Herschel SPIRE fourier transform spectrometer: calibration of its bright-source mode     

Nanyao Lu  Edward T. Polehampton  Bruce M. Swinyard  Dominique Benielli  Trevor Fulton  Rosalind Hopwood  Peter Imhof  Tanya Lim  Nicola Marchili  David A. Naylor  Bernhard Schulz  Sunil Sidher  Ivan Valtchanov 《Experimental Astronomy》2014,37(2):239-252

The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two detector setting modes: (a) a nominal mode, which is optimized for observing moderately bright to faint astronomical targets, and (b) a bright-source mode recommended for sources significantly brighter than 500 Jy, within the SPIRE FTS bandwidth of 446.7–1544 GHz (or 194–671 microns in wavelength), which employs a reduced detector responsivity and out-of-phase analog signal amplifier/demodulator. We address in detail the calibration issues unique to the bright-source mode, describe the integration of the bright-mode data processing into the existing pipeline for the nominal mode, and show that the flux calibration accuracy of the bright-source mode is generally within 2 % of that of the nominal mode, and that the bright-source mode is 3 to 4 times less sensitive than the nominal mode.  相似文献   

Herschel SPIRE FTS spectral mapping calibration     

Dominique Benielli  Edward Polehampton  Rosalind Hopwood  Ana Belén Griñón Marín  Trevor Fulton  Peter Imhof  Tanya Lim  Nanyao Lu  Gibion Makiwa  Nicola Marchili  David Naylor  Locke Spencer  Bruce Swinyard  Ivan Valtchanov  Matthijs van der Wiel 《Experimental Astronomy》2014,37(2):357-367

The Herschel SPIRE Fourier transform spectrometer (FTS) performs spectral imaging in the 447–1546 GHz band. It can observe in three spatial sampling modes: sparse mode, with a single pointing on sky, or intermediate or full modes with 1 and 1/2 beam spacing, respectively. In this paper, we investigate the uncertainty and repeatability for fully sampled FTS mapping observations. The repeatability is characterised using nine observations of the Orion Bar. Metrics are derived based on the ratio of the measured intensity in each observation compared to that in the combined spectral cube from all observations. The mean relative deviation is determined to be within 2 %, and the pixel-by-pixel scatter is ～ 7 %. The scatter increases towards the edges of the maps. The uncertainty in the frequency scale is also studied, and the spread in the line centre velocity across the maps is found to be ～ 15 km s ^{? 1}. Other causes of uncertainty are also discussed including the effect of pointing and the additive uncertainty in the continuum.  相似文献   

Seasonal variability of rainfall extremes     

Trevor Dickinson 《大气与海洋》2013,51(4):288-296

Monthly rainfall extremes have been analyzed for three stations in Southern Ontario. The double exponential probability distribution was fitted to the extreme values for each month considered, each duration selected, and sets of annual extremes. A station‐year approach yielded monthly and annual extreme value distributions for the lumped region of Southern Ontario. The analysis has revealed a pronounced seasonal pattern in the rainfall extremes – the amount of rain expected with a selected probability of occurrence during the summer being considerably greater than the rainfall that might be expected to be exceeded at the same probability level during the spring or fall. The extent of the seasonal variability was found also to vary with duration. The implications of the variability are seen to be significant for the estimation of the magnitude and frequency of floods.  相似文献