Dawn approaches Ceres, From opnav images to first orbit Options

[hendric]

I read somewhere (maybe twitter or facebook) from the Dawn team that the "white" spot actually has an albedo closer to asphalt. So the spot is dark, and the rest of Ceres uber-dark. Super-dark? Ceres-dark?

Edited: Nevermind, can't find it now, and it looks like Ceres itself is close to asphalt albedo, so the white spot is brighter, but I couldn't find constraints on how much.

[Habukaz]

I took the animation from Toma's post, reduced the gamma with a slight compression to the color space to increase contrast of surface features. They're composited together and rotated 90* to the left because I find it easier to track elements that way.

http://i.imgur.com/98lPRNQ.gif

What's up with the last frame (after the the white spots have just stopped rolling downward in your version) in that + Toma's original animations? It looks like it contains more detail; it looks sharper than the rest of the frames.

[ZLD]

What's up with the last frame (after the the white spots have just stopped rolling downward in your version) in that + Toma's original animations? It looks like it contains more detail; it looks sharper than the rest of the frames.

The sharpness or blur of the frames is mostly due to artifacts introduced in the compression of the animated gif. The raw images would be much better quality, likely closer to that final frame. The public has not yet had access to those though.

[Phil Stooke]

This is a map made from the six processed frames I posted earlier. The relative brightness of different bright spots is affected by my processing and can't be taken too seriously. Also, registration is not very precise so positions can't be trusted. In fact, just ignore it altogether!

Phil

[vikingmars]

This is a map made from the six processed frames I posted earlier. The relative brightness of different bright spots is affected by my processing and can't be taken too seriously. Also, registration is not very precise so positions can't be trusted. In fact, just ignore it altogether! Phil

WOW !
Thanks so much to our Cartographer-in-Chief !
Phil, you're the best !

[elakdawalla]

Now I'm glad I've procrastinated so long from finishing my blog post on these images

[atomoid]

I read somewhere (maybe twitter or facebook) from the Dawn team that the "white" spot actually has an albedo closer to asphalt. So the spot is dark, and the rest of Ceres uber-dark. Super-dark? Ceres-dark?

Edited: Nevermind, can't find it now, and it looks like Ceres itself is close to asphalt albedo, so the white spot is brighter, but I couldn't find constraints on how much.

i think you probably read this "Ceres is very dark and reflects only nine percent of the incident sunlight. The bright spots are brighter by approximately 50 percent – and thus as dark as an asphalt surface."

[Gerald]

Animated longitude/latitude projection, merged version, animated reprojection, and animated reprojection with grid:


For the merge of the individual lon/lat projections I've intended to weight most the projected ring between 0.7 and a little less 1.0 radii - with maximum weight at 0.85 radii - of the source images.
That ring seemed to be more distinguished due to the proximity to the terminator. Although using this outer zone of the soure images is rather sensitive to the registering and shape parameters; for the sake of making features visible I've accepted some distortions in this version.
I see a chance to retrieve some albedo, roughness, and inclination/topographic information; it will take more effort to find out to which degree this is possible.

Images and gifs of this post are based on the file pia19179-16.gif.

[Ian R]

Wow

Gerald, just what do you use, exactly, to reproject the raw images to a cylindrical format?

[Ian R]

Here's a polar projection of Gerald's amazing mosaic, centered on the south pole, and contrast enhanced using Prime Number Tone Mapping:

[Ian R]

I've taken Gerald's latest DAWN-derived map, mixed it with Phil's HST-derived map, and created this view of Ceres, with the south pole at center:

[Phil Stooke]

If you overlay Gerald's opnav-3 map on mine you will find that there is a difference between them, as if the individual images are rotated differently before reprojection. I am only playing with the images, and any error in orientation is probably mine - you might want to use Gerald's map for more accurate positions.

Also - great combinations of maps, Ian. It's great to see the way these things come together here.

Phil

[Ian R]

That's precisely what I did, Phil.

[Gerald]

Gerald, just what do you use, exactly, to reproject the raw images to a cylindrical format?

I'm working with ellipsoids for the projections.
For this sequence I've been assuming a rotational ellipsoid, width 106 pixels, height 96 pixels; tested several combinations around these values.
Slightly dirty, the ellipsoid is derived from a sphere by reducing only the y-coordinate non-proportional, not (yet) by proper 3d rotation, since the axis tilt is small enough for using this as a first approximation.
The tilt of the rotation axis of the underlying sphere is -14 degrees around the x-axis , and -10 degrees around the z-axis (determined by patient try and error), relative to the y-axis resulting in a globe like this:

The precise subpixel-position of Ceres in the raw images is determined by a specific object tracker.

I've implemented the needed reprojection software in native C++ from scratch.

Btw.: Great view from the south pole!

[Julius]

The first far out images of Ceres make it look very similar to a Saturnian moon.