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Victoria University Antarctic Research Expedition Science and Logistics Reports 1981-82: VUWAE 26

Erebus Studies and IMESS (K4)

Erebus Studies and IMESS (K4).

NARRATIVE:

The field work began with a helicopter inspection of the telemetry transmitters by Stan Whitfield and Jon Prosser on 26 October 1981. At Hoopers Shoulder and Abbotts Peak, the equipment was working and intact, except for the guy wires on the antenna mast. The turnbuckles had unscrewed in the wind - sometimes completely. The Gel/cell batteries measured 14V, even when the solar panels were shielded from the sun. At the summit, the antenna cable was broken, and the ventilation pipe to the buried battery box was tilted ominously. The transmitter was not working. The protective polythene film had been stripped off the infrasonic microphone and the aperture was blocked with snow.

In the period 10-30 November, the USARP party serviced the Abbott and Hooper stations, retrieved and overhauled the summit transmitter, installed new permanent telemetry seismographs at "Bomb" and "Terror" (Fig. 1), and installed a temporary telemetry seismograph near Bird Hut for the purpose of recording the large seismic explosions fired in McMurdo Sound on 23 and 27 November by Lyle McGinnis. I assisted in recording the 23 November explosions before ascending to the fang with the Event 4 party on 24 November.

Between 28 November and 13 December, I operated a tape seismograph at the hut (from 1217 NZST, 29 Nov.); rebuilt the old infrasonic microphone, reinstalled it at the Winch Site, and connected it to the monitor speaker in the hut (from 2300 NZST, 30 Nov.); reinstalled the telemetry transmitter to give seismic recordings at Scott Base (from noon, 2 Dec); installed the new infrasonic microphone (consisting of 2 Philips 8 inch Hi Z speakers mounted on opposite sides of a 0.05m chipboard box and connected in parallel so as to reduce seismic response) on the main crater floor (3 Dec.); located and repaired 4 breaks in the loop and renewed 350m of damaged wire, and (with Pat Tinnelly) surveyed the position of the loop around the crater rim (5 Dec.); rebuilt the infrasonic preamp/VC (1020 Hz), and installed it, together with the new Geotech model 45.50/46.22 preamp/VCO (1360 Hz) for the loop, in the transmitter box at the summit (noon, 6 Dec.); and made trial electromagnetic transmissions from a 100W audio signal generator and portable loop from the edge of the summit plateau to the main loop (8 Dec.).

Problems encountered in carryout out the work were moisture damage to the old infrasonic microphone and the preamp/VCOs; the persistent drifting of the infrasonic VCO (1020 Hz) out of its frequency range due to an unexpected failure of the main battery; the tendency for the induction loop to become unburied and the insulation to crack off exposed wire; and the majority decision by the N.Z. party to leave the mountain earlier than planned as a combined group with the U.S. party. In fact the helicopter problem delayed this and we descended on 13 December.

The Japanese party were based at McMurdo for their entire period from 23 November to early January. They began by deploying their "DAR" slow speed tape seismographs on the flanks of Erebus. While these were recording (≧ 20 days), the party played back the telemetry tapes as they finished recording at Scott Base, and made continuous slow speed index recordings and high speed recordings of selected events on a visicorder. Photocopies were made for distribution to all collaborating scientists. All DAR seismographs page 17 were then retrieved for return to Japan. The Citizen quartz clock with the Sony UFR data recorder at Scott Base, which had hardly tolerated the ionosondes, was replaced with a new TCG-1000B clock made by the Eikura Transmitting Co. Also a 4 channel pen recorder was installed temporarily at Scott Base to allow real time monitoring of 4 telemetry channels in addition to the permanently installed San-ei Sokki monitoring recorder.

TRANSPORT:

All transport to and from Antarctica was by Hercules, and all transport within Antarctica was by helicopter. The latter was a major source of uncertainty in planning the expedition, because the helicopters were to be shared between Northern Victoria Land and the McMurdo area. It was believed that close support at the summit of Erebus, which had never been freely available, would be denied this year because it risked too large a proportion of the available aircraft. Consequently, the Japanese changed their plan from a wire telemetry seismic network on the summit plateau to a more flexible separate station network on the flanks of the volcano.

In the event, helicopters were withdrawn completely between 5 and 10 December due to serious faults which were at first thought to be unrepairable. The squadron deserves the highest possible recommendation for their fast solution to the problem, but the initial instructions to all NZARP parties to standby for immediate return to base, and the subsequent lack of definite information, resulted in stop-gap measures which could have been avoided.

WEATHER:

The weather was good except for a severe storm when the Event 4 party was at the Fang. No time was lost at the summit due to weather conditions, but an attempt to carry out the spear viscometer program in the final days at the summit was abandoned due to murk inside the crater.

COMMUNICATIONS:

Two VHF hand radios, a Compak, and a USARP radio provided excellent communications with Scott Base and Macsideband. The ability to communicate directly on VHF with the Science Lab at Scott Base at almost any time, and from almost any place (even the main crater floor) was especially valuable, and the expedition owes a lot to the Post Office and to Ross Mason. Less satisfactory was the dearth of information from Scott Base about the withdrawal of the helicopters.

EQUIPMENT:

Two of the three preamp/VCOs at the summit transmitter site were damaged beyond repair by corrosion. Because air temperatures were expected to fall below the operating limit of the electronics, both the transmitter and the VCOs were buried in warm ground. The VCOs were in a deeper reaching box however, the inside of which experienced copious condensation which penetrated the plastic freezer bags in which the 2 VCOs were sealed. The third VCO (1020 Hz) in both a bag and metal box was less affected, while the transmitter which remained below freezing point was undamaged. As only one new preamp/VCO was available, the recording of the level of audible sound in the crater was abandoned for 1982. The wooden cabinet of the old infrasonic microphone was badly split by moisture from the warm ground around it, although it had been sealed in polythene rubbish bags. The plastic was apparently stripped off by the weather.

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The main carbonaire battery (supplied by the Americans) may also have been affected by its burial in warm ground. Condensation in the ventilation pipe blocked it with ice, and some of the 30 cells which were only 1/3 discharged (as confirmed by the volume of zinc electrode remaining) inexplicably gave no voltage, and were discarded. When reconnected on 6 December, the remaining good cells gave 12V, but by 12 December they had fallen to 8V, forcing the complete replacement of the battery after we were supposed to have left the mountain.

The induction loop had become unburied over at least 350m of its length due to strong winds (which had also unwound the turnbuckles on the antenna guy wires). Where so exposed, the PVC insulation had cracked badly, and the wire had to be replaced and reburied. Until it is all reburied more deeply, this maintenance work will continue to be necessary in the future. If neglected, wind noise in the records and early breaks in the cable will soon render it useless.

RECOMMENDATIONS:

A determined attempt should be made next season to shift the ENE section of the induction loop (which tends to become unburied) to higher less steep ground, and bury it more deeply. Electro magnetic surveys of the summit plateau using the buried loop and a portable transmitting loop, which were proved feasible this season, should be given priority next season. The preamplifier/VCO in use for the infrasonic telemetry (1020 Hz) which proved intolerant of battery voltage fluctuations should be replaced with one similar to that in use with the loop.

Regarding the recording of the telemetry signals at Scott Base, it is noted that although the science technicians in 1981 were shown how to check the subcarrier frequencies, this was not done, and they are unable to say when the failures of the 1020, 1360 and 1700 Hz signals from the summit occurred during the year. Scott Base has since been provided with a simple tunable audio filter to make checking the subcarrier frequencies a routine matter.