Cassini instruments provide complementary information about the structure of Saturn's rings. Narrow and wide angle cameras provide images in the visible region of the electromagnetic spectrum much like a digital camera does. The images have information about how the ring structure differs both with distance from the planet and with position around the equatorial circle. However, resolution is usually limited to few kilometers at best.

Radio and stellar occultations of the rings also provide important information about ring structure, but only along a one-dimensional track through the rings. The radial resolution can be as fine as 50 meters (164 feet). An "image" is then constructed by assuming circular symmetry over the ring region of interest. Color is usually added to encode other information related to the observed structure.

This image compares structure of Saturn's rings observed by these two approaches. The upper half is a natural color mosaic of images of the illuminated side of the rings by the Cassini narrow-angle camera (see PIA06175). The bottom simulated image is constructed from a radio occultation observation conducted on May 3, 2005. For another view created using this process, see PIA07872. Color in the lower image is used to represent information about ring particle sizes.

Three simultaneous radio signals of 0.94, 3.6, and 13 centimeter wavelength (Ka-, X-, and S-bands) were sent from Cassini through the rings to Earth. The observed change of each signal as Cassini moved behind the rings provided a profile of the distribution of ring material as a function of distance from Saturn, or an optical depth profile. This simulated image was constructed from the measured optical depth profiles.

Shades of purple, primarily over most of the middle ring, the B ring, and the inner portion of the outer ring, the A ring, indicate regions where there is a lack of particles less than 5 centimeters (about 2 inches) in diameter. Green and blue shades indicate regions where there are particles of sizes smaller than 5 centimeters (2 inches) and 1 centimeter (less than one third of an inch), respectively, primarily in the outer A ring and within most of the inner ring, the C ring. The saturated broad white band near the middle of the B ring is the densest region of the rings, over which two of the three radio signals were blocked at 10-kilometer (6-mile) resolution, preventing accurate color representation. From other evidence in the radio observations, all ring regions appear to be populated by a broad range particle size distribution that extends to boulder sizes (several to many meters across).

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radio science team is based at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. For more information on the radio science team visit http://saturn.jpl.nasa.gov/spacecraft/instruments-cassini-rss.cfm. The imaging team homepage is at http://ciclops.org.