Abstract: | The Planck HFI spectral response was determined through a series of ground
based tests conducted with the HFI focal plane in a cryogenic environment prior
to launch. The main goal of the spectral transmission tests is to measure the
relative spectral response (including the level of out-of-band signal
rejection) of all HFI detectors to a known source of electromagnetic radiation
individually. This was determined by measuring the output of all detection
channels for radiation propagated through a continuously scanned polarizing
Fourier transform spectrometer. As there is no on-board spectrometer within
HFI, the ground-based spectral response experiments provide the definitive data
set for the relative spectral calibration of the HFI. The spectral response of
the HFI is used in Planck component separation and data analysis; this includes
extraction of CO emission observed within Planck bands, dust emission, Sunyaev
Zeldovich sources, and intensity to polarization leakage. The HFI spectral
response data have also been used to provide unit conversion and colour
correction analysis tools. While previous papers have already described the
pre-flight experiments conducted on the Planck HFI, this paper focuses on the
analysis of the pre-flight spectral response measurements and the derivation of
data products, e.g. band-average spectra, unit conversion coefficients, and
colour correction coefficients, all with related uncertainties. Verifications
of the HFI spectral response data are provided through comparisons with HFI
flight data. This validation includes use of HFI Zodiacal emission observations
to demonstrate out-of-band spectral signal rejection better than 10^8. The
accuracy of the HFI relative spectral response data is verified through
comparison of complementary bandpass based and flight-data based unit
conversion coefficients and colour correction coefficients. |