Magellan EDR/RAW Data Options

[Brian Swift]

Just curious, has anyone gone spelunking in the Magellan SAR EDR (raw) dataset?

https://pds-imaging.jpl.nasa.gov/data/magellan/edr/

Looks like a set of 9-track mag tapes were copied to CD-ROMs for preservation,
and at some point the CD files were put online in PDS.

In starting to look at it, I realized that lack of knowledge of
mag tape volume/label/file/record structure and terminology may impede
younger explorers of this dataset.

[Phil Stooke]

I have used the mosaicked (tiled) data, not the raw 'noodle' data (long strip from one orbit). But I completely agree that much better access is needed, beginning with a good map-based search tool. I haven't checked for quite a while, though. Must be 10 years since I worked on Venus. I used to think I could do an atlas of Mercury and Venus exploration and I made a good start, but a lifetime isn't long enough to do everything I want to do.

One thing I did notice: USGS's Map-a-planet, which I used to use all the time until it was revamped and made less convenient, had 3 global mosaics corresponding to radar image cycles 1, 2 and 3. One mosaic often helped fill a gap in another. But where a gap still remained, occasionally on those CD-ROMs a later version of a mosaic would include a bit of extra coverage and fill the gap. But searching for that magic tile was a real pain. That's where a fully updated dataset with good map search capabilities would really help - show all products within the selected box.


Phil

[mcaplinger]

I have used the mosaicked (tiled) data, not the raw 'noodle' data (long strip from one orbit).

The recollections of a recovering Magellan data processor: The noodle data came in two flavors: the really raw data that Brian is talking about, and the so-called F-BIDR (Full resolution basic image data record, https://pds-geosciences.wustl.edu/missions/...idr/dataset.cat -- map-projected noodles). Even during the mission, I didn't know anyone brave enough to look at the EDRs, and even using the F-BIDRs was considered pretty hard-core; not sure if going back to the EDR would really confer much benefit, but it would require a detailed knowledge of SAR processing.

[JohnVV]

this is an old thread but

For about the next week i will have on my G-drive a massive C1 Venus map
it is 131072 x 65536 pixels and 8 Gig's in size

see the celestia forum post on this
https://celestia.space/forum/viewtopic.php?f=5&t=21899

[kymani76]

I get this result when using Venus Magellan SAR FMAP Left Look Global Mosaic at 225m/px with 600m/px stereo-derived DEM overlayed.
This version is 168976x76983 px weighing 13 GB.
There is also a version at 75m/px available, but i haven's tried it yet. It's a huge download at 109 GB! And you need lots of RAM to open it.
As you may noticed, I prefer white to black rendering of Magellan's data, which renders the surface in much more "photographic" way.

[Phil Stooke]

Hot off the press:

https://twitter.com/ThePlanetaryGuy/status/...066117344014343

Volcanic eruption/surface changes seen on Venus in old Magellan data.

If you wonder why it took so long, this is a very small area on a big planet. It also points to the fact that there is no convenient way to get into Magellan data now the fine old USGS Map-a-planet has been replaced by the clumsy Map-a-planet 2. If Venus science is going to prosper it really really really needs a kind of Quickmap interface to all 3 cycles of Magellan data, plus earth-based radar imaging and the ability to add new mission data as it arrives.

Phil

[mcaplinger]

https://www.science.org/doi/10.1126/science.abm7735

"We therefore cannot exclude the possibility that the flows were present when the Cycle 1 image was taken, but were not apparent in the image, perhaps because the surface texture makes the flows more distinguishable at the lower incidence angle of Cycle 2."

Seems like this is most likely a radar artifact to me.

[Phil Stooke]

That does indeed apply to the putative lava flow, but the change in the 2 km-wide caldera is, I think, incontestable.

Phil

[mcaplinger]

That does indeed apply to the putative lava flow, but the change in the 2 km-wide caldera is, I think, incontestable.

Hmm. Well, I don't know. Google for "SAR layover". I worked on Magellan just enough to be very skeptical of changes in SAR data acquired with much different geometries. I would hope that the reviewers knew more about it than I do.

[Phil Stooke]

I know about layover, but the changes don't look like layover to me. But we will see.

Phil

[StargazeInWonder]

What seems to be brightening marking both sides of the smaller, earlier version of the caldera do seem to be real topographical features that are substantially different in the later image. Of course, there's no possible limit to the weird interactions that could make terrain look different from different radar angles, but this would be a really insidious artifact if it is an artifact. I guess for anyone to evaluate it fully they'd have to add a study of what sorts of other apparent differences have been seen elsewhere on Venus to see how unique this apparent difference is.

[kymani76]

For a little visual aid here is 3D view of the Maat Moons rendered at 4x vertical exaggeration , looking towards southeast, the area from the article is in the front. The Magellan DEM is really rough and blocky, producing kind of an artificial bench that is not really there, but it could possibly be a downward movement of lava that we are seeing. Unfortunately it will be a long wait until we get 250m/pixel DEM planned by the VERITAS mission for a better view.

[StargazeInWonder]

And after a few years' more wait, EnVision will provide 60m spatial resolution topography.

However, if there was any significant change during just a year of Magellan's mission, it seems likely that some more significant change will be there to be discovered after ~35 years, unless, improbably, there's just one location on Venus where change occurs.

[JohnVV]

" The Magellan DEM is really rough and blocky"
and that is a major under statement

i have been able to clean it up a little bit bit not to much

[StargazeInWonder]

The radar maps in Fig. 2 A and B are annoyingly misaligned, something that is easy to miss with the eye, but longitude lines offered as references above Fig. 2A don't even remotely align with the un-labeled lines that appear between 2A and 2B. When I try to overlay the figures in Photoshop and "blink" them, the differences are apparent and cannot be resolved in any way with a mere translation between them. It feels like the text talks past this issue, saying that "the black box in © indicates the extent of the unrectified images in panels A and B," but it is clear that those panels, while obviously matching approximately, differ by more than the sizes of the features being discussed. It's strange. I can't tell if the work is sloppy or if the artifacts produced by the different geometries is simply enormous, but one or the other seems to be in play.