Radio tomography based on satellite beacon experiment and FORMOSAT- 3/COSMIC radio occultation

Transcription

1 Radio tomography based on satellite beacon experiment and FORMOSAT- 3/COSMIC radio occultation Mamoru Yamamoto (1), Smitha V. Thampi (2), Charles Lin (3) (1) RISH, Kyoto University, Japan (2) Space Physics Laboratory, VSSC/ISRO, India (3) National Cheng Kung University, Tainan, Taiwan

2 Topics Digital receiver for satellite-ground beacon experiment Tomographic observation of the Ionospheric variability over Japan Comparison with FORMOSAT3/COSMIC (F3/C) Mid-latitude Summer Nighttime Anomaly (MSNA) observations in detail Recent expansion of the beacon receiver network

3 Radio beacon experiment of the ionosphere km height 1 pass duration = 10-15min Satellite including FORMOSAT-3 Shortest path Ionosphere Receiver on the ground Raidowave path VHF(150MHz)/UHF(400MHz) beacon signals are transmitted from satellite, and received on the ground. Radiowaves propagate through the Ionosphere that is dissipative media where refractive index is modulated owing to the local plasma density. Radiowave ray paths are then bended from the shortest path. The ray paths vary at different wave frequency. From close analysis of phase difference between two signals, we can estimate total electron content (TEC) between the satellite and the receiver.

4 GNU Radio and USRP Main component of GRBR LINUX PC GNU Radio Software toolkit for SDR (Software Defined Radio), a free software. USRP (Universal Software Radio Peripheral, see picture) A/D (64MHz) + signal processing board well associated with GNU Radio. Picture of USRP GNU Radio USRP

5 Block diagram of GRBR filter filter filter Signal processing on USRP board. A/D speed is 64 MHz. filter Yamamoto, EPS E-letter, filter filter Record complex time series of both 150 and 400 MHz data. Sound speaker. Signal processing in LINUX PC with GNU Radio under Python. Further tuning is done for multichannel experiment.

6 Comparison between ITS30S and GRBR at Shigaraki (daytime data) TEC estimates agree well. GRBR shows wider coverage than ITS30S.

7 Experiment GRBR network over E longitude * F3/C radio occultation Tomographic Reconstruction * Algorithm Algebraic Reconstruction Technique (ART) Initialization IRI 2007 model (Bilitza and Reinish,2008) Yamamoto, EPS, 2008 Thampi and Yamamoto, EPS, 2010 Ionosondes Wakkanai (45.16 N, E; 36.4 N magnetic) Kokubunji (35.71 N, E; 26.8 N magnetic) GPS- GEONET TEC NETWORK Observation Period July- August 2008

8 Tomographic observations EIA related enhancements More pronounced in the afternoon hours during summer MSNA has day-to-day variability in both intensity, and latitudinal extent MSNA (> 35 N geographic) Phase reversal in the diurnal variation of electron density EIA Equatorial Ionization Anomaly

9 60 o N 30 o N 0 o 30 o S 60 o S MSNA - Global Picture June Sols. 22 LT 12 LT x MSNA in the northern hemisphere -very prominent over Japanese sector 180 o W 120 o W 60 o W 0 o 60 o E 120 o E 180 o W Dec. Sols. 22 LT 12 LT 60 o N 30 o N 0 o 30 o S 60 o S 180 o W 120 o W 60 o W 0 o 60 o E 120 o E 180 o W 3 x Global maps of MSNA and Weddell Sea Anomaly F3/C data Lin et al., JGR, 2009 DMSP data Horvath and Lovell, JGR, 2009 CHAMP data Liu et al., JGR, 2010 Liu et al, JGR, 2010 Weddell Sea Anomaly

10 Tomographic observations F3/C observations Thampi et al, Radio Sci., 2011 (in press)

11 Comparison Tomography and F3/C At 28 N, apart from this difference in the time of the diurnal maximum, F3/C observations agree with tomography reasonably well. At 40 N, the decrease in electron density from 2000LT to 2200LT is more in the F3/C data than in tomography, but both measurements show that density at 2000LT and 2200LT are greater than the daytime values. In general, the comparison is good above ~250 km. Thampi et al, Radio Sci., 2011 (in press)

12 More about MSNA generation from Tomography There is an additional accumulation of ionization at the same altitude at latitudes >~36 N, which in the evening hours, close to and after the F-region sunset, which can be understood as a consequence of the windinduced lifting of the ionosphere MSNA is absent at lower altitudes hmf2 changes from 225 km at 14 LT to 275 km at 20 LT -can be due to the equatorward winds operating at night Equatorward winds in the geomagnetic frame the major factor causing MSNA Thampi et al, Radio Sci., 2011 (in press)

13 Bahir Dar, Ethiopia (~37deg. E) Observation network in Asia-Pacific+ Africa GRBR Running Planned (soon) (soon) (soon) Nairobi Kenya (~37deg. E) India group RISH/STEL/NICT SRI International SE Asia RISH: EAR. GRBR STEL:OMTIs NICT:SEALION Pacific SRI International: VHF radar, ionosonde, beacon receivers India MST radar, rocket experiment, beacon receivers Africa Recent installation of GRBR in Kenya and Ethiopia.

14 Example of Observation Schedule satellites COSMOS 2429 COSMIC FM5 (NG) COSMIC FM6 (NG) RADCAL DMSP F15 CNOFS OSCAR 25 OSCAR 23 COSMOS 2414 COSMOS 2407 Site: Bac Lieu (Vietnam), Date: April 10, 2010 Max EL > 30 deg. (for C/NOFS, EL > 20 deg.) Total 24 observations +200ppm +80ppm -80ppm -200ppm Multi-channel observation (-200ppm, -80ppm, +80ppm) Time (UT)

15 Summary TEC between satellite (incl. FORMOSAT-3) to the ground is measured by the digital beacon receiver GRBR. GRBR can receive simultaneous signals from many satellites. Flexible band selection is another benefit. Tomographic observations of the ionosphere over Japan are shown, and compared with F3/C radio occultation. They agree well, showing ability of the beacon tomography for the study of local phenomena. GRBR network is now rapidly expanded over Africa, Asia and Pacific for studies of the low-latitude ionosphere.

16 Acknowledgements The work of ST and HL is supported by the Japan Society for the Promotion of Science (JSPS) foundation. We thank NICT, Japan, for the ionosonde data, UCAR CDAAC ( TACC of Taiwan CWB for the F3/C data and NSPO operational team for the F3/C tri-band beacon experiment. Thank you

17 MSNA - more observations Monthly mean GPS- TEC in July shows that for latitudes >35 N, TEC values remain high up to 2300 LT, and there is a small reduction in TEC around 12 LT in July, and latitudinally the TECs are slightly higher near N than that at 30N during LT. Weaker signature in TEC compared to that in the electron density at 300 km MSNA is clearly seen in the fof2 values from Wakkanai in the May-Aug Period Thampi et al., JGR, 2009

18 MSNA : Ionosonde observations This increase in hmf2 before the F-region sunset has an important role in the formation of MSNA Using MU radar observations, it was shown that during summer nighttime of low solar activity period, the equatorwardwinds are greater than the HWM predicted winds by ~50 m s -1 [Kawamura et al, 2000] Equatorward winds in the geomagnetic frame the major factor causing MSNA

19 More about MSNA generation Weff = (Vcos D ±U sin D) cos (I) sin (I) Effective wind produced by zonal and meridional winds of 100 m/s at 60S and 50N. The solid lines represent nighttime situation when the wind directs eastward and equatorward, while dashed lines represent daytime situation when the wind direction reverses. Liu et al, JGR, 2009 (In press) The large declination at the WSA region makes the zonal wind contribution more effective, making the effective wind at SP (WSA) is 1.33 times of that in the northern hemisphere MSNA region. For the Northern hemisphere, the meridional wind and inclination plays the major role, since the Declination is small