Pulse Shaping for Time of Arrival Analysis at HAARP

The High-frequency Active Auroral Research Program (HAARP) is an HF transmitter which can, using amplitude modulated signals, produce very low frequency waves by modulating the conductivity of the ionosphere in the presence of electrojet currents. Time of arrival (TOA) analysis was developed to resolve the spatial distribution of electrojet currents in a multi-path propagation environment, and requires that the generated VLF wave have a changing frequency with respect to time. In this work, we explore the effect of pulse shape, length, and pointing direction of the heating beam on the received signal. Preliminary work assessed a set of six-second TOA pulses and suggested relations between pulse shape and amplitude of successive ionospheric reflections (IR) which were isolated by pointing direction. Now the ten-second pulses will be considered and assessed for the same relation. In addition, observed differences between the six and ten second pulses will be interpreted with the aid of magnetometer data to account for changes in electrojet and isolate the effects of the changing pulse length. Comparing these findings to established Stokes parameter ionospheric measurement techniques, findings can be correlated to discern their value as physical descriptors of the D-Region ionosphere.