On or about October 16, 2024, the National Weather Service will deploy an update to the processing of GONG near real time space weather data that will yield additional and more standardized World Coordinate System (WCS) information in the GONG H-alpha FITS file headers. The existing WCSNAME, CTYPE1 and CTYPE2 header keywords will be modified to reflect a Helioprojective-cartesian WCS, and the following new keywords will be added: CDELT1, CDELT2, CUNIT1, CUNIT2, CROTA1, CROTA2, SOLAR_R and TIMESYS. These changes better define the relationship between image pixels and solar coordinates, allowing users to more easily relate positions on the observed images to locations on the Sun.
The following table provides excerpts from the beginning of an example header, before (right) and after (left) this change is implemented. The areas highlighted in green represent modifications to existing entries, while those highlighted in orange reflect new entries not previously included. The eight greyed out lines have been added here purely to align entries and aid in this visual comparison.
SIMPLE = T / Fits standard BITPIX = 16 / Bits per pixel NAXIS = 2 / Number of axes NAXIS1 = 2048 / Axis length NAXIS2 = 2048 / Axis length EXTEND = T / File may contain extensions GONGKEY1= '--------- Gong Keywords Section 1: Solarsoft ----------------' ORIGIN = 'National Solar Observatory -- GONG' / FITS file originator OBS-SITE= 'NSO/GONG NETWORK' / Instrument Site location TELESCOP= 'NSO-GONG' / NSO/GONG Network OBS-URL = 'http://gong.nso.edu' / The GONG website DATE = '2024-10-03T09:37:02' / Date FITS file was generated DATE-OBS= '2024-10-03T09:35:42' / Observation start date and time (UTC) TIME-OBS= '17:35:43' / Observation start time (UTC) WAVELNTH= 6562.808 / [A] exact wavelength of obs WCSNAME = 'Helioprojective-cartesian' / WCS system name CTYPE1 = 'HPLN-TAN' / Axis 1 gives helioprojective westward angle CTYPE2 = 'HPLT-TAN' / Axis 2 gives helioprojective northward angle CRPIX1 = 1024.5 / Pixel corresponding to Sun's center on axis 1 CRPIX2 = 1024.5 / Pixel corresponding to Sun's center on axis 2 CRVAL1 = 0.00000 / Helioprojective westward angle at CRPIX1 CRVAL2 = 0.00000 / Helioprojective northward angle at CRPIX2 CDELT1 = 1.065717083395 / Angular change per pixel along axis 1 CDELT2 = 1.065717083395 / Angular change per pixel along axis 2 CUNIT1 = 'arcsec ' / Units of CRVAL1 and CDELT1 CUNIT2 = 'arcsec ' / Units of CRVAL2 and CDELT2 CROTA1 = 0.0 / [deg] Counter-clockwise rotation of axis 1 CROTA2 = 0.0 / [deg] Counter-clockwise rotation of axis 2 TIMESYS = 'UTC ' / Time Scale specification SOLAR_R = 959.145375055823 / [arcsec] solar semi-diameter EPH_RA = -2.970422793 / Right Acension (radians) EPH_DEC = -0.073735784 / Declination (radians) IMTYPE = 'H-ALPHA ' IMGMN01 = 1798.370971680 / Image mean IMGRMS01= 1457.310424805 / Image RMS (Standard Deviation) IMGSKW01= -0.329404384 / Image skewness IMGMIN01= -2 / Image Min IMGMAX01= 5333 / Image Max IMGADV01= 1415.644531250 / Image Average Deviation IMGVAR01= 2123753.750000000 / Image Variance IMGKUR01= -1.760743022 / Image Kurtosis
| SIMPLE = T / Fits standard BITPIX = 16 / Bits per pixel NAXIS = 2 / Number of axes NAXIS1 = 2048 / Axis length NAXIS2 = 2048 / Axis length EXTEND = T / File may contain extensions GONGKEY1= '--------- Gong Keywords Section 1: Solarsoft ----------------' ORIGIN = 'National Solar Observatory -- GONG' / FITS file originator OBS-SITE= 'NSO/GONG NETWORK' / Instrument Site location TELESCOP= 'NSO-GONG' / NSO/GONG Network OBS-URL = 'http://gong.nso.edu' / The GONG website DATE = '2024-10-03T09:36:18' / Date FITS file was generated DATE-OBS= '2024-10-03T09:35:42' / Observation start date and time (UTC) TIME-OBS= '17:35:43' / Observation start time (UTC) WAVELNTH= 6562.808 / [A] exact wavelength of obs WCSNAME = 'Heliocentric-cartesian (approximate)' CTYPE1 = 'GONGX ' / Coordinate Axis Label CTYPE2 = 'GONGY ' / Coordinate Axis Label CRVAL1 = 0.00000 / Reference Pixel value CRVAL2 = 0.00000 / Reference Pixel value CRPIX1 = 1024.0 CRPIX2 = 1024.0
EPH_RA = -2.970422793 / Right Acension (radians) EPH_DEC = -0.073735784 / Declination (radians) IMTYPE = 'H-ALPHA ' IMGMN01 = 1798.370971680 / Image mean IMGRMS01= 1457.310424805 / Image RMS (Standard Deviation) IMGSKW01= -0.329404384 / Image skewness IMGMIN01= -2 / Image Min IMGMAX01= 5333 / Image Max IMGADV01= 1415.644531250 / Image Average Deviation IMGVAR01= 2123753.750000000 / Image Variance IMGKUR01= -1.760743022 / Image Kurtosis |