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Category Archives: LiDAR

Last week I had the chance to explore the upper McKenzie River valley in the Oregon Cascades. My tour guide was a UO PhD student in volcanology. She was showing me the range of interesting lava-water interaction features that characterize the valley. A very cool and unbelievably scenic place. 

Luckily, she has some LiDAR data of the area. This was my first chance to hit the field with LiDAR in hand of an area covered by old-growth forest. In other words, entirely non-trivial vegetation cover that is disconcerting in both its density and its scenic values. Two main conclusions: 

1. It is amazing how well the LiDAR data reveal the topography through a dense forest cover. I knew this, but living it for a day was very convincing. Many small to medium scale details in the surface of a thickly forested Holocene lava flow are painfully obvious in the imagery (below). For the desert rat in me, they were easier to see in the imagery than they were on the ground at first. Eventually, I was able to relate the two once I could see past the forest, but the imagery was far more revealing of the local geomorphology. 

Typical scene in the field area…locally, forest cover is thicker. Photo from surface of the lava flow evident in imagery below.

2. The LiDAR in this case also revealed some major features that had previously gone unnmapped at a fundamental level. We found / explored a very prominent volcanic feature in the midst of the lava flow that, according to the 24k USGS base and the 10 m DEM, does not exist. However, it is almost absurdly obvious in the LiDAR data. Mind you, this feature is not trivial in scale. It tops out at nearly 90 m above the valley floor and is has a 150 by 200 m footprint. It (the ‘Pimple’) is extremely steep-sided (as we discovered climbing to the top). It is also enigmatic geologically…potentially a glacially modified and exhumed volcanic fissure. Not sure on that.

Looking down from the Pimple. A seriously steep hike.

The 24k topographic map rendition of the area shown in the two LiDAR images.

Slope-shaded map of the LiDAR data

Hillshade map of the LiDAR data.

The point is that this very conspicuous feature is very mappable, but was overlooked in the development of the 24k map. A bit surprising in that it corresponds to a major ‘peak’ in the forest canopy. I will admit, however, that if you were out there in the rain, you could walk right by it. Certainly makes you wonder what else out there has gone unnoticed by the USGS topographic maps we once relied so heavily upon. Yikes…

Thanks to ND for the field trip and the LiDAR map snips.

 

Posted via email from Fresh Geologic Froth

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Sure, I have gone on and on about the amazing visualizations you can get with some tweaking of LiDAR data; however, it turns out that a pretty basic representation is also quite useful…contours. Yes, contours. Sometimes smaller scale features remain somewhat ambiguous in hillshades or slopeshades, but high-res, short interval contours from the LiDAR data can eliminate most of the ambiguity. In this case, it is a tiny area that I have struggled with on the Owyhee River. Here, a large landslide entered from the north, shoved the river channel to the south, and the river eventually worked its way back to the north to some extent. The array of surficial deposits in the void that comprises the right hand side of the image south of the river record this sequence of events as well as subsequent sedimentation by tributary fans. The contours really highlight the fans, and in conjunction with discernible drainage patterns evident in the LiDAR, it is clear what is fan and what is river, right?

2-m Contours were generated in GlobalMapper and exported as shapefile to view in Arc.
Note, Ian Madin (at DOGAMI) gave me the tip on contours especially as they relate to resolving fan features. He was right…it works!

Posted via email from Fresh Geologic Froth

I created this lake by generating a contour from the LiDAR dataset at an elevation of 1046 m. GlobalMapper does this in about 1.5 minutes. Then, exported the vector as a shapefile, cut out the parts of the line that occur downstream from the dam, stitch the remaining loose ends, build a poly from the line and there it is.

This lake has an interesting topographic correspondence with the old landslides on the south side of the Hole in the Ground as well as the ancient fan remnants that come in from the north side. Don't forget that much of the topography you can see through the lake didn't exist at the time of the lava dam. The valley floor was probably formed on the Bogus Rim lava which forms the flat-topped features that flank the left and right banks of the river near the eastern end of the lake. The top of the Bogus Rim lava is only about 25 m below the surface of this lake. Thus, the link between this lake and the landslides is dubious as there was nowhere for the landslides to slide.

Posted via email from Fresh Geologic Froth

Today, I found out that the Oregon Department of Geology and Mineral Industries (DOGAMI) is releasing LiDAR-based base maps of the Portland area. Some previous discussions I have had with Ian Madin, Chief Geoscientist at DOGAMI have centered on just how much better and more geo-accurately LiDAR data can resolve natural and cultural features. Clearly, he has put this to the test. There are also various ways that the data can be processed to accentuate the natural features as well as the constructed ones, thus producing very nice and accurate base maps.

Here is a link to some examples of their new LIS maps (lidar Imagery Series) to replace USGS topo quads where they have the data: http://www.oregongeology.org/sub/news&events/archives/press-release-2009-08-21.pdf

The image at top shows an example of both the bare earth and the highest hit images of a quarter quad. Of course, I think this is nothing short of revolutionary because I am growing tired of DRGs of 24 and 100k maps. This type of base image is far superior to traditional 24k topographic maps in many ways (maybe not all). Kudos to DOGAMI for setting the bar for us all. I only hope that we can get some of these for Nevada before I retire. Ironically, I already have the data in hand for DOGAMI to make some similar maps for an area in Oregon where I have been working for the past several years.

Posted via email from Fresh Geologic Froth