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diff --git a/noao/onedspec/doc/calibrate.hlp b/noao/onedspec/doc/calibrate.hlp new file mode 100644 index 00000000..cf68ac29 --- /dev/null +++ b/noao/onedspec/doc/calibrate.hlp @@ -0,0 +1,195 @@ +.help calibrate Mar93 noao.onedspec +.ih +NAME +calibrate -- Apply extinction corrections and flux calibrations +.ih +USAGE +calibrate input output [records] +.ih +PARAMETERS +.ls input +List of input spectra to be calibrated. When using record format +extensions the root names are specified, otherwise full image names +are used. +.le +.ls output +List of calibrated spectra. If no output list is specified or if the +output name is the same as the input name then the calibrated spectra +replace the input spectra. When using record format extensions the output +names consist of root names to which the appropriate record number +extension is added. The record number extension will be the same as the +input record number extension. The output spectra are coerced to have +real datatype pixels regardless of the pixel type. +.le +.ls records (imred.irs and imred.iids only) +The set of record number extensions to be applied to each input and output +root name when using record number extension format. The syntax consists +of comma separated numbers or ranges of numbers. A range consists of +two numbers separated by a hyphen. This parameter is not queried +when record number formats are not used. +.le +.ls extinct = yes +Apply extinction correction if a spectrum has not been previously +corrected? When applying an extinction correction, an extinction file +is required. +.le +.ls flux = yes +Apply a flux calibration if a spectrum has not been previously calibrated? +When applying a flux calibration, sensitivity spectra are required. +.le +.ls extinction = <no default> +Extinction file for the observation. Standard extinction files +are available in the "onedstds$" directory. +.le +.ls observatory = ")_.observatory" +Observatory at which the spectra were obtained if not specified in the +image header by the keyword OBSERVAT. The default is a redirection to the +package parameter of the same name. The observatory may be one of the +observatories in the observatory database, "observatory" to select the +observatory defined by the environment variable "observatory" or the +parameter \fBobservatory.observatory\fR, or "obspars" to select the current +parameters in the \fBobservatory\fR task. See \fBobservatory\fR for +additional information. +.le +.ls ignoreaps = no +Ignore aperture numbers and apply a single flux calibration to all +apertures? Normally multiaperture instruments have separate sensitivity +functions for each aperture while long slit or Fabry-Perot data use a +single sensitivity function where the apertures are to be ignored. The +sensitivity spectra are obtained by adding the aperture number as an +extension to the sensitivity spectrum root name. When apertures are +ignored the specified sensitivity spectrum name is used without adding an +extension and applied to all input apertures. +.le +.ls sensitivity = "sens" +The root name for the sensitivity spectra produced by \fBsensfunc\fR. +Normally with multiaperture instruments, \fBsensfunc\fR will produce a +spectrum appropriate to each aperture with an aperture number extension. +If the apertures are ignored (\fIignoreaps\fR = yes) then the sensitivity +spectrum specified is used for all apertures and no aperture number is +appended automatically. +.le +.ls fnu = no +The default calibration is into units of flux per unit wavelength (F-lambda). +If \fIfnu\fR = yes then the calibrated spectrum will be in units of +flux per unit frequency (F-nu). +.le +.ls airmass, exptime +If the airmass and exposure time are not in the header nor can they be +determined from other keywords in the header then these query parameters +are used to request the airmass and exposure time. The values are updated +in the input and output images. +.le +.ih +DESCRIPTION +The input spectra are corrected for extinction and calibrated to a flux +scale using sensitivity spectra produced by the task \fBsensfunc\fR. +One or both calibrations may be performed by selecting the appropriate +parameter flags. It is an error if no calibration is specified. Normally +the spectra should be extinction corrected if also flux calibrating. +The image header keywords DC-FLAG (or the dispersion type field in the +"multispec" world coordinate system), EX-FLAG, and CA-FLAG are checked for +dispersion solution (required), previous extinction correction, and +previous flux calibration. If previously calibrated the spectrum is +skipped and a new output image is not created. + +The input spectra are specified by a list of root names (when using record +extension format) or full image names. The output calibrated spectra may +replace the input spectra if no output spectra list is specified or if the +output name is the same as the input name. When using record number +extensions the output spectra will have the same extensions applied to the +root names as those used for the input spectra. + +When applying an extinction correction the AIRMASS keyword is sought. +If the keyword is not present then the airmass at the time defined +by the other header keywords is computed using the +latitude of the observatory and observation parameters in the image +header. The observatory is first determined from the image under the +keyword OBSERVAT. If absent the observatory specified by the task +parameter "observatory" is used. See \fBobservatory\fR for further +details of the observatory database. If the air mass cannot be +determined an error results. Currently a single airmass is used +and no correction for changing extinction during the observation is +made and adjustment to the middle of the exposure. The task +\fBsetairmass\fR provides a correction for the exposure time to compute +an effective air mass. Running this task before calibration is +recommended. + +If the airmass is not in the header and cannot be computed then +the user is queried for a value. The value entered is then +recorded in both the input and output image headers. Also if +the exposure time is not found then it is also queried and +recorded in the image headers. + +The extinction correction is given by the factor + + 10. ** (0.4 * airmass * extinction) + +where the extinction is the value interpolated from the specified +extinction file for the wavelength of each pixel. After extinction +correction the EX-FLAG is set to 0. + +When applying a flux calibration the spectra are divided by the +aperture sensitivity which is represented by a spectrum produced by +the task \fBsensfunc\fR. The sensitivity spectrum is in units of: + + 2.5 * Log10 [counts/sec/Ang / ergs/cm2/sec/Ang]. + +A new spectrum is created in "F-lambda" units - ergs/cm2/sec/Angstrom +or "F-nu" units - ergs/cm2/sec/Hz. The sensitivity must span the range of +wavelengths in the spectrum and interpolation is used if the wavelength +coordinates are not identical. If some pixels in the spectrum being +calibrated fall outside the wavelength range of the sensitivity function +spectrum a warning message giving the number of pixels outside the +range. In this case the sensitivity value for the nearest wavelength +in the sensitivity function is used. + +Multiaperture instruments typically have +a separate aperture sensitivity function for each aperture. The appropriate +sensitivity function for each input spectrum is selected based on the +spectrum's aperture by appending this number to the root sensitivity function +spectrum name. If the \fIignoreaps\fR flag is set, however, the aperture +number relation is ignored and the single sensitivity spectrum (without +extension) is applied. +.ih +EXAMPLES +1. To flux calibrates a series of spectra replacing the input spectra by +the calibrated spectra: + + cl> calibrate nite1 "" + +2. To only extinction correct echelle spectra: + + cl> calibrate ccd*.ec.imh new//ccd*.ec.imh flux- + +3. To flux calibrate a long slit spectrum: + +.nf + cl> dispaxis = 2 + cl> calibrate obj.imh fcobj.imh +.fi +.ih +REVISIONS +.ls CALIBRATE V2.10.3 +This task was revised to operate on 2D and 3D spatial spectra; i.e. long +slit and Fabry-Perot data cubes. This task now includes the functionality +previously found in \fBlongslit.extinction\fR and \fBlongslit.fluxcalib\fR. + +A query for the airmass and exposure time is now made if the information +is not in the header and cannot be computed from other header keywords. +.le +.ls CALIBRATE V2.10 +This task was revised to operate on nonlinear dispersion corrected spectra +and 3D images (the \fBapextract\fR "extras"). The aperture selection +parameter was eliminated (since the header structure does not allow mixing +calibrated and uncalibrated spectra) and the latitude parameter was +replaced by the observatory parameter. The observatory mechanism insures +that if the observatory latitude is needed for computing an airmass and the +observatory is specified in the image header the correct calibration will +be applied. The record format syntax is available in the \fBirs/iids\fR +packages. The output spectra are coerced to have real pixel datatype. +.le +.ih +SEE ALSO +setairmass, standard, sensfunc, observatory, continuum +.endhelp |