NAME

absfity -- Smooth an FOS sensitivity curve.

USAGE

absfity table wave output

DESCRIPTION

This routine smooths the sensitivity curve created by the absseny task; smoothing is done by fitting a least squares cubic spline through the raw input data. The least squares spline has nodes either equally spaced in wavelength (specified by the nodes parameter) or unequally spaced (specified in the input table innodes). This task generates the output inverse sensitivity image required by the Routine Science Data Processing (RSDP) system.

PARAMETERS

table [file name]

Name of the input table that contains the raw sensitivity values. This table is normally generated by the absseny task. It has the following columns:

     'WAVELENGTH' - Wavelengths (real).
     'VALUE'      - Raw sensitivity values (real).

The WAVELENGTH column must be in ascending wavelength order.

wave [file name]

Image containing the wavelengths for which the output inverse sensitivity file is to be generated. This file must have the header keywords FCHNL, NCHNLS, OVERSCAN, and NXSTEPS; these keywords describe the X-pattern information for the output sensitivity file. This wavelength file is generated by calfos.

output = "absfity" [file name]

Name of the output file that will contain the inverse sensitivity image used by RSDP. The output image will have the same length as the input image wave.

(nodes = 10) [integer, min=3, max=30]

The number of equally spaced nodes to be used in the cubic spline fit. If the optional table innodes is specified, this parameter is ignored.

(append = yes) [boolean]

Append results to an existing table?

If append = yes, a single column called FIT, which contains the fitted sensitivity value at each wavelength, will be added to the input table. If append = no, a new table is created having the name specified by output.

(innodes = " ") [file name]

Name of an optional input table containing positions of the unequally spaced input nodes, specified in wavelength units. The only required column is WAVELENGTH. The table must have at least 3 rows (node positions) and no more than 30. Wavelengths must be in increasing order. If this parameter is not used (i.e., it is set to " "), then the nodes parameter is used, giving the number of equally spaced node positions.

(outnodes = "outnodes") [file name]

Name of the output table giving the cubic spline node values, in both wavelength and sensitivity. This table has the columns WAVELENGTH and VALUE.

(niter = 10) [integer, min=1, max=100]

The number of least squares iterations of the Levenberg-Marquardt method that are to be performed.

(template = "fos$templates/yinvtemplate.r2h") [file name]

Name of the input template image header used to construct the output inverse sensitivity image.

EXAMPLES

1. Compute the inverse sensitivity image using unsmoothed values in a table called abstab (which was created by absseny). Values will be computed for wavelengths in the input image wavein.c1h (produced by calfos).

	fo> absfity abstab wave.c1h out.hhh

If an examination of the fitted values added to the table abstab indicate that the fit was inadequate, then rerun the routine using either more or fewer node posititions (as required), for example:

	fo> absfity abstab wave.c1h out2.hhh nodes=15

BUGS

REFERENCES

Howard Bushouse, STSDAS

HELP

For assistance using this or any other tasks, please contact help@stsci.edu or call the help desk at 410-338-1082.

SEE ALSO

absseny