I’m sitting down to write in our basecamp outside the small town of Hawi (pronounced: ha-vee) on the big island of Hawaii after watching another colorful sunset over the Pacific ocean and having a ukulele jam session on my new banjolele. Thanks to Richard and Jane at the Hawi Gallery for teaching us how to play the ukulele!
I’ve learned a few interesting new skills (besides banjolele) over the past few days. The field campaign has been running as smoothly as the gas-powered drill we have been working with — only some very minor setbacks, most of which involve maintaining the drill that is the subject of this analogy…
The samples are bagged and labeled so that Brendan can later perform the Brazilian splitting test on them to measure tensile strength. This test is completed by cutting a smaller slice of rock from the core and loading it into a machine called a Versaloader. The strength is measured at the moment the rock sample breaks. This measurement of tensile strength can be compared to the Schmidt hammer measurements of the compressional strength (discussed in an earlier post) to tell us about the erodibility of each sample, with respect to its location across the precipitation gradient.
If you thought diamond tipped drills were the the last of the badass tools in the geologist’s toolbox, you were wrong. We also have lasers.
Lasers have been instrumental in mapping the channel geometries on both sides of the Kohala Peninsula. Earlier this year, Brendan was successful in applying for an NCALM grant that generated a high-resolution, digital elevation model of a large portion of his field area. Woah: lasers, NCALM, digital elevation models…what are those?
NCALM stands for The National Center for Airborne Laser Mapping. The organization is based out of Houston, TX and flies a plane that is equipped with an airborne light detection and ranging (LiDAR) system. This system rapidly shoots lasers at the surface of the earth and records the light that is reflected back at the plane into a receiver, which generates georeferenced (keyed to a GPS point) elevation data. A computer program then processes that data and compiles it into a digital elevation model (DEM) — a file that can be converted to a 3D representation of the earth’s surface. This is what the “Terrain” option you see on Google Maps uses to generate those 3D topographic maps – although the resolution is much lower than NCALM data.
But wait a minute, what about the fact that half this field area is in the jungle? No worries, there is an app for that, too: it’s called vegetation removal. Not a machete, but an algorithm, filters out signals that are from the trees to generate a DEM that is vegetable-free! You don’t even have to get your hands dirty. Once you filter out the vegetation on a DEM, you can see some pretty amazing things, like hidden Cambodian temples. In fact, our data has such high-resolution that we can resolve both ancient and modern Hawaiian agricultural structures in some of the field sites we are working in. Unfortunately, I can’t show you an image of this because the NCALM data for this area is not yet public.
Of course, the limiting factor in flying LiDAR is cloud cover. The pilots who performed the LiDAR scans of Brendan’s area attempted 8 flyovers to get the data that Brendan had requested, but were unable to get part of a section on the wet side due to laserproof clouds. As with any data set, there are limitations. We often do the best we can do resolve those limitations, so in this case, we took to the ground to survey the stream profiles with our own mini-lasers to fill in the missing pieces.
On Friday morning, Brendan and I will head up to Pololu Valley on the wet side of the peninsula for a 3-day backpacking excursion to describe the erosional processes that are shaping the 1000 ft + valley walls.
That is all for now, but as a farewell, here is a picture of a waterfall we saw on our 2nd day off, last Sunday:
Don’t forget to follow @KLKgeo and #HIgeo2013 on instagram/twitter/facebook for (more frequent) live updates from the field. Cheers!
- Airborne laser spots ancient city complex of roads, canals hidden under dense Cambodian forest (globalnews.ca)
- From the Edge of the Rain Shadow (klkgeo.wordpress.com)