Frequently Asked Questions - Images and Data
Frequently Asked Questions - Images and Data
- What is the Cassini-Huygens Mission's data release policy? I've heard that there will be a one-to-two year delay in public access to the data.
- Where can I get the highest-resolution images of Saturn?
- When will recent images of Saturn be released?
- Why is there is a blue area on the top right region of Saturn?
- I was looking at your picture of Enceladus and when I magnified it several times, it looks like it has something orbiting it (like debris). Is this the case?
- In the latest pictures I have been looking at, there at no moons or stars. Why not?
- Images' captions often contain information on size and distance. Why are spatial orientations not included?
- Why are so few of the Cassini pictures in color?
- What controls when a picture is taken?
What is the Cassini-Huygens Mission's data release policy? I've heard that there will be a one-to-two year delay in public access to the data.
We intend to make key results available to the public as soon as we can, which should be nearly immediately. We're releasing an image per week until May 21, 2004, when we'll start to release them daily (five days per week). They'll appear initially at our project web site, http://saturn.jpl.nasa.gov, and for the longer term at http://photojournal.jpl.nasa.gov/index.html . We'll release data from instruments other than the camera as significant results become available. You'll find them at our web site, and probably even more frequently at each investigation's site (that is, the web site for each group responsible for an instrument package), which can be linked to from our site.
However, it can be up to one year from receipt of data before all of the data is delivered to the Planetary Data System. It's a challenge for our scientists to deliver even on this time scale, considering that they will receive about 1 gb per day on a slower day, and up to 4 gb per day on a good day for four years. The time and effort needed to process, calibrate, validate, and format this volume of data is substantial -- not to mention designing the observations and creating the files that enable the spacecraft to acquire the data in the first place, and then doing any scientific analysis. Nevertheless, we intend to hold them to this schedule, even at the expense of some data collection if necessary. So all of the data should be available to you not later than one year after collection, and you can access significant parts of it much sooner.
Where can I get the highest-resolution images of Saturn?
Visit the Cassini homepage at http://saturn.jpl.nasa.gov and The Planetary Photojournal at http://photojournal.jpl.nasa.gov/targetFamily/Saturn.
When will recent images of Saturn be released?
They are being released weekly until May 21, 2004, when we'll begin to release them daily.
Why is there is a blue area on the top right region of Saturn?
As Cassini approaches Saturn, most of the planet's northern hemisphere is in the shadow of the rings, with the exception of a small blue sliver visible on the limb. That sliver is sunlight that has passed through the Cassini Division in the rings and is being scattered by the cloud-free upper atmosphere. For a good view of this phenomenon, see the image titled Saturn in Color.
I was looking at your picture of Enceladus and when I magnified it several times, it looks like it has something orbiting it (like debris). Is this the case?
No, we are unable to see that. Chances are you're seeing "noise" in the image, or possibly the effects of distortion in your magnification lens.
In the latest pictures I have been looking at, there at no moons or stars. Why not?
Saturn's brightness makes moons and stars difficult to see. The same effect occurs when you notice that you can't see stars near Earth's bright full moon.
In an image released in March 2004, (http://photojournal.jpl.nasa.gov/catalog/PIA05383 ) there are 3 moons visible, and the text tells you where to find them. As the text points out, the imaging team enhanced the brightness of the moons to aid visibility.
Images' captions often contain information on size and distance. Why are spatial orientations not included?
Examining two-dimensional images of three-dimensional space is one of the scientists' toughest tasks. Without looking at detailed information, determining where objects are (relative to Cassini) is sometimes difficult for them as well.
In writing captions, scientists try to provide a consistent amount of spatial and geometric information. For example, in captions of images showing a single moon, the north orientation is noted, as well as which hemisphere is shown. Imaging team members try to present Saturn and its moons "north-up" (or close to it) and note when that's not the case. Usually, when Saturn or the ring plane is shown, north orientation is not noted since the planet's "equatorial" rings make that obvious. Captions also indicate images that are taken from just above or below the ring plane, and often discuss the ways that "above" and "below" images can differ in appearance.
A way to visualize the geometry of Cassini images is to view the same scene using a space simulation viewer like the NASA Solar System simulator. Enter the date shown in the caption, then choose "as seen from Cassini." Additionally, choosing a day before or after the image was taken can help better visualize was Cassini "saw" as it explores the Saturnian region.
Why are so few of the Cassini pictures in color?
Creating color images is a complex task requiring much more labor and computer time than black and white images. This is because all Cassini images are recorded in black and white. The camera records the amount of light (not the color of the light) coming through a filter in front of the sensor. It is the filters that come in color.
To create color images scientists take three black and white images of the same target with the red, green, and blue (RGB) filters. In other words, one image records the amount of red light (using a red filter), another records the amount of green and one the amount of blue light (using green and blue filters respectively). Color renditions of the scene are then constructed on the ground by combining images taken with the different filters.
Unfortunately, these three images are not taken simultaneously. Consequently, intricate fitting and geometric transformations are needed to construct the color image because the spacecraft, planet, rings and moons have all moved a little during the time it takes to record the images using the different filters.
What controls when a picture is taken?
The scientists determine this when they do the observation designs. The path of Cassini is known, as are the paths of the Saturn's moons, so it's a matter of looking at the varying geometry with time and selecting the camera pointing directions and shuttering times that will gather the most scientifically interesting images. These commands are then built into sequences that are sent to the spacecraft from days to weeks in advance of the observations.