[X] My Assistant

[mcaplinger]

Some of the images have been posted on missionjuno.

You will immediately notice that there is something weird about them. Yes, we know about this, and I'll say more about it when I can. In the meantime, anything people can do to process them would be appreciated. I've had some success using https://github.com/chunglabmit/pystripe

[siravan]

Is there any possibility of changing the exposure time? I don't know if JunoCam can handle shorter exposures, but if it can and the exposure time is reduced 4x, it may improve the SNR by a factor of ~2. Unfortunately, it will also increase the file size by 4x, which may not be possible or practical.

[mcaplinger]

Is there any possibility of changing the exposure time? I don't know if JunoCam can handle shorter exposures, but if it can and the exposure time is reduced 4x, it may improve the SNR by a factor of ~2. Unfortunately, it will also increase the file size by 4x, which may not be possible or practical.

I'm not following why you think using a shorter exposure time would help, or why it would increase the file size. Junocam is a pushframe imager, so we could reduce the exposure time as much as we wanted below the nominal 1 IFOV of blur at 3.2 msec. As far as we can tell, the noise and offset is largely independent of exposure time. You can see this for yourself by comparing the RGB, methane, and single-band lightning search images.

[Brian Swift]

I'm not following why you think using a shorter exposure time would help, or why it would increase the file size. Junocam is a pushframe imager, so we could reduce the exposure time as much as we wanted below the nominal 1 IFOV of blur at 3.2 msec. As far as we can tell, the noise and offset is largely independent of exposure time. You can see this for yourself by comparing the RGB, methane, and single-band lightning search images.

I think they are suggesting taking 4 images, each with 1/4 exposure time and averaging/summing them together to beat down noise (which as I recall would run into limitations either on a buffer size or how fast data can be moved to RAM).

the noise and offset is largely independent of exposure time

Since turning the instrument on and off ain't happening (for good reason). I was curious if there is any effect for either of:
1) taking several exposures as fast as possible (min exposure time, min INTERFRAME_DELAY) followed by a normal exposure.
2) taking a very long well-filling exposure, followed immediately by a normal exposure.

Of course I don't know if the instrument is capable of either of these operations.

ps. thanks for the responses to my questions. I am curious which specific ITAR sections are limiting you disclosure ability.

[mcaplinger]

I think they are suggesting taking 4 images, each with 1/4 exposure time and averaging/summing them together to beat down noise

It takes about 150 msec to read out a one-band image and about 255 msec for a three-band image, plus exposure time. So the typical visible exposure time of 3.2 or 6.4 msec is only a small fraction of that time. It might be barely possible to take one-band images at an interframe of say 160 msec, which would overlap downspin by more than 50%. That could help somewhat but it's a pretty big impact for not much return, it seems to me. 4X is just not possible.

1) taking several exposures as fast as possible (min exposure time, min INTERFRAME_DELAY) followed by a normal exposure.
2) taking a very long well-filling exposure, followed immediately by a normal exposure.

Both 1 and 2 would be limited in their cadence ("followed by/immediately" is no faster than the amount of time it takes to read the previous images out of DRAM to the s/c, many seconds). We've taken a range of exposure times (RGB/CH4/lightning) already and there seems to be very little difference in behavior with exposure time or from frame to frame at the standard interframe time. The fact that the offset occurs with images of black space suggests little dependence on signal level, we think it is a shift between the reset and video level coming out of the CCD.

I am curious which specific ITAR sections are limiting you disclosure ability.

I'm not a lawyer, I just know what they tell me I can and can't say. Some of this is now covered by EAR rather than ITAR, but it's not clear that it's helped. Maybe https://www.space.commerce.gov/regulations/...ol-regulations/ would have some useful background. If you argued that this is being overapplied, I wouldn't disagree with you, but it's above my pay grade.