IAP, the thermal plasma analyzer on DEMETER

The Instrument d’Analyse du Plasma (IAP) on board DEMETER provides a nearly continuous survey of the main parameters of the thermal ion population with two main objectives. The first one is to detect disturbances in the ionosphere that may arise from the coupling between seismic events on the ground and the upper atmosphere and ionosphere. The second objective is to provide with a sufficient time resolution the ionospheric parameters such as the plasma density and the ion composition that are needed to analyze the plasma wave data from the ICE and IMSC experiments. In addition the IAP observations will allow to build a large database that can be used in the frame of space weather studies, for example to analyze the dynamics of the mid-latitude ionosphere in response to magnetic storms. The instrument makes use of two analyzers to measure: (i) the energy distribution of the rammed ions and (ii) the direction of their bulk velocity. The basic principle of this well-known technique of measurement [Hanson, W.B., Heelis, R.A., 1975. Techniques for measuring bulk gas motions from satellites. Space Sci. Instrum. 1, 493–524] is recalled in Section 3 completed by a description of the analyzers with their associated electronics and of the modes of operation of the instrument. Following a brief presentation of the data analysis algorithm and its application to real data, some examples of observations made during the first months of operation of the satellite are displayed in the last section and illustrate the IAP capabilities.