Date of Award:

5-1995

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Electrical and Computer Engineering

Committee Chair(s)

Kay D. Baker

Committee

Kay D. Baker

Committee

Doran J. Baker

Committee

Ronney D. Harris

Committee

John C. Kemp

Committee

Frank J. Redd

Abstract

The electron density of the ionosphere can be measured using rocket-borne probes that measure changes of the impedance of an antenna as it traverses the plasma. The resistive component of the antenna impedance is difficult to measure accurately in the D region of the ionosphere (50-90 km) because it has such a small value and is in series with a much larger capacitive reactance. The resistance term is squared during data analysis and this further adds to the inaccuracy. Previous data analysis has usually ignored the resistive term and led to errors of as much as 35% for the altitude range of 70 to 90 km with larger errors below 70 km.

The objective of this work was to find ways to improve the accuracy of electron density measurements and extend them to lower portions of the D region. The investigation shows that this can be done in three ways: (1) by improving the data analysis with a more complete model for the impedance of an antenna in a plasma, (2) by using improved electronic circuitry, and (3) by modifying the mechanical payload configuration.

To use the improved model for antenna impedance, estimates for the earth's magnetic field, electron temperature, and electron collisional frequency are entered and then an iterative process is used to the reduce errors caused by inaccuracy in these estimates. This technique converges after twelve iterations to values of electron density that are within 1% of the values for the model used.

The electronic circuitry is improved by a new digital superheterodyne circuit, utilizing modern integrated circuits, that gives better separation of the antenna resistance and reactance measurements.

To take advantage of the improved data analysis it is necessary to modify the mechanical configuration to reduce the wake effects from the body by guarding them out of the measurements.

Use of these combined modifications should improve the accuracy so that the total errors are less than 10% for an altitude range of 70 to 90 km for quiet day conditions and down to 60 km for a strong polar cap or auroral absorption event.

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