Instantaneous prediction of ionospheric transmission circuits by the communication Zone Indicator ("COZI")

Detection of long-distance echoes by an oblique-incidence hf sounder with directive antenna provides a novel technique for predicting ionospheric transmission conditions to remote points. Measurements on oscilloscopic echo patterns can be correlated with (a) field strength of remote cw stations, (b) response of remote beacons synchronously triggered by the sounder, or (c) predictions based upon CRPL-Signal Corps world-wide contours of ionospheric layer heights and muf s. The results indicate that most of the echoes are due to energy backscattered at the earth, lonospherically reflected en route. Further, the transmission time (slant range) to the leading edge of the backscatter pattern measures reasonably well the skip distance (ground range) for long distances. Thus the backscatter echoes may be attributed to a ground area near and somewhat beyond skip distance to which communication is possible. A PPI echo display with a rotating directive antenna reveals in a striking manner the azimuthal variation of skip distance, giving at a glance the possible distant conmunication zones. Transmission modes, such as F-layer and sporadic-E layer reflections are readily discernible. Diurnal variation of the communication zones may be determined by comparing PPI photographs taken throughout the day. Results, recently declassified by the government, are given in a series of PPI photographs and corresponding azimuthal maps, commencing more than four years ago. Early equipment consisted of 20- kw peak power pulsers, with nominal lO0-microsecond pulse width and 20 per second repetition rate. Horizontal rhombics and multielement rotatable Yagi antennas were employed. Later, longer pulse widths up to 2 milliseconds and peak powers less than I kw were employed with results equally useful for many applications. Backscatter patterns have been observed on 9, 12, 16, and 22 mc. The first demonstration of the PPI technique is shown in a nighttime photograph taken at
S
. Dartmouth, Mass. on May 6, 1948 at 16 mc. A typical diurnal variation of PPI patterns is shown in a series of photographs taken at 15-minute intervals, at 22 mc, on January 19, 1950. Effect of different frequencies is shown in a series of PPI photographs taken at 12, 16, and 22 inc. F-layer and sporadic-E modes are noted. Suggested applications of the "COZI" technique includes assisting communication services in better circuit utilization, for implementing ionospheric prediction services, and as a new tool for ionospheric research.