Images and mosaics

This page contains images and photomosaics that I have created from raw spacecraft images, in most cases as 'by-products' while creating planetary maps. In some cases these images/mosaics are spectacular and in all cases they are either completely new or better (IMHO) than similar stuff available elsewhere (after all, if this weren't the case I would simply have used what was available elsewhere !).

Some of these images are also available through links on other pages at this site.

Click the images for full size versions.

Jupiter's Great Red Spot from Voyager 1
The Great Red Spot from Voyager 1 This is a 4x3 mosaic of individual color images of Jupiter's Great Red Spot. Each individual color image was created from raw orange and violet images that had to be individually calibrated and processed. I also created synthetic green images because no green images were obtained during this particular imaging sequence. Processing the raw images involved calibrating them, reprojecting them to simple cylindrical projection, mosaicking them and then rendering the cylindrical mosaic on an ellipsoid using a typical viewing geometry (there is no such thing as a "correct viewing geometry" because the images were obtained over a 37 minute period with Jupiter rotating). I then fixed the color balance. The final step was to sharpen the resulting image a bit, mainly to compensate for all of the resampling that the previous processing steps required. For this version of the image I also increased the contrast and sharpness to better reveal various small scale details.

This mosaic reveals lots of small scale details, for example features that seem to be vertical relief and cloud shadows are visible at various locations, especially southeast of Great Red Spot.

The 24 individual images I used were obtained by Voayger 1 on March 4,1979 at a distance of about 1.85 million km. The first image (C1635314.IMQ) was obtained at 07:08:36 and the last one (C1635400.IMQ) at 07:45:24. The resolution is roughly 18 km/pixel.

Mosaics of some of these images have appeared before as 'official' image releases but interestingly, only 3x2 images were used in all cases. The offical mosaic can be seen here. There is a false color version (lots of blue color) that is better known; it's available here.

Jupiter's Great Red Spot from Voyager 2
The Great Red Spot from Voyager 2 A 5x3 mosaic of Voyager 2 images Jupiter's Great Red Spot (GRS). The image processing was very similar to the processing described above for the Voyager 1 mosaic with the exception that here green images were available.

The 45 individual images used for creating this mosaic were obtained by Voyager 2 on July 8, 1979 when the spacecraft was 1.45 million km from Jupiter; the resolution is roughly 14 km/pixel.

This mosaic reveals that many changes occurred in the GRS area in the four months that separate this mosaic and the Voyager 1 mosaic above. In particular, the white spot south of the GRS in the Voyager 2 mosaic is not the same spot as the one visible in the Voyager 1 mosaic.

New - Jupiter's Great Red Spot from Voyager 2 (a more distant view)

The Great Red Spot from Voyager 2 Another Voyager 2 mosaic of the Great Red Spot, this time a 3x2 mosaic.

The 18 individual images used for creating this mosaic were obtained by Voyager 2 on July 7, 1979 when the spacecraft was 2.7 million km from Jupiter; the resolution is roughly 26 km/pixel.

It is interesting to compare this mosaic to the higher resolution Voyager 2 mosaic above. This one was obtained about 30 hours (3 Jovian rotations) earlier. The changes in this short period of time are remarkable.

Jupiter from Voyager 2
A global Voyager 2 view of Jupiter This 3x3 mosaic of Jupiter was created from images taken by the Voyager 2 spacecraft on June 30, 1979 from a distance of 8.7 million km. It is created from orange and violet filtered images used as red and blue respectively. When the spacecraft was this close to Jupiter it photographed it using only these two filters so I had to use a synthetic green image. In cases like this it is common for the synthetic image to be simply the average of the other two images but looking at images taken from a greater distance I noticed that the green images look far more like the orange than violet ones. This had the effect that if I made the areas that are supposed to be approximately white (e.g. the North Tropical Zone) white Jupiter's overall color became too reddish. So instead of using the average of orange and violet I determined which combination of the orange and violet images was most similar to an actual green image in a least squares sense by measuring the color of several areas in the images (e.g. the Great Red Spot, a white oval, a dark belt and a bright zone). The resulting synthetic green image was remarkably similar to an actual green image.

The first steps were to radiometrically correct the orange and violet images and then to remove noise using Photoshop.

I then reprojected the orange and violet images to simple cylindrical projection. To do this I had to partially reverse engineer the spacecraft's viewing geometry, I knew its location relative to Jupiter but not the direction in which its camera was looking. I then aligned the images to each other and created the synthetic green images. The cylindrical map was a necessary step, because of Jupiter's rapid rotation it is not possible to mosaic the images themselves directly. I then added fictional data to a small, blank area near the north pole and fixed the terminator (this was necessary due to Jupiter's rotation while the images where obtained). The final step was to render the resulting map from the spacecraft's location making Jupiter 'self-illuminating' and using no light source.

This resulted in this spectacular 2048x2048 pixel image. Strangely, this is the only Voyager high resolution global mosaic of Jupiter that I have ever seen. This is all the more strange since doing mosaics like this is relatively easy using todays software and computers. However, this wasn't the case back in 1979 when the images were taken.

Jupiter's Great Red Spot from Voyager 2
Jupiter's Great Red Spot This is a 3 image mosaic of Jupiter's Great Red Spot, the solar system's largest weather system. It is bigger than the Earth and has been present at least since the 19th century and possibly for a much longer time.

This mosaic was created from images obtained by the Voyager 2 spacecraft on July 6, 1979 from a distance of 3.8 million km. It was created similarly to the global mosaic of Jupiter (below), except for two things: Effects of varying illumination across the images have been removed. Finally, contrast and color saturation were enhanced somewhat to increase the visibility of various features.

The mosaic shows the Great Red Spot viewed from directly above. This eliminates the foreshortening that was present in the original images since Voyager 2 was located a little north of the equatorial plane when the images were taken. However, the red spot is approximately 22 degress south of the equator. This is also the reason the white oval south of the Great Red Spot appears almost circular here while in the original images it appears elongated in the horizontal direction.

Ganymede in color
These color images of Ganymede were obtained by Voyager 1 (top row), Galileo (lower left) and Voyager 2 (lower right and center). The Voyager images are composed from orange, blue and violet filtered images and the Galileo image from IR-7560, green and violet. The red/pink color in the bright crater in the Galileo image is present because some of the source images were saturated at this spot. I used images like these to colorize my map of Ganymede.
A global view of Ganymede
This is a well known Voyager 2 color image of Ganymede. It is composed from orange, blue and violet filtered images used as red, green and blue respectively. This is a reprocessed version where noise was first removed from the source images, thus almost no spurious, sharply defined blue or red spots appear in the image. The source images have also been slightly rotated in 3D space to account for the fact that the spacecraft's location relative to Ganymede changed slightly between the individual images.

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