Wavelength Calibration

Wavelength calibration is currently supported for 1D spectra. Given a list of spectral lines with known wavelengths and estimated pixel positions on an input calibration spectrum, you can currently use specreduce to:

1. Fit an astropy model to the wavelength/pixel pairs to generate a spectral WCS solution for the dispersion.

2. Apply the generated spectral WCS to other Spectrum1D objects.

1D Wavelength Calibration

The WavelengthCalibration1D class can be used to fit a dispersion model to a list of line positions and wavelengths. Future development will implement catalogs of known lamp spectra for use in matching observed lines. In the example below, the line positions (pixel_centers) have already been extracted from lamp_spectrum:

import astropy.units as u
     from specreduce import WavelengthCalibration1D
     pixel_centers = [10, 22, 31, 43]
     wavelengths = [5340, 5410, 5476, 5543]*u.AA
     test_cal = WavelengthCalibration1D(lamp_spectrum, line_pixels=pixel_centers,
                                                                            line_wavelengths=wavelengths)
calibrated_spectrum = test_cal.apply_to_spectrum(science_spectrum)

The example above uses the default model (Linear1D) to fit the input spectral lines, and then applies the calculated WCS solution to a second spectrum (science_spectrum). Any other 1D astropy model can be provided as the input model parameter to the WavelengthCalibration1D. In the above example, the model fit and WCS construction is all done as part of the apply_to_spectrum() call, but you could also access the WCS object itself by calling:

test_cal.wcs

The calculated WCS is a cached property that will be cleared if the line_list, model, or input_spectrum properties are updated, since these will alter the calculated dispersion fit.

You can also provide the input pixel locations and wavelengths of the lines as an QTable with (at minimum) columns pixel_center and wavelength, using the matched_line_list input argument:

from astropy.table import QTable
pixels = [10, 20, 30, 40]*u.pix
wavelength = [5340, 5410, 5476, 5543]*u.AA
line_list = QTable([pixels, wavelength], names=["pixel_center", "wavelength"])
test_cal = WavelengthCalibration1D(lamp_spectrum, matched_line_list=line_list)