Lunar regolith changing greyscale

[echard]

During the course of my pasttime of debating (if you can call it that) with hoaxers on youtube, I can usually debunk the typical hoaxer questions fairly easily.

However, I had a question posed to me I can't answer or find any mention of anywhere.

When the Apollo astronauts were walking around and disturbing the lunar regolith, the Hasselblad photos and videos shows the astronaut-disturbed regolith darker than the surrounding undisturbed regolith.

In the recently released Kaguya photos, the A15 site shows the disturbed regolith distinctly lighter than the undisturbed.

www.jaxa.jp/press/2008/05/20080520_kaguya_e.html

Has the regolith changed greyscale over the last 37 years? Did the ascent stage have some effect? Or possibly is the opposition effect making it appear lighter?

What do you all think?

[PhantomWolf]

There are a couple of things. First it depends on the area, some areas are darker when disturbed because they have a darker layer underneath, others get lighter because they have a lighter layer underneath. However in this case the difference is what you are looking at. In the Apollo 15 photos the walking about uncovered a darker layer of regolith, but the Kaguya photos aren't showing the astronaut disturbed area, rather the Rocket cause disturbance. This disturbance has caused a change in the way the surface in the area scatters the light, essentically flattening it out a bit and making it more mirror-like. That causes it to reflect more light, so it appears brighter.

[laurel]

So this is the same kind of phenomenon that makes the rover tracks look so bright in the Apollo 14 photo on this Clavius page?
www.clavius.org/bibzz2.html

[PhantomWolf]

Looks like it yes.

[Bob B.]

I suppose also that imaging through different filters could change the appearance. The contrast between varied surfaces could change dramatically when viewed through filters of different colors. For instance, just because one surface appears darker in white light doesn't mean it will in, say, red light. Not all photos are created equal and we cannot assume they should always look the same. Do we know for sure what filters, if any, were used in the Kaguya image?

[echard]

After reading www.clavius.org/bibzz2.html (thanks for the link laurel) I understand that compacting the lunar soil has the effect of making it appear brighter.

So was the LM descent engine compacting the regolith as is passed over, or blowing the top surface away to reveal a lighter strata? A mix of the two?

[PhantomWolf]

Aug 29, 2008 0:04:29 GMT -4 echard said:

After reading www.clavius.org/bibzz2.html (thanks for the link laurel) I understand that compacting the lunar soil has the effect of making it appear brighter.

So was the LM descent engine compacting the regolith as is passed over, or blowing the top surface away to reveal a lighter strata? A mix of the two?

Not quite either. I suspect that the layer underneath merely was more compacted already. When the top loose layer was blown away, the compacted layer underneath appears brighter because it reflects more light back rather then scattering it.

Bob also has a point, and sometimes you'll see images taken that show areas differently because of the different wavelengths of light it reflects. I believe the Clemintine image of Apollo 15 is like this, it was using light invisible to the human eye. I'm assuming the Japanese were using visible light without filtering.

[JayUtah]

I meant to respond in this thread earlier.

First, we have to consider that the Kayuga image is the product of an algorithm. That is, while it also preserves the contour information revealed by varying amounts of reflected light, it is also presenting information calculated among images of different wavelengths taken through dichroic filters. This is how most space photography is done. So while it is a true-intensity image to some extent, it is also a false-intensity image.

It may, for example, display the difference between infrared emission and ultraviolet reflection at each pixel, with "bright" values indicating a proportionally larger difference. That would be done by subtracting, pixel-wise, the intensity of a pixel from an infrared image of that spot from the pixel intensity of an ultraviolet image of the same spot. Naturally where the image is dark (e.g., in the shaded portion of a crater) then the resulting values will probably still be small, and therefore dark.

This is how scientists use photography to glean more information from space probes than just what the terrain looks like. By knowing how various substances emit and reflect light in various wavelengths, and programming those characteristics into computers to discriminate based on those relationships, you can produce images of great scientific value.

So keep that possibility somewhere in your noggin: you may not be looking at intensities immediately visible to the human eye.

Now with that said, Jack Schmitt noticed from afar that the LM seemed to be surrounded by lighter regolith. This was from one of the geology stations. So that's a point in favor of the literal interpretation of the Kayuga data.

He theorized that since the lighter-weight particles of the regolith tend to be the darker-colored ones, thus as the exhaust swept the surface, the lighter particles were more susceptible to entrainment and displacement, leaving behind a greater proportion of lighter-colored, heavier-weight particles.

Keep in mind that the area revealed by Kayuga is many meters in diameter, corresponding to an area of wide exhaust dispersion (i.e., from a high altitude) and therefore quite subtle dynamic fluid pressure. We're talking about fluid pressures that may not have even blown the fluff off a lunar dandelion.

Now this differs remarkably from the brutal mechanical displacement achieved by shuffling astronaut footprints. As has been theorized at a different magnitude of scrutiny, the upper layer of lunar regolith is generally whiter than underlying layers, simply due to bleaching effects from the intense ultraviolet of sunlight. So as the layers are disturbed and darker, previously shaded layers are made more visible, you see the darkening effect of a more vigorous disturbance.

[dragonblaster]

I thought the Heiligenschein was due to glass spherules in the regolith, and that compressing it would push them closer together, giving a stronger effect.

[JayUtah]

I thought the Heiligenschein was due to glass spherules in the regolith, and that compressing it would push them closer together, giving a stronger effect.

Let's take a few steps back.

Heiligenschein is a specific optical effect, and not everything you see in Apollo photographs is due to it. Heiligenschein is the retroreflective effect of solid transparent spheroids. Terrestrially it occurs mostly from water droplets. Superterrestrially it occurs when flying over clouds: the "pilot's glory." It's an easily seen, easily reproduced, and easily explained phenomenon.

But retroreflection can also be just plain old backscatter. This includes the pure shadow-hiding effect, and is a common photometric principle.

[Kiwi]

Oct 20, 2008 13:10:40 GMT -4 JayUtah said:

It's an easily seen, easily reproduced, and easily explained phenomenon.

To everyone except HBs.

[raven]

Oct 22, 2008 7:00:00 GMT -4 Kiwi said:

Oct 20, 2008 13:10:40 GMT -4 JayUtah said:

It's an easily seen, easily reproduced, and easily explained phenomenon.

To everyone except HBs.

That appears, sadly, to be a given.