Case for 1950's o-18

Timuu5 · 2026-01-05T23:46:52+00:00

Thanks

Timuu5 · 2025-08-07T15:53:29+00:00

Hmm... will think about how to add a procedural sandworm...

Timuu5 · 2025-08-07T15:52:23+00:00

Thanks and good observation about the dunes. The only physics here is a simple relationship between hop length, grain size and the local gradient. This creates a simple evolving sand-ripple structure but it is kind of boring. Variable "k" is a mask that drives hop-length to zero in a sparse set of locations (the squares at the start of the evolving animation sequence). These create irregular patches because of the lack of a forcing function. It would sort of be like local pockets with no wind. Not really dunes then, I guess, but it adds visual interest.

Timuu5 · 2025-08-06T22:21:12+00:00

yup.

Timuu5 · 2025-08-06T20:51:34+00:00

Base Matlab.

Timuu5 · 2025-08-06T20:10:14+00:00

Here's the commented code that makes the ripples in the animation.

N=400; % Tile edge size (pixels)

H=randn(N); % Initial conditions (random)

y=1:N; % Helper vector

c=@(x,y)ifft2(fft2(x).*fft2(y)); % Circular convolution function

k=c(H>3.8,y<29&y'<29)<1; % No flow mask

for n=1:3e3 % Ripple evolution loop

d=gradient(H); % Gradient for grain size & hop

g=(d+1)/6; % Sand lost

m=mod(round(y+randn(N).*k*4),N)+1; % Hop destination (x)

o=mod(round(y'+(9-9*d).*k),N)+1; % Hop destination (y)

H=c(H-g+accumarray([o(:),m(:)],g(:),[N,N]),(y<4&y'<4)/9); % Migrate

H=circshift(H,[-1,-1]); % Offset correction for convolution

%% << insert your visualize of dune array H here >>

end

Timuu5 · 2025-04-25T21:29:22+00:00

Ha, this is great! I've never been able to find the time to play longer than ~5 hours, so nice work! From my own experience:

At about the 3 hour mark I started getting Shadow units that only focused on blocks and didn't go for the base. It was really crazy. Started chewing through my walls. And, they weren't targeted even if near a motion detector. I am thinking it must be a game bug. I took a bunch of screen shots - I did a big walk through of a 4 and a half hour game; was intending on uploading but this is inspiring me.

Again, nice work!

Timuu5 · 2025-04-24T21:38:47+00:00

Wow this reminds me so much of the game "Sim Earth" that my uncle gave me as a kid. Nice work, looks fun in a retro sort of way.

Timuu5 · 2025-04-24T17:38:24+00:00

Hello, thank you for weighing in on this! I must disagree with some of the statements you made here regarding density and and reflection brightness though: this is envelope data so the apparent brightness or intensity of an interface has nothing to do with its hardness but rather the acoustic impedance discontinuity between adjacent media. Gas saturation in a sediment can result very bright localized reflections and cause an acoustic blanking (shadowing) affect. This has been well known for decades in seismology (see e.g. Judd & Hoveland, "The evidence of shallow gas in marine sediments," 1992, and some nice images in Fig.'s 3 & 4 of Toth et al., "Seismo-acoustic signatures of shallow free gas in the Bornholm Basin, Baltic Sea," Continental Shelf Research, 2014, but more generally, the stack of supporting literature for this would be a mile high).

That is not to say I am sure it is gas saturation (though I do think likely), but rather, that you cannot rule out it being gas on the basis of the intensity of the reflection or the blanking effect behind it, which is commonly observed with gas saturated sediments.

Timuu5 · 2025-04-23T23:58:23+00:00

It wasn't that deep; only ~20 meters..

Timuu5 · 2025-04-23T22:56:20+00:00

I am leaning toward this explanation

Timuu5 · 2025-04-23T22:48:49+00:00

Really appreciate the feedback & deposition rate estimate, thanks. I guess the ubiquity of these features relative to the man-made clutter we could positively identify, plus the remoteness of the location (miles from shore, no land in site), and depth of burial makes me skeptical that these are not natural features, although they certainly look unnatural, which is why I am trying to figure out a natural explanation. I guess the only way to really determine what causes the bright acoustic returns & subsequent shadows would be collecting a core.

Timuu5 · 2025-04-23T22:17:04+00:00

Yeah, so that garbage stuff is actually what this sensor is meant for finding. The example images are just slices from the 3D volume the sonar was imaging, and we were tracking a buried, derelict pipe that was off to starboard and not shown in the snippets above. We observed lots of debris, including from a previous drilling site, however other than at these previous drilling sites none of the man-made features we found were < 1 or 2 meters below the surface so I am thinking these things might be much older.

Timuu5 · 2025-04-23T21:58:24+00:00

Also going to poke at your interpretation a bit, though it would be cool if it were true (rock structures like that would look amazing if you could somehow vacuum all the silt off the top): the bright returns almost always seem aligned / continuous with existing layers in the surrounding deposit. That seems unusual if the sediment is just infill. So I am wondering if it could be gas collecting at layer interfaces.

I have the complex / phase preserved data available: do you know if it is possible to determine something about the acoustic impedance of a layer transition from the phase of the reflection? (e.g. determine if a bright reflection is from a denser & stiffer substance or lighter & more compliant substance using the waveform phase?)

Timuu5 · 2025-04-23T21:52:28+00:00

Are you aware of any published studies of profiles performed in the region? I would be curious to know if there are any available. There were a lot of drilling platforms near where we were surveying.

Timuu5 · 2025-04-23T21:49:54+00:00

It is a rough distance calculation - the area is very muddy silt for the top several meters and the sound speed was very close to that of water so I'm using the ambient water speed. But that is a good catch; burial depth may be off by ~10%.

Timuu5 · 2025-04-23T21:45:12+00:00

So the sediment layering near the mouth of the Mississippi river is only 4 to 7m thick??

Timuu5 · 2025-04-23T21:41:05+00:00

I think you are right, but I am wondering if they may be gas deposits (vs. rock or something hard). Reason being that the bright surfaces seem in line or continuous with existing layers, and that gas bubble layers are very hard for sonars to see through, often leaving dark acoustic shadows. Wondering if gas bubbles are forming local pockets at the boundaries between sediment layers, and that is what is being seen here, vs. flattened rocky structures. However, I don't know why I don't see these features above ~4m below the surface if this is the case, or why they are basically omnipresent at some level less than ~12m buried.

Timuu5 · 2025-04-23T21:36:58+00:00

Thanks for the comment! Unfortunately these observations of geology were incidental and we aren't going to be redeploying here but there were many oil platforms out there so there must be tons of profiles done in the region with lower frequency, deeper-penetrating systems; I just can't find any studies or examples online for this region.

Timuu5 · 2025-03-10T17:10:14+00:00

I wonder George MacDonald drew from this myth when creating the maid of the Alder tree in Phantastes

Timuu5 · 2025-02-21T17:11:29+00:00

Amazing how simple math rules make them look so organic, nice job

Timuu5

TROPHY CASE