days back in May assisting the USGS (United States Geological Survey) retrieve more than 1800 seismic array nodes deployed in Grant county for the LArge-n Seismic Survey in Oklahoma (LASSO). By 6:30 a.m., we’d be given our designated lines (north/south or east/west streets with node placements) and wouldn’t be back at the hotel until 12 hours later to unload them in a crate.
On these lines, we would have to pull to the side of the road every quarter mile, find a flag accompanied with a wooden block telling us that the node was nearby, find the node and dig it up, turn it off using a remote, cover the hole, and drive to the next one. Jen was in charge of digging up the node and turning it off, whereas I was in charge of navigation, running to get Jen supplies —i.e. shovel, metal detector, wooden stick— and keeping the music “phresh”. We were also dousing ourselves every two hours with sun spray and bug spray, which didn’t really help because there was always a tick on Jen.
By day two we became experts in finding the nodes. Then day three rolled around and put our node scavenging skills to the test.
Jen and I were really cranking out all the nodes in the morning, keeping a rhythm and not wasting any time. Every now and then we’d find a mowed-over flag, but would be able to find the block nearby. And if we couldn’t find the block, we were able to see something that resembled a hole and we would then use a metal detector to confirm our guess. We were averaging a node pickup every two minutes…and then one location threw our average overboard.
Five minutes after pulling to the side of the road and looking for the flag and/or block:
Jen: “Where’s the node?!”
Noor: “I don’t know. The GPS says it should be right where I’m standing.”
Rigorous and random digging ensues for 20 minutes.
There was no flag, or block, or any sign of a hole. Instead, we found a bunch of tall grass mowed over, spread across the side of the road. So, we took out the metal detector and found…aluminum cans! But no node. After a while, we decided that it was a lost cause and drove up to the next node, pulled it, and stopped for lunch.
After we’d eaten, we came across the same issue with another node until Jen had an idea:
Sweeping the area using the metal detector and looking at the GPS
Jen: “Maybe the node is on the other side of the drainage ditch from where the GPS says. Let’s line up. You stand where it is supposed to be and I will go to the other side of the ditch near the field. Then, we’ll see if the metal detector picks up anything where I’m standing.”
By using this method, we were able to find the node on the other side of the bank, exactly where Jen was standing. We retrieved the node, avoided the Wolf spider soon-to-be-mama, did a mini celebration, thanked our full tummies, and went on to the next node… until Jen had another brilliant idea.
Jen: “What if the people who put that node down did the same thing to that other location?”
Noor: “That would make sense. It looked like the same type of open area/environment and it is on the same east/west line.”
Jen: “Ok, we’ll go back now and if we don’t find it after five minutes, let’s just move on.”
After doing a proper three-way turnaround and not putting the truck in reverse for a ½ mile —which Jen very much likes to do— we got to the first location and aligned ourselves with the GPS. I stood where the GPS indicated the node was and Jen stood on the opposite side of the ditch. I ran to the truck to grab the metal detector and comb the area where Jen was standing. The detector beeped loudly after a few seconds and we found the node! After another mini celebration, we retrieved the node, packed up the metal detector and continued with our line, getting back in the rhythm, and conquered the rest of the day.
Noor Ghouse Senior Seismic Analyst
Jennifer Morris Education Outreach and Public Relations Manager