How does the Junocam work on JUNO

How does JunoCam differ from a normal CCD camera?

JunoCam used different technologies than the typical frame camera you buy in a store. A typical color digital camera uses a Bayer filter pattern, a series of alternating small blue and green filters, followed by a series of alternating small green and red filters, with each filter covering one pixel, followed by a series of alternating small blue and green filters, and so on further. Instead, JunoCam has four filter strips, each 1600 pixels wide. There are three in the visible range, the standard filters for red, green, and blue, depending on how the human eye works. The fourth is in the near infrared and is designed for methane. Each of the three visible filter strips is approximately 150 pixels high; The methane filter strip is slightly larger than one of the visible filter strips.

JunoCam uses two other concepts that you won't see in the typical digital camera. One of them is time lag and integration. The lighting level on Jupiter is approximately 1/27 the lighting level on Earth orbit (Jupiter orbits approximately 5.2 AU). Juno rotates at 2 RPM. Short exposure would cause too much noise due to poor lighting. A short exposure would be too blurry thanks to this rotation. Time lag and integration means taking a series of short duration exposures and integrating them by shifting subsequent images to account for the rotation.

The other key technique is that JunoCam is a push frame imager as opposed to a framing imager. A frame arises when the time delay and integration is complete (the number of TDI steps is commandable). This frame is moved to local storage. JunoCam toggles between visible and methane channel, which means that a minute later, another visible frame is created thanks to JunoCam's rotation rate at 2 rpm. The result is a jumble of partially overlapping framelets that require extensive floor processing to understand the images.

JunoCam is designed to provide optimal performance one hour before and one hour after the next approach. This should perform well on the closest approximation, but most importantly, it should also perform well over Jupiter's polar regions. JunoCam won't work as well Juno is a long way from Jupiter (which is most of its orbit).

uhoh

Very nice! Thank you for the nice letter. I had no idea about the NIR filter!

uhoh

Is there a way to add the link to the JunoCam article here too? Then you could cite Figure 12 and Figure 13 as well and include them in the answer. It's kind of "aha". Definitely not the RGB filters that are used to simulate human color vision!

Gerald

Nice to see someone knowledgeable about JunoCam! I invested some time to correct the outdated Wikipedia paragraph in the German Wikipedia (de.wikipedia.org/wiki/Juno_(Raumsonde)#JunoCam). However, the English Wikipedia version via JunoCam (en.wikipedia.org/wiki/JunoCam#Specifications) is still based on an obsolete technical document from 2005. Since Wikipedia is often used as a reference, it might be useful to use an English / American To be corrected by native speakers. I've seen the same confusion as in the question several times on forums.

Gerald

... BTW: Although the color filters are around 150 pixels high (plus a gap of around 5 pixels), the display for the framelets is only 128 pixels, so for small TDI you don't get a mix of two colors.

Gerald

@uhoh: Thanks for taking this part. I would think Figure 15 is copyrighted by MSSS. All paper is copyrighted by the authors of the paper. Candice Hansen is JunoCam PI, Glenn Orton (JPL) is usually the contact for terrestrial observations. It is probably best to contact the lead author i.e. Candice Hansen with a brief request for approval using the image on Wikipedia: psi.edu/about/staffpage/cjhansen They will then forward the request to MSSS if necessary.