We describe the current state of the ground segment of Herschel-SPIRE photometer data processing, approximately
one year into the mission. The SPIRE photometer operates in two modes: scan mapping and chopped
point source photometry. For each mode, the basic analysis pipeline - which follows in reverse the effects from
the incidence of light on the telescope to the storage of samples from the detector electronics - is essentially
the same as described pre-launch. However, the calibration parameters and detailed numerical algorithms have
advanced due to the availability of commissioning and early science observations, resulting in reliable pipelines
which produce accurate and sensitive photometry and maps at 250, 350, and 500 μm with minimal residual
artifacts. We discuss some detailed aspects of the pipelines on the topics of: detection of cosmic ray glitches,
linearization of detector response, correction for focal plane temperature drift, subtraction of detector baselines
(offsets), absolute calibration, and basic map making. Several of these topics are still under study with the
promise of future enhancements to the pipelines.
Bolometers are very simple devices. In principle, the behaviour of a bolometer can be described by a simple model along
with a small number of parameters. The SPIRE instrument for the Herschel Space Observatory contains five arrays of
NTD germanium spiderweb bolometers containing up to 139 pixels. We show from characterisation measurements on the
ground using the flight read-out system that the bolometers follow the ideal model extremely well, are very stable, and that
the read-out system is sufficiently well behaved to take advantage of this. Calibration should be greatly simplified by being
able to take advantage of this behaviour.
We describe the on-board electronics chain and the on-ground data processing pipeline that will operate on data from the
Herschel-SPIRE photometer to produce calibrated astronomical products. Data from the three photometer arrays will be
conditioned and digitised by on-board electronics and sent to the ground with no further on-board data processing. On
the ground, the data pipeline will process the data from point source, jiggle-map, and scan-map observations in a fully
automatic manner, producing measured flux densities (for point source observations) or maps. It includes calculation of
the bolometer voltages from the raw telemetry, glitch removal, and corrections for various effects including time
constants associated with the detectors and electronics, electrical and optical crosstalk, detector temperature drifts, flatfielding,
and non-linear response of the bolometers to strong sources. Flux density calibration will be with respect to
standard astronomical sources with the planets Uranus and Neptune being adopted as the baseline primary standards.
The pipeline will compute estimated values of in-beam flux density for a standard flat νS(ν) source spectrum.
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'.
SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to be flown on ESA's Herschel Space Observatory. It contains a three-band submillimetre camera and an imaging Fourier transform spectrometer, and uses arrays of feedhorn-coupled bolometric detectors operating at a temperature of 300 mK. Detailed software simulators are being developed for the SPIRE photometer and spectrometer. The photometer simulator is based on an adaptable modular representation of the relevant instrument and telescope subsystems, and is designed to produce highly realistic science and housekeeping data timelines. It will be used for a variety of purposes, including instrument characterisation during ground testing and in orbit, testing and optimisation of operating modes and strategies, evaluation of data reduction software using simulated data streams (derived by "observing" a simulated sky intensity distribution with the simulator), observing time estimation, and diagnostics of instrument systematics. In this paper we present the current status of the photometer simulator and the future development and implementation strategy.