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6.5 Data collection
For each ice station, photographs were taken and the following were manually noted: a. The ice station number;
b. Date of data collection;
c. Time (UT) that data collection commenced;
d. Weather conditions (cloud amount, sun, wind, snow, etc.), general ice and snow conditions. (More detailed information is available from meteorological records maintained on RSV Aurora Australis);
e. Ice thickness at the measurement site; f. Depth of snow at the measurement site;
g. It was noted if any biology groups were working near the UV work site and if so, at what distance;
h. Access® database file number that contained the measurements of UV radiation (at 1 Hz for a minute) across wavelengths 305-395 and PAR, both at the surface and beneath the ice plus snow and then beneath ice only; and
i. Any problems encountered.
The PUV system was set up as described below (Figure 6.2 is a photograph of typical measurement site set up). The deckbox and computer (which was sitting on a heated wheat bag) were placed on a small table positioned next to the study site. The table and equipment were shielded with an insulated blanket to minimise the effect of extreme cold and wind-blown snow on the operation of the computer. When the measurement process was to be initiated, the operator of the computer was able to sit at the table and pull the insulated blanket over their head and back to prevent snow blowing in on the keyboard.
Despite these precautions, the computer failed after exposure at three ice stations. Measurements could not be made at ice station number 4. A replacement computer was sourced and assistance was obtained from the IT personnel onboard to install the PROFILER® software. There were also a further four ice stations at which the UV group did not take measurements – stations 7 and 12 were for biologists only; station 9 had very thick and deformed ice that was impenetrable by an auger; and the combination of strong wind, blowing snow and thick ice with thick snow cover at station 11 determined that it was to be a lay-day for the UV group.
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Figure 6.2: Operation of the computer at an ice station. The operator sat at the table on which the deckbox and computer were placed. The table and equipment could be shielded with the blue insulated blanket to minimise the effect of extreme cold and wind-blown snow on the operation of the computer. The PUV-2510 was set up on a tripod close to the study site (right hand side of Figure 6.1b and left hand side of Figures 6.2 and 6.3). The PUV-2500 was attached to one end of a folding ‘Z’ frame – a hinged metal pole (see Figure 6.5 – being fed into hole in ice). Cables connected both sensors to computer.
Figure 6.3: Researchers removing snow after ‘with-snow measurements’ completed. The radius of the snow-free circle had to be at least twice the thickness of the ice.
The following protocol was followed when taking measurements:
1. With the best possible site chosen (a snow-covered area not yet trampled and sea ice less than a metre thick), an auger was used to drill a 35-cm diameter hole (see Figure 6.3 – centre of photo) through which to pass the submersible sensor. At this point, the thickness of the ice plus snow was measured. It was the thickness of the ice that determined the circumference of the area from which snow should be removed after the first ‘with-snow’ measurements were completed. The radius of
Chapter 6 – SIPEX voyage
the snow-cleared circle (with the sub-ice sensor position at the centre) was at least twice the thickness of the ice (see Figure 6.4).
Figure 6.4: Operation of the ‘Z’ frame – pulling down on the upper arm of the frame caused the lower arm to lift into a position horizontal to the under surface of the ice.
2. A lightproof cap was placed over the sensors (PUV-2500 and PUV-2510) and the PROFILER® software was run for a minute to facilitate ‘dark corrections’.
3. The caps were removed and the ‘Z’ frame, with PUV-2500 attached, was passed vertically through the hole in the ice to the point where the lower end of the middle section of the ‘Z’ was at the bottom edge of the hole (Figures 6.4 and 6.5).
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4. The upper-most ‘arm’ of the ‘Z’ frame was levered down towards the surface of the ice (preferably by a tall second assistant! – see Figure 6.6), thus causing the ‘arm’ under the ice to be lifted into a horizontal position just under the ice via a pulley system (see Figure 6.4).
Figure 6.6: Takingmeasurements under snow-free area on right. A second suite of measurements were taken under the snow-free area behind the operators of the ‘Z’ frame.
5. With the sensor in place under the ice and snow (a horizontal distance of 2.4 m from the hole), the PROFILER® software was initiated and run for a minute to gather measurements of radiation passing through the ice plus snow. The sensor was then removed from the hole in the ice, a circle of the predetermined circumference was scribed in the snow, and a ‘ruler’ was inserted into the snow at a number of places (typically ~8) in this circle to determine an average snow depth for the area, which was noted in the record book at the site. The snow was then shovelled from the surface of the ice.
6. Once again the PUV-2500 sensor was inserted into the hole in the ice and positioned at the centre of the now snow-free circle. The PROFILER® software was initiated again, and run for a minute to determine levels of radiation passing through the ice only. The sensor’s equilibrium position was such that it was hanging perpendicular to the under surface of the ice, with the sensor facing up in the centre of the ‘reserved area of clean snow’ (see Figure 6.4 – bottom arm of folding frame extends to the right to the centre point of the snow-free ice). The photo in Figure 6.6 was taken at ice station number 13, where a second set of subsurface measurements were taken from the same hole, but in a different direction, under a different thickness of ice and snow.
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Figu re 6. 7 : Th is fi gu re re pr es en ts th e r ad ia tio n p at hs fo r e ac h o f t he m ea su re m en ts (i .e . i ce wi th s no w, i ce wi th ou t s no w a nd ic e- fre e wa te r.Chapter 6 – SIPEX voyage
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