# Reference Files¶

The rscd correction step uses an RSCD reference file.

## RSCD Reference File¶

REFTYPE

RSCD

Data model

RSCDModel

The RSCD reference file contains coefficients used to compute the correction.

### Reference Selection Keywords for RSCD¶

CRDS selects appropriate RSCD references based on the following keywords. RSCD is not applicable for instruments not in the table. All keywords used for file selection are required.

Instrument

Keywords

MIRI

INSTRUME, DETECTOR, DATE-OBS, TIME-OBS

### Standard Keywords¶

The following table lists the keywords that are required to be present in all reference files. The first column gives the FITS keyword names. The second column gives the jwst data model name for each keyword, which is useful when using data models in creating and populating a new reference file. The third column gives the equivalent meta tag in ASDF reference file headers, which is the same as the name within the data model meta tree (second column).

FITS Keyword

Data Model Name

ASDF meta tag

AUTHOR

model.meta.author

author

DATAMODL

model.meta.model_type

model_type

DATE

model.meta.date

date

DESCRIP

model.meta.description

description

FILENAME

model.meta.filename

N/A

INSTRUME

model.meta.instrument.name

instrument: {name}

PEDIGREE

model.meta.pedigree

pedigree

REFTYPE

model.meta.reftype

reftype

TELESCOP

model.meta.telescope

telescope

USEAFTER

model.meta.useafter

useafter

NOTE: More information on standard required keywords can be found here: Standard Required Keywords

### Type Specific Keywords for RSCD¶

In addition to the standard reference file keywords listed above, the following keywords are required in RSCD reference files, because they are used as CRDS selectors (see Reference Selection Keywords for RSCD):

Keyword

Data Model Name

DETECTOR

model.meta.instrument.detector

### Reference File Format¶

RSCD reference files are FITS format, with 1 BINTABLE extension. The FITS primary HDU does not contain a data array. The BINTABLE extension uses the identifier EXTNAME = “RSCD” and the characteristics of the table columns are as follows:

Column name

Data type

Notes

subarray

char*13

FULL or subarray name

char*4

SLOW or FAST

rows

char*4

EVEN or ODD

tau

float32

e-folding time scale, in units of frames

ascale

float32

$$b{1}$$ in equation 2

pow

float32

$$b{2}$$ in equation 2

illum_zp

float32

$$illum_{zpt}$$ in equation 2.1

illum_slope

float32

$$illum_{slope}$$ in equation 2.1

illum2

float32

$$illum2$$ in equation 2.1

param3

float32

$$b{3}$$ in equation 2

crossopt

float32

$$Crossover Point$$ in equation 2.2

sat_zp

float32

$$sat_\text{zp}$$ in equation 3.1

sat_slope

float32

$$sat_\text{slope}$$ in equation 3.1

sat_2

float32

$$sat_2$$ in equation 3.1

sat_mzp

float32

$$sat_\text{mzp}$$ in equation 3

sat_rowterm

float32

$$evenrow_{corrections}$$ in equation 3.1

sat_scale

float32

$$scale_\text{sat}$$ in equation 3

The entries in the first 3 columns of the table are used as row selection criteria, matching the exposure properties and row type of the data. The remaining 14 columns contain the parameter values for the double-exponential correction function.

The general form of the correction to be added to the input data is:

corrected data = input data + dn_accumulated * scale * exp(-T / tau)  (Equation 1)


where:

• T is the time since the last group in the previous integration

• tau is the exponential time constant found in the RSCD table

• dn_accumulated is the DN level that was accumulated for the pixel from the previous integration.

In cases where the last integration does not saturate, the $$scale$$ term in equation 1 is determined according to:

$$scale = b{1}* [Counts{2}^{b{2}} * [1/exp(Counts{2}/b{3}) -1 ]\; \; (Equation \; 2)$$

The following two additional equations are used in Equation 2:

$$b{1} = ascale * (illum_{zpt} + illum_{slope}*N + illum2* N^2) \; \; (Equation \; 2.1)$$

$$Counts{2} = Final \, DN \, in \, the \, last \, group \, in \; the \, previous \, integration \, - Crossover \, Point \; \; (Equation \; 2.2)$$

where:

• N in equation 2.1 is the number of groups per integration

• Crossover Point in equation 2.2 is column CROSSOPT in the RSCD table.

If the previous integration saturates, $$scale$$ is no longer calculated using equations 2 - 2.2. Instead it is calculated using equations 3 and 3.1:

$$scale_\text{sat} = slope * Counts{3} + sat_\text{mzp} \; \; (Equation \; 3)$$

$$slope = sat_{zp} + sat_{slope} * N + sat_2*N^2 + evenrow_{corrections} \; \; (Equation \; 3.1)$$

where:

• $$Counts{3}$$ is an estimate of what the last group in the previous integration would have been if saturation did not exist

• $$scale_\text{sat}$$ is sat_scale in the RSCD table

• $$sat_\text{mzp}$$ is sat_mzp in the RSCD table

• $$sat_\text{zp}$$ is sat_zp in the RSCD table

• $$sat_\text{slope}$$ is sat_slope in the RSCD table

• $$sat_2$$ is sat2 in the RSCD table

• $$evenrow_{corrections}$$ is sat_rowterm in the RSCD table

• N is the number of groups per integration