1. 1 Receiving Ground-based VLF Transmissions with RPI on IMAGE Bodo W. Reinisch Environmental, Earth, and Atmospheric Sciences Department Center for Atmospheric Research University of Massachusetts Lowell AFRL Hanscom AFB 19 December 2002

2. 2 IMAGE Spacecraft 500-m dipoles in spin plane 20-m dipole along z <10 W radiated power 3 kHz – 3 MHz 300 Hz bandwidth

3. 3 Cavity

4. 4 Overview of Radio Plasma Imager (RPI) RPI transmits coded EM waves and receives echoes at 3 kHz to 3 MHz –Uses advanced digital processing techniques (pulse compression & spectral integration) RPI uses a tri-axial orthogonal antenna system –500 meter tip-to-tip X and Y axis dipole antennas –20 meters tip-to-tip Z axis dipole antenna –X axis antennas are used for transmissions –Echo reception on all three Basic RPI measurements of an echo at a selected frequency –Amplitude –Time delay (distance or range from target) –Direction of arrival –Wave polarization (ordinary or extra-ordinary) –Doppler Spectrum In situ density and resonances measurements

5. 5 RPI Block Diagram

6. 6 Transmission with Tuned Antennas

7. 7 RPI Specifications

8. 8 Local plasma resonances X- mode echo trace Sounding in the Polar Cap S/C Z trace

9. 9 Field-Aligned Propagation Plasmagram [Reinisch et al., GRL, 4521, 2001] SX from southern HP NX from northern HP SX+NX double reflection Recalculated Echo traces Plasma resonances

10. 10 Empirical Magnetospheric Density Distribution Average 2000-2001 L = 7 6 5 June 2001 0800 LT March 2001 1200 LT

11. 11

12. 12

13. 13 05 Apr 2001

14. 14

15. 15 Seattle, NLK 24.8

16. 16 Seattle, NLK 24.8

17. 17 Seattle, NLK 24.8

18. 18 Maine, NAA 24.0

19. 19 Australia NSW 19.8 Maine NAA 24.0

20. 20 Backup

21. 21 Antenna Coordinates and Wave Polarizations

22. 22 Quadrature Samples

23. 23 The Wave Normal

24. 24 Wind – RPI

25. 25 Signal Transmitted by RPI Signal Received by WBD IMAGE to Cluster Radio Wave Transmission Experiment, 23 April 2002 Received Waveform with Fitted Pulse and Background Levels 04:44:3704:44:3904:44:4104:44:43 E (microvolts / m) -0.5 0.0 0.5 1.0 E (microvolts / m) -0.5 0.0 0.5 1.0 -1.5 1.5 SC2 Salsa SC3 Samba Spectrograms of Received Signal at Each Spacecraft 04:41:0004:41:30 04:42:00 04:42:30 04:43:00 04:43:30 04:44:0004:44:30 Ez Freq [kHz] 502 504 506 508 510 Ez Freq [kHz] 502 504 506 508 510 Ez Freq [kHz] 502 504 506 508 510 Ey Freq [kHz] 502 504 506 508 510 10 -16 10 -15 10 -14 10 -13 10 -16 10 -15 10 -14 10 -13 10 -16 10 -15 10 -14 10 -13 10 -16 10 -15 10 -14 10 -13 V 2 m -2 Hz -1 SC4 Tango SC3 Samba SC2 Salsa SC1 Rumba Relative positions roughly to scale University of Iowa Funding for this experiment provided by NASA

26. 26

27. 27 RPI Specs