FITS2HV

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This page describes solar FITS files keywords and their meaning in relation to the Helioviewer Project. A description of the FITS format can be found here and here.

Contents

General requirements

The following table lists the information needs in the meta-data header in order for the file to be Helioviewer Project compliant, along with some common keys used to identify that information. Note that the FITS keywords in your data may not be the same as the ones listed here; rather, you should identify the keyword which corresponds to the concept in the left hand column.

NOTE: at present we are currently restricting CRPIXn to point to Sun center, which requires that any CRVALn values be set to zero. The FITS standard allows CRVALn to be non-zero, such as with sub-field images. We are at present assessing the need for this restriction.

General
conceptTypical FITS keyword name
bits per pixelBITPIX
number of pixels in the x directionNAXIS1
number of pixels in the y directionNAXIS2
x position, Center of the sun in image pixelsCRPIX1
y position, Center of the sun in image pixelsCRPIX2
x direction, arcseconds per pixelCDELT1
y direction, arcseconds per pixelCDELT2
solar radius in image pixelsRSUN
distance to the Sun from the detectorDSUN
date and time of observationDATE-OBS
observatoryTELESCOP
instrumentINSTRUME
detectorINSTRUME
measurementWAVELNTH
nicknameno equivalent





Hinode

XRT

XRT
FITSHV Default value
FITS default value
hv
BITPIX?
?
bits per pixel
NAXIS1?
?
number of pixels in the x direction
NAXIS2?
/
number of pixels in the y direction
DATE-OBS n/ayyyy-mm-ddThh:mm:ss.mm, date and time of the beginning of the observation CCSDS format
TELESCOPHinode
SolarB
Observatory
INSTRUMEXRT
XRT
Instrument
??????
???
Detector
???one of the choices below
???
Measurement
n/aXRTObservatory-Instrument-Detector Nickname (see note 'a')
??
?
x position, Center of the sun in image pixels
??
?
y position, Center of the sun in image pixels
CDELT1?
?
x direction, arcseconds per pixel
CDELT2?
?
y direction, arcseconds per pixel
??solar radius in image pixels

For more details on XRT FITS keywords go to http://xrt.cfa.harvard.edu/MODA/XRTKeywords05-10-16.pdf



PROBA2

SWAP

FITSHV Default value
FITS default value
hv
BITPIX16
8
bits per pixel
NAXIS11024
1024
number of pixels in the x direction
NAXIS21024
1024
number of pixels in the y direction
DATE-OBS n/ayyyy-mm-ddThh:mm:ss.mm, date and time of the beginning of the observation CCSDS format
TELESCOPPROBA2
PROBA2
Observatory
INSTRUMESWAP
SWAP
Instrument
??????
SWAP
Detector
???174
174
Measurement
n/aSWAPObservatory-Instrument-Detector Nickname (see note 'a')
??
?
x position, Center of the sun in image pixels
??
?
y position, Center of the sun in image pixels
CDELT13.17123287671252
3.17123287671252
x direction, arcseconds per pixel
CDELT23.16226783968713
3.16226783968713
y direction, arcseconds per pixel
??solar radius in image pixels

For more details on SWAP FITS keywords go to http://proba2.oma.be/index.html/swap/swap-analysis-manual/article/data-products?menu=23




FITSHelioviewer
KeywordDefault valueEquivalent conceptDefault value
BITPIX16bits per pixelsame as FITS
CDELT13.17123287671252x direction, arcseconds per pixelsame as FITS

For more details on SWAP FITS keywords go to http://proba2.oma.be/index.html/swap/swap-analysis-manual/article/data-products?menu=23



SDO

AIA

FITSHV Default value
FITS default value
hv
BITPIX32
32
bits per pixel
NAXIS14096
4096
number of pixels in the x direction
NAXIS24096
4096
number of pixels in the y direction
DATE_OBS or DATE__OBSn/ayyyy-mm-ddThh:mm:ss.mmZ, date and time of observation CCSDS format
TELESCOPSDO
SDO/AIA
Observatory
INSTRUMEAIA
AIA
Instrument
INSTRUMEAIA
AIA
Detector
WAVELNTHone of the choices below
4500, 1700, 304, 1600, 171, 193, 211, 335, 94, 131
Measurement
n/aAIAObservatory-Instrument-Detector Nickname (see note 'a')
CRPIX1 or X0_LF or X0_MP2048
2048 or NAN (see note 'c')
x position, Center of the sun in image pixels
CRPIX2 or Y0_LF or Y0_MP2048
2048 or NAN
y position, Center of the sun in image pixels
CDELT10.599900
0.599900
x direction, arcseconds per pixel
CDELT20.599900
0.599900
y direction, arcseconds per pixel
DSUN_OBS???solar radius in image pixels

For more details on AIA FITS keywords go to ???



SOHO

EIT

FITSDefault valuehv
NAXIS11024number of pixels in the x direction
NAXIS21024number of pixels in the y direction
DATE_OBSn/ayyyy-mm-ddThh:mm:ss.mmmZ, date and time of observation CCSDS format
TELESCOPSOHOObservatory
INSTRUMEEITInstrument
INSTRUMEEITDetector
WAVELNTHone of 171, 195, 284, 304Measurement
n/aEITObservatory-Instrument-Detector Nickname (see note 'a')
CRPIX1512x position, Center of the sun in image pixels
CRPIX2512y position, Center of the sun in image pixels
CDELT12.63x direction, arcseconds per pixel
CDELT22.63y direction, arcseconds per pixel
SOLAR_R369.88solar radius in image pixels

For more details on EIT FITS keywords go to http://umbra.nascom.nasa.gov/eit/eit_guide/

LASCO C2

FITSDefault valuehv
NAXIS11024number of pixels in the x direction
NAXIS21024number of pixels in the y direction
DATE_OBSn/ayyyy-mm-dd
TIME_OBSn/ahh:mm:ss.mmm
TELESCOPSOHOObservatory
INSTRUMELASCOInstrument
DETECTORC2Detector
n/aLASCO C2Observatory-Instrument-Detector Nickname
FILTER + POLAROrange + ClearMeasurement
n/awhite lightMeasurement Nickname
CRPIX1512x position, Center of the sun in image pixels
CRPIX2512y position, Center of the sun in image pixels
CDELT111.9x direction, arcseconds per pixel
CDELT211.9y direction, arcseconds per pixel
RSUN80.814221solar radius in image pixels

For more details on LASCO C2 FITS keywords at http://lasco-www.nrl.navy.mil/keywords.html

LASCO C3

FITSDefault valuehv
NAXIS11024number of pixels in the x direction
NAXIS21024number of pixels in the y direction
DATE_OBSn/ayyyy-mm-dd
TIME_OBSn/ahh:mm:ss.mmm
TELESCOPSOHOObservatory
INSTRUMELASCOInstrument
DETECTORC3Detector
n/aLASCO C3Observatory-Instrument-Detector Nickname [a]
FILTER + POLARClear + ClearMeasurement
n/awhite lightMeasurement Nickname
CRPIX1512x position, Center of the sun in image pixels
CRPIX2512y position, Center of the sun in image pixels
CDELT156.0x direction, arcseconds per pixel
CDELT256.0y direction, arcseconds per pixel
RSUN17.173021solar radius in image pixels

For more details on LASCO C3 FITS keywords go to http://lasco-www.nrl.navy.mil/keywords.html

MDI

FITSDefault valuehv
NAXIS11024number of pixels in the x direction
NAXIS21024number of pixels in the y direction
DATE_OBSn/ayyyy-mm-ddThh:mm:ss.mmmZ, date and time of observation CCSDS format
TELESCOPSOHOObservatory
INSTRUMEMDIInstrument
INSTRUMEMDIDetector
n/aMDIObservatory-Instrument-Detector Nickname
DPC_OBSRn/aMeasurement
n/a"magnetogram"
or
"continuum"
Measurement Nickname - if DPC_OBSR contains alternatively "Magnetogram" or "Continuum"
CRPIX1512x position, Center of the sun in image pixels
CRPIX2512y position, Center of the sun in image pixels
CDELT11.9840299x direction, arcseconds per pixel
CDELT21.9840299y direction, arcseconds per pixel
R_SUN488.48498solar radius in image pixels

For more detail on MDI keywords go to http://soi.stanford.edu/sssc/doc/keywords.html



STEREO

The STEREO mission consists of two nearly identical spacecraft, one traveling ahead of the Earth (STEREO-A) and one traveling behind the Earth (STEREO-B) at approximately 1-AU from the Sun. The distance of each spacecraft from the Sun is a function of time. This means that the angle subtended per pixel varies as a function of time during the mission, and the apparent radius of the Sun in pixels also varies. These variations are more significant than in other missions (such as SDO and SOHO) that basically observe along the Sun-Earth line. These variations must be taken into account when attempting to overlay data from one spacecraft.

The two different points of view of the STEREO spacecraft mean that each instrument has a different line of sight through the plasma. The difference between the points of view is less pronounced at earlier times in the mission when the points of view were less significantly different. But as the spacecraft drift apart, the difference becomes much more pronounced. Therefore, overlaying images from STEREO-A and STEREO-B should be done with caution.

Currently beacon data is NOT supported, only the full quality STEREO data is processed. There is a currently a lag of 2-4 days between real time and the most recently available best quality STEREO image data.


EUVI

FITSDefault valuehv
NAXIS12048number of pixels in the x direction
NAXIS22048number of pixels in the y direction
DATE-OBSn/ayyyy-mm-ddThh:mm:ss.mmmZ, date and time of observation CCSDS format
OBSRVTRYSTEREO_A or STEREO_BObservatory (HVS value is stored as STEREO-A or STEREO-B)
n/aSECCHIInstrument
DETECTOREUVIDetector
WAVELNTHone of 171, 195, 284, 304Measurement
n/aEUVI-A or EUVI-BObservatory-Instrument-Detector Nickname (note the dependence on OBSRVTRY).
CRPIX11024x position, Center of the sun in image pixels
CRPIX21024y position, Center of the sun in image pixels
CDELT1n/ax direction, arcseconds per pixel
CDELT2n/ay direction, arcseconds per pixel
RSUNn/asolar radius in image pixels

For more details on EUVI FITS keywords go to http://sohowww.nascom.nasa.gov/solarsoft/stereo/secchi/doc/FITS_keywords.pdf

COR1/COR2

It should be noted that in general the Sun is not centered behind the coronagraph disk.

FITSDefault valuehv
NAXIS1COR2: 2048, COR1: variablenumber of pixels in the x direction
NAXIS2COR2: 2048, COR1: variablenumber of pixels in the y direction
DATE-OBSn/ayyyy-mm-ddThh:mm:ss.mmmZ, date and time of observation CCSDS format
OBSRVTRYSTEREO_A or STEREO_BObservatory (HVS value is stored as STEREO-A or STEREO-B)
n/aSECCHIInstrument
DETECTORCOR1 or COR2Detector
WAVELNTHn/aMeasurement
n/aCOR1-A or COR2-A
COR1-B or COR2-B
Observatory-Instrument-Detector Nickname (note the dependence on OBSRVTRY).
CRPIX1COR2: 1024, COR1: variablex position, Center of the sun in image pixels
CRPIX2COR2: 1024, COR1: variabley position, Center of the sun in image pixels
CDELT1n/ax direction, arcseconds per pixel
CDELT2n/ay direction, arcseconds per pixel
RSUNn/asolar radius in image pixels

For more details on COR1/COR2 FITS keywords go to http://sohowww.nascom.nasa.gov/solarsoft/stereo/secchi/doc/FITS_keywords.pdf


Notes

(a): Observatory-Instrument-Detector Nickname refers to what a solar physicist commonly calls the particular experimental apparatus that we have classified via its parent Observatory, parent Instrument and Detector. It's the common name used in conversation. The nickname should probably be the name used in the user interfaces of HV and JHV.

(b): Measurement Nickname refers to what a solar physicist commonly calls a well-known type of measurement made by a given Observatory-Instrument-Detector apparatus. The nickname should be used where it is indicated.

(c): NAN means "not a number".

Where to place a JP2 file given the positioning information above

  1. Radius of the Sun in metres: r0= 695500000
  2. Meters per pixel: k = r0/(solar radius in image pixels)
  3. If we assume the center of the Sun is (0,0), then the bottom left hand corner in metres is k*(-CRPIX1, -CRPIX2).
  4. Offset between Sun center and image center in metres is k*( CRPIX1-NAXIS1/2, CRPIX2-NAXIS2/2 )
  5. More detailed information on solar co-ordinates and pointing on the solar disk can be found at http://gong.nso.edu/data/DMAC_documentation/Vmbical/Solar_coord_defined.html

See also

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