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Juno perijove 4, February 2, 2017
JRehling
post Mar 6 2017, 09:29 PM
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FYI, Io shadow passes across Jupiter occur every 42 hours and last about 2 hours – 5% of the time. This is similar for Europa, so Jupiter has the shadow of one of them or the other about 10% of the time. Ganymede and Callisto will bump that total up somewhat, depending on the season. So in ~10 random passes that image all the day-lit side of Jupiter, you'd expect about one pass with a satellite shadow.
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Bjorn Jonsson
post Mar 7 2017, 12:24 AM
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Now at last I took the time to finish the Juno-related software development I started around the time of the Juno Earth flyby back in 2013. Now I can reproject the raw framelets to simple cylindrical projection and render the resulting maps, resulting in nice images.

Here is a test image. This is image 119 ("radiation trend monitoring"). It was obtained on February 2, 2017 when Juno was ~340,000 km from Jupiter's center on the outbound leg of its trajectory. I selected this image because it's a global image where limb fits are trivial - this makes debugging stuff easier.

Attached Image
Attached Image


The left version is the image with almost no processing except for color correction and some sharpening. In the right version global illumination has been removed using a modified Lommel-Seeliger function and the contrast greatly exaggerated. In the original images the area near Jupiter's right limb is saturated in the red and green channels, resulting in very low contrast and slightly strange color. Interestingly, the saturated value in the original raw images is 240.

The contrast is rather low. I suspect I need to add square root encoding to the processing to increase the contrast; I noticed that Gerald does this.

One thing that caused me some minor headaches was a part the SPICE instrument kernel file, specifically this section:

CODE
      --- 0,0---------------------|----------------------.      | 230 pixels
  4.94 deg | RED     128 pix      *                      |     --------
      ---  `----------------------|------------------1600,128
                                  |
                                  V +Yjc

           |                   61.69 deg                 |      Boresight
           |---------------------------------------------|    (+Zjc axis)
           |                                             |      is into
                                                                the page


Maybe I'm missing something elementary but the value 61.69 deg seems strange and I get weird results if I use it. However, a 58.015 deg field of view for all 1648 pixels works perfectly and is also consistent with the 58 deg value for JunoCam that I've seen elsewhere and it's also consistent with JunoCam's focal length and pixel size.

As usual a big part of the work involved correcting the pointing. I used SPICE kernels and software I wrote using the SPICE toolkit to get the spacecraft position and pointing and to optionally correct the pointing (somewhat comparable to what the ISIS3 deltack program does). For the interested, here is an example of the output. It's somewhat similar to a PDS label file but with some 'new' custom labels that I added.

CODE
/* Spicegeom version 2017-02-28 */
TARGET_NAME="Jupiter"
SPACECRAFT_NAME="Juno"
IMAGE_NUMBER="        -1"
IMAGE_TIME="2017-FEB-02 15:57:44.297"
SC_TARGET_POSITION_VECTOR=(-148470.35180453,63094.92703727,-301286.56346215)
TARGET_CENTER_DISTANCE=341757.236215459
SUB_SPACECRAFT_LATITUDE=-61.833627009783
SUB_SPACECRAFT_LONGITUDE=203.026167185770
SUB_SPACECRAFT_LINE_SAMPLE=832.2795709754
SUB_SPACECRAFT_LINE=738.4562742541
SAMPLE_TO_BE_CORRECTED=494.0000000000
LINE_TO_BE_CORRECTED=753.0000000000
SAMPLE_CORRECTION=-20.0000000000
LINE_CORRECTION=7.0000000000
NORTH_AZIMUTH=90.45299584
FIELD_OF_VIEW=58.01500000
/* LOOK_AT includes a possible user-specified correction to LINE[_SAMPLE] */
/* In contrast, SUB_SPACECRAFT_LINE[_SAMPLE] does not include this correction */
LOOK_AT_X=-143367.5394205331
LOOK_AT_Z=-292943.9225293422
LOOK_AT_Y=61006.4711387579
PLANETOGRAPHIC_SUB_SPACECRAFT_LATITUDE=-64.90958822
SUB_SOLAR_LATITUDE=-2.582962
SUB_SOLAR_LONGITUDE=100.197161
SOLAR_DISTANCE=815580051.923982
PLANETOGRAPHIC_SUB_SOLAR_LATITUDE=-2.953164
PHASE_ANGLE=93.724392


Next: Processing a much closer and higher resolution image of Jupiter.
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mcaplinger
post Mar 7 2017, 01:42 AM
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QUOTE (Bjorn Jonsson @ Mar 6 2017, 04:24 PM) *
Maybe I'm missing something elementary but the value 61.69 deg seems strange and I get weird results if I use it.

61.69 is simply the crosstrack FOV if the camera were a perfect pinhole camera with the given pixel pitch and focal length; i.e., degrees(1600*7.4e-3/10.997) = 61.69.

Of course, the camera is not a perfect pinhole camera so you shouldn't expect the 61.69 to be particularly meaningful; it's in a comment after all.

The I kernel (and the frames kernel for Junocam) are admittedly works in progress. I hope to have another update in a few months.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
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Gerald
post Mar 7 2017, 08:26 AM
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QUOTE (Bjorn Jonsson @ Mar 7 2017, 01:24 AM) *
The contrast is rather low. I suspect I need to add square root encoding to the processing to increase the contrast; I noticed that Gerald does this.

The square root encoding returns low contrast, similar to the raws, but it covers most of the dynamical range of "natural" colors.
One option I'm using to enhance the images is a gamma-stretch of the illumination-adjusted version, by a gamma of 4 with respect to the square-root encoded version, i.e. by using the square of the (approximately) radiometrically calibrated data.
In your enhanced image, I see, that you get color banding, as others including me, had been getting for quite a period of time. That's due to the piece-wise linear de-companding function, substantially deviating from square-root encoding.
Your Lommel-Seeliger model seems to work considerably better than the very simple Lambert model I'm using. Thanks for this hint! I've been going to infer the illumination model empirically.
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Bjorn Jonsson
post Mar 8 2017, 01:36 AM
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QUOTE (Gerald @ Mar 7 2017, 08:26 AM) *
In your enhanced image, I see, that you get color banding, as others including me, had been getting for quite a period of time. That's due to the piece-wise linear de-companding function, substantially deviating from square-root encoding.
Your Lommel-Seeliger model seems to work considerably better than the very simple Lambert model I'm using. Thanks for this hint! I've been going to infer the illumination model empirically.

I found the SQROOT companding table and added it to my software - I'm now getting greatly improved results by decompanding the data. Here is first a simple cylindrical map with global illumination removed. Latitude is planetographic. Lommel-Seeliger works better than simple Lambert, especially in the modified form I'm using. The modification is to apply an exponent to the cosines of the incidence and emission angles. I'm currently using a value of 1.1 but this can probably be improved slightly. I also experimented with a Backstorm function but it probably doesn't work as well as modified Lommel-Seeliger (I need to check this more carefully though).

Attached Image


It should be noted that to correct the color where R/G is saturated I made some manual modifications to the map in Photoshop and I also made minor adjustments near the terminator.

And here are new versions of the images I posted yesterday. These new versions are significantly better.

Attached Image
Attached Image


The color correction I'm using is preliminary (without it the images are far too yellowish). It will probably change a bit but nevertheless this shouldn't be too far from Jupiter's true color.
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Gerald
post Mar 8 2017, 03:26 AM
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Montage of cylindrical planetocentrical PJ04 maps (Lambert, gamma-stretched), with 20 pixels per degree :
Attached Image

Full latitudinal coverage, north up. Longitude cropped to a range of 72 degrees.
Png version with 60 pixels per degree, 31 MB.

Best available weights for linearized (r/g/b): (0.82 / 1.0 / 2.17)

Edit:
The companding table is documented in the JunoCam SIS, finally released in the PDS imaging node for Juno.
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Gerald
post Mar 8 2017, 10:00 PM
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The individual cropped cylindrical PJ-04 maps, some of which the above montage is composed of.
Caution: The fully resolved images are 30-times larger than the thumbnails.
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Roman Tkachenko
post Mar 9 2017, 01:23 PM
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Dark Spot and Jovian 'Galaxy' (Enhanced Color)


--------------------
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Gerald
post Mar 9 2017, 09:01 PM
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Nice!

Some more recreation:
Oval BA and "FFRs" interpreted as rising sun over a stormy sea.
Attached Image
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Bjorn Jonsson
post Mar 9 2017, 09:55 PM
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QUOTE (Roman Tkachenko @ Mar 9 2017, 01:23 PM) *
Dark Spot and Jovian 'Galaxy' (Enhanced Color)

This looks awesome. In particular I notice that lots of cloud shadows and vertical relief are visible, especially the small whitish clouds in the right half of the image.
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JRehling
post Mar 10 2017, 05:01 AM
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As we all know, Jupiter has a visible "surface" that is constantly fluctuating, mainly in that different latitudes rotate at different rates, sliding past one another over time. There is other variation as well, as belts, zones, and features within them shift over time. Therefore, no fixed map of Jupiter can exist.

Here is a map of Jupiter the way it looks now – I provide this as a reference to current Juno observations… and as a shameless plug to my astrophotography. This is based on images I took on March 1, 2, 3, and 9. I previously made a map of Jupiter 11 months ago, and the primary changes one notices in this time are:

The North Temperate Zone has changed from white to orange (or: stripes which are more orange than white).
Oval BA has shifted a great deal with respect to the Great Red Spot.
The pale band feeding into the GRS from its east is extremely turbulent over a large range of longitudes, whereas it appeared very laminar last year.
The GRS may be a little more orange (as opposed to more red).

This may help people orient towards a few of the features we see in Juno images that are too zoomed-in to show planet-wide context.
Attached thumbnail(s)
Attached Image
 
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Gerald
post Mar 10 2017, 10:51 AM
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QUOTE (JRehling @ Mar 10 2017, 06:01 AM) *
The North Temperate Zone has changed from white to orange (or: stripes which are more orange than white).

We had an NTB outbreak last year near solar conjunction, before PJ02,

and an SEB-outbreak near the end of 2016 / early 2017.
QUOTE (JRehling @ Mar 10 2017, 06:01 AM) *
The pale band feeding into the GRS from its east is extremely turbulent over a large range of longitudes, whereas it appeared very laminar last year.


Up to data Jupiter images (with data/time) and maps are surely welcome for Juno's Jupiter observation planning, either by direct submission to the missionjuno planning site, or in collaboration with Marco Vedovato. Those observations are required to extrapolate the positions of Jupiter features for the consecutive perijove. It feeds into the points of interest (POIs) which are considered for voting.
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stevesliva
post Mar 10 2017, 05:17 PM
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QUOTE (Bjorn Jonsson @ Mar 9 2017, 04:55 PM) *
This looks awesome. In particular I notice that lots of cloud shadows and vertical relief are visible, especially the small whitish clouds in the right half of the image.


Am I wrong in thinking the "galaxy" is an anticyclone and most of the smaller vortices are cyclones?
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Gerald
post Mar 11 2017, 01:45 AM
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Roman's image shows parts of the northern hemisphere (with north to the right). So structurally, at least, the vortices appear like you're assuming.
The image of oval BA, in contrast, shows part of the southern hemisphere (with north up). Therefore, the largest ovals structurally appear to be anticyclones, too, despite likely rotating in the opposite sense.
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Gerald
post Mar 11 2017, 08:24 PM
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I wondered, whether the polar CH4 images can be patched with approach images.
For PJ04 north polar region (#098), at least, images #092, #094, and #096 seem to be sufficient to close the gaps:
Attached Image

The animated gif shows steps of filling in appropriately reprojected patches.
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