First Echoes from Radio Plasma Imager (RPI) on IMAGE Satellite – 23 Apr 2000
On 12 Apr prior to deployment of the 250m X and Y antenna wires, RPI was operated in Active Sounding, Relaxation Sounding, and Thermal Noise modes to obtain a system noise baseline measurement.

Figure 1 – Measurement Program 61 (Active Sounding) with antenna wires stowed.

Figure 2 – With antennas halfway out (125m) RPI transmits and receives the first plasmasphere radio echoes.

Figure 2 shows echoes rising out of a plasma resonance at 143kHz.Since the echoes are coming from the earthward direction, increasing range from the satellite means “lower altitude”.Stripes at the bottom are leakage of the transmitted pulse into the rcvrs, which is being sampled for timing purposes during IOC.The echo itself has an upper and lower “ghost” that

Figure 3 – The echoes increase in range as IMAGE rises away from the plasmasphere.

Figure 4 – IMAGE location during measurements
will also be removed in the future.About 7/8th of the way up the frequency scale, the lower “ghost” rises out of the transmitter pulse, so the “true” range to the plasmasphere echo is the middle of these three traces.143kHz is consistent with expected plasma resonances at the current position of IMAGE as shown in Fig 4, the center of the small green ball, where the plasmaspause and magnetopause shown (the light grey lines) are the intersection of each with the orbit plane.In Fig 3 as IMAGE rises away from the plasmasphere, the “triple” echoes increase in range.Also the local resonance has dropped to 70kHz due to lower plasma density.The very strong echoes at 600kHz are at the natural resonance frequency of the dipole antenna currently deployed which is 250m tip-to-tip.This indicates the signal strength we should have at all frequencies after antenna deployment is complete.Figure 4 shows the satellite location at 23:50 UT, the light grey lines indicate the predicted plasmapause and magnetopause locations as derived from a magnetosphere model developed at Goddard Space Flight Center.

RPI Team:

Univiversity of Massachusetts Lowell: PI: Bodo Reinisch, Mark Haines, Gary Sales, Ivan Galkin, George Cheney, Kevin Roche, Grigori Khmyrov, Klaus Bibl, Stephen Stelmash, Steven Myers, Jason Grochmal, Xequing Huang.

Goddard Space Flight Center:

James Green, William Taylor, Robert Benson, Shing Fung, Scott Boardsen
Rice University:Patricia Reiff
Stanford University:Donald Carpenter

Marshall Space Flight Center: Dennis Gallagher

Paris Observatory Meudon: Jean-Louis Bougeret, Robert Manning