Physics based calibration of the Herschel/SPIRE bolometers

Abstract

The bolometers (and readout circuitry) in the SPIRE instrument on the Herschel Space Observatory are among the best understood and well characterised of any sub‐mm astronomy instrument to date. SPIRE contains five arrays of NTD germanium spiderweb bolometers with up to 139 pixels per array. Their behaviour has been shown to be extremely stable as seen by repeated measurements in the years between initial array level and final instrument level tests, and can be described extremely well by a simple physical model (the ideal bolometer model). Calibration of the bolometers must take into account the non‐linear response when viewing bright sources, and the effect of fluctuations in the heat sink temperature. The simple and well‐understood behaviour of the detectors, coupled with the stable conditions expected in flight, mean that in contrast to previous sub‐mm instruments, physical models can be used to improve or possibly replace empirical calibration methods. We describe how this can be done, and use the large amount of data from ground measurements to show that we can use models to accurately calculate the absolute power detected by the bolometers.

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