Comparison of thermal plasma observations on SCATHA and GEOS

The SCATHA and GEOS 2 observations are compared in order to determine the relationship between the hidden ion population measured by SCATHA, and the missing density component of the GEOS particles detectors. Analysis shows that the wave instruments on GEOS measure the cold plasma population which is only visible to the SCATHA/UCSD detector in eclipse. Given a -28 V bias, the GEOS suprathermal plasma analyzers can also measure this plasma, at the cost of little or no energy resolution on the cold plasma. It is not clear if the missing component of the plasma found at apogee on GEOS-1 is identified.