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Orbital Segments Option
GTRN allows you to average the geomagnetic transmission function over segments of orbits, as well as over the whole orbit. The TRP module provides the same capability for trapped proton spectra. In the current versions of these modules, these orbital segments are delineated by boundaries in McIlwain L. This capability may be particularly useful in making comparisons with on-orbit data. (The CRRES/MEP and CRUX experiments used such L-bands in analyzing their SEU rates.) This capability may also be useful in making decisions about when to carry out mission-critical operations.
If you choose this option, you must specify the lower bounds on the L-bins of interest. In general, the first lower bound should be set to zero, since McIlwain L values slightly less than one are occasionally encountered.
You may specify up to maximum of ten lower bounds. The lower bound of the next bin serves as the upper bound of the previous bin. The last L-bin will include all L values greater than or equal to the last lower-bound value you enter.
A separate GTRN output file / TRP output file is produced for each lower bound.
At small McIlwain L, the segment-averaged transmission function should be smaller than the whole-orbit-averaged transmission function. At large McIlwain L, the segment-averaged transmission function should be larger than the whole-orbit-averaged transmission function.
Note that this orbital segments option is not available with the pre-calculated transmission functions and pre-calculated trapped proton spectra, which are accumulated over the whole orbit, by definition.
Finally, some users prefer to bin their orbit segments according to geomagnetic cutoff rigidity. In the dipole-field model approximation, the vertical cutoff rigidity is related to McIlwain L by the simple formula:
Rcv = 14.5/L2
where the vertical cutoff (Rcv) is expressed in GV. Note that the coefficient "14.5" changes with time, as the Earth's magnetic field decays. For further information, see D.F. Smart and M.A. Shea, "The Change in the Geomagnetic Cutoffs Due to Changes in the Dipole Equivalent of the Earth's Magnetic Field", Proc. 23rd International Cosmic Ray Conference (Calgary) 3, 781-784 (1993).
