Enter latitude and longitude for the location of interest. For latitude, the default is for positive values to refer to locations north of the equator and negative values for locations south of it. This can be reversed by selecting "S degrees" as the latitude unit. Similarly, the default for longitude is for positive values to refer to locations west of the equator and negative values to refer to locations east of the equator. Selecting "E degrees" will reverse this behavior. Longitude may be entered as a value from -180 to +359.99 degrees.
Enter either the elevation, barometric station pressure or the atmospheric depth of the location. Select the button to the left of the value that is entered to indicate which one should be used. The units for the entered value may be selected using buttons to the right of the value
Internally the elevation and barometric values are both converted to atmospheric depth in g/cm2. The model used to convert elevation to atmospheric pressure is an approximation. The conversion from pressure to depth is exact, however the proper pressure value is generally only available from a barometer located at the site. The "Station Pressure" is the mean, uncorrected barometer reading for a location. Values from the National Weather Service are generally corrected back to their equivalent value at sea-level and are unsuitable for this calculation.
The Solar Modulation parameter is used to account for the effect of sunspot activity on the neutron flux. For most calculations this effect is less than 10% of the total flux and the default 50% value is sufficient. This effect may be included in the calculation by entering a value between 0 and 100, signifying the percentage of modulation. A value of 0 is the minimum neutron flux, corresponding to an active sun period. The value of 100 is the maximum flux, corresponding to a quiet sun. Refer to JESD89B Annex A, page 61 for more information.
Pressing will validate the entered values and output the relative flux. The elevation, station pressure and atmospheric depth calculated from the input value and all of them are output. The Fa, Fb and Rc parameters (refer to JESD89B Annex A) are output for reference.
Values of geomagnetic vertical cutoff rigidity used to calculate the relative neutron flux
were provided by the U.S. Federal Aviation Administration Civil Aerospace Medical Institute, Protection and Survival Research Laboratory. The cutoff values were calculated by D. F. Smart and M. A. Shea using the International Geomagnetic Reference Field for 2010.
References
M. S. Gordon, P. Goldhagen, K. P. Rodbell, T. H. Zabel, H. H. K. Tang, J. M. Clem, and P. Bailey, "Measurement of the Flux and Energy Spectrum of Cosmic- Ray Induced Neutrons on the Ground," IEEE Transactions on Nuclear Science, vol. 51, no. 6, pp. 3427-3434, Dec. 2004.
J. Clem and L. Dorman, "Neutron monitor response functions," Space Sci. Rev., vol. 93, no. 1-2, pp. 335-363, 2000, and references therein.
A. Belov, A. Struminsky, and V. Yanke, "Neutron Monitor Response Functions for Galactic and Solar Cosmic Rays", 1999 ISSI Workshop on Cosmic Rays and Earth, poster presentation and personal communication, 1999.
D. F. Smart and M. A. Shea, "Final Report: Vertical Geomagnetic Cutoff Rigidities for Epoch 2010" and "Table from IGRF 2010 field," Appendices A and G in K. Copeland, CARI-7 Documentation: Geomagnetic Cutoff Rigidity Calculations and Tables for 1965-2010, Federal Aviation Administration Office of Aerospace Medicine Report DOT/FAA/AM-19/4 (2019).
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