Cassini ISS: Imaging Science Subsystem


PIA17172 was taken on July 19, 2013 when NASA's Cassini spacecraft slipped into Saturn's shadow and turned to image the planet using the Imaging Science Subsystems.



About ISS

The Cassini Imaging Science Subsystem (ISS) consisted of two fixed-focal length imaging cameras. The higher-resolution Narrow Angle Camera (NAC) and lower-resolution Wide Angle Camera (WAC) were both equipped with a dual set of filter wheels which allowed for color imaging from the ultraviolet, across the visible portion of the electromagnetic spectrum and into the near-infrared. The cameras were built by NASA's Jet Propulsion Laboratory.
Scientific objectives for ISS include the following:
  • Study the compositional, photometric and polarimetric properties of Saturn's atmosphere
  • Study atmospheric dynamics on Saturn and Titan
  • Investigate Saturn's auroral phenomena
  • Reveal the structure and morphology of Saturn's main rings
  • Study the processes and phenomena that drive the diffuse rings of Saturn
  • Refine the orbits of Saturn's small satellites and search for previously undetected moons
  • Study the geology and surface morphology of Saturn's retinue of icy satellites
  • Map the icy satellites of Saturn cartographically and compositionally
  • Reveal and investigate the surface structure of Titan
  • Learn about meteorology in the atmosphere of Titan

ISS Cameras:

  • Narrow-Angle Camera (NAC)
  • Wide-Angle Camera (WAC)
ISS Instrument Characteristics*
General Characteristics
CCD Type three-phase, front-side illuminated
Pixel Size 12 mm
Format 1024 x 1024
Digitization 12 bits, 4095 DN
Read Noise Level 12 e-
NAC WAC
Telescope Design Reflector Refractor
Focal Length (mm) 2002.70 ± 0.07 200.77 ± 0.02
Focal Speed 10.5 3.5
Pixel Angular Size (μrad) 5.9907 59.749
Field of View (mrad) 6.134 61.18
FWHM of PSF (pixels) 1.3 1.8
Spectral Range (nm) 200–1050 380–1050
Filter Positions 12 x 2 filter wheels 9 x 2 filter wheels
* values taken from Table VII of Porco et al. (2004) in Space Science Reviews
The ISS dual-camera architecture was similar to that of the camera systems carried aboard the twin Voyager spacecraft. A 2000-mm focal length reflecting telescope focused incoming light onto the detector of ISS' NAC, giving it a field of view 0.35° across. There was a 1024x1024 Charged-Coupled Device (CCD) at the heart of each camera. The CCD in the WAC sat at the focal point of a 200mm focal length refracting telescope. WAC pixels had a pixel scale of ~60 µrad/pixel. NAC pixels, at ~6 µrad/pixel, had a pixel scale that was 10 times finer. The NAC responded to photons within a spectral range of 200 through 1100 nm. The design of the telescope limited the spectral response of the WAC to 380-1100nm. Spectral filters allowed the cameras to isolate different windows across these spectral ranges.
The engineering details of the ISS instrument and the science objectives it was built to address are described in further detail in the Space Science Reviews paper by Porco et al. (2004).

ISS Data

Data Search Tools

Read these Important Notes about looking for ISS images of rings and moons using the Image Atlas and OPUS search tools.
  • PDS Imaging Atlas is a parameter-based search tool that can be used to find ISS data based on a very wide range of instrument parameters. This system delivers raw VICAR files
  • The OPUS search engine allows for an interactive search of the ISS data in the PDS archive based on a wide variety of search parameters, including observation geometry and target. Although It is optimized for ring and small-moon studies, this system delivers calibrated images.
  • The Master Schedule is a time-ordered listing of observations by all instruments. This may help find data based on particular events, however the Image Atlas and OPUS tools linked above will be much simpler to use in most circumstances.
  • The Event Calendar is an interactive event-finding tool that can be used to search for data associated with particular events.
  • Titan Trek is focused on finding remote-sensing data, including ISS data, in the context of Titan's surface

Browse Raw Data Products

Cassini ISS Online Data Volumes
  • These Data Volumes provide data sets of raw images (EDRs) from ISS and are located at the PDS Imaging node.
  • The Data Volumes include ISS Raw Ground Calibrations, Earth/Venus/Jupiter EDR images as well as the Saturn EDR images.
  • Additional information can be found at the PDS Imaging Node.

Derived Data Products

Analyzing ISS Data

The team delivered raw images. In addition, calibrated ISS images are available at the Ring-Moon Systems Node (RMS) through OPUS, or through direct access from the calibrated Cassini ISS directory at the RMS Node.

Once data products have been selected and retrieved, users will need appropriate software to read, manipulate and display that data. Software packages that will enable users to make use of ISS data are listed below.

Calibration
  • CISSCAL is the official calibration software for ISS data. The user will need CISSCAL software files (see cisscal.tar.gz under extras) and CISSCAL support files (see calib.tar.gz under calib). See the ISS User’s Guide for details on the use of CISCAL.

Display and Analysis
  • ISS images are compatible with the Integrated Software for Imagers and Spectrometers (ISIS) software package which is available through the USGS Flagstaff web site.
  • CAVIAR is an IDL based software package designed for the astrometric measurement of natural satellite positions in images taken using the Imaging Science Subsystem (ISS) of the Cassini spacecraft. For more information, see Cooper, et al., A&A 610, A2 (2018), DOI: 10.1051/0004-6361/201731713.
  • OMINAS OMINAS (pronounced like ‘ominous’) is an IDL-based software environment for the reduction and analysis of data taken by any space-based or planet-based system. The linked github repository includes extensive documentation.
  • CASVU (temporarily unavailable) is designed specifically for ISS image data analysis. CASVU are in the final stages of development. It and the associated users’ manual will be available soon. It operates under IDL and can be run under IDL VM software which is available at no cost. We will supply links to the appropriate pages when they become available.

  • Display
      Images archived by the PDS, when accompanied by their respective label files, can be viewed using NASAView which is available through the PDS Software Download web page.
    • Piotr Masek has developed the Cassini Orbiter Image Viewer, an easy to use, MS Windows, viewer for Cassini ISS images. Although it is not designed for doing science, it does let you look at the images quickly and offers some toggles (no detailed control) to stretch & rotate images.




For questions and comments, visit the PDS Cassini Contact Page