file: GLLUVS1:[GLL_RAW.PDS_ARCHIVE.GEN_TEMPLATES]uvs_look_geometry.doc referred to in the UVS LOOK labels as UVSLOOK.TXT Designed Oct 27, 2000 - K.E.Simmons Updated Jan 17, 2001 - Simmons This file contains general information about the UVS LOOK vector geometry files. It is based on GGGS extractions done by Pat Shriver and modelled after the EUV LOOK files done by Jim Adams for the EUV. This general description describes the models, procedures and supplemental files associated with the UVS Torus geometry (xxx.LOOK) files. PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 FILE_RECORDS = 8 PRODUCT_ID = "UVS_LOOK_GEOMETRY.DOC" PRODUCT_NAME = "GALILEO UVS LOOK VECTOR DATA DESCRIPTION" PRODUCT_CREATION_DATE = 2001-01-17 SPACECRAFT_NAME = "GALILEO ORBITER" INSTRUMENT_NAME = "ULTRAVIOLET SPECTROMETER" MISSION_PHASE_NAME = "JUPITER ORBIT OPERATIONS" TARGET_NAME = "IO-TORUS" DESCRIPTION = " This description file, and the referenced data files, were produced by the Galileo UVS/EUV team at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado at Boulder. Refer to the Galileo UVS/EUV instrument paper 'Galileo Ultraviolet Spectrometer Experiment', Vol 60, Space Science Reviews, pages 503-530, by C.W. Hord et al, for hardware and calibration information. Also see the UVS instrument template. It may also be useful to compare the UVS pointing geometry files to the EUV pointing geometry files. The xxx.LOOK files contain position vectors utilized by the CITEP Io Torus software package. The Colorado Io Torus Emissions Package, or CITEP, is a computer package designed to simulate emissions from the Io plasma torus surrounding Jupiter. Specific information on the CITEP package can be found at: http://dosxx.colorado.edu/torus/citep.html. The data contained in these files are position vectors based on the spacecraft's location relative to the torus at a specific time and the UVS instrument's field of view (FOV). The offset tilted dipole (OTD) used is based on Dessler, A. J., ed., Physics of the Jovian Magnetosphere, New York, Cambridge University Press, 1983, from his table on page 7. (The following is extracted from the Galileo Geometry and Graphics Software, GGGS, vector generation code: Model |M| Tilt Sys. III Long. Offset Offset Lat. Long. (deg) (deg) (Rj) (deg) (deg) D4 4.225 10.8 200.8 0.101 5.1 155.6 OTD 4.35 9.5 208.8 0.068 -12.6 174.2 O4 4.28 9.6 201.7 0.131 -8.0 148.57 P11A 4.208 10.0 198.8 0.108 4.8 143.07 |M| = magnetic field strength (?) Tilt & Sys. III Long. = the magnetic field axis Tilt towards the Sys. III Long. of Jupiter wrt Jupiter spin axis Offset (Rj, Lat., Long.) = the offset of the torus axis wrt magnetic field axis Note that the O4 & P11A models are actually spherical harmonic models with the equivalent System III OTD values as listed above. The D4 and OTD values listed above are "true" OTD models. The code in this routine makes use of the O4 model offset values as shown above. However, the values for the Tilt and Sys. III Long. differ.) Each UVS real-time summation period for a given observation ID is contained in a separate data file (xxx.DAT). There are two UVS pointing vector files for each UVS data file. One file of pointing data is given for the F-channel FOV and one file for the N/G-channel FOV. Their label files contain only the start time for the geometry and a reference to this description document. There is also an information file, specified by the same filename and the .FOV extension, containing details regarding which SPICE kernels were used, the date of creation of the pointing vector files and some additional FOV geometry parameters for the F-channel FOV. The pointing files, xxx.LOOK, contain the actual pointing vector information. The beginning of the pointing data file gives the file creation date, SCLK evaluation time and which UVS FOV was being used to obtain the data and on which to calculate the pointing geometry. Next, the spacecraft's (X,Y,Z) position, in Kms, relative to the center of the torus is given. These are followed by a series of torus pointing vectors, for the five FOV values described below, for the specific summation packet, defined in the file name, for this observation ID. The time used to determine the vectors is the approximate midpoint of the UVS integration summation period. Thus, if there are ten summation buffers contained in a specific observation ID then there will be twenty files of look geometry, one for each of the two FOV channel data pairs in each UVS summation buffer. Each pointing vector entry (line) contains the following data: Vector = [radius (km), theta (deg), z (km)] The radius is the perpendicular distance (km) from the Io torus center to the intersection of the UVS look vector with the torus. Theta is the corresponding Jupiter W. Longitude (deg) of the intersection of the UVS look vector and the torus point. 'z' is the altitude (km) that the intersection point lies above or below the plane of the torus. The following is an example from the C03A_C3NPRO01_06_G.LOOK file: Thu Sep 14 20:38:45 2000 1/03681375:00:0:0 N/G Channel -2218413.2 -1284065.8 -633835.77 5.9488979 159.28382 -0.016741044 5.9503633 159.28502 -0.14397070 5.9518288 159.29478 -0.27119948 5.9532947 159.31307 -0.39841809 5.9547617 159.33990 -0.52561723 End of data file example. In the above example, from data file C03A_URT_C3NPRO01.DAT, there are ten summation buffers in this data file therefore there are twenty .LOOK files containing geometry information: ten .LOOK files contain F-channel FOV geometry for the ten summation periods and ten .LOOK files contain G/N FOV geometry for the same ten summation periods. The .LOOK file names reflect the channel and summation packet number with respect to the observation ID. A diagram of the UVS instrument's field of view (FOV) is shown below. Pointing vector geometry is provided for five central meridian values. Generally for Torus observations, the UVS FOV's long dimension is perpendicular to the Torus/Jupiter-equator, where the 'TOP' is the edge toward the North Pole. The GGGS program divides the FOV into a grid of points (shown with "x"s) and interpolates these grids for the five pointing vector values (shown with "0"s). A single UVS packet observation: Each of the 5 given pointing vectors are marked with an '0' TOP x-------x | | | 0 | First pointing value | | x x | | | 0 | Second pointing value | | x x | | | 0 | Third pointing value = Boresight | | x x | | | 0 | Fourth pointing value | | x x | | | 0 | Fifth pointing value | | x-------x BOTTOM The F-channel and G/N-channel FOVs are nested such that their Boresights are identical. Each observation ID has a supplemental geometry file, xxx.FOV, containing the additional information and references pertinent to this observation, provided by the GGGS 'Display FOV' menu item, ............................................................." END