AI6YR Ben
Oh wow, photos of the damage from the M7.0 earthquake in Alaska (originally Yukon Geological Survey on FB, via Dan Shugar). #earthquake #Alaska #landslide
Dec 16 at 1:47amWeb
Show threadAI6YR BenDec 16
Sentinel-1 before/after (in 3D) of that last one... Which I pulled off Copernicus a second ago. Wow! #MountKingGeorge #MtKingGeorge #geology #landslide #earthquake #RemoteImaging
Show threadAI6YR BenDec 16
This could be a synthetic aperture radar artifact, but at the base of that landslide is a strange topology anomaly. 🤔
Show threadAI6YR BenDec 16
Hmm, what funky object is radar reflective in a weird way on an ice sheet? Ice itself? Ground down granite? So many odds things out there, LOL.
Show threadAI6YR BenDec 16
Oooh, the second one, the strange ring, is this. I wonder if that's volcanic? There appears to be a lot of dust stuck to the walls of the snow around that structure, which is causing those reflections. 🤷 #mystery #geology
Show threadAI6YR BenDec 16

This one looks like there's a door in it 🤪

Secret villain lair?

Spaceship?

(probably the top of a buried mountain 😉 )

For the record, 60.4893, -139.9348

#mystery

Show threadAI6YR BenDec 16
Oooh, it's VERY radar reflective. Whatever it is. Super secret Canadian military base encased in a glacier? 🤪
Show threadAI6YR BenDec 16
DEM layer is completely whacko at that location. 🤨 #gis
Show threadFreddyB Aviation PhotographyDec 16

@ai6yr We find stuff like this a lot out in BF Nowhere and some of it is specific to the use of SAR and they use them to monitor movement etc

Integration of Corner Reflectors for the Monitoring of Mountain Glacier Areas with Sentinel-1 Time Series
https://www.mdpi.com/2072-4292/11/8/988

Show threadAI6YR BenDec 16
@cvvhrn Oooh, corner reflector on a glacier to monitor movement... that *WOULD* explain that strange signature!
Show threadFreddyB Aviation PhotographyDec 16
@ai6yr You also get weird stuff like this and its almost always in the boundaries of of a military or restricted area (Edwards) which are calibration marks for satellite and airborne optical systems
Show threadT. J. BombadilDec 16
@cvvhrn @ai6yr Here’s another one. https://maps.app.goo.gl/h29RT9amLFB11EM37?g_st=ipc
Bevor Sie zu Google Maps weitergehen

Show threadMatthew DockreyDec 16
@cvvhrn @ai6yr Amusingly, the calibration targets for optical measuring systems look exactly like that, just on a glass slide with the largest square only 10mm across.
Show threadmidendianDec 16
@attoparsec @cvvhrn @ai6yr indeed they are both called “USAF target” regardless of scale!
Show threadllewellyDec 16
@ai6yr very rough rocks can be highly radar reflective. That's what all the "bright areas" on early radar maps of Venus turned out to be. It's just a very difficult place to lose a cow.
Show threadMichael BuschDec 16

@llewelly

My first guess would have been coherent backscatter from multiple reflections within a pit.

Polarization maps would help resolve that, if @ai6yr has them.

Show threadllewellyDec 16
@michael_w_busch @ai6yr well, your guess is probably better than mine.
Show threadMichael BuschDec 16

@llewelly @ai6yr

In the case of Venus, some of the radar bright regions are metallic frost that condenses out on the tops of mountains.

Fortunately, we do not have to deal with that possibility around here.

Show threadAI6YR BenDec 16
@michael_w_busch @llewelly Looks like the flaws are from the Copernicus DEM layer, which apparently has a problem acquisition on glaciers. From visual inspection, it looks like pits/crevasses which have material deposition on top of the ice (from the mountains... I assume eroded rocks of some sort), which must be causing that backscatter on those particular satellites they used. Must be particularly reflective material that is in those pits.
Show threadAI6YR BenDec 16
@michael_w_busch @llewelly Radar reflective crevasse? LOL.
Show threadAI6YR BenDec 16
@michael_w_busch @llewelly No idea what these are, but that glacier has a lot of these on the surface... looks like pits of some sort. Probably end up as unintentional radar reflectors!
Show threadMichael BuschDec 16

@ai6yr @llewelly

It does not require particularly reflective material to get coherent backscatter, just two signal paths that have the same path length (e.g. double bounces where swapping the inbound and outbound gives the same length).

Ice and snowpack are infamous for this happening.

Because the backscatter is coherent, it is also a great way to mess up phase and get glitches in SAR elevation maps.

Polarization maps can resolve it by separating even-order scattering from odd-order.

Show threadAI6YR BenDec 16
@michael_w_busch @llewelly Oooh, interesting, didn't know it just requires the same path length! I did figure it was some kind of SAR artifact 🤪
Show threadMichael BuschDec 16

@ai6yr @llewelly

On this I recommend Elachi & van Zyl's "Introduction to the Physics and Techniques of Remote Sensing", which Jakob van Zyl taught me from in grad school.

(Both authors were experts on SAR, so the book covers it extensively as compared to other remote sensing techniques.)

Show threadAI6YR BenDec 16
@michael_w_busch @llewelly Thanks! I teach undergrads how to use the tools and the principles of remote sensing, but we don't get into the physics and math (only the application), and I have come in to this in a roundabout manner (ie using the tools for practical reasons, vs. the theoretical/academic route), so this is all appreciated!
Show threadThomas SturmDec 16
@ai6yr Stay away from my house!
Show threadLisa Lorenzin KR4LFE (she/her)Dec 16
@ai6yr maybe the CIA lost a radioactive source there, too...
Show threadAI6YR BenDec 16
@llorenzin 😂
Show threadFreddyB Aviation PhotographyDec 16

@ai6yr My god its full of stars

https://www.youtube.com/watch?v=cHWs3c3YNs4

2001: A Space Odyssey, black monolith

YouTube
Show threadderptronDec 16

@cvvhrn 2001 is really violent to wake up to if you start watching it late and pass out at the beginning. Set at a reasonable speaking volume...BAM!!!

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAoooooAAAAAAAAAAAAAAAAAAooooAAAAAOOOOOOOOAAAAAAAAAAAAAOAOAOOAOOAOOAAAAAAAAAAAAAAAAA

Show threadTomKrajci 🇺🇦 🏳️‍🌈 🏳️‍⚧️Dec 16

@ai6yr

That looks like Devil's Tower.

I think I hear weird music....

https://www.youtube.com/watch?v=nkykqyMEarA

Close Encounters of the Third Kind: Communicating with music

YouTube
Show threadShawnT 🔧🐀Dec 16
@KrajciTom @ai6yr
Aye yah,
Aye yah ehh.
Show threadLazarou Monkey Terror 🚀💙🌈Dec 16
@ai6yr that would have been a sight to behold!
Show threadEmily VelascoDec 16
@ai6yr wow!
Show threadMiss WarcraftDec 16
@ai6yr Watching the Earth remodel itself is stunning. Thinking how long it took to get the continents where they are. Earth quakes moving stuff, volcanoes spewing lava adding more soil.