CpFilterScanTask#

class lsst.cp.pipe.CpFilterScanTask(**kwargs)#

Bases: PipelineTask

Create filter scan from appropriate data.

This task constructs a filter scan from a sequence of flat exposures taken in the following manner:

  • A monochromator is set to a target wavelength.

  • An optional spectrum may be taken with the fiber spectrograph to provide an independent measure of the peak wavelength and bandpass.

  • A flat exposure is taken with a “reference filter,” usually a white-band or empty filter, that provides a baseline source brightness at the monochromator’s target wavelength.

  • A flat exposure is taken with the filter to be scanned.

  • Optional electrometer/photodiode data may also be taken during the two flat exposures to correct for source brightness variations.

From these pairs of exposures, we can determine the filter throughput by calculating the flux per second with the filter: \(F_filter(\lambda0) = median(f_amplifiers) / t_exposure\) And without: \(F_reference(\lambda0) = median(f_amplifiers) / t_exposure\) where the f_amplifiers are the per-amplifier statistics calculated by IsrTask. If the illumination source was perfectly stable, the filter throughput at that wavelength would simply be: \(throughput_raw(\lambda0) = F_filter / F_reference\)

We can correct for any illumination changes with the optional the electrometer measurements, E, which provide an independent measure of the incident flux for the two exposures, such that: \(throughput(\lambda0) = throughput_raw * E_reference / E_filter\)

Repeating this procedure at multiple monochromator settings builds up a catalog of throughput measurements across the filter bandpass. Additional differences can exist between the monochromator setting (retrieved here from the EFD) and the actual wavelengths of light that are permitted, so a matching CpMonochromatorScan can be generated to determine what the actual values of \(\lambda0\) observed were.

Methods Summary

run(inputExpHandles[, inputElectrometerHandles])

Construct filter scan from the header and visit info of processed exposures.

Methods Documentation

run(inputExpHandles, inputElectrometerHandles=None)#

Construct filter scan from the header and visit info of processed exposures.

Parameters#

inputExpHandleslist [lsst.daf.butler.DeferredDatasetHandle]

Input list of exposure handles to combine.

inputElectrometerHandleslist [lsst.daf.butler.DeferredDatasetHandle], optional # noqa W505

Input list of electrometer/photodiode measurement handles to combine.

Returns#

resultslsst.pipe.base.Struct

The results struct containing:

outputData

Final combined filter scan, with a single table containing the measured throughput for all input filters at the various wavelength values indicated in the exposure’s observationReason (astropy.table.Table).