Calibration of the AKARI far-infrared imaging Fourier-transform spectrometer

Abstract

The Far-Infrared Surveyor (FIS) onboard the AKARI satellite has a spectroscopic capability provided by a Fourier transform spectrometer (FIS-FTS). FIS-FTS is the first space-borne imaging FTS dedicated to far-infrared astronomical observations. We describe the calibration process of the FIS-FTS, and discuss its accuracy and reliability. The calibration is based on observational data of bright astronomical sources as well as two instrumental sources. We have compared the FIS-FTS spectra with the spectra obtained from the LongWavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO), having a similar spectral coverage. The present calibration method accurately reproduces the spectra of several solar system objects having a reliable spectral model. Under this condition the relative uncertainty of the calibration of the continuum is estimated to be ±?15% for SW, ±10% for 70- 85 cm-1 of LW, and ?20% for 60-70cm-1 of LW; and the absolute uncertainty is estimated to be +35%/-55% for SW, +35%/-55% for 70-85cm-1 of LW, and +40%/-60% for 60-70cm-1 of LW. These values have been confirmed by comparisons with theoretical models and previous observations by the ISO/ LWS. © 2010. Astronomical Society of Japan.