VISIONS OF SATURN Visions of Saturn, Volumes I and II offer the following selection of NASA images: Images of SATURN in the Range 33575.27 - 43901.56 in GIF Format. Introduction The pictures on this CD-ROM were taken by NASA'S Voyagers 1 and 2 spacecraft during their epic tours of the solar system. NASA has made these images available to researchers and libraries and with this disk we make them available to the computer hobbyist. These are full resolution (800 pixels by 800 scan lines) digital images returned by the Voyager cameras and represent the best nearest-encounter images for the planet and its moons. No additional processing has been performed to enhance the images. The image files are contained in directories named after the principal target of the image. In alphabetical order, the image directories for the Saturn volumes are: CALIB - Calibration images CALYPSO - Images of satellite Calypso DIONE - Images of satellite Dione ENCELADU - Images of satellite Enceladus EPIMETHE - Images of satellite Epimetheus HELENE - Images of satellite Helene HYPERION - Images of satellite Hyperion IAPETUS - Images of satellite Iapetus JANUS - Images of satellite Janus MIMAS - Images of satellite Mimas PANDORA - Images of satellite Pandora PHOEBE - Images of satellite Phoebe RHEA - Images of satellite Rhea SATURN - Images of Saturn S_RINGS - Images of the rings of Saturn TELESTO - Images of satellite Telesto TETHYS - Images of satellite Tethys TITAN - Images of satellite Titan UTIL - Additional viewing programs These images have had no enhancement processing applied to them and are "as received" from deep space. Why not enhanced? Image processing technology is advancing at a remarkable rate and new techniques may not be compatible with the results of old. So examine these files and learn how to improve them yourself--it will be as much fun as simply viewing them. File names Each image has a unique name constructed from the clock count of Voyager's Flight Data Sub-system (FDS). The FDS count gives the time at which the image was captured. The general form of a file name is "Cxxxxxxx.yyy". The character "C" at the beginning designates the "xxxxxxx" as the seven digit FDS count associated with the image. There are two "yyy" (extensions) associated with each image: the "GIF" extension denoting the file that contains the actual image and the "DOC" extension denoting a file containing technical information of interest having to do with the like named "GIF" file. Image history NASA released these images in what we'll call the "IMQ" format. The IMQ format compressed the images using a lossless first- difference Huffman encoding scheme. This is a fine scheme as far as compression efficiency is concerned; however, it has a couple of drawbacks: the decoding is slightly more complicated than the GIF format and the format is simply not known in the PC community. The "IMQ" format files were broken apart yielding the "DOC" files on this disk and a compressed image. The compressed image was then expanded into its full form and re-compressed into the "GIF" format. This process for one CD-ROM takes days when fully automated and running on the fastest of PCs. The encoding of the images into the "GIF" format was completely lossless in respect to image detail. The "colors" that the "GIF" files render reflect the filter used when taking the picture (noted in the "DOC" file). When the filter effect is not obvious a grayscale is used. To create a true color picture of an object it would be necessary to take several images captured at about the same time with different filters and combine them such that an individual pixel's color reflected the value of the same spot through the different filters. DOC files Each of the GIF images has a separate DOC file that bears the same filename. These DOC files tell about the viewable image and look something like the one below. /* IMAGE DESCRIPTION SPACECRAFT_NAME = VOYAGER_1 MISSION_PHASE_NAME = SATURN_ENCOUNTER TARGET_NAME = TITAN IMAGE_ID = '1516S1-002' IMAGE_NUMBER = 34909.12 /*FLIGHT DATA SUBSYSTEM (FDS) IMAGE_TIME = 1980-11-11T19:52:34Z EARTH_RECEIVED_TIME = 1980-11-11T21:19:46Z INSTRUMENT_NAME = WIDE_ANGLE_CAMERA SCAN_MODE_ID = '3:1' SHUTTER_MODE_ID = BOTSIM GAIN_MODE_ID = LOW EDIT_MODE_ID = '1:1' /*FULL RESOLUTION FILTER_NAME = CH4_JS FILTER_NUMBER = 0 EXPOSURE_DURATION = 15.3600 NOTE = "MULTISPECTRAL LONGITUDE COVERAGE" The individual specifications are broken out as follows: SPACECRAFT_NAME = Spacecraft name associated with the image. Valid values are VOYAGER_1 and VOYAGER_2. MISSION_PHASE_NAME = Name of mission phase for this image (URANUS_ENCOUNTER, JUPITER_ENCOUNTER, SATURN_ENCOUNTER, or NEPTUNE_ENCOUNTER). TARGET_NAME = Observational target of the image. IMAGE_ID = Image identification, which takes the form: nnnnes+ddd, where 'nnnn' = picture sequence number for a given day, 'e' = planet of encounter (J=Jupiter, S=Saturn, U=Uranus, N=Neptune), 's' = Voyager spacecraft (1 or 2), - sign indicates before and a + sign indicates after closest planetary approach. 'ddd' = number of days from closest approach. IMAGE_NUMBER = The unique number which identifies this image. IMAGE_NUMBER is extracted from the Flight Data Subsystem (FDS) clock count at time of image acquisition. For Voyager images the number is a seven-digit value, with 5 digits to the left of the decimal point (the modulo 16-bit (65536) count and 2 digits to the right of the decimal point (the modulo 60 count). IMAGE_TIME = Time at which image was acquired, in the format yyyy-mm-dd-hh:mm:ss. The time system is Universal Time (UTC). 'yyyy' = year, 'mm' = month, 'dd' = day of month, 'hh' = hour, 'mm' = minute, 'ss' = second. EARTH_RECEIVED_TIME = Time at which image data was received on earth, in the format yyyy-mm-dd-hh:mm:ss. The time system is Universal Time (UTC). 'yyyy' = year, 'mm' = month, 'dd' = day of month, 'hh' = hour, 'mm' = minute, 'ss' = second. INSTRUMENT_NAME = Camera used to acquire the image. Values are NARROW_ANGLE_CAMERA or WIDE_ANGLE_CAMERA. SCAN_MODE_ID = Scan rate of vidicon read out. Values can be '1:1', '2:1', '3:1', '5:1', and '10:1'. The instrument scan rate affects the radiometric properties of the camera because of the dark current buildup on the vidicon. SHUTTER_MODE_ID = Instrument shutter mode. Permitted values are: NAONLY - narrow angle camera shuttered only; WAONLY - wide angle camera shuttered only; BOTSIM - both cameras shuttered simultaneously; BSIMAN - BOTSIM mode followed by NAONLY; BODARK - shutter remained closed for narrow and wide angle camera; NADARK - narrow angle read out without shuttering; WADARK - wide angle read out without shuttering. GAIN_MODE_ID = Gain mode (LOW or HIGH) of the camera. EDIT_MODE_ID = Edit mode of the camera. Values are '1:1',which indicates the full resolution of the vidicon, and '3:4', '1:2', '1:3', '1:5', and '1:10' for partial resolution images. Indicates amount of data read from the vidicon. FILTER_NAME = Optical filter used for the image. Permitted values are CLEAR, CH4_U, CH4_JS, UV, VIOLET, BLUE, GREEN, ORANGE, and NAD. FILTER_NUMBER = Optical filter number, contains the unique number associated with the optical filter for the image. Needed to differentiate between the two CLEAR filters on the Voyager narrow angle camera. EXPOSURE_DURATION = Exposure duration for the image, in seconds. NOTE = Observational intent of the image. Final note: We would like to thank NASA for making this project possible. WeMake CDs, Inc. Indianapolis, Indiana