Computer Science – Performance
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsh31b..08k&link_type=abstract
American Geophysical Union, Spring Meeting 2009, abstract #SH31B-08
Computer Science
Performance
7554 X-Rays, Gamma Rays, And Neutrinos, 7924 Forecasting (2722)
Scientific paper
A potential in-flight calibration method for NOAA's Solar X-ray Imager (SXI), to be flown on the O-series Geostationary Operation Environmental Satellites (hereafter referred to as SXI-O), which uses the Crab nebula, is analyzed. Calculations of the Crab nebula's signal, Poisson noise and electronics noise are performed to determine the feasibility of future in-flight calibrations. Such calibration is necessary to aid in understanding instrument performance changes over time. Performance degradation is possible due to thin film filter failure, high voltage system changes, optical and detector contamination, and mechanism failures. Entrance filter and voltage system degradations have occurred on the SXI instrument on-board GOES-12, highlighting the need for accurate calibration techniques. Solar flares, which emit 1-8 angstrom X-rays, and subsequent solar phenomena, like coronal mass ejections, emit energy in the 6-60 angstrom X-ray range. This is also SXI-O's wavelength measurement requirement, and within the range of emission of one of the brightest astronomical X-ray sources, the Crab Nebula. Previous measurements of the Crab Nebula flux in the 6-60 angstrom range were made by the focal plane crystal spectrometer on the Einstein Observatory, and are used in this analysis. These signal and noise calculations integrate the wavelength dependant flux, taking into account components of SXI-O, which include the primary mirror, filters, detectors, and detector electronics. The sources of noise that are analyzed include the shot noise from the signal, the detector's dark current and charge transfer efficiency noise, the electronics read noise, and the quantization noise. The results of these analysis show that in-flight calibration of SXI-O using the Crab nebula is possible, and the longest single exposure of which the instrument is capable (65 sec) yields a signal to noise ratio somewhat insufficient to meet SXI-O's 20% photometric accuracy requirement. However, summing several 65 second images would increase the signal to noise ratio, making such a calibration readily possible.
Hill Steven M.
Klett K. K.
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