L4 Data Product

FITS HDU Structure

Image HDU array: (4,r,c), where r and c depend on cropping. ERR HDU array: (1,4,r,c) DQ HDU array: (4,r,c) KL_THRU HDU array: (2,2,2) CT_THRU HDU array: (2,2) Below is an example.

Index	Name	Datatype	Array Size
0	Primary	None	0
1	Image	float32	(4, 54, 54)
2	ERR	float32	(1, 4, 54, 54)
3	DQ	uint16	(4, 54, 54)
4	KL_THRU	float32	(2, 2, 2)
5	CT_THRU	float32	(2, 2)

Header

Primary Header (HDU 0)

Keyword	Datatype	Example Value	Description
SIMPLE	bool	True	conforms to FITS standard
BITPIX	int	8	array data type
NAXIS	int	0	number of array dimensions
EXTEND	bool	True	Denotes FITS extensions
VISITID	str	0200001001001001001	The full visit ID assigned to this pointing
CDMSVERS	str	2.1.0	SSC CDMS pipeline build version used to generate L1
FSWDVERS	str	1.1.5.1	Record of the CGI FSW dictionary used to parse the telemetry
MOCK	bool	True	Only used for simulated data examples
TELESCOP	str	ROMAN	Telescope name
INSTRUME	str	CGI	Instrument designation
DETECTOR	str	EXCAM	Name of the detector
ORIGIN	str	DRP	Who is responsible for the data
FILETIME	str	2026-02-20T06:41:40.140828+…	When file was created
DATAVERS	int	1	Version of data (increments for reprocessing)
PROGNUM	str	02000	The Program ID in visit hierarchy (first 5 digits)
EXECNUM	str	01	The Execution Number in visit hierarchy (digits 6-7)
CAMPAIGN	str	001	The Pass/Campaign in visit hierarchy (digits 8-10)
SEGMENT	str	001	The Segment Number in visit hierarchy (digits 11-13)
OBSNUM	str	001	The Observation Number in visit hierarchy (digits 14-16)
VISNUM	str	001	The Visit number in visit hierarchy (digits 17-19)
CPGSFILE	str	campaign_020000100100100100…	Campaign-level XML containing the current visit
AUXFILE	str	aux_0200001001001001001.txt	An AUX file associated with this observation
VISTYPE	str	CGIVST_TDD_OBS	The visit file template used for this observation
TARGET	str	ScienceStar	Name of pointing target
RA	float	0.0	Planned RA
DEC	float	0.0	Planned DEC
EQUINOX	float	2000	J2000
RAPM	float	0.0	RA proper motion
DECPM	float	0.0	DEC proper motion
PSFREF	int	0	Whether this is a PSF reference observation or not
OPGAIN	str	1000	Planned EXCAM EM gain or “AUTO”
PHTCNT	str	AUTO	Whether photon counting mode is planned, or if set to “AUTO”. “FALSE” = Photon-counting mode not planned. “TRUE”=Photon-
FRAMET	str	30	Planned exposure time per frame or if set to “AUTO”. Taken from the observation plan
PA_V3	float	-999.0	Observatory position angle
PA_APER	float	-999.0	Position angle in the CGI aperture
SVB_1	float	-999.0	Sun unit vector in the body frame axis 1
SVB_2	float	-999.0	Sun unit vector in the body frame axis 2
SVB_3	float	-999.0	Sun unit vector in the body frame axis 3
ROLL	float	-999.0	S/C roll angle wrt the reference frame
PITCH	float	-999.0	S/C pitch angle wrt the reference frame
YAW	float	-999.0	S/C yaw angle wrt the reference frame
FILENAME	str	cgi_0200001001001001001_202…	The name of the file
OBSNAME	str	SCI	User-defined label for the associated observation plan
WBJ_1	float	-999.0	S/C angular momentum axis 1
WBJ_2	float	-999.0	S/C angular momentum axis 2
WBJ_3	float	-999.0	S/C angular momentum axis 3
KLIP_ALG	str	ADI

Image Header (HDU 1)

ERR Header (HDU 2)

Keyword	Datatype	Example Value	Description
XTENSION	str	IMAGE	Image extension
BITPIX	int	-64	array data type
NAXIS	int	4	number of array dimensions
NAXIS1	int	54	Raw data axis 1 size
NAXIS2	int	54	Raw data axis 2 size for SCI frames (1200) or ENG frames (2200)
NAXIS3	int	4	Length of third array dimension (axis 3)
NAXIS4	int	1
PCOUNT	int	0	number of parameters
GCOUNT	int	1	number of groups
EXTNAME	str	ERR	FITS extension name
TRK_ERRS	bool	False	Whether individual errors are tracked (T/F)
LAYER_1	str	combined_error	Type of error reported in this error slice
BUNIT	str	photoelectron	Physical unit of the array (brightness unit)
KGAINPAR	float	0.0	Calculated K-gain parameter (DN to electrons)
KGAIN_ER	float	0.0	Kgain error
RN	float	-999.0	Read noise (e-)
RN_ERR	float	-999.0
DESMEAR	bool	False	Desmearing used in L1→L2a pipeline (0/1)
HISTORY	str	Interpolated over 0 bad pi…	Processing history

DQ Header (HDU 3)

Keyword	Datatype	Example Value	Description
XTENSION	str	IMAGE	Image extension
BITPIX	int	16	array data type
NAXIS	int	3	number of array dimensions
NAXIS1	int	54	Raw data axis 1 size
NAXIS2	int	54	Raw data axis 2 size for SCI frames (1200) or ENG frames (2200)
NAXIS3	int	4	Length of third array dimension (axis 3)
PCOUNT	int	0	number of parameters
GCOUNT	int	1	number of groups
BSCALE	int	1	Linear factor in scaling equation. Needed for non-standard FITS data types
BZERO	int	32768	Offset for 16-bit unsigned data type (FITS format determined)
EXTNAME	str	DQ	FITS extension name

KL_THRU Header (HDU 4)

Keyword	Datatype	Example Value	Description
XTENSION	str	IMAGE	Image extension
BITPIX	int	-64	array data type
NAXIS	int	3	number of array dimensions
NAXIS1	int	2	Raw data axis 1 size
NAXIS2	int	2	Raw data axis 2 size for SCI frames (1200) or ENG frames (2200)
NAXIS3	int	2	Length of third array dimension (axis 3)
PCOUNT	int	0	number of parameters
GCOUNT	int	1	number of groups
UNITS	str	Separation: EXCAM pixels. K…
EXTNAME	str	KL_THRU	extension name
COMMENT	str	array of shape (N,n_seps,2)…

CT_THRU Header (HDU 5)

Keyword	Datatype	Example Value	Description
XTENSION	str	IMAGE	Image extension
BITPIX	int	-64	array data type
NAXIS	int	2	number of array dimensions
NAXIS1	int	2	Raw data axis 1 size
NAXIS2	int	2	Raw data axis 2 size for SCI frames (1200) or ENG frames (2200)
PCOUNT	int	0	number of parameters
GCOUNT	int	1	number of groups
UNITS	str	Separation: EXCAM pixels. C…
EXTNAME	str	CT_THRU	extension name
COMMENT	str	KLIP Throughput as a functi…