Optimum observing modes for the Herschel/SPIRE photometer system

SPIRE is one of three instruments on board ESA's Herschel space observatory, due for launch in 2008. The instrument comprises both a photometer and Fourier transform spectrometer. The Herschel mission has a limited operational lifetime of 3.5 years and, as with all space-based facilities, has very high development and operational costs. As a result observing time is a valuable and limited resource, making efficiency of crucial importance. In this paper we present recent results derived from the SPIRE photometer simulator, detailing the optimum observing mode parameters to be employed by the Herschel/SPIRE system. We also outline the effiency of various modes, leading to the conclusion that scan mapping is the optimal mode for the mapping of regions greater than ~4' × 4'.