Search

The Rockwell Collins SELSCAN adaptive high-frequency (HF) radio system, using an Air Force AN/ARC-190 transceiver, was operated over a 2615-km temperate latitude path for 24 hours. Propagation was monitored by an FMCW chirp oblique sounder. Voice and data transmissions were used to assess the quality of the selected channels. The SELSCAN always found a usable channel, and usually a very good one, even when propagation was limited to a small range of frequencies. A parallel effort to develop a test bed for experimentation with alternative probing waveforms is described. Results are incomplete because of difficulties with equipment and software. A theoretical analysis of probing waveforms for use with adaptive HF systems is presented. Finally, some recommendations are made for the application of adaptive HF. Keywords include: Adaptive High-Frequency Radio, HF Radio Communications, AHF, Oblique Ionograms, and SELSCAN.

This report describes the preliminary design of an automatic adaptive HF radio network for use in a post-nuclear environment. The radio features a multipath-resistive signaling waveform and a linking protocol that will enable an inexperienced operator to establish contact with any station in its network, provided that propagation support between the two stations exists. If propagation support does not exist on any of the assigned channels, the radio will continually cycle through all of its assigned channels until contact is established, or until the attempt is aborted. Thus, contact will be made as soon as propagation conditions permit. An adaptive radio system of the type described here will provide significant improvement over conventional HF communication systems in its linking protocol and its ability to adapt to changing propagation conditions. The radio is expected to be low in cost and highly portable so that it can be proliferated easily to provide emergency communications between users. The radio is not intended to be used for extended exchanges nor to be competitive with the sophisticated systems currently being considered for MEECN applications in the extremely hostile propagation and jamming environment that follows immediately after a nuclear attack.

A three-site television-aided tracking network was constructed and fielded for the STRESS series of barium releases. The real-time tracks of the barium-ion clouds were used to deduce the ground locations where the coverage of a communications satellite would be affected by the structured ionization in the clouds, so that an instrumented test aircraft could be vectored to these locations. Six releases were successfully tracked during the December 1976 through March 1977 test windows. The TV network acquired the barium-ion clouds as early as times corresponding to a 3 deg solar depression angle and maintained track until the sun set on the cloud 40 to 45 minutes later. The differences between cloud tracks generated by this television network and by an incoherent scatter radar that had also tracked the clouds could usually be ascribed to the two systems intentionally focusing on different regions of the amorphous ion cloud, and did not arise from inconsistencies in the tracking algorithms. Operating experience of the TV-tracking system showed that the most useful tracking procedure for experiments such as STRESS, though not necessarily the most accurate, was a single-site track that uses an empirical model for the cloud altitude after release. Projection of the second DIANNE rocket probe trajectory onto cloud photographs from various round stations showed that the rocket did not encounter the region of peak electron density in its passage through the cloud.

Anomalous radar returns seen on ionograms following ionospheric barium releases are analyzed to determine their origin and their interpretation. Two types of echoes are identified; one type originates from the barium cloud and the other type from layers formed by the descent of barium ions into the E-region. A review is made of sporadic-E literature because some of the explanations of the origin and reflection mechanisms proposed for sporadic-E appear to be applicable to barium echoes. Data from past barium releases were also reviewed to supplement the STRESS data base. The findings indicate that reflection from an overdense layer or target is not the cause of the barium-associated returns. Thus, the maximum frequencies of the returns cannot be interpreted as a maximum plasma frequency. Gradient reflection and scatter from weak or strong irregularities are both plausible mechanisms for both types of echoes. The characteristics of the E-region returns and their likely cause (compression due to wind shear) suggest that these layers are thin with sharp boundaries and a rough underside. (Author)

Ionospheric parameters obtained by the Chatanika radar during the ICECAP '73 launches are presented and discussed. For each of the four launch days considered (21, 22, 24, and 27 March 1973), the radar results have been compared and found consistent with measurements made with other sensors operating in support of ICECAP. Joule heating is found to be an important part of the auroral energy budget. The ratio of joule heating to particle energy flux obtained from photometric measurements range from a high of 0.67 on the 22 March 1973 launch to a low of 0.52 on the 27 March 1973 launch. Particle energy flux estimated from radar data is found to agree to within a factor of 2 with photometric results. During cloudy periods when optical observations cannot be made, the radar can provide backup to this type of measurements. (Author)

This report describes the TV tracking system, the slow-scan TV system, the KEL ionosonde, and the magnetometer that were operated in support of the PLACES experiment conducted at Eglin AFB, Florida in December 1980. A procedure for determining the proper launch time and aim point for both the beacon rockets and the probe rocket was developed after post-mission analysis of the first two releases. This procedure contributed to a successful beacon occultation for Event IRIS, and a successful probe penetration for Event JAN.