The Far-Infrared Surveyor (FIS) for AKARI*

The Far-Infrared Surveyor (FIS) is one of two focal-plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 $\mu \rm m$, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcminutes, and the pixel pitch matches the diffraction limit of the telescope. Derived point-spread functions (PSFs) from observations of asteroids are similar to those given by the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and the performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.