Instrument Functional Description: The VIS Instrument is a Set of three Low Light Level Cameras. Two of these Cameras share primary and some secondary Optics and are designed to provide Images of the Nighttime Auroral Oval at Visible Wavelengths. A Third Camera is used to monitor the Directions of the Fields-of-View of the Auroral Cameras with respect to the sunlit Earth and return Global Images of the Auroral Oval at Ultraviolet Wavelengths. The VIS Instrumentation produces an Auroral Image of 256 × 256 Pixels approximately every 24 s dependent on the Integration Time and Filter selected. The Fields-of-View of the two Nighttime Auroral Cameras are 5.6 × 6.3° and 2.8 × 3.3° for the Low and Medium Resolution Cameras, respectively. The Medium Resolution Camera was never activated. One or more Earth Camera Images of 256 × 256 Pixels are produced every 5 min, depending on the commanded Mode. The Field-of-View of the Earth Camera is approximately 20 × 20°. See: http://vis.physics.uiowa.edu/vis/vis_description/vis_description.htmlx Reference: Frank, L.A., J.B. Sigwarth, J.D. Craven, J.P. Cravens, J.S. Dolan, M.R. Dvorsky, J.D. Harvey, P.K. Hardebeck, and D. Muller, The Visible Imaging System (VIS) for the Polar Spacecraft, Space Science Review, Vol. 71, pp. 297-328, 1995. Data Set Description: The VIS Earth Camera Data Set comprises all Earth Camera Images for the selected Time Period. Full Coordinate Information is included for Viewer Orientation. In addition, a Rotation Matrix and a Table of Distortion-correcting Look Direction Unit Vectors are provided for the Purpose of calculating Coordinates for every Pixel. To facilitate viewing of the Images, a Mapping of Pixel Value to a recommended Color Table based on the Characteristics of the selected Filter will be included with each Image. A Relative Intensity Scale is provided through an Uncompressed Count Table. Approximate Intensity Levels in kiloRayleighs are given in an Intensity Table. For detailed Information on Intensities, see Sensitivities_and_Intensities.txt at https://cdaweb.gsfc.nasa.gov/Polar_VIS_docs/SENSITIVITIES_AND_INTENSITIES.TXT. Supporting Software is available at: http://vis.physics.uiowa.edu/vis/software/ Included is an IDL Program that displays the Images with the recommended Color Bar, provides approximate Intensities, Coordinate Data for each Pixel, and includes multiple Options for Image Manipulation.
Version:2.3.1
Instrument Functional Description: The VIS Instrument is a Set of three Low Light Level Cameras. Two of these Cameras share primary and some secondary Optics and are designed to provide Images of the Nighttime Auroral Oval at Visible Wavelengths. A Third Camera is used to monitor the Directions of the Fields-of-View of the Auroral Cameras with respect to the sunlit Earth and return Global Images of the Auroral Oval at Ultraviolet Wavelengths. The VIS Instrumentation produces an Auroral Image of 256 × 256 Pixels approximately every 24 s dependent on the Integration Time and Filter selected. The Fields-of-View of the two Nighttime Auroral Cameras are 5.6 × 6.3° and 2.8 × 3.3° for the Low and Medium Resolution Cameras, respectively. The Medium Resolution Camera was never activated. One or more Earth Camera Images of 256 × 256 Pixels are produced every 5 min, depending on the commanded Mode. The Field-of-View of the Earth Camera is approximately 20 × 20°. See: http://vis.physics.uiowa.edu/vis/vis_description/vis_description.htmlx Reference: Frank, L.A., J.B. Sigwarth, J.D. Craven, J.P. Cravens, J.S. Dolan, M.R. Dvorsky, J.D. Harvey, P.K. Hardebeck, and D. Muller, The Visible Imaging System (VIS) for the Polar Spacecraft, Space Science Review, Vol. 71, pp. 297-328, 1995. Data Set Description: The VIS Earth Camera Data Set comprises all Earth Camera Images for the selected Time Period. Full Coordinate Information is included for Viewer Orientation. In addition, a Rotation Matrix and a Table of Distortion-correcting Look Direction Unit Vectors are provided for the Purpose of calculating Coordinates for every Pixel. To facilitate viewing of the Images, a Mapping of Pixel Value to a recommended Color Table based on the Characteristics of the selected Filter will be included with each Image. A Relative Intensity Scale is provided through an Uncompressed Count Table. Approximate Intensity Levels in kiloRayleighs are given in an Intensity Table. For detailed Information on Intensities, see Sensitivities_and_Intensities.txt at https://cdaweb.gsfc.nasa.gov/Polar_VIS_docs/SENSITIVITIES_AND_INTENSITIES.TXT. Supporting Software is available at: http://vis.physics.uiowa.edu/vis/software/ Included is an IDL Program that displays the Images with the recommended Color Bar, provides approximate Intensities, Coordinate Data for each Pixel, and includes multiple Options for Image Manipulation.
| Role | Person | |
|---|---|---|
| 1. | FormerPI | spase://SMWG/Person/Louis.A.Frank |
| 2. | GeneralContact | spase://SMWG/Person/Robert.M.Candey |
| 3. | MetadataContact | spase://SMWG/Person/Lee.Frost.Bargatze |
Scientific Description of the VIS Instrument
Sensitivity and Intensity Calculation
Polar VIS Coordinate Calculation
Scientific Analysis Software
Access to Data in CDF Format via ftp from SPDF
Access to Data in CDF Format via http from SPDF
Access to ASCII, CDF, and Plots via NASA/GSFC CDAWeb
Epoch Time, Image Center Time, The Time assigned to an Image is the Center Time of the Integration Period within a Resolution of 50 ms
Time PB5, Image Center Time
Uncleaned 256 × 256 Ultraviolet Image in Quasi-Logarithmically Compressed, QLC, Counts. Image Pixel Counts Range from 0 to 255. They are stored in a Two-Dimensional 256 × 256 byte Array. Images from the Earth Camera (Sensor 0) are conventionally displayed with Row 1 at the Top, Row 256 at the Bottom, Column 1 on the Left, and Column 256 on the Right. The Conventional Image Display for the Low Resolution Camera (Sensor 1) is rotated 180° so that the Row 1-Column 1 Pixel is at the Lower Right Corner and the Row 256-Column 256 Pixel is at the Upper Left Corner. When displayed in this Manner, the Spacecraft Spin Axis is oriented to the Right in the Display, the X-component is defined as the Center of the Image Look Direction, and the Y-component is the Cross Product of the Spin Axis and the Look Direction.
Cleaned and Filtered 256 × 256 Ultraviolet Image in Quasi-Logarithmically Compressed, QLC, Counts. These are Image Pixel Counts that have been calibrated using the following Routines. For the Earth Camera: Horizontal Smooth EC 4 if the Modified Julian Date (MJD) is greater than 3429 (Correction required after an Event in 2005), Horizontal Smooth EC 6 if the Modified Julian Date (MJD) is greater than 4307 (Correction required after an Event in 2007), Subtract Cosmic Rays, Subtract Slopes (Adjusts for Biases across the CCD), Remove Weave (Corrects for Interference from Low Resolution Camera), Flat Field (Corrects for other Characteristics of the CCD) [Note: depending on Viewing Geometry, not all Irregularities can be fixed completely; in particular, a wide Diagonal Stripe may still be Visible], Dayglow Subtract, Nightglow Minimum. For the Low Resolution Camera: Subtract Cosmic Rays, Subtract Slopes, Flat Field, Smooth Filter. The Data Structure is the same as the Raw Image Counts.
Image Display with Geographic Grid Overlay in Quasi-Logarithmically Compressed, QLC, Counts, use Short Time Spans
Image Display, Azimuthal Projection to Geographic in Quasi-Logarithmically Compressed, QLC, Counts, Fixed Sun Orientation, use Short Time Spans
Image Display, Azimuthal Projection to Magnetic Local Time and Invariant Latitude in Quasi-Logarithmically Compressed, QLC, Counts, use Short Time Spans
Movie Display of Cleaned Ultraviolet Images in Quasi-Logarithmically Compressed, QLC, Counts
Movie Display, with Geographic Grid Overlay in Quasi-Logarithmically Compressed, QLC, Counts, use Short Time Spans, use Short Time Spans
Movie Display, Azimuthal Projection to Geographic in Quasi-Logarithmically Compressed, QLC, Counts Fixed Sun Orientation, use Short Time Spans
Movie Display, Azimuthal Projection to Magnetic Local Time and Invariant Latitude in Quasi-Logarithmically Compressed, QLC, Counts, use Short Time Spans
Cleaned and Filtered Ultraviolet Images. These are Image Pixel Counts that have been calibrated using the following Routines. For the Earth Camera: Horizontal Smooth EC 4 if the Modified Julian Date (MJD) is greater than 3429 (Correction required after an Event in 2005), Horizontal Smooth EC 6 if the Modified Julian Date (MJD) is greater than 4307 (Correction required after an Event in 2007), Subtract Cosmic Rays, Subtract Slopes (Adjusts for Biases across the CCD), Remove Weave (Corrects for Interference from Low Resolution Camera), Flat Field (Corrects for other Characteristics of the CCD) [Note: depending on Viewing Geometry, not all Irregularities can be fixed completely; in particular, a wide Diagonal Stripe may still be Visible], Dayglow Subtract, Nightglow Minimum. For the Low Resolution Camera: Subtract Cosmic Rays, Subtract Slopes, Flat Field, Smooth Filter. The Data Structure is the same as the Raw Image Counts.
Image Display with Geographic Grid Overlay, use Short Time Spans
Image Display, Azimuthal Projection to Geographic, Fixed Sun Orientation, use Short Time Spans
Image Display, Azimuthal Projection to Magnetic Local Time and Invariant Latitude, use Short Time Spans
Movie Display of Cleaned Ultraviolet Images
Movie Display with Geographic Grid Overlay, use Short Time Spans
Movie Display, Azimuthal Projection to Geographic, Fixed Sun Orientation, use Short Time Spans
Movie Display, Azimuthal Projection to Magnetic Local Time and Invariant Latitude, use Short Time Spans
Sensor Number: 0=Earth Camera, 1=Low Resolution Camera, 2=Medium Resolution Camera (never activated)
Half of the Length of the Integration Period for the Image measured in ms.
Twelve Filters are available for Visible Imaging. The Filter Number, 1-12, is given here. Ultraviolet Imaging is done with one Filter only, which is designated here as Filter Number 0. In Addition, the Peak Wavelength is given in Angstroms for each selected Filter. For detailed Information on Filter Characteristics, see the Text in the Sensitivities_and_Intensities.txt File.
Presumed Altitude of Emissions - The presumed Altitude of the Emissions seen in the Image varies with the Characteristics of the Filter used.
Platform Pointing Angle from Nadir - This is the Platform Pointing Angle of Rotation around the Spin Axis measured from Nadir.
Geographic Latitude Grid, provided for each Pixel
Geographic Longitude Grid, provided for each Pixel
Right Ascension, Geocentric Inertial, GCI, Coordinates, provided for each Pixel
Declination Angle, Geocentric Inertial, GCI, Coordinates, provided for each Pixel
Altitude at Line-of-Sight - The Altitude along Tangent to Line-of-Sight, provided for each Pixel
Earth Pointing Flag: 0=Off Earth, 1=On Earth
Spacecraft Position Vector, Geocentric Inertial, GCI, Coordinates - The Spacecraft Position Vectors are for the Image Center Time.
Spacecraft Velocity Vector, Geocentric Inertial, GCI, Coordinates - The Spacecraft Velocity Vectors are for the Image Center Time.
Spacecraft Spin Axis Unit Vector, Geocentric Inertial, GCI, Coordinates
Coordinate System Rotation Matrix, Image Coordinates to Geocentric Inertial, GCI, Coordinates - The Rotation Matrix may be used with the Look Direction Vector Table to obtain Pointing Vectors in GCI Coordinates for each Pixel. The Resulting Vectors may be used to calculate Coordinates for the observed Positions of the Pixels. The General Method used is described below in the Coordinate_Calculation.txt File. Column 1 Labels from MATRX_COLUMNS: ["X axis","X axis","X axis"] Column 2 Labels from NORM_CART: ["X(norm)","X(norm)","X(norm)"]
Look Direction Unit Vectors for the Earth Camera - The Rotation Matrix may be used with the Look Direction Vector Table to obtain Pointing Vectors in GCI Coordinates for each Pixel. The Resulting Vectors may be used to calculate Coordinates for the observed Positions of the Pixels. The General Method used is described below in the Coordinate_Calculation.txt File.
Zenith Angle of Center Line-of-Sight at Intersection with Earth - This is the Angle between the Geocentric Vector through the observed Point, assuming the Presumed Altitude of Emissions and the Reverse of the Image Center Line-of-Sight Vector.
Sun Direction Unit Vector, Geocentric Inertial, GCI, Coordinates
Solar Zenith Angle at Intersection of Center Line-of-Sight with Earth - This is the Angle of the Sun from Zenith at the observed Point of the Center Line-of-Sight, assuming the Altitude given by the Presumed Altitude of Emission
RGB Color Lookup Table - This is the recommended Color Table to be used with the Upper and Lower Color Limits.
Lower Limit for remapping Color Table to Pixel Range - The Low and High Color Limits are recommended for remapping the Color Table Entries, as follows: For Pixel Values less than the Low Limit, use the Color at Table Position 1. For Pixel Values greater than or equal to the Low Limit and less than or equal to the High Limit, use the Color at Table Position (pix-low)/(high-low) × 255 + 1. For Pixel Values greater than the High Limit, use the Color at Table Position 256.
Upper Limit for remapping Color Table to Pixel Range - The Low and High Color Limits are recommended for remapping the Color Table Entries, as follows: For Pixel Values less than the Low Limit, use the Color at Table Position 1. For Pixel Values greater than or equal to the Low Limit and less than or equal to the High Limit, use the Color at Table Position (pix-low)/(high-low) × 255 + 1. For Pixel Values greater than the High Limit, use the Color at Table Position 256.
Data Quality Flag - The Data Quality Word has Bits set to 1 when the listed Conditions are True. Bit #31 is the Most Significant Bit in the Word, and it will not be used as a Flag. These are the Bit Assignments: Bit 0 - Image Data Frame Sync, Error Bit 1 - Image Data Frame Counters, Error Bit 2 - Image Data Fill Frame Flag.
Project Standard Value Assignments - The Post Gap Flag has these possible Values: 0 - No Gap occurred immediately prior to this Record, 1 - The Gap occurred because the Instrument was not in a Mode that allowed for the Production of Images for the selected Sensor, 2 - The Gap occurred because Level Zero Data were Missing, 3 - The Gap occurred because Level Zero Data were too Noisy to extract Images.
Expanded Count Table: Quasi-Logarithmically Uncompressed Pixel Counts - The Image Pixel Counts are quasi-logarithmically compressed to the Range 0-255. This Table gives the Average of the Uncompressed Range for each Compressed Count Value. Table Entries 1-256 correspond to Compressed Counts 0-255, respectively.
Approximate Intensity Levels for each Filter - Approximate Intensity Levels in kiloRayleighs are given for each Compressed Count Value. Table Entries 1-256 correspond to Compressed Counts 0-255, respectively. Intensity Calculation is described in the Sensitivities_and_Intensities.txt File.
Image Header Bytes Column 1 Labels from HEADER_BLOCK: [sync byte 1,sync byte 2,sync byte 3,image block type,image block number,highest image block number,block size LSB,block size MSB,X size LSB,X size MSB,Y size LSB,Y size MSB,base,gain,active sensor,filter wheel step,field stop step,azimuth,elevation,nadir high,nadir low,msec_lo LSB,msec_hi MSB,sec_lo LSB,sec_lo NSB,sec_hi MSB,tjd_lo LSB,tjd_hi MSB,image number,CCD status 1 vdump LSB,CCD status 2 vdump MSB,CCD status 3 rdump LSB,CCD status 4 rdump MSB,CCD status 5 oscan LSB,CCD status 6 oscan MSB,CCD status 7 anti-bloom rates,CCD status 8 time base,CCD status 9 hdump LSB,CCD status 10 hdump MSB,CCD status 11 A/D convs LSB,CCD status 12 A/D convs MSB,CCD status 13 cycle LSB,CCD status 14 cycle MSB,CCD status 15 flag bits,CCD status 16 erase,CCD status 17 images,CCD status 18 exp time LSB,CCD status 19 exp time NSB,CCD status 20 exp time MSB,CCD status 21 delay convs,,,orbit clock LSB,orbit clock MSB,MM2S 16 LSB,MM2S 15 MSB,N2S pitch P90 LSB,N2S pitch P90 MSB,sector count LSB,sector count MSB,s-lo LSB at start cycle,s_lo NSB at start cycle,ms_hi MSB at start cycle,sectors exp bits 11-4] Column 2 Labels from HEADER_BLOCK: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
Image Row Number of Coordinates
Image Column Number of Coordinates
Image Row Number
Image Column Number
Header Block Number
Header Field Names