D. M. Haines

Ionospheric sounding in support of over‐the‐horizon radar

Precise coordinate registration for HF over-the-horizon (OTH) radar applications requires accurate knowledge of the ionospheric structure. In the mid-1980s Digisonde 256 systems were deployed in the American sector to provide this information from strategically located sites via telephone lines to the user. The mid-1990s saw the development of a new advanced system, the Digisonde portable sounder, or DPS, now being deployed in Australia in support of the Australian OTH radar system. A summary of the new features provided by the DPS is as follows: low radio frequency power (300 W); narrow transmission bandwidth; advanced automatic scaling; and control and data access via the Internet. The availability of real-time electron density profiles as function of time from a network of stations makes it possible to calculate the three-dimensional electron density distribution in the region of interest using Fourier transform techniques. The resulting density maps are the basis for the OTH radar coordinate registration. The DPS uses Doppler interferometry to determine the development of ionospheric irregularities.

First results from the Radio Plasma Imager on IMAGE

The Radio Plasma Imager (RPI) is a 3 kHz to 3 MHz radio sounder, incorporating modern digital processing techniques and long electronically-tuned antennas, that is flown to large radial distances into the high-latitude magnetosphere on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite. Clear echoes, similar to those observed by ionospheric topside sounders, are routinely observed from the polar-cap ionosphere by RPI even when IMAGE is located at geocentric distances up to approximately 5 Earth radii. Using an inversion technique, these echoes have been used to determine electron-density distributions from the polar-cap ionosphere to the location of the IMAGE satellite. Typical echoes from the plasmapause boundary, observed from outside the plasmasphere, are of a diffuse nature indicating persistently irregular structure. Echoes attributed to the cusp and the magnetopause have also been identified, those from the cusp have been identified more often and with greater confidence.

The feasibility of radio sounding in the magnetosphere

A radio sounder outside the plasmasphere could provide nearly continuous remote density measurements of the magnetopause and plasmasphere, as well as other important density features elsewhere in this region. Using digital integration and tuned reception at frequencies from a few kilohertz to a few megahertz with 400-m to 500-m tip-to-tip dipole antennas and 10 W transmitter power, such a sounder would be capable of 10% density resolution and 500 to 1300 km spatial resolution in only a few minutes at distances of up to 4 RE. By providing such detailed observations of its principal density structures, such a sounder would then clearly revolutionize magnetospheric research.

Radio sounding in space: magnetosphere and topside ionosphere

Abstract Modern sounding techniques have been developed for the space-borne exploration of Earths magnetosphere and topside ionosphere. Two new satellite instruments will use the advanced techniques of the ground-based Digisondes. The Radio Plasma Imager (RPI), a low-frequency sounder with 500-m dipole antennas designed to sweep from 3 kHz to 3 MHz, will be part of NASAs IMAGE mission to be launched in February 2000 into an elliptical orbit with an altitude at apogee of 7 R e . While in the magnetospheric cavity, RPI will receive echoes from the magnetopause and the plasmasphere and will measure the direct response of the magnetospheres configuration to changes in the solar wind. With three orthogonal dipole antennas (two 500-m tip-to-tip antennas in the spin plane used for transmission and reception, one 20-m antenna along the spin axis for reception only) the arrival angle of returning echoes can be determined with high accuracy. The other instrument is the TOPside Automated Sounder (TOPAS), which was originally conceived for the Ukrainian WARNING mission with a launch date in 2001. Using one antenna for transmission and three orthogonal 10-m antennas for reception, TOPAS will be able to determine the arrival angle of ionospheric echoes and their wave polarization. It will then be possible to automatically scale the topside ionograms and calculate the electron density profiles in real time. Operating as a high-frequency radar, TOPAS will for the first time measure topside plasma velocities by tracking the motions of plasma irregularities.

High latitude Digisonde measurements and their relevance to IRI

Abstract Digisondes operating at high latitudes provide new insights into the structure and dynamics of the polar cap and auroral ionosphere. These instruments derive the electron density profiles from vertical incidence ionograms, and the horizontal and vertical plasma velocities using the interferometric Doppler imaging drift technique. Multi-beam and polarization measurements in the ionogram unambiguously define the critical frequency of the E and F layers even in the presence of spread F and large scale patches. Occurrence of the patches is controlled by the configuration of the polar cap convection pattern which in turn is driven by the Bz and By components of the interplanetary magnetic field. To specify the UT and seasonal variations of the polar cap F region for IRI requires the knowledge of the prevailing convection pattern. This paper describes the applied techniques to measure profiles and drifts at high latitudes and the status of the analysis on polar cap patches and their transport across the polar cap.

The IMAGE mission and first observations from the radio plasma imager

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission is NASAs first satellite mission designed to image Earths magnetosphere using remote sensing techniques. Extreme and far ultraviolet (EUV, FUV), energetic neutral atom (ENA), and radio plasma (RPI) imagers are mapping the aurora, the helium ions of the plasmasphere, the plasma sheet and polar cusp, and the total plasma distribution from the ionosphere to the magnetopause. IMAGE was launched on 25 March 2000 into an elliptical polar orbit with an altitude of 7 R/sub E/ at apogee and 1000 km at perigee. First observations obtained by RPI in the sounding and relaxation mode are reported.