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Space Topics: Cassini-Huygens

Visual and Infrared Mapping Spectrometer (VIMS)

Optical Remote Sensing Instrument for the Cassini Orbiter

Scientific Objectives - How It Works - Saturn Exploration Context - VIMS Facts

Scientific Objectives

The Visual and Infrared Mapping Spectrometer (also known as the Visible and Infrared Mapping System, or VIMS) is mapping the color properties of the atmospheres of Saturn and Titan, the surfaces of the moons, and the rings in order to study their composition and structure. Specifically:

To study the Saturn and Titan atmospheres:

• To study the behavior of winds and storms over time.
• To determine the compositions of the atmospheres and clouds, and how they vary from place to place.
• To search for lightning.
• To determine the temperatures, internal structure, and rotation of Saturn's deep atmosphere.

To study Saturn's rings:

• To study the structure and composition of Saturn's rings, and how they vary from place to place.

To study Saturn's moons:

• To map the composition of the surfaces of Saturn's moons, including Titan, in order to determine their geologic histories.
• To search for active volcanism on Titan.

How It Works

Click to enlarge > Cassini's Optical Remote Sensing Pallet All of Cassini's Optical Remote Sensing instruments are located on a pallet on one side of the orbiter. Credit: NASA / JPL

Click to enlarge > Fields of view of the Cassini Optical Remote Sensing Instruments All of Cassini's Optical Remote Sensing instruments (ISS, UVIS, VIMS, and CIRS) share the same boresight. This diagram compares the fields of view of the four instruments. VIMS' field of view is shown in green.

The Visual and Infrared Mapping Spectrometer consists of two instruments, one that studies visible light (VIMS VIS) and one for infrared light (VIMS IR). Spectrometers split incoming light into its component wavelengths, and measure the intensity of each wavelength. A mapping spectrometer can do that task for many points simultaneously, building up an image that is incredibly rich with color information. VIMS images contain information on 352 different wavelengths of light from ultraviolet to the mid infrared. This is much higher spectral resolution than the Imaging Science Subsystem can manage, but the spatial resolution of VIMS is roughly 100 times lower than the resolution of ISS.

VIMS produces what scientists refer to as "image cubes." A monochrome image is two-dimensional: it has information in two spatial directions (x and y, or north-south and east-west). A color image adds a third dimension: wavelength. But ordinary color images only have information along three points along the wavelength dimension. VIMS has a lot more depth, 352 points along the wavelength dimension. As a result, VIMS images are truly three-dimensional.

How Does VIMS Fit in the Context of Saturn Exploration?

Nothing like VIMS has ever been sent to Saturn. The Voyagers carried an infrared point spectrometer, but that instrument sampled wavelengths mostly longer than what VIMS can detect. And the near-infrared wavelengths to which VIMS is sensitive are key to mapping the locations of likely surface materials for the icy satellites. The only similar instrument that has ever been sent to the outer solar system is the Near Infrared Mapping Spectrometer aboard the Galileo mission to Jupiter.

VIMS Facts

VIMS consists of two instruments, a "pushbroom" mapping spectrometer covering ultraviolet and visible wavelengths (VIMS VIS) and a "whiskbroom" mapping spectrometer covering infrared wavelengths (VIMS IR).