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排序方式: 共有354条查询结果,搜索用时 15 毫秒
351.
Chris Pearson Tanya Lim Chris North George Bendo Luca Conversi Darren Dowell Matt Griffin Terry Jin Nicolas Laporte Andreas Papageorgiou Bernhard Schulz Dave Shupe Anthony J. Smith Kevin Xu 《Experimental Astronomy》2014,37(2):175-194
The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ~8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter. 相似文献
352.
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
353.
Bernhard Schlamadinger Benoit Bosquet Charlotte Streck Ian Noble Michael Dutschke Neil Bird 《Climate Policy》2013,13(2):199-208
Abstract The European Commission is mandated to consider the inclusion of credits from land-use projects under the clean development mechanism (CDM) and joint implementation (JI), beginning with the second period of the European Union's emission trading scheme (ETS) in its report due in July 2006. Temporary credits from afforestation and reforestation under the CDM are seen by many as posing a technical problem for their use under the ETS. This article summarizes three feasible, efficient and environmentally sound alternatives for achieving the integration of such temporary credits in the European emissions trading market starting in 2008. The first proposal integrates tCERs and lCERs (temporary credits) into the EU ETS by allowing for their direct use for compliance purposes. The second proposal builds on the idea of swapping temporary credits for EU allowances (EUAs) by Member States. The third proposal would not require a political decision at the EU level. Instead supportive Member States or private carbon fund operators would agree to swap temporary credits for the CERs or ERUs they hold in their accounts. All three solutions would be linked to a risk-mitigation strategy based on levying a fee or fixing an exchange rate, which would allow governments to hedge the risk of losing temporary credits. 相似文献
354.
Abstract This article collates definitions of some key terms commonly used in greenhouse gas reporting and accounting for the Land Use, Land-Use Change and Forestry (LULUCF) sector, and highlights areas of ambiguity and divergent interpretations of key concepts. It uses the example of harvested wood products to demonstrate the impact of different interpretations. The objective is to facilitate clear communication amongst negotiators and practitioners in relation to the terms emissions, removals, sources and sinks. Confusion and misunderstandings that have arisen in the past are rooted in diverging interpretations of the terms ‘emissions’ and ‘removals’ in the context of land use and wood products. One interpretation sees emissions and removals to be approximated by a change in carbon stocks in a number of selected carbon pools that may include or exclude harvested wood products. Another interpretation views emissions and removals as gross fluxes between the atmosphere and the land/wood products system. The various alternative approaches that have been proposed for reporting for harvested wood products are applicable to one or the other of these interpretations: the stock-change and production approaches, focused on stock changes, are applicable to the first interpretation; whereas the atmospheric flow and simple decay approaches focus on fluxes, as in the second interpretation. Whether emissions/removals are approximated by stock change or from gross fluxes, it is critical that a consistent approach is applied across the whole LULUCF/AFOLU sector. Approaches based on stock change are recommended over those based on fluxes. 相似文献