UVIS Calibration Dataset Overview : The UVIS instrument is part of the remote sensing payload  of the Cassini orbiter spacecraft. UVIS has two  spectrographic channels that provide images and spectra  covering the ranges from 56 to 118 nm and 112 to 191 nm. A  third optical path with a solar blind CsI photocathode is  used for a high signal-to-noise ratio stellar occultation by  rings and atmospheres. A separate hydrogen deuterium  absorption cell measures the relative abundance of deuterium  and hydrogen from their lyman-alpha emission. These  channels are referred to as EUV, FUV, HSP, and HDAC in this  document. The UVIS science objectives include investigation  of the chemistry, aerosols, clouds, and energy balance of  the Titan and Saturn atmospheres; neutrals in the Saturn  magnetosphere; the deuterium-to-hydrogen ratio for Titan and  Saturn; icy satellite surface properties; and the structure  and evolution of Saturns rings. The basic instrument  design adapts proven design concepts using a grating  spectrometer followed by a multi-element detector. We chose  to use imaging, pulse-counting microchannel plate detectors  because of more than a decade of experience using this kind  of detector equipped with a CODACON readout anode. The  CODACON (Coded Anode Array Converter) acts as a photon  locator. The photon counts are accumulated in an external  memory to build a picture that is periodically read out for  transfer to the spacecraft memory and eventually, transmission  to the ground. The two dimensional format for the CODACON  detectors allows simultaneous spectral and one-dimensional  spatial coverage. The detector format is 1024 x 64 (spectral  by spatial). The Cassini HDAC consists of a channel electron Multiplier  photodetector equipped with 3 absorption cell filters: a  hydrogen cell, a deuterium cell and an oxygen cell. The  oxygen cell is not utilized in flight. The hydrogen and  deuterium cells function as adjustable absorption filters.  In each cell a hot tungsten filament disassociates the  hydrogen and deuterium molecules into atoms, producing an  atomic density determined by each of 16 different filament  temperatures. These atoms resonantly absorb the hydrogen  and deuterium Lyman-alpha lines passing through the cells.  Cycling the filaments on and off and comparing the  differences in signal gives a direct measurement of the  relative hydrogen and deuterium signals. Each cell has two  filaments controlled by separate filament current  regulators. Only one filament at a time per cell is used  during flight. A Pulse Amplifier Discriminator detects  photoelectrons from the CEM and sends pulses to the UVIS  instrument logic. UVIS contains a high speed photometer  with an integration time as short as 2.0 ms to observe  stars occulted by the rings of Saturn. The photon counts  collected from the photocathode are passed as a time ordered  sequence to the instrument, then to spacecraft memory for  transfer to the ground. The data in a UVIS observation are a copy of what was in  the UVIS memory buffer. That is, the observation consists of  unprocessed experiment data stored in binary format. An  observation belongs to one of four different types of data  product: a spectrum, a time series of spatial-spectral  images, a time series of detector counts, or an image at one  wavelength. Each observation has a unique identifier that  associates it with a time range and with the configuration  of the instrument during that time. Each data product  contains one observation and is completely defined by a PDS label. The objects are correct in the sense that they conform to PDS formatting requirements and are consistent with data  archived by the UVIS team. They are complete in that they  represent all data taken by the UVIS instrument. In addition, CODMAC level 3 data products are derivable from the archived data and an associated set of calibration data.  A UVIS spatial spectral cube (which corresponds to a  PDS Qube data structure) is a time ordered sequence  of two-dimensional matrices of EUV or FUV detector counts.  In the simplest case, a cube is a time ordered sequence of  1024 x 64 matrices in which each element of the matrix is  the number of counts taken at an individual detector cell  during a fixed time interval. The time interval is defined  in the instrument configuration associated with the  observation. In more complex cases, each integer in the  cube corresponds to a sub region of the detector and is  derived by summing over both the spatial and spectral  dimensions. For example, if the binning defined on the  spectral and spectral dimensions is two, a cube consists  of 32x512 integers, where each integer is derived by summing  contiguous pairs of cells in the spatial and spectral  dimensions. The cube object is a sequence of 1024x64 in  which all data is located in a 32x512 subregion the  upper left hand corner of which will be located at 0,0. All  other locations in the cube contain null values. A still  more complex case involves cubes derived from a set of sub  regions of the detector. In this case, the detector is  divided into a set of active rectangular sub regions ( windows). Each window can be binned in the manner  described above. When binning and windowing is applied  data is in the upper left hand corner of the window.  For example, if a detector window is defined with its upper  left corner at 10, 10) and its lower right corner at (20, 20)  and its binning is defined to be (2, 2) then the data for the  Nth spectrum is found in the rectangle with a upper left  corner equal to (10, 10, N) and a lower right hand corner equal  to (15, 15, N) in the Qube. A data product (also referred to as an observation) is a  cube generated during a particular instrument  configuration. All instrument configuration information  including window, bin, and integration time specifications are contained in the PDS object label. For a more extensive description of the UVIS instrument and the structure and organization of data on this volume see the file ROOT/DOCUMENTATION/UVIS.TXT on this archive volume. Parameters  :  The following observation types are found on this volume. CALIB: Measurement of EUV and/or FUV emissions from a solar/stellar target for the purpose of calibrating wavelength scale, photometric  sensitivity, and detector flat fields. The observation type for each observation is found in OBSERVATION_TYPE column of INDEX.TAB. The specific purpose of each observation may be found in the object DESCRIPTION field contained in the label. Processing  :  The observation data products are generated by the Laboratory for Atmospheric and Space Physics at the University of Colorado using the Data Archiving and Processing System (DAPS) software. This software receives telemetry packet SFDUs from the Telemetry Data System, extracts science and engineering data, archives the data in a database management system and produces PDS data and label object files located on a CD-ROM or DVD physical storage medium. All time information is generated from the spacecraft clock using  the Cassini SCLKSET files. The DAPS system uses NAIF software and project generated SPICE Kernels to generate pointing information. All of these values are contained in the PDS object label. Data : A UVIS spatial spectral cube is a time ordered sequence of 1024 x 64 matrices in which each element of the matrix is the number of counts taken at an individual detector pixel during a fixed time interval. The time interval is set in the instrument configuration associated with the observation.  UVIS is capable of windowing and binning the EUV and FUV detectors. In these more complex cases, each integer in the cube corresponds to a rectangular subregion of detector cells and is derived by summing over the spatial and spectral dimensions. For example, if the binning defined on the spectral and spatial dimensions is two, the cube consists of 32x512 integers, where each integer is derived by summing the counts from disjoint 2x2 subregions of the detector. The PDS Qube object is a sequence of 1024x64 samples, in which all data are located in a 32x512 sub-region in the upper left hand corner, located at (0,0). All other locations in the PDS Qube contain null values. A still more complex case involves cubes derived from a set of sub regions of the detector called windows. In this case, the detector is divided into a set of active rectangular sub regions (windows). Each window can also be binned in the manner just described. The data stored in the PDS Qube are located in the upper left hand corner of the window. For example, if a detector window is defined with its upper left corner at (10,10) and its lower right corner at (20, 20) and its binning is defined to be (2,2) then the data for the Nth sample is found in the rectangle with a upper left corner equal to (10, 10, N) and a lower right hand corner equal to (15, 15, N) in the 1024x64 sample of the PDS Qube. A data product (also referred to as an observation) is a cube generated during a particular instrument configuration, including pointing and instrument set up. All instrument configuration information including window, bin and integration time specifications are contained in the PDS object label. The following diagrams illustrate these configurations as contained in a sample of a PDS Qube. 0 *************************** *ddddddddddddddddddddddddd* *ddddddddddddddddddddddddd* *ddddddddddddddddddddddddd*  *ddddddddddddddddddddddddd* *ddddddddddddddddddddddddd* 64 *************************** 0 1024 Fig. 2.2.2.1 An unbinned, single windowed sample where d is data. 0 *************************** *ddddddddddddnnnnnnnnnnnnn* *ddddddddddddnnnnnnnnnnnnn* 32 *ddddddddddddnnnnnnnnnnnnn*  *nnnnnnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 64 *************************** 0 512 1024 Fig. 2.2.2.2 An unbinned window with an upper left hand corner at 0, 0,  and a lower right hand corner at 512, 32. Where d is data, n is null. 0 *************************** *dddddnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 32 *nnnnnnnnnnnnnnnnnnnnnnnnn*  *nnnnnnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 64 *************************** 0 0 256 1024 Fig. 2.2.2.3: A window binned by 32 in the spatial dimension and 2 in the spectral dimension with an upper left hand corner at 0, 0, and a lower right hand corner at 512, 32. Where d is data and n is null. 0 *************************** *dddddnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 32 *nnnnnnnnnnndddddddddddddd*  *nnnnnnnnnnndddddddddddddd* *nnnnnnnnnnndddddddddddddd* 63 *************************** 0 0 256 512 1023 Fig. 2.2.2.4: Two windows where the first is binned by 32 in the spatial dimension and 2 in the spectral dimension and where the first has an upper left hand corner at 0, 0, and a lower right hand corner at 512, 32. The second is unbinned with an upper left hand corner at 512, 32 and a lower right corner at 1023, 63. Where d is data and n is null.   Calibration data are used to transform detector counts into geophysical units. The EUV, FUV channels have an associated calibration process. FUV and EUV data are converted to Rayleighs.  The UVIS team supplies calibration data files. The calibration process is described below and in the PDS label file associated with the calibration. data file.  Calibration data consist of an MxN matrix and a scalar value. Each matrix and scalar should be used to scale the individual integrations of a raw data product. The result is a calibrated data product which is isomorphic to the original containing data in units of kilorayleighs. In addition, each calibration data product contains a mapping of detector lines to wavelengths which is stored in the BAND BIN_CENTER keyword value. Calibration data are archived as a PDS Qubes with the dimensions 1024x64x1 or 1024x1x1. All instrument configuration data for the observation is contained in the associated PDS label; in addition the label contains instructions for using the calibration data and a detector column to wavelength mapping and the scalar multiplier  which is stored in the CORE_MULTIPLIER value). In addition to this mechanism, non-standard calibration routines developed by UVIS team members may be provided. These routines may require user input and control. These procedures are not supported nor are their validity guaranteed, however to the extent that they are intended for general use by the UVIS team, we will submit algorithms and associated data and documentation.  Ancillary Data  :  The UVIS team supplies calibration data files and the algorithms used to generate the FUV and EUV calibration data. The calibration algorithms are archived as text files in the SOFTWARE/CALIB directory of the PDS data volume. The file names contain channel and version information. These algorithms generate calibration data which is located in the CALIB/VERSION_n/... directories. The algorithms are provided as a description of the process by which calibration data is generated. They are not used to calibrate raw data. Coordinate System  : In the UVIS data products, all time values that are represented as strings are in UTC time. All time values are derived from the spacecraft clock using the SCLKSCET translation table supplied by the Cassini project. All pointing data are expressed in the J2000 coordinate system.  Software : LASP provides software for reading PDS data products. This software is located in the ROOT/SOFTWARE/READERS directory. The software requires Java 1.4 compatible class libraries and RSI/IDL version 6.  Instructions for running the routines are located in the file  READERS_README.TXT, located in the same directory.  These readers are provided as a convenience for users to access the data. Users may choose another approach if desired. The readers enable users to load PDS objects into an RSI/IDL process where they are represented as 3 dimensional arrays of integers corresponding to the PDS Qube object in which they are stored. PDS label data are stored in an IDL structure variable.  DISC FORMAT : This disc has been formatted so that a variety of computer systems (e.g. IBM PC, Macintosh, Sun, VAX) may access the data. Specifically, the disc is formatted according to the UDF-Bridge DVD format standard which provides ISO 9660 level 2 standard compatibility. For further information, refer to the ISO 9660 Standard Document: RF# ISO 9660-1988, 15 April 1988.  Specific to the ISO 9660 level 2 standard, filenames on this CD conform to the 27.3 file naming convention i.e., 1. The file name portion may be up to 29 characters long; or 2. The extension may be up to 29 characters long, 3. In no case, however, may the total file name length, including the . exceed 31 characters.

Confidence Level Overview : The UVIS data objects are organized into separate observations. Each observation contains data taken from one configuration of the instrument. There may be more than one observation generated from one instrument configuration. This may occur because science data generated by the UVIS instrument is dropped when corrupted data is detected or transmission failures occur. The UVIS ground system detects this and divides the data into two observations, one terminated prior to the data drop the next beginning immediately afterword. The start time and duration of an observation correspond to the actual times of the first and last records in the observation. Incomplete observations are filled with zeroes. Over 95% of data taken by the instrument is contained in the UVIS archive.  Only one hardware feature affects UVIS data. A light leak in the instrument casing causes an increase in the background counts in the lower half of the EUV channel wavelength range. This effect is detectable by visual inspection of a graph of the data. No tools for detection or correction of these background counts exists. One anomaly in the flight software caused data errors to appear when multiple windows which do not cover the entire EUV or FUV detector are defined. In an observation, the data errors appear as randomly located spikes in detector count values, and one  completely incorrect spatial line located at a random spatial  index. These errors are detectable by visual inspection of a  plot of the data. The anomaly was fixed by a revison to the software and effects data between launch and 2001-071 09:00:00 UTC Review : This volume has completed a peer review by the PDS. The peer review panel consisted of Lyle Huber, Mitch Gordon, Steven Adams, Ron Joyner and Mark Vincent representing PDS, David Judd and Wayne Pryor from the, UVIS team Diane Connor from the Cassini Project and Kurt Retherford and John Clarke as outside users.