Juno, perijove 14, July 16, 2018 |
Juno, perijove 14, July 16, 2018 |
Jul 21 2018, 10:08 AM
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#46
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Member Group: Members Posts: 923 Joined: 10-November 15 Member No.: 7837 |
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Jul 21 2018, 11:42 AM
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#47
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Member Group: Members Posts: 923 Joined: 10-November 15 Member No.: 7837 |
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Guest_avisolo_* |
Jul 21 2018, 01:09 PM
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#48
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Guests |
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Jul 21 2018, 07:59 PM
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#49
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Member Group: Members Posts: 923 Joined: 10-November 15 Member No.: 7837 |
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Jul 21 2018, 08:01 PM
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#50
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IMG to PNG GOD Group: Moderator Posts: 2250 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Image PJ14_30 in approximately true color/contrast and enhanced versions. The PJ14 images include beautiful observations of a small red spot near latitude 16.5 degrees south. The spot is slightly more than 5000 km long and its color is similar to the color of the Great Red Spot.
And below is a schematic image showing the resolution in one of the above images (the image that is roughly centered on the spot). The resolution is highest northeast of the red spot. A subset from the image metadata: IMAGE_TIME = 2018-07-16T05:28:29.317 MISSION_PHASE_NAME = PERIJOVE 14 PRODUCT_ID = JNCE_2018197_14C00030_V01 SPACECRAFT_ALTITUDE = 7960.3 km SPACECRAFT_NAME = JUNO SUB_SPACECRAFT_LATITUDE = -13.7571 SUB_SPACECRAFT_LONGITUDE = 79.186 TITLE = PJ14 South Equatorial Belt north Resolution at nadir: ~5.4 km/pixel |
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Jul 22 2018, 01:46 PM
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#51
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Member Group: Members Posts: 923 Joined: 10-November 15 Member No.: 7837 |
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Jul 22 2018, 05:58 PM
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#52
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Senior Member Group: Members Posts: 2504 Joined: 13-September 05 Member No.: 497 |
One of the methane band images is unsharp, obviously due to motion blur, but on the other hand, it doesn't show the stray light issues with TDI enabled for long exposure time. We've concluded that the issues with the methane images are not stray light per se but are being caused by blooming of charge from the visible bands migrating up into the CH4 region more than we had expected from ground testing. We tried a couple of things: just turning the TDI off and letting the image blur alongspin (which works but obviously the images are very blurry) and moving the CH4 readout region as far as possible from the visible bands (which showed some modest improvement but isn't a panacea.) The latter will affect the geometric information in a way not currently captured in the instrument metadata. You can expect some similar tests in future perijoves. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Jul 22 2018, 06:52 PM
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#53
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
The thing I love about that "small red spot" is that it's a cyclone rather than an anticyclone like the GRS. I'm not sure if there's any imagery of comparable resolution of a reddish cyclone. That offers some promise for understanding the atmospheric dynamics better.
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Jul 22 2018, 08:28 PM
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#54
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Senior Member Group: Members Posts: 2504 Joined: 13-September 05 Member No.: 497 |
The thing I love about that "small red spot" is that it's a cyclone rather than an anticyclone like the GRS. I think these features are called "barges" by the Jupiter community, but I'm not sure what distinguishes a barge from a spot if anything. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Jul 23 2018, 08:32 PM
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#55
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IMG to PNG GOD Group: Moderator Posts: 2250 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
Image PJ14_20 in approximately true color/contrast and enhanced versions:
And a small subset from the image metadata: IMAGE_TIME = 2018-07-16T05:04:32.049 MISSION_PHASE_NAME = PERIJOVE 14 PRODUCT_ID = JNCE_2018197_14C00020_V01 SPACECRAFT_ALTITUDE = 12204.7 SPACECRAFT_NAME = JUNO SUB_SPACECRAFT_LATITUDE = 51.3607 SUB_SPACECRAFT_LONGITUDE = 54.3512 TITLE = PJ14 Jet N5 Resolution at nadir: ~8.2 km/pixel |
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Jul 24 2018, 02:03 PM
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#56
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
We've concluded that the issues with the methane images are ... being caused by blooming ... Did you consider to replace TDI 64 CH4 images by pairs of TDI 32 images? Blooming would be halved, and TDI would shift the saturated pixels by 32 rows less. Of course, required storage would be doubled for the same number of collected photons. Btw., in the meawhile, I've rendered hipassed maps of PJ14, part 3, highly resolved cylindrical maps of close-ups, and drafts of the departure sequence. Attempts to visualize short-term southern CPC motion are on an early state. At least this preliminary 6-image animated gif should provide an idea of the motion, and of the type of the involved vortices. The upper left vortex in the GIF is the most southern CPC, approximately the center of an almost pentagonal cluster of six circumpolar cyclones, three of which are shown. Interestingly, a pretty large anticyclone made it into the gap between those three cyclones. Note, that the FFRs (folded filamentary regions) in the lower left are cyclonic, too, like usual. In the upper right, there is another anticyclone, but its rotation isn't well-resolved in this animation. Some of the apparent motion is due to residual global geometrical distortions. And on the raw pixel level, we probably have some aliasing, which might be confused with small-scale motion. |
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Jul 24 2018, 03:01 PM
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#57
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Senior Member Group: Members Posts: 2504 Joined: 13-September 05 Member No.: 497 |
Did you consider to replace TDI 64 CH4 images by pairs of TDI 32 images? Even if everything was perfect (geometric registration, digitization, etc.) a pair of images of TDI N/2 would only improve the SNR by sqrt(2) relative to a single image of TDI N. We did some tests with lower TDI several orbits ago and will likely repeat them with the new CCD readout region, but we don't have a good model for how much this will help, and it's obviously a tradeoff between blooming and SNR. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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Jul 24 2018, 11:01 PM
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#58
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Member Group: Members Posts: 403 Joined: 18-September 17 Member No.: 8250 |
... will affect the geometric information in a way not currently captured in the instrument metadata. Could changes to readout locations (or other instrument command parameters that are not reflected in the metadata) be recorded in the RATIONALE_DESC and/or DESCRIPTION strings. |
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Jul 24 2018, 11:27 PM
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#59
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Member Group: Members Posts: 403 Joined: 18-September 17 Member No.: 8250 |
We've concluded that the issues with the methane images are not stray light per se but are being caused by blooming of charge from the visible bands migrating up into the CH4 region more than we had expected from ground testing. Is the CCD substrate voltage (VSUB) a command-able parameter? If it can be increased, it should reduce blooming. |
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Jul 25 2018, 03:07 AM
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#60
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Senior Member Group: Members Posts: 2504 Joined: 13-September 05 Member No.: 497 |
Is the CCD substrate voltage (VSUB) a command-able parameter? No, and it's set by the hardware to a very large value which maximizes antiblooming at the cost of reduced full well. Which doesn't help in this case because the CCD vertical registers are not connected to the substrate. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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