A GPS-based method for pressure corrections to neutron monitor data

Abstract

Galactic cosmic rays are high-energy particles in the heliosphere. When entering the atmosphere of earth, they interact with the nuclei of air molecules, which then cascade down to the earth's surface. The nuclear active secondary particles of the cascade consist of protons and neutrons, and the amounts of these different species are dependent on the thickness of the atmosphere. Neutron monitors detect these nuclear active secondaries, and to normalise these counting rates from day to day requires accurate pressure measurements e.g. Krilger (2006). With a normal barometer, accurate pressure measurements can be obtained, but it has been found that when a strong wind blows, the pressure drops. According to Malan and Moraal (2002) this drop in pressure can be explained by the Bernoulli effect. The idea therefore is to make use of the latest technology, in this case the Global Positioning System (GPS), to correct for this environmental effect. GPS technology makes it possible to determine the column density of air above a certain area with high precision, but it is greatly affected by precipitable water vapour in the atmosphere e.g. Combrink (2003). The idea then is to determine a method for using the strong points of both sets of data, to find a possible data set in which both weather conditions (wind and humidity) are corrected for. If this is possible it will greatly increase the accuracy of neutron monitor data around the world.