3 Scientific Endeavours and Achievements

The 3/4 channel sky monitor was essentially the same as used in the earlier 1990 study at Tent Island, but the data-logger now used a PC laptop driven from 12V external batteries and could run for a 12 hour period unattended. The computer control of the spectrometer had been substantially altered, and now was much more convenient to use, and could take sky page break spectra more quickly. A diffuse reflectance attachment had been made to allow measurements of the colour of sea-ice algae.

We joined Haskell and colleagues at the camp site near Tent Island, and with good weather we were able to establish our sky monitor and our polarisation spectrometer and start measurements immediately (October 23, 1992). The polarisation and sky light distribution showed very similar behaviour to that observed during 1990. The maximum polarisation in the sun-zenith plane in a direction 90° away from the sun reached 40%, which was the value observed in 1990 and contrasts with a typical value of 70-80% observed in New Zealand. The UVB levels were not enhanced, and this was consistent with the preliminary ozone levels recorded by Sylvia Nicol.

There was very tittle algae under the sea-ice at the Tent Island site at that time. It was clear that we would not be able to get sufficiently dense samples to reliably measure their colour in situ (the intention had been to study the colours and UV sensitivity without artihcial concentration), and this part of the programme was dropped.

We were able to accumulate sufficient sky data within 5 days, and with the improved data programmes we were able to analyse for preliminary results immediately. Bad weather then held up our move to Lake Vanda for 2 days, but we spent time continuing our data analysis and helping with the Haskell event.

We travelled to Lake Vanda by helicopter on 31 October. We spent a few hours opening the station. We were unable to get power from the local battery system (which hovered around 10V), and found the switches to the solar panels confusing- in no position did they appear to produce a charging current. We used our own generator and batteries.

We started our measurements during the evening of the first day there. The weather was very settled, showing the same pattern each day: fine clear skies during the evening and night, but very thin high cloud from mid morning to mid afternoon. On the 4 November the thin high cloud held off till noon so we were able to measure through the maximum of the sun's altitude. The preliminary analysis showed that the maximum sky polarisation was between 50 and 60%, which was substantially higher than at Tent Island, and this confirmed our hypothesis about the effects of the surface reflection (surface albedo).

The high walls of the Wright Valley restricted the north and south horizons and reduce the total intensity of sky tight falling onto the surface. We measured the horizon and will make corrections for this effect when we determine the total surface intensities. On the last day the helicopter stopped at Bull Pass for an hour around noon, and we took total intensity measurements there to compare with those at the Lake Vanda site. The horizon at the Bull Pass site was substantially lower.

page break

We returned to New Zealand earlier than we had planned. This shortening of the event was the result of the fine weather encountered at both sites. In all we only lost a couple of days due to cloud coverage.