RF Impedance Probe Measurements of Ionospheric Electron Densities

The Aerobee-Hi rocket , N ASA 4.07, obta ined vertical electron density profiles in the ionosphere simultaneously by the Seddon OW propagation technique and b y an RF imp edance probe technique. The experimental goal was to assess the performa nce of t he RF probe against t he accurate values from the O'vV method . In the RF probe method, t he electron density N was deri ved from the dielectric constant J{ of t he medium at a frequency / = 7.75 Mc/s. If t he ea rth 's magnetic fi eld is neglected, t he relation between these qua nt it ies may be given a s K = 1(SI N/f2) . An expression for t he dielectric constant including t he effects of t he eart h's magnetic fi eld is derived . The fractional error in t roduced by neglecting the ear th 's fi eld is of t he order of (fH// )' where / H is t he electron gyrofrequency. It was concluded t hat, with allowance for t he posi tive ion sheath around t he rocket, t he R F impeda nce probe can yield reliable values of electron density. These values were ob tained from cha nges in t he capacitive par t of t he probe's impedance. Small , apparent ly a nomalous changes in t he resist ive par t were also oLserved.