Physics – Space Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm41a1172g&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SM41A-1172
Physics
Space Physics
2794 Instruments And Techniques, 7894 Instruments And Techniques, 7984 Space Radiation Environment
Scientific paper
Since Aug 2001 a Compact Environmental Anomaly Sensor (CEASE) has been operating aboard a Department of Defense (DoD) geosynchronous satellite, providing nearly continuous measurements of energetic electron and proton flux in geosynchronous orbit. CEASE is designed principally as a real-time operational tool for operators and engineers managing spacecraft in the hostile space radiation environment, with a resulting heavy emphasis on miniaturization and minimal telemetry and commanding capability. However, the instrument's design and data processing scheme also allows for the extraction of scientifically useful information, such as differential energetic electron and proton spectra at temporal resolutions in principle as short as 5 seconds. Since CEASE's detectors respond simultaneously to protons and electrons, it is critical to understand each detector's separate response to electrons and protons over the full energy range experienced by the instrument in order to be able to extract information such as differential energy spectra. By necessity, the CEASE detector geometry factors have been determined through numerical analysis using Monte Carlo-based radiation transport codes. CEASE's location in geosynchronous orbit, however, provides an opportunity to intercompare temporally coincident measurements made by other geosynchronous spacecraft such as the National Oceanic and Atmospheric Administration's Geosynchronous Operational Environmental Satellites (GOES) series. A comparison was made between one of the CEASE dosimeter channels--labeled DD2HFB--and GOES-8 and -11-derived integral proton flux. Previous modeling results show the DD2HFB channel to be essentially insensitive to electrons and to respond to protons over an effective range of 38-53 MeV Since contributions from galactic cosmic rays are removed from the GOES data, it is necessary to apply a similar correction to the CEASE data. An empirical relationship was determined between the background DD2HFB GCR count rate and the Climax ground neutron monitor count rate. The daily-averaged neutron monitor count rate obtained from Space Physics Data System was then used with this function to compute a daily GCR correction. The daily-averaged GOES 38-53 MeV proton flux was computed from the corresponding >30, >50, and >60 MeV integral flux values using a piecewise power-law fit. An excellent linear correlation was found between the corrected CEASE DD2HFB count rate and GOES 38-53 MeV flux, with a degree of freedom adjusted coefficient of determination (DOF r2) of 0.99. The correlation results in an effective geometric factor of 0.92 cm2-sr, approximately 60% larger than the value previously determined for this dosimeter channel through modeling. The cause for this difference is not yet understood, although one possibility is the assumed effective energy range of proton response. Future work to characterize/verify this CEASE dosimeter geometry factor will use a variance minimization technique to determine the effective range of proton energy response as well as convolve the GOES integral proton spectra with the modeled proton response curve to compute the expected DD2HFB counting rate.
Golightly Michael J.
Knorring C. L.
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