PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "A file describing the UVIS PDS data products." PUBLICATION_DATE = 2005-02-08 END_OBJECT = TEXT END Cassini Ultraviolet Imaging Spectrograph Project PDS Data Product Software Interface Specification SIS ID IO-AR-024 Approved: _______________________________________ Larry Esposito Principal Investigator ______________________________________ Diane Conner Cassini Archive Data Engineer ______________________________________ Lyle Huber PDS Atmospheres Node ______________________________________ Laverne Hall PDS Project Manager February 8, 2005 Laboratory for Atmospheric and Space Physics University of Colorado I CONTENTS CONTENTS II ACRONYMS III 1. INTRODUCTION 1 1.1 Purpose and Scope 1 1.2 Contents 1 1.3 Applicable Documents and Constraints 1 2. Data Product Characteristics and Environment 1 2.1 Instrument Overview 1 2.2 Data Product Overview 2 2.2.1 Spectra 3 2.2.2 Spatial Spectral Cubes 3 2.2.3 Image at one Wavelength 5 2.2.4 Time Series 5 2.2.5 Calibration Data 6 2.2.6 Data Product Organization 6 2.2.7 Additional Data Products 7 2.3 Data Processing 7 2.3.1 Data Processing Level 7 2.3.2 Data Product Generation 9 2.3.2.1 Computation of Time 9 2.3.2.2 Computation of Pointing Geometry 9 2.3.2.3 Computation of Calibration Data 11 2.3.3 Data Product Use 11 2.3.4 Labeling and Identification 11 2.4 Standards Used in Generating Data Products 12 2.4.1 PDS Standards 12 2.4.2 Time Standards 12 2.4.3 Coordinate Systems 12 2.5 Data Validation 12 2.6 Documentation 13 3. APPLICABLE SOFTWARE 13 3.1 Utility Programs 13 Appendix A A PDS Qube Label 14 Appendix B An HSP PDS Time Series Object Label 16 Appendix C An HDAC PDS Time Series Object Label 18 Appendix D Definitions Of UVIS PDS Keywords 20 Appendix E The CALINFO.TXT File 21 Appendix F The SOFTWAREINFO.TXT File 21 Appendix G The INDXINFO.TXT File 22 Appendix H The DOCINFO.TXT File 22 Appendix I The DATAINFO.TXT File 22 II ACRONYMS ASCII American Standard Code for Information Interchange CEM Channel Electron Multiplier CsI Cesium Iodide CODMAC Committee on Data Management and Computation DAPS Data Archiving and Processing System EUV Extreme Ultraviolet FUV Far Ultraviolet HDAC Hydrogen-Deuterium Absorption Cell HSP High Speed Photometer JPL Jet Propulsion Laboratory LASP Laboratory for Atmospheric and Space Physics, University of Colorado NAIF Navigation and Ancillary Information Facility NASA National Aeronautics and Space Administration ODL Object Description Language PDS Planetary Data System SFDU Standard Formatted Data Unit SIS Software Interface Specification TBD To Be Determined TDS Telemetry Delivery Subsystem UVIS Ultraviolet Imaging Spectrograph III 1. INTRODUCTION 1.1 Purpose and Scope This Software Interface Specification (SIS) provides users of the Ultraviolet Imaging Spectrograph (UVIS) a detailed description of the product and how it was generated. UVIS data consist of a sequence of measurements taken by one of four instrument detectors. UVIS data products are generated from these data. Each data product described in this document is a set of instances of standard objects defined by the Planetary Data System (PDS). Readers are provided with the essential information required to understand and manipulate these data products as PDS objects. The intended users for this SIS are software developers of the programs used in generating the data products and scientists who analyze the data. These scientists include those associated with the Cassini Project and those in the general planetary science community. This SIS contains enough information to enable readers to write software to manipulate UVIS data and to undertake the interpretation of these data. 1.2 Contents This Data Product SIS describes how the UVIS instrument acquires its data, and how the data are processed, formatted, labeled, identified, validated and archived. The document discusses standards used in generating the product and software that may be used to access the product. The data product structure and organization are described in sufficient detail to enable a user to read the product. Example data product labels are included as appendices. 1.3 Applicable Documents and Constraints This Data Product SIS is derived from the following documents: 1. Cassini Program Data Management Plan, JPL D-12560, PD 699-061, Rev. B, April 1999 2. The Cassini Program Science Management Plan, JPL D-9178, PD 966-006, Issue 007, June 2003. 3. Cassini/Huygens Archive Plan for Science Data, JPL D-15976, 699-068, Version 3, June 2004. 4. UVIS Command and Telemetry Dictionary. 5. The Cassini Ultraviolet Imaging Spectrograph, submitted to Space Science Reviews, 3 October 2000. 6. Planetary Data System Data Preparation Workbook, February 1, 1995, Version 3.1, JPL D-7669, Part 1. 7. Planetary Data System Data Standards Reference, June 1, 1999, Version 3.6, JPL D-7669, Part 2. Finally, this SIS is consistent with the contract negotiated between the Cassini Project and the UVIS Principal Investigator (PI) in which experiment data records and documentation are explicitly defined as deliverable products. 2. Data Product Characteristics and Environment 2.1 Instrument Overview The UVIS instrument is part of the remote sensing payload of the Cassini - 1 - 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 to observe 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 a 1024 x 64 (spectral by spatial) array. The Cassini HDAC consists of a channel electron multiplier (CEM) 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 dissociates the hydrogen and deuterium molecules into atoms, producing an atomic density determined by each of 16 different filament currents each yielding a different cell temperature. 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 1.0 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. 2.2 Data Product Overview 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 data objects are validated and conform to PDS formatting requirements. The PDS objects represent all data taken by the UVIS instrument in the period covered by a data volume. In addition, CODMAC level 3 data products are derivable from the archived data and an associated set of calibration data. - 2 - In the following we use the term "Qube" as defined in the PDS standards to refer to a three dimensional matrix of data otherwise known as a "cube". 2.2.1 Spectra The EUV and FUV channels can be read out to produce spectra. Each spectrum is generated by accumulating detector counts over a fixed time interval. The time interval is defined in the instrument configuration associated with the observation. A spectrum consists of a sequence of counts, each count being associated with a detector column (or columns). In the simplest case, a spectrum is a sequence of 1024 integers where each integer is the total number of counts in a detector column taken during a fixed time interval. In more complex cases, each integer in the spectrum corresponds to a set of columns and is derived by summing over both the spatial and spectral dimensions. For example, if the binning defined on the spectral dimension is two, a spectrum consists of 512 integers, where each integer is derived by first summing the 64 elements of each column then summing contiguous pairs of the 1024 sums resulting in 512 numbers. A data product (also referred to as an observation) is a sequence of spectra taken from during the same instrument configuration. It is also possible to limit data to a rectangular sub-region of the detector (a window). A window can be binned in the manner just described. The EUV and FUV spectra are archived as a 1024x1xN PDS Qube, that is, N spectra, each containing 1024 integers representing detector counts. For binned data, data are located on left side of the region from which the data were derived and the Qube is padded with null values. For example, if the binning of the detector is 64 in the spatial dimension and 2 in the spectral dimension then each 1024x1 sample of the Qube will contain an initial sequence of 512 counts followed by 512 null values. The following diagrams illustrate these configurations as contained in a sample of a PDS Qube. dddddddddddddddddddddddddd 0 1024 Fig. 2.2.1.1 An unbinned spectrum dddddddddddddnnnnnnnnnnnnn 0 512 1024 Fig. 2.2.1.2 A spectrum binned by 2 where d is data and n is null nnnnndddnnnnnnnnnnnnnnnnnnn 0 256 512 1024 Fig. 2.2.1.2 A spectrum with one window where the window is defined by the upper left hand corner (256, 0) and the lower right hand corner (512, 64) and the window is binned by 64 in the spatial dimension and by 2 in the spectral dimension. The letter d is data and n is null. 2.2.2 Spatial Spectral Cubes A UVIS spatial spectral cube is a time ordered sequence of two-dimensional matrices of EUV or FUV detector counts. 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 pixel during a fixed time interval. - 3 - The time interval is set in the instrument configuration associated with the observation. In more complex cases, each integer in the cube corresponds to a range 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 contiguous pairs of pixels in the spatial and spectral dimensions. 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. - 4 - 0 *************************** *dddddnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 32 *nnnnnnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* *nnnnnnnnnnnnnnnnnnnnnnnnn* 64 *************************** 0 256 512 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 *************************** 0 256 512 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. 2.2.3 Image at One Wavelength The UVIS instrument can generate an image data product from the FUV or EUV detectors. These images consist of a sequence of lines. A line is a sequence of 1 to 64 integers representing detector counts in the spatial dimension. Each line in the image contains data from the same detector column. The lines in the sequence are time ordered. A data product consists of a set of data taken during a single instrument configuration. The "image at one wavelength" product is archived as a 1x64xn PDS Qube. When windowing or binning is defined the data are located in a sub-region of the Qube as described in the previous secion. All instrument configuration data for an observation is contained in the associated PDS label. 2.2.4 Solar and Stellar Brightness Time History The UVIS instrument can generate time series from the HSP and the HDAC channels. A time series consists of a sequence of photometer counts each taken during a fixed time interval. An observation consists of a time series taken during a particular instrument configuration. The time series generated by the HDAC channel may have additional complexity. If all the filament levels are 0 then the HDAC is in photometer mode and its output is a time series of detector counts. If there is a non-zero filament level the detector is in modulation mode and the time series can be mapped into a table of 32 columns, each column corresponding to an HDAC filament voltage level in the order: d1...d16, h1...h16 where d1..d16 correspond to the 16 voltage levels of the d cell and h1..h16 the same for the h cell. The time series can be mapped to the table by mapping contiguous subsequences into the successive columns of the table. The length of the subsequence is determined by the dwell time parameter of the instrument configuration. A data product consists of a set of data taken during a single instrument configuration. - 5 - The UVIS solar and stellar brightness time history data product is archived as a PDS time series object. All instrument configuration data for an observation is contained in the associated PDS label. 2.2.5 Calibration Data 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. HSP and HDAC calibrations do not currently have a software implementation, however a description of the calibration procedure for the HSP is located in SOFTWARE/CALIB/HSP_CALIBRATION.TXT. Similar documentation for HDAC, EUV and FUV calibrations are under development and will be included in the SOFTWARE/CALIB directory. 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. Calibration data files are associated with the corresponding raw data file by having the same name. Users seeking to calibrate their data should use the calibration data files. The calibration process is described below and in the PDS label file associated with the calibration data file. The algorithms are provided as a description of the process by which calibration data is generated. 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 these algorithms, 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. 2.2.6 Data Product Organization There is a one to one mapping between an observation and a PDS data object. An observation is a sequence of data taken from a channel during a time period in which the instrument configuration remains unchanged. In other words, when the instrument is set to a particular state, the data taken during that state is an observation. When the instrument state changes, the next set of data is a new observation. An observation can be uniquely identified by the channel from which data were taken, and the time of the first data. All UVIS observations have a name of the form where the date is derived from the spacecraft clock using the SCLKSCET file provide by the Cassini TDS. The time of the first data is the time at the - 6 - end of the first integration period. In order to determine the exact time at which an observation began, the integration time should be subtracted from the start time. All observations are archived as one of the data product types described above. Therefore each observation is represented as a PDS data object. Each object is contained in a file and has an associated label file. Each file contains exactly one observation. The name of the file consists of the channel and the observation start time. The files are located in a PDS data volume in the /DATA/ directory. The parameter is the UTC day in which the observation began. This directory contains both PDS data files (.DAT) and their corresponding label files (.LBL). For example, one might find the files /DATA/D2001_001/FUV2001_001_01_02.DAT (and .LBL) on the PDS data volume. See below for more details on naming conventions. Every observation taken from the FUV and EUV channels has an associated calibration data file. These calibration files are named in the same manner as data files except that these files are found in the CALIB/VESION_/ directory. 2.2.7 Additional Data Products Additional data products may be defined and produced. It is the goal of the UVIS team to provide a scientifically rich set of products. 2.3 Data Processing 2.3.1 Data Processing Level This documentation uses the Committee On Data Management And Computation (CODMAC) data level numbering system. The data files referred to in this document are considered "level 2" or "Edited Data" (equivalent to NASA level 0); they are generated from level 1 or "Raw Data", i.e., the telemetry packets within the project-specific Standard Formatted Data Unit (SFDU) record. Refer to Table 1. Table 1. Processing Levels for Science Data Sets NASA CODMAC Description Packet data Raw - Level 1 Telemetry data stream as received at the ground station, with science and engineering data embedded. Level-0 Edited - Level 2 Instrument science data (e.g., raw voltages, counts) at full resolution, time ordered, with duplicates and transmission errors removed. - 7 - Level 1-A Calibrated - Level 3 Level 0 data that have been located in space and may have been transformed (e.g., calibrated, rearranged) in a reversible manner and packaged with needed ancillary and auxiliary data (e.g., radiances with the calibration equations applied). Level 1-B Resampled - Level 4 Irreversibly transformed (e.g., resampled, remapped, calibrated) values of the instrument measurements (e.g., radiances, magnetic field strength). Level 1-C Derived - Level 5 Level 1A or 1B data that have been resampled and mapped onto uniform space- time grids. The data are calibrated (e.g., radiometrically corrected) and may have additional corrections applied (e.g., terrain correction). Level 2 Derived - Level 5 Geophysical parameters, generally derived from Level 1 data, and located in space and time commensurate with instrument location, pointing, and sampling. Level 3 Derived - Level 5 Geophysical parameters mapped onto uniform space- time grids. - 8 - 2.3.2 Data Product Generation The observation data products are generated by the Laboratory for Atmospheric and Space Physics 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. Instrument configuration parameter values are extracted from the DAPS data archive. 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. The time between initial availability of telemetry data from the TDS and archiving of a final form is a nominal maximum of one week. The size of a UVIS observation data product varies between a nominal minimum/maximum of 1 KB to 500 MB. The total estimated volume of the UVIS data products over the course of the Cassini mission is approximately 40 GB. The production rate is between 0 and 100 observations per day with the nominal rate on the order of 10 observations per day. PDS data products are generated by the DAPS software, initiated manually. The physical volume on CD-ROM or DVD is produced at LASP. 2.3.2.1 Computation of Time Values The conversion of spacecraft time to UTC can be expressed in the following informal algorithm: Given the spacecraft time (SCTime, SCTimeFine) and the largest sclkTime0 value less than the (SCTime, SCTimeFine) value as obtained from the project supplied SCLKSCET file, and the UTC0 value which corresponds to sclkTime0 and the clockRate0 corresponding to sclkTime0 apply the following computation: Seconds = SCTime - floor(sclkTime0) clockTicks = SCTimeFine / 1000.0 - (sclkTime0-floor(sclkTime0)/256 deltaTime = (seconds + clockTicks) * clockRate0 result = deltaTime*1000 The UTC time corresponding to SCTime and SCTimeFine is obtained by adding the result (in milliseconds) to UTC0. The value of the START_TIME parameter is generated from the SCTime and SCTimeFine values. These values are specified by the spacecraft clock a the end of the first detector integration. In order to determine the time at which the UVIS detector began taking data, subtract the INTEGRATION_DURATION value from the START_TIME value. 2.3.2.2 Computation of Pointing Geometry The geometry values included in the data object labels are computed using the geometry_engine.pro and geometer.pro software contained under the SOFTWARE/GEOM directory and the NAIF SPICE software library. The latter is freely available for most platforms and operating systems (FTP site: naif.jpl.nasa.gov pub/naif/toolkit directory). In order to perform these calculations, the SPICE software requires kernel files including a spacecraft clock coefficients file (.tsc), a leap seconds file (.tls), a Cassini planetary constants file (.tpc), a Cassini Spacecraft Frame Definitions Kernel (.tf), a UVIS Instrument Kernel (.ti), and all sp kernels relevant to the time of the observations. Kernels can also be obtained from the NAIF FTP site. Users seeking geometry information do not need to use these programs because the geometry information is also included in the PDS labels. All geometry values in the label are computed at the time given by the START_TIME keyword value. Geometry values in the labels include: - 9 - RIGHT_ASCENSION: right ascension of the instrument axis on the celestial sphere. Computed using CSPICE_PXFORM and CSPICE_RECRAD DECLINATION: declination of the instrument axis on the celestial sphere. Computed using CSPICE_PXFORM and CSPICE_RECRAD SUB_SOLAR_LATITUDE: latitude of sub-solar point (using nearpoint method) (deg). Computed using CSPICE_SUBSOL and CSPICE_RECLAT SUB_SOLAR_LONGITUDE: longitude of sub-solar point (using nearpoint method) (deg). Computed using CSPICE_SUBSOL and CSPICE_RECLAT SUB_SPACECRAFT_LATITUDE: latitude of sub-spacecraft point (using nearpoint method) (deg). Computed using CSPICE_SUBPT and CSPICE_RECLAT SUB_SPACECRAFT_LONGITUDE: longitude of sub-spacecraft point (using nearpoint method) (deg). Computed using CSPICE_SUBPT and CSPICE_RECLAT PHASE_ANGLE: phase angle on the specified target at the specified time at the point intersected by the instrument boresight (deg). Computed using CSPICE_ILLUM. EMISSION_ANGLE: emission angle on the specified target at the specified time at the point intersected by the instrument boresight (deg). Computed using CSPICE_ILLUM. SOLAR_INCIDENCE_ANGLE: solar incidence angle, measured from the local target surface. Computed using CSPICE_ILLUM. CENTRAL_BODY_DISTANCE: distance above target surface (km). Computed using CSPICE_SUBPT. SC_PLANET_POSITION_VECTOR: low order 3-elements of the state of the spacecraft with respect to planet. If the target is a satellite, this value is with respect to the planet that the satellite orbits. Computed using CSPICE_SPKEZR. SC_PLANET_VELOCITY_VECTOR: high order 3-elements of the state of the spacecraft with respect to planet. If the target is a satellite, this value is with respect to the planet that the satellite orbits. Computed using CSPICE_SPKEZR. SC_TARGET_POSITION_VECTOR: 3-element vector with position of S/C wrt to target (km) in inertial frame. Computed using CSPICE_SPKEZR. SC_TARGET_VELOCITY_VECTOR: 3-element vector with velocity of S/C wrt to target (km/sec) in inertial frame. Computed using CSPICE_SPKEZR. SC_SUN_POSITION_VECTOR: 3-element position of Sun with respect to the target body. Computed using CSPICE_SPKEZR. SC_SUN_VELOCITY_VECTOR: 3-element velocity vector of S/C wrt to sun (km/sec). Computed using CSPICE_SPKEZR. PLANET_CENTER_POSITION_VECTOR: 3-element position of planet with respect to the solar system barycenter. Computed using CSPICE_SPKSSB PLANET_CENTER_VELOCITY_VECTOR: 3-element velocity vector of planet with respect to the solar system barycenter. Computed using CSPICE_SPKSSB All geometry values are derived using the SPICE software suite, which is freely available for most platforms and operating systems. - 10 - The EUV and FUV detectors have the following dimensions of the field of view: High resolution: FUV = (60mrad x 0.75mrad), EUV = (60mrad x 1mrad) Low resolution: FUV = (60mrad x 1.5mrad), EUV = (60mrad x 2mrad) Occultation: FUV = (60mrad x 8mrad), EUV = (60mrad x 8mrad) There is no optical distortion in the detector, so the pointing geometry of any pixel on the detector can be computed from these numbers and the location of the center of the detector. 2.3.2.3 Computation of Calibration Data Computation of calibration data uses LASP produced IDL software and data. The source code and data files are located in /SOFTWARE/CALIB/VERSION_ where the integer n is a version ID. The version ID is incremented whenever there is a change to the software or data. The SOFTWARE/CALIB/CALIB_README.TXT file describes the mechanism by which calibration data are generated. This file is not included in this document because it will change with new calibration versions. Additional documentation regarding the theoretical aspects of calibration can be found in HSP_CALIBRATION.TXT, HDAC_CALIBRATION.TXT, and CALIBRATION_NOTES.DOC all located in the SOFTWARE/CALIB directory. The calibration data generated by this software are archived in the CALIB/VERSION_n directory. The CALIB/CALINFO.TXT files describes the organization of calibration data files and how it is used to calibrate raw data. The CALINFO.TXT is included in this document in Appendix E. 2.3.3 Data Product Use LASP provides software for reading PDS data products. This software is located in PDS/SOFTWARE/READERS and is contained in a Java executable jar file called READ_PDS_OBJECT.JAR. 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 user 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. 2.3.4 Labeling and Identification Every UVIS PDS object has a data set identifier. This identifier is found in each data product label. The UVIS ID has the form CO--UVIS-2--V1.0, in which CO is the Cassini Orbiter, S is a PDS target ID, UVIS is the instrument name, 2 indicates the CODMAC data level, is a description of the data set. The description is one of: SPEC (spectrum), IMG (image at one wavelength), CUBE (a PDS Qube object), or SSB (solar stellar brightness time history). The target is J for data taken at Jupiter, X for cruise data, and S for data taken during the Saturn phase of the mission. Each UVIS data object fills one file. The file contains exactly one data object. Each file has an associated label file containing the detached labels for each data product in the file. The file name identifies the contents of the file. The form of the file name is