Changes at Low Ridge Haven Options

[fredk]

It's been pretty slow in the Spirit forum recently, but hopefully this will reawaken it.

A new thin dark streak is visible in the latest sol 961 rear hazcam, that wasn't visible in the previous shot, from sol 924. It's visible in both L and R hazcam views. It looks remarkably like a dust devil streak, but the scale is very small. Here's the R hazcam from sol 894 subtracted from the 961 image:

The dark streak cuts across more or less from left to right about a third of the frame down from the top. Other differences are visible, mostly around rocks, due to the change in sun angle between the frames.

To demonstrate that the dark streak isn't just an effect due to that change in sun angle, look at these three frames:
sol 856, local time 11:07
sol 961, local time 11:21
sol 894, local time 11:45

You can see that the shadows move progressively from the sol 856 to 961 to 894 frames above, as you'd expect from the local times they were taken. But if you flip between the three frames, you can see the dark streak only in the middle (sol 961) frame. If the streak were due to changing sun angle it would be at least as strongly visible in the 856 or 894 frame. Therefore it's not due to sun angle.

As I said, this is way too small for a dust devil streak. And, I don't think we're anywhere near dust devil season. My guess about the origin of this is a small "crumble event" on one of those dark rocks in the upper left, followed by the normal winds blowing some dark dust downwind.

Anyone know if the streak direction is consistent with what the winds should be doing now? Has anyone else noticed changes near Spirit?

[djellison]

Look at the change in the shadow cast by the aft solar array on the ground - that's quite a lot of solar-angle change - and looking at the three frames - the change you identify would seem to be consistant with a change of illumination more than anything else.

I have - however - been looking hard for changes in lots of images and I've not found anything yet. What WILL be interesting is the changes in tiny ripples upon which the rover is now sat.

Doug

[helvick]

Look at the change in the shadow cast by the aft solar array on the ground - that's quite a lot of solar-angle change - and looking at the three frames - the change you identify would seem to be consistant with a change of illumination more than anything else.

Interesting. An additional new picture would provide a definite answer. I see your point Doug but it seems to contiguous and localised to just be shadows. It would be great if it did turn out to be a streak.

[fredk]

Doug, the local time difference between the sol 856 and 961 frames is 14 minutes, which corresponds to a solar angle change of just 3.5 degrees. For sols 961 and 894, the difference is 24 minutes, or 6 degrees. The change in solar panal shadows looks quite large because of the height of the panels above the ground and the closeness of the panel shadows to the hazcam. 3.5 degrees is not a lot of change!

But the strongest argument that the dark streak is not the result of the change in sun angle is in my third from last paragraph in my post above! Any such putative darkening of a patch of soil due to changing solar angle must be monotonic with that angle over such a small range of angles, whereas my three frames show that it clearly is not.

Notice also that the dark streak crosses areas of ground that are at different inclinations, due to ripples etc. Why would differently oriented patches of surface respond to changing solar angle in the same way? Look for example at the largest rock closest to the rover (pixel location 680x375 or so). There are large variations in surface inclination angle in the soil surrounding it, but these do not show up in my difference image - the entire area (except for the rock's shadows) is very close to uniform on the difference image.

Also we don't see any other such darkened (or lightened) patches of soil elsewhere. Just one curiously linear darkened patch. Finally, the dark streak is darkest at the left, near my putative source, and thins to the right.

Altogether, an argument that the streak is an illumination feature necessarily takes on a conspiratorial character: differently oriented patches of soil, coincidentally lined up in a streak, responding in a bizarre non-monotonic way to small changes in solar angle.

Edit: that's conspiratorial in the sense of "contrived", of course no-one's conspiring here!

Actually there is another simple explanation: the feature is the shadow of something off the frame to the upper right. But that's even more conspiratorial!

[djellison]

Oh crikey - I was looking at something else.....you may have spotted something I was looking in the 800,280 sort of area.... I'll see what I can come up with for anim-difference images

OK - the anim is a work in progress- but this is the difference between the 961 image, and the average of the preceeding three images. Bloody good 'spot' there Fred - nicely found. I'm going to 'phone it in' as it were.

Doug

Attached thumbnail(s)

 

[helvick]

Any such putative darkening of a patch of soil due to changing solar angle must be monotonic with that angle over such a small range of angles, whereas my three frames show that it clearly is not.

Actually the change in solar elevation angles are even less than you indicate because of the change in noon solar elevation as she passed through mid winter. Also there is also a change in solar azimuth that might have been relevant had the solar elevation angle been low enough to cast shadows from landscape features off to the left. It isn't and as you point out anything that could cause such a shadow would be really conspiratorial.

Sol 856 LT 11:07 - Elevation 53.5deg Az 3.9deg
Sol 961 LT 11:21 - Elevation 50.7deg Az 351.7deg
Sol 894 LT 11:45 - Elevation 49.5deg Az 347.0deg

I cannot see how you would get an area of shadow across the entire region in question that would only appear on Sol 961. We still need another photo to be sure but it does look like a clear change to me.

[dvandorn]

I guess I'm missing something -- except for the minor sun angle changes, I can't see what you're talking about in the three image set. I see what appears to be a dark groove in the very-low-sun-angle image, but I can't identify it in any of the three images. Or any albedo change in them.

Maybe my eyes are just getting too old for this...

-the other Doug

[djellison]

The attachment that Fred did - and the one I did - are basically the difference between the Sol 961 image, and the other RHAZ images. So that dark streak is something that has changed between the last RHAZ image, and that Sol 961 one. It reminds me of the sort of trail left behind after a DD in Mark's enhanced DD movies.

Doug

[climber]

The attachment that Fred did - and the one I did - are basically the difference between the Sol 961 image, and the other RHAZ images. So that dark streak is something that has changed between the last RHAZ image, and that Sol 961 one. It reminds me of the sort of trail left behind after a DD in Mark's enhanced DD movies.
Doug

Not joking (realy). How far is this? Look prety close though. Any notice of a side effect on power supply (clean up)?

[djellison]

I'm not sure to be honest - probably best to match these features Nav or Pancam and work the range from that.

Perhaps - if we're lucky - they will do another Navcam pan from this position and then we can compare with earlier Navcam pans and vertically project it to see the track.

Doug

[fredk]

Dvandorn and anyone having trouble seeing this in the original images, here's a 3-frame gif that should help. Frame one is sol 894, unprocessed. Frame two is sol 961, unprocessed. Frame three is frame 2 minus frame 1, and then brightened:

Look for the (subtle!) change between the first two frames at the position of the streak in the difference image (frame 3). It's subtle but I was able to spot it before I made the difference image.

As I said above, I doubt this is a devil. I think small "crumble event" followed by ordinary winds is our best bet. I think we expect some level of steadyish winds all winter?

[helvick]

Not joking (realy). How far is this? Look prety close though. Any notice of a side effect on power supply (clean up)?

Not yet, power has just begun to climb again from the 280whr/sol low point it has been at for the past month or so to 287whr/sol on or about sol 957/958. We've had very regular power reports from Spirit over the past six weeks and there has been no evidence at all of any cleaning (yet).
We'll see if the next power figures show any change but I wouldn't expect it - I think it is very unlikely that this just happened so whatever effect it would have had would already have been seen.

[dilo]

Fred, your observation is interesting but what disappoint me is that this streak coincide exactly with regions with higher slope (even if with different sign comparing left portion with right). Based on this, I tend to think is a consequence of small illumination differences and/or deposition of some dust layer with slightly different light scattering properties... (not necessarily localized only in this point as for a dust devil track).

[fredk]

Dilo, the ground here has regions with greatly differing inclinations. Recall what I said in my second post about the area around the big rock. Why don't we see these kind of changes anywhere else?

Obviously a new image (after sol 961) would be great to have. But we've waited over a month since the previous rear hazcam image! Hopefully we won't have to wait as long for the next one...

[djellison]

That's what I thought dilo - but the change is real imho.

Doug