In-flight characterisation of Herschel-SPIRE optical performances

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel Space Observatory, launched in May 2009 and now orbiting L2. This long wavelength instrument covers 200 to 670 microns with a three band photometric camera and a two band imaging Fourier Transform Spectrometer. We discuss the in-band SPIRE optical performances as obtained from measurements made during in-orbit Commissioning and Performances Verification Phases. Complementary to the characterization of the instrument spectral characteristics, attention is focused here on a set of dedicated observations made of unresolved bright sky targets mainly obtained through the use of standard operating mode such as scan mapping. These tests were aimed at measuring the geometry of the respective Photometer and Spectrometer field-of-views as well as the spatial response of the end-to-end optical chain, from telescope to focal plane detectors in all spectral bands. Implications for instrument flight calibration parameters are reported. Finally comparison with model-based results from design & build expectations and previously reported ground-measured characteristics is given before concluding on the excellent state of the in-flight Herschel/SPIRE optical performances; one of the key factors in the realization of the full scientific potential of the Herschel observatory in the SPIRE spectral bands.