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Level 1: raw data and meta-data

Level 1 of Lyra data consist in a set of four (seven, when acquisition is performed with two units at the same time) fits files:

  • a standard file named lyra_yyyymmdd-hhmmss_lev1_std.fits (or lyra_yyyymmdd-hhmmss_lev1_bst.fits, when a back-up unit is used)
  • a calibration file named lyra_yyyymmdd-hhmmss_lev1_cal.fits (or lyra_yyyymmdd-hhmmss_lev1_bca.fits, when a back-up unit is used)
  • a file with rejected samples named lyra_yyyymmdd-hhmmss_lev1_rej.fits (or lyra_yyyymmdd-hhmmss_lev1_bre.fits, when a back-up unit is used)
  • a metadata file named lyra_yyyymmdd-hhmmss_lev1_met.fits

These files contain a common primary header and a secondary header, which depends on the file type (std, met, cal, rej). The primary header has the following configuration:

fits keywords for lev1 Lyra product: primary header
KEYWORD EXAMPLE OF VALUE COMMENT
SIMPLE T Written by PyFits
BITPIX 8 array data type
NAXIS 0 number of array dimensions
EXTEND T File contains extensions
ORIGIN ’ROB-SIDC’  
TELESCOP ’PROBA2’  
INSTRUME ’LYRA ’  
OBJECT ’EUV solar irrad’  
OBS_MODE ’nominal standard’ std., ecl., cal. (std. or bak.), met., or rej.
DATE ’2009-07-31’ FITS file creation date (yyyy-mm-dd)
DATE-OBS ’2009-07-30T00:00:00.000’ UTC start of observation
DATE-END ’2009-07-30T23:59:59.990’ UTC end of observation
DATE-BUP ’2010-05-01T00:00:00.004000’ UTC start of update
DATE-EUP ’2010-05-01T21:41:22.150995’ UTC end of update
DATASRC ’Redu ’ Receiving ground station
ALGOR_V ’EDG=2.1 ’ softs versions
LEVEL ’1 ’ Calibration level
CAL_FILE lyra_cal_20090730-000000’ File version number
UNITS ’2 ’  
FILENAME ’lyra_20090730-000000_lev1_std_v01.fits’ Name of this FITS file
END    

The standard file

The standard file contains all the acquired samples corresponding to uncalibrated solar signal measurements.

"Uncalibrated" does not only mean that raw LYRA count rates [1] are shown instead of physical units; the curves also still include a long-term trend due to instrumental degradation, dark currents (which are not substracted at this level), daily and orbital variations due to on-board temperature changes, regular disturbances per orbit due to spacecraft rotations, and possible disturbances due to commanding. Gaps may be caused by missing downlinks or calibration campaigns.

As an illustration, see the curve below:

The keywords contained in the secondary header are:

fits keywords for lev1 standard Lyra product: secondary header
KEYWORD EXAMPLE OF VALUE COMMENT
XTENSION ’BINTABLE’ binary table extension
BITPIX 8 array data type
NAXIS 2 number of array dimensions
NAXIS1 41 length of dimension 1
NAXIS2 7488 length of dimension 2
PCOUNT 0 number of group parameters
GCOUNT 1 number of groups
TFIELDS 6 number of table fields
TTYPE1 ’TIME ’ TIME in UTC (yyyy-mm-dd)
TFORM1 ’1D ’ TIME data type: Real*8 (double precision)
TUNIT1 ’s ’ TIME physical unit: seconds of day
TTYPE2 ’CHANNEL1’ CHANNEL1: Lyman alpha
TFORM2 ’1D ’ CHANNEL1 data type: Real*8 (double precision)
TUNIT2 ’kHz ’ CHANNEL1 physical unit: kiloHertz
TTYPE3 ’CHANNEL2’ CHANNEL2: Herzberg
TFORM3 ’1D ’ CHANNEL2 data type: Real*8 (double precision)
TUNIT3 ’kHz ’ CHANNEL2 physical unit: kiloHertz
TTYPE4 ’CHANNEL1’ CHANNEL3: Aluminium filter
TFORM4 ’1D ’ CHANNEL3 data type: Real*8 (double precision)
TUNIT4 ’kHz ’ CHANNEL3 physical unit: kiloHertz
TTYPE5 ’CHANNEL1’ CHANNEL4: Zirconium filter
TFORM5 ’1D ’ CHANNEL4 data type: Real*8 (double precision)
TUNIT5 ’kHz ’ CHANNEL4 physical unit: kiloHertz
TTYPE6 ’QFACTOR ’ QFACTOR: calculated TIME quality factor
TFORM6 ’1B ’ QFACTOR data type: Interger*1 (byte)
TUNIT6 ’ ’ QFACTOR physical unit: none
EXTNAME ’FREQ LEVEL 1’ Name of binary table extension
END    

The calibration file

This file contains all the data dedicated to the calibration of the instrument:

  • dark current measurement
  • LEDs signal

The secondary header is similar than in the case of a standard file.

The rejected file

This file gathers all the samples that must be rejected because:

  • they immediately follow a transition between two different acqusition configurations and might be corrupted.
  • they are part of the warm-up process before the instrument goes in acquisition mode.
  • they are outliers.

The secondary header is similar than in the case of a standard file.

The metadata file

Those files contain the information that will be needed to calibrate the data. It is composed of three tables:

  • the first one contains the information extracted from the housekeepings: temperature, pointing, and distance from the Sun to the spacecraft
  • the second one contains the information extracted from the status of the instrument
  • the third one contains the calibration voltage measurements of the VFCs (voltage-to-frequency convertors) used by the instrument.

The keywords contained in the header of the first table are:

fits keywords for lev1 metadata Lyra product: secondary header, first table
KEYWORD EXAMPLE OF VALUE COMMENT
XTENSION ’BINTABLE’ binary table extension
BITPIX 8 array data type
NAXIS 2 number of array dimensions
NAXIS1 28 length of dimension 1
NAXIS2 2900 length of dimension 2
PCOUNT 0 number of group parameters
GCOUNT 1 number of groups
TFIELDS 5 number of table fields
TTYPE1 ’TIME_UTC ’ TIME in readable format
TFORM1 ’26A ’ TIME data type: String
TUNIT1 ’s ’ TIME physical unit: seconds of day
TTYPE2 ’TIME ’ TIME in seconds of the day
TFORM2 ’D ’ TIME data type: Real*8 (double precision)
TUNIT2 ’s ’ TIME physical unit: seconds of day
TTYPE3 ’TEMPERATURE’ TEMPERATURE of LYRA detectors
TFORM3 ’E ’ TEMPERAT. d. type: Real*4 (floating point)
TUNIT3 ’deg C ’ TEMPERATURE physical unit: degree Celcius
TTYPE4 ’POINTING’ POINTING calculated with SPICE (yaw,pitch,roll)
TFORM4 ’2E ’ POINTING data type: Real*4 (floating point)
TUNIT4 ’arcsec ’ POINTING physical unit
TTYPE5 ’DISTANCE’ DISTANCE calculated with SPICE
TFORM5 ’D ’ DISTANCE data type: Real*8 (double precision)
TUNIT5 ’km ’ DISTANCE physical unit: km between s/c and Sun
EXTNAME ’HK LEVEL 1’ Name of first metadata tableHK
END    

The keywords contained in the header of the second table are:

fits keywords for lev1 metadata Lyra product: secondary header, second table
KEYWORD EXAMPLE OF VALUE COMMENT
XTENSION ’BINTABLE’ binary table extension
BITPIX 8 array data type
NAXIS 2 number of array dimensions
NAXIS1 45 length of dimension 1
NAXIS2 1 length of dimension 2
PCOUNT 0 number of group parameters
GCOUNT 1 number of groups
TFIELDS 11 number of table fields
TTYPE1 ’TIME_UTC ’ UTC TIME
TFORM1 ’26A ’ UTC data type: A26
TUNIT1 ’s ’ UTC seconds
TTYPE2 ’TIME ’ TIME in seconds of the day
TFORM2 ’D ’ TIME data type: Real*8 (double precision)
TUNIT2 ’s ’ TIME physical unit: seconds of day
TTYPE3 ’HEAD ’ HEAD used for detection (1, 2, 3, off=0)
TFORM3 ’B ’ HEAD data type: Integer*1 (byte)
TUNIT3 ’ ’ HEAD physical unit: none
TTYPE4 ’MODE ’ MODE: nominal=1 or backup=0
TFORM4 ’B ’ MODE data type: Integer*1 (byte)
TUNIT4 ’ ’ MODE physical unit: none
TTYPE5 ’COVER ’ COVER: closed=1 or open=0
TFORM5 ’B ’ COVER data type: Integer*1 (byte)
TUNIT5 ’ ’ COVER physical unit: none
TTYPE6 ’VISLED ’ VISLED: visible led used=1 or not used=0
TFORM6 ’B ’ VISLED data type: Integer*1 (byte)
TUNIT6 ’ ’ VISLED physical unit: none
TTYPE7 ’UVLED ’ UVLED: ultraviolet led used=1 or not used=0
TFORM7 ’B ’ UVLED data type: Integer*1 (byte)
TUNIT7 ’ ’ UVLED physical unit: none
TTYPE8 ’DARKCURR1’ Dark current of channel1 detector
TFORM8 ’D ’ DARKCURR1 data type: Real*8 (double precision)
TUNIT8 ’kHz ’ DARKCURR1 physical unit: kilohertz
TTYPE9 ’DARKCURR2’ Dark current of channel2 detector
TFORM9 ’D ’ DARKCURR2 data type: Real*8 (double precision)
TUNIT9 ’kHz ’ DARKCURR2 physical unit: kilohertz
TTYPE10 ’DARKCURR3’ Dark current of channel3 detector
TFORM10 ’D ’ DARKCURR3 data type: Real*8 (double precision)
TUNIT10 ’kHz ’ DARKCURR3 physical unit: kilohertz
TTYPE11 ’DARKCURR4’ Dark current of channel4 detector
TFORM11 ’D ’ DARKCURR4 data type: Real*8 (double precision)
TUNIT11 ’kHz ’ DARKCURR4 physical unit: kilohertz
EXTNAME ’STATUS LEVEL 1’ name of binary table extension
END    

The keywords contained in the header of the third table are:

fits keywords for lev1 metadata Lyra product: secondary header, third table
KEYWORD EXAMPLE OF VALUE COMMENT
XTENSION ’BINTABLE’ binary table extension
BITPIX 8 array data type
NAXIS 2 number of array dimensions
NAXIS1 41 length of dimension 1
NAXIS2 1 length of dimension 2
PCOUNT 0 number of group parameters
GCOUNT 1 number of groups
TFIELDS 7 number of table fields
TTYPE1 ’TIME_UTC’  
TFORM1 ’26A ’  
TUNIT1 ’s ’  
TTYPE2 ’TIME ’ TIME in seconds of the day
TFORM2 ’D ’ TIME data type: Real*8 (double precision)
TUNIT2 ’s ’ TIME physical unit: seconds of day
TTYPE3 ’MODE ’ MODE: nominal=1 or backup=0
TFORM3 ’B ’ MODE data type: Integer*1 (byte)
TUNIT3 ’ ’ MODE physical unit: none
TTYPE4 ’VFC1 ’ VFC1
TFORM4 ’2E ’ VFC1 data type: Real*4 (floating point)
TUNIT4 ’ ’ VFC1 physical unit: none
TTYPE5 ’VFC2 ’ VFC2
TFORM5 ’2E ’ VFC2 data type: Real*4 (floating point)
TUNIT5 ’ ’ VFC2 physical unit: none
TTYPE6 ’VFC3 ’ VFC3
TFORM6 ’2E ’ VFC3 data type: Real*4 (floating point)
TUNIT6 ’ ’ VFC3 physical unit: none
TTYPE7 ’VFC4 ’ VFC4
TFORM7 ’2E ’ VFC4 data type: Real*4 (floating point)
TUNIT7 ’ ’ VFC4 physical unit: none
EXTNAME ’VFC LEVEL 1’ name of binary table extension
END    

[1] The amount of signal received by the detector in counts, divided by integration time.