Mapping Near-Equatorial Particle Distributions to Higher Latitudes: Estimates of Accuracy and Sensitivity
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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Particle distributions measured near the magnetic equator are often mapped to higher latitudes to obtain estimates of global distributions. There are at least four sources of error in this mapping process 1 neglect of the electric field term in the equation of motion, 2 the adiabatic invariant approximation to the equation of motion solution, 3 the inaccuracies of magnetic field models used to map from a near-equatorial position to a lower altitude position along a magnetic field line, and, 4 the uncertainties generated by mapping measurements from an imperfect instrument. In the heart of the inner proton belt, the error is less than 10 for energies up to 10MeV, 15 for 100MeV, and 50 for 1 GeV. The error for electrons is less than 10 for energies from 10 keV to 100MeV for radial positions less than 2.5 Re, and less than 6 at the heart of the inner belt. These results indicate that in-situ flux measurements made by a near-equatorial satellite with arbitrarily high accuracy in energy and pitch angle could be used to create particle distribution functions at higher latitudes using standard mapping techniques with an error of order 105. The major limitation on both energy and angle measurement accuracy will be the contamination due to electrons and protons penetrating shielding, spreading in energy, and arriving at the detector at angles other than the nominal look angle.
- Atmospheric Physics