Images from JIRAM, A very interesting data set Options

[Bjorn Jonsson]

It is easy to forget that JunoCam isn't the only instrument aboard Juno that can obtain images. The Jovian Infrared Auroral Mapper (JIRAM) instrument can obtain images in two infrared bands. One of these, centered at a wavelength of 4.78 µm, shows thermal radiation emitted from Jupiter. This radiation is caused by heat from Jupiter's warm interior - as a result there is no difference between the dayside and nightside in these images. Therefore they are great for looking at Jupiter's north pole which isn't visible in the JunoCam images because it is currently winter in Jupiter's northern hemisphere.

Here is a tweened time-lapse created from three JIRAM image mosaics obtained over an interval of slightly less than three hours shortly before perijove 4 on February 2, 2017:

 jup_jiram_npole_anim_20170202.mp4 ( 2.11MB ) Number of downloads: 890


Because Juno was approaching Jupiter the image sharpness increases from start to finish.
In case you are unable to play the MP4 file above the time-lapse can also be viewed at Vimeo (the quality is somewhat lower though): https://vimeo.com/263221959

All of the JIRAM images through perijove 6 are available at the Planetary Data System Atmospheres Node and can be converted to PNG files using IMG2PNG. Thousands of images have been obtained by JIRAM.

Usually a spacecraft's highest resolution imaging instrument is a visible light camera but Juno is an exception. JIRAM's resolution is higher than JunoCam's. While JIRAM's images are small compared to the JunoCam images (only 432 pixels in the horizontal direction) it has much narrower field of view than JunoCam (5.9 degrees vs. JunoCam's 58 degrees). Combined, this means that the JIRAM images have about three times higher resolution than the JunoCam images but they also cover a much smaller area.

Here is a mosaic of Jupiter's north polar region from the data that was used to create the animation above:



This shows all nine circumpolar cyclones (CPSs) in their full glory. The mosaic shows the north polar region from directly above and is in orthographic projection. It is centered on the north pole. These images have been processed to show details in the areas that appear very dark in the original images. Comparing JIRAM images to visible light (JunoCam) images reveals that the JIRAM images are somewhat similar to inverted visible light images; features that appear bright at visible wavelength are usually dark in 4.78 µm images and vice versa.

Because JIRAM has obtained a lot of images, often with an interval of only 30 seconds, they can be animated. Below are two animated GIF examples. First an animation of 186 JIRAM images obtained over a period of 1 hour and 35 minutes on August 1, 2016 from a distance of approximately 8 million km:



And another animation that consists of 145 JIRAM images obtained over a period of 1 hour and 16 minutes on August 26, 2016 from a distance of approximately 1.6 million km. Even though it may look as if the spacecraft is traveling south to north this is not the case; it is the direction in which the spacecraft is looking that changes. The Great Red Spot is clearly visible:



In both of the animations the images have been processed to reveal details in areas that appear very dark in the original data. However, I decided not to remove noise or make the animations more 'stable'. Both because it would have been a lot of work but also because I actually prefer these animations without 'cleanup'. They appear more realistic that way. This is a matter of taste but sometimes less is more when it comes to image processing.

[Gerald]

I finally found time to convert JIRAM IMG files of orbits 09 to 26 into PNG, and updated the website above.
Thus far, I've only provided zipped PNGs, no large synopses, yet.
Some of the JIRAM image products consist of two framelets, (presumably) of a 4.5 to 5.0 µm region in the upper half and a 3.3 to 3.6 µm region in the lower half. In those cases, the products I'm providing suffer from the significantly different signal levels making the ~3.3 µm region almost black, if there is a signal in the ~5 µm region. I might find time to fix that issue at some point in the future, but probably not too soon. The 3.3 µm primarily shows aurorae. I think that it's an emission line of the trihydrogen cation H₃⁺, IIRC.
I even didn't find enough time yet to take a thorough look at the majority of this large number of images. But what I've seen is beautiful, including images of Io with more than 30 hot spots. Enjoy! There is a lot to discover.