I need to map a river bank that has recently undergone some serious erosion. The site is about 1200 feet long and the new raw eroded face is bout 15-20 feet high- above that is the old slope approximately the same height. All steep like the back of your head. It's on the outside of the bend of a river- right now the edge of water is inaccessible and the water appears to be maybe 5-10 feet deep adjacent to the edge of water.?ÿThe river?ÿgradient isn't really steep - probably less than 2 feet of drop in the 1000 feet.
My question is how well defined would the edge of water be using aerial based LiDar?
If I waited 4 weeks until a sand bar emerges on the south side of the river 250 feet away from the face and used a terrestrial scan station. what would that give me for a defined edge of water?
Thoughts? experiences?
signed-
"homies ain't fast ropin' off the guardrail down to the river."
The scanner will leave a big black hole where the water is but the edge area may not be very definite within a few feet. You will also get a lot of below ground returns. If you look at a slice there may be an obvious perfectly flat bottom.
Dave is correct about the Black Hole. Can you set up on the opposite bank? If so you can scan the face/slope and take some reflectorless shots along the edge of water to create a "breakline" that you can use to trim the point cloud.?ÿ
Would the scan give a better water line from a scanner just above the water on the opposite bank or from an airborne unit? I have to wait about 4 weeks for the water to drop before I can get out on the sandbar on the to the south.
Survey limits are the 2 yellow arrows- sandbar is the red arrow....
I would fly that in a heartbeat. We do a lot of combination sonar and drone jobs. This one would be perfect for it.
Water filled roadside ditch.
Intensity colors, note red fence below ground on left (caused by laser reflecting off of the water):
Colors from scanner camera:
Here is a cross-section in ortho mode:
Very good example Dave. We are getting much better results with regular photos via drone.
My first few jobs I was not extracting any photo data near or in the water. On one job I accidentally grabbed a group of points that extended across a shallow cutoff. To my surprise the data worked with both the sonar and the line of check shots I took wading with the rover.
It seems that anything clear and under 2 feet deep gives me good data. It helps if the bottom is gravel. It doesnt replace my sonar or groud truthing, but it sure boosts the confidence when they all work together.
This is a bit of a hijack but the Navy is now using an airborne lidar system to scan the water for mines.?ÿ The story wasn't real specific but I believe they're getting returns from beneath the surface that allow them to spot the mines when post processed back on the ship.?ÿ?ÿ http://www.foxnews.com/tech/2018/07/20/helicopter-fired-navy-laser-weapon-helps-attack-and-destroy-sea-mines.html
Very good example Dave. We are getting much better results with regular photos via drone.
My first few jobs I was not extracting any photo data near or in the water. On one job I accidentally grabbed a group of points that extended across a shallow cutoff. To my surprise the data worked with both the sonar and the line of check shots I took wading with the rover.
It seems that anything clear and under 2 feet deep gives me good data. It helps if the bottom is gravel. It doesnt replace my sonar or groud truthing, but it sure boosts the confidence when they all work together.
A drone is on our list but we haven't got there yet.?ÿ It has to do with Fire Dept reluctance due to drones in fire areas (we fly an air force) more than money because drones are fairly cheap.?ÿ Our co-workers have gotten other agencies to fly drones but just for video and photos since the drone operators are usually Sheriffs Deputies.?ÿ We would use it for aerial remote sensing mainly.?ÿ We had an assignment last year that a drone would've been perfect, we scanned it all, that was "interesting," given some of the places we took the scanners (ran two on that project).
That was the first time when the Chief in charge asked me what I need and I said get me an Engine crew.?ÿ Done! Wow that was easy.?ÿ The 45 year old Captain helped me haul the scanner all over that place; it was funny listening to him trash talking the 20 something crew members.?ÿ He was over there pointing at us, see those old guys, they do what has to be done when it has to be done, lunchtime may not come at 12pm exactly.
The LiDAR used by the Navy (and others) is the "Green" LiDAR
https://www.ngs.noaa.gov/corbin/class_description/Nayegandhi_green_lidar.pdf
This is typically not used by the regular professional consumers?ÿ - This is the real deal. It can burn through trees and accept multiple returns allowing you the know how tall the vegetation is and how deep the water is...
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@stlsurveyor?ÿ ?ÿThank you for that link.?ÿ I'd wandered what kind of?ÿ advancements/changes that they'd made that allowed them to penetrate the water deep enough to be useful.?ÿ ?ÿI browsed through it and will be going back to it later to fully digest.?ÿ?ÿ
My first thought is to walk the 1200 feet of the water's edge with GPS. Use that line to clip the Lidar data set.
