Starship Asterisk*

http://hirise.lpl.arizona.edu/faq/ wrote:
What do RED, BG, and IR mean?
These are shorthand titles for the different types of CCDs HiRISE has. The HiRISE camera has three different color filtered CCDs: red ("RED"), blue-green ("BG"), and near-infrared ("IR"). The wavelengths of these filters are as follows: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers

What are the BG and IR EDRs, and How are They Different from RED?
There are ten RED CCDs, two BG CCDs, and two IR CCDs. Combining the images taken by the three different color filters allows us to create "false" color images. The BG and IR CCDs are aligned with the center two RED CCDs, providing a two-CCD-wide color swath. This means that the images captured in the BG and IR products are aligned with the images captured in the RED4 and RED5 CCDs.

What does “false color” Mean?
"False" color means that the color you see in HiRISE images is not the "true" color human eyes would see on Mars. This is because the HiRISE camera views Mars in a different part of the spectrum than human eyes do. Nevertheless, false color imagery is extremely valuable because it illuminates the distinction between different materials and textures.

http://www.doc.govt.nz/parks-and-recreation/places-to-visit/northland/kaitaia-area/cape-reinga-and-te-paki/ wrote:
Cape Reinga & Te Paki sand dunes

Yeudas wrote:I don't think that the black sand is the one that felt in cascade.
If you look to this picture of dust evil trails, you can see that actually the black sand appears when the pink and clear sand is removed:

http://apod.nasa.gov/apod/ap091021.html

So the upper level of clear sand should be the one that flowed when ice melted.
How is explained the fact that only a thin layer of light sand covers everywhere the darker level?
Is it a phenomena of oxidization?

http://en.wikipedia.org/wiki/Hematite wrote:
<<Hematite is the mineral form of iron(III) oxide (Fe₂O₃), one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron. While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.

Huge deposits of hematite are found in banded iron formations. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.

The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odyssey spacecraft in orbit around Mars. The mineral was seen in abundance at two sites on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris. Several other sites also showed hematite, e.g., Aureum Chaos. Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution.>>

http://en.wikipedia.org/wiki/Heavy_mineral_sands_ore_deposits wrote:
<<Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones. Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals exist within streambeds, but most are of a low grade and are relatively small. Specific trap sites for heavy mineral sand placer deposits are in beaches on the leeward side of headlands, as this forms a low-energy zone which traps sediments carried along by the longshore drift. Also, sand bars developed at the mouths of rivers which feed the placer deposits are rich trap sites where the winnowing action of the waves are most efficient, because heavy minerals, if they are going to be too heavy to be moved, will deposit at an isthmus in preference to drifting too far down the beach.>>

drollere wrote:visually, probably the ugliest image ever posted on APOD.

DonAVP wrote:Reminds me of the fences you see at beaches that keep the sand from blowing away.

http://en.wikipedia.org/wiki/Sand_fence wrote:
<<A sand fence is a structure similar to a Snow fence used to force drifting of sand to occur in a desired place. Sand fences are employed in desert and erosion control and for example to minimize the amount of sand drift on roadways..



The drifting and settling of sand behind and in front of a such a fence occurs because the wind speed on both the downwind and windward side is less than that on the far windward side, allowing light materials such as sand to settle there. This creates a pile both in front of and behind the sand fence causing more sand to drop out. Conveniently the sand does not drop on the barrier itself, otherwise it would soon be buried and rendered useless. Once sand is deposited, it begins to form a self replicating dune.>>

planetquinn wrote:If you flip the image 180 degrees it is easier to grasp. The streams then appear to be flowing down instead of up.