  The Spectral Energy Distribution (SED) mode of the Multiband Imaging
Photometer for Spitzer (MIPS) Space Telescope provides low-spectral resolution
(R ~ 15-25) spectroscopy in the far infrared using the MIPS 70 um detector. A
reflective grating provides a dispersion of 1.7 um per pixel, and an effective
wavelength coverage of 52.8--98.7 um over detector rows 1-27. The final 5
detector rows are contaminated by second-order diffracted light and are left
uncalibrated. The flux calibration is based on observations of MIPS calibration
stars with 70 um flux densities of 0.5--15 Jy. The point-source flux
calibration accuracy is estimated to be 10% or better down to about 0.5 Jy at
the blue end of the spectrum and to 2 Jy near the red end. With additional
uncertainties from the illumination and aperture corrections included, the
surface brightness calibration of extended sources is accurate to ~15%.
Repeatability of better than 5% is found for the SED mode through multiple
measurements of several calibration stars.
