Wavelength calibration and spectral line bending determination of an imaging spectrometer

摘要

After alignment of an imaging spectrometer, the image of a special wavelength should in theory strictly meet with the design value and is focused on a certain column of the CCD focal plane. Since the imaging spectrometer is usually used in spatial or aerial environment, the optical components and the detector will departure from the regulated place and leads to focusing the image onto the deflected position of the focal plane in the spectral direction. Since the onboard readjustment of an inaccurate imaging spectrometer is usually unavailable, the equivalent task should be performed by certain post processing method. In this paper, we present a wavelength calibration method based on a fitting algorithm. Because of the linear diffraction feature of a grating, first order fit is adopted for the calibration. Using a standard mercury lamp as the light source during the calibration, the experimental imaging data collected from the whole CCD focal plane is used for the wavelength calibration to construct the actual wavelength distributing curve. Because of spectral line bending (smiling) of the imaging spectrometer, the wavelength calibration result of each row of the CCD plane differs so that a row-by-row calibration work should be carried out. The total row-by-row calibration result not only provides a full-scale and high-precision calibration effort, but also brings forward a smiling evaluation method for the whole imaging spectrometer. Using a standard Hg-Cd lamp as both the illuminating light source and the object, the spectroscopic image of the slit focusing onto the CCD focal plane of a calibrated imaging spectrometer is collected. In certain rows of the image, the center position of every spectral line is recorded. Through the comparison of recorded positions of different rows, the smiling of the calibrated imaging spectrometer is worked out, which meets with the design value.