Radio wave power distribution at HF frequencies as modelled for the Radio Receiver Instrument (RRI) on the epop satellite mission G. C. Hussey, R. G. Gillies, G. J. Sofko, and H. G. James SuperDARN Workshop 2011 30 May 3 June Dartmouth College, Hanover, New Hampshire, USA
Outline Introduction CASSIOPE-ePOP / RRI-SuperDARN experiment Magnetoionic theory Results Conclusions
The CASSIOPE epop satellite CAScade, Smallsat, and Ionospheric Polar Explorer satellite launch in late 2011??, 350 1500 km, elliptical, polar orbit 8 scientific instruments constitute enhanced Polar Outflow Probe (epop) mission Radio Receiver Instrument (RRI) will measure radio waves transmitted from ground-based radars such as SuperDARN
RRI-SuperDARN experiment
HF propagation in ionosphere Two Propagation modes (O- and X-modes) Quasi-longitudinal (QL) propagation: wave propagation roughly parallel to B-field modes have circular polarization states of opposite sense Quasi-transverse (QT) propagation: wave propagation roughly perpendicular to B-field modes have linear polarization states Between QL and QT propagation, two ellipses of opposite sense propagate
Magnetoionic Polarization States O Mode Polarization X Mode Polarization Resultant Polarization + = QL Propagation + = QT Propagation + = In Between QT and QL
SuperDARN Geometry Ray path through ionosphere Magnetic field lines lie in xz plane North x axis z axis West Initial electric field orientation (Transmitter location) East y axis South
Mode Power Modelling Upon entering the ionosphere, EM wave splits into the two allowed modes Initial polarization O mode X mode x axis y axis z axis External B field
X-mode Relative Power (Saskatoon SD, 12.5 MHz) N Boresight Magnetic North X-mode relative power (db) 40.0 30.0 W E 20.0 60 o 10.0 30 o Elevation Angle = 0 o 0.00 S
X-mode Relative Power (PrinceGeorge SD, 12.5 MHz) N Boresight Magnetic North X-mode relative power (db) 40.0 30.0 W E 20.0 60 o 10.0 30 o Elevation Angle = 0 o 0.00 S
Consequence for HF Propagation Modelling backscatter by SuperDARN is dominated by X-mode (QT) due to radar geometry: north viewing radar with horizontally polarized wave essentially QT X-mode ray path modelling may be better represented by X-mode as opposed to O-mode for transmitter frequencies near the plasma frequency: propagation and refractive index of modes can be significantly different choice of appropriate mode to model is important
Relative Power at RRI; altitude 1500 km; X = f 2 p /f 2 radar 25 20 Extraordinary Mode Relative Power (X > 0.3) f=14.5 MHz, N e =10 12 m -3, X=0.384 f=9.5 MHz, N e =5*10 11 m -3, X=0.447 f=12.5 MHz, N e =10 12 m -3, X=0.516 Relative Power (db) 15 10 5 0 0 20 40 60 80 Latitude Tx
Relative Power at RRI 25 20 Extraordinary Mode Relative Power (0.1 < X < 0.3) f=14.5 MHz, N e =5*10 11 m -3, X=0.192 f=12.5 MHz, N e =5*10 11 m -3, X=0.258 Relative Power (db) 15 10 5 0 0 20 40 60 80 Latitude Tx
Relative Power at RRI 25 20 Extraordinary Mode Relative Power (X < 0.1) f=14.5 MHz, N e =10 11 m -3, X=0.038 f=12.5 MHz, N e =10 11 m -3, X=0.051 f=9.5 MHz, N e =10 11 m -3, X=0.089 Relative Power (db) 15 10 5 0 0 20 40 60 80 Latitude Tx X mode only band
Conclusions relative power distribution between O- and X-modes of wave propagation were modelled for SuperDARN SuperDARN geometry results in X-mode polarization dominating the transmitted signal at low elevation angles where: radar waves propagate in QT regime backscatter is typically received by SuperDARN overhead and behind transmitter, propagation is mostly QL and the two modes have comparable power SuperDARN-RRI experiment will allow for a more detailed study of the scatter volume physics, as well as the large-scale ionospheric state