CLUSTER EFW Electric Field in ISR2
Electric Field in ISR2 is obtained from
CAA C[1-4]_CP_EFW_L3_E
The EFW instrument measures the electric field only in the spacecraft
spin plane, therefore a spin-plane oriented coordinate system is best
suited for scientific studies involving the electric field. The ISR2
(Inverted Spin Reference) system, also known as DSI (Despun System
Inverted), is such a system. The X and Y axes are in the spin plane,
with X pointing as near sunward as possible and Y perpendicular to the
sunward direction, positive towards dusk. The Z-axis is along the
(negative) spacecraft spin axis, towards the north ecliptic. The
coordinate system is called “Inverted” because the actual spin axis of
Cluster is pointing towards the south ecliptic. The difference between
ISR2 (DSI) and the GSE (Geocentric Solar Ecliptic) is a tilt of 2° to 7°
of the Z-axis performed in order to avoid shading of the EFW probes by
the spacecraft.