K132 : Optical Properties of Sea Ice
New Zealand Antarctic Research Programme 1990/91
Antarctica New Zealand October-November 1990
1 AIMS OF EXPEDITION
The aim of Event K132 "Optical Properties of Sea Ice" was to monitor the changing optical properties of sea ice as the spring warming occurs. This was accomplished using two optical techniques. Firstly, we employed a technique developed by ourselves over recent years that measures the spatial spreading of light in sea ice, and thus determines, among other things, the transparency of sea ice to visible and UV light. Secondly, we employed a laser that emits a very short light pulse (3 nano sec long) to measure the temporal spreading of light in sea ice. This result gives us the distribution of path lengths for light in sea ice and allows us to predict the value of the backscattered and transmitted radiation fields. Because of the observed strong dependence of the optical properties on ice structure and its time dependence, it was important to be on the ice as early as possible.
The New Zealand pre-Antarctic planning phase of our expedition went well. At all times Antarctic Division staff were very helpful, in particular, the "sea ice" meeting in the Antarctic Division office at Christchurch before Tekapo was useful.
All our cargo arrived at Scott Base on time. Some of the boxes were damaged although the equipment they contained was in good condition.
R G Buckley, H J Trodahl, J Southon, V Homewood
5 PREPARATIONS FOR THE FIELD
We were met on arrival (October 12) at the ice runway by John Alexander and shortly after arriving at Scott Base had an event briefing with him. This was a useful and to the point working meeting that sorted out all our uncertainties. We also got a brief report on the ice conditions in the region in which we intended to work. We spent October 13 and 14 preparing to go into the field, testing equipment and being issued with field gear and food. On October 15 all members undertook the sea ice travel course, with V Homewood completing the full survival course (October 16 and October 17). R G Buckley, J H Trodahl and J Southon travelled by toboggan to the experimental site on October 16 and V Homewood on October 18. We were able to complete our initial optical measurements the night we arrived, October 16, which was one of the major achievements of this year's event. John Alexander and Eric Saxby were helpful in getting us away. Due to ice conditions at the transition in front of Scott Base, we had problems leaving the Base and had to travel via the ice shelf and Willy's field road.
6 - FIELD TRANSPORT
|(i)||Toboggan - worked well when required, issued with a box sledge and Tamworth sledge to take our gear out to experimental sites from the wannigan. Due to the length of our equipment, it has proved vital to have a Tamworth to transport it on the ice. The fixed bar on the Tamworth was also essential.|
|(ii)||Helicopter - the helicopter trip of 29 October was very successful. The weather was very good, sunny with no wind, and we were able to visit 3 different sites in McMurdo Sound. Two sites were similar to each other and a third near the ice edge on thin ice was somewhat different. We had no problems, the crew were very helpful and we got all that we intended done.|
7 EVENT DIARY
See Appendix A.
8 EVENT MAP
We were camped for the entire time of our event near Inaccessible Island.
We had very good weather for the first 10 days of our field programme which allowed us to obtain data very early in the season, ie on October 16. This is the earliest date on which we have ever collected data. After that there were a number of days where we were restricted to the wannigan.
10 FIELD EQUIPMENT
|(i)||All field clothing was found to be of a high standard. We also found that it is important that field personnel are issued with the older heavy jackets.|
|(ii)||In general, field equipment was of a high standard. Although we were issued with 2 box sledges it was not possible with them alone to transport our equipment to the experimental site. For this we required, and were issued with, a Tamworth and a box sledge. The Tamworth, due to its length, is essential for transporting our equipment between experimental sites in the vicinity of the wannigan.|
|(iii)||The members of the event felt that in general the Scott Base diet contained too much meat, although in all other respects the base and the field diet is good.|
|(iv)||We had two wannigans issued to us this year, NZ3 and NZ8. These proved to be essential for the success of this year's event. This is particularly true for NZ8. The experiment we undertook was technically demanding in that it required the operation page 5 in the field of a dye laser, high speed optical detector, oscilloscope and a computer. Without access to the dry warm atmosphere of NZ8 this experiment would not have been the success it was. We are grateful for the use of NZ8. I would like to point out the importance of not only the extra room, but also the access to a warm and dry space that is incompatible with NZ3 where we sleep and cook. NZ3 tends to be too wet to operate electronic equipment in.|
11 RADIO COMMUNICATIONS
|(i)||In general radio communications with Scott Base were good. However, we did have some problems with both of the radios issued. It would appear that the contact to the battery pack is failing and for reliable communications the battery had to be held up against the radio at all times, with some inconvenience.|
|(ii)||Radio sked times were set in a flexible way to suit both ourselves and Scott Base. However, Scott Base was not reliable in keeping the evening sked nor at times the morning one.|
12 ENVIRONMENTAL IMPACT
All waste was separated into burnable and non-burnable and returned to Scott Base. Human waste was disposed of in the sea ice as in earlier years.
We would like to thank DSIR Antarctic for logistic support, in particular John Alexander, Eric Saxby and Ron Rogers. Also we are grateful for support from the technical staff of DSIR Physical Sciences and Victoria University of Wellington.
APPENDIX A EVENT DIARY - K132, October 1990
|October 11 Thursday||Fly from Wellington to Christchurch, stay at Windsor Hotel|
|October 12 Friday||Fly to Scott Base from Christchurch, check that all the boxes have arrived in Antarctic.|
|October 13 Saturday||Begin to have issued field gear, check it and begin packing.|
|October 14 Sunday||Continue with checking of gear and issue of field gear.|
|October 15 Monday||Sea ice' travel course. Continue packing in the evening.|
|October 16 Tuesday||Travel to experimental site and set up tents. Had a number of problems in getting away due to pressure ridges around Scott Base. Had to go across the ice shelf. Camp set up between Tent and Inaccessible Islands. Perform transmission and backscattering measurements - a good data set collected in very good conditions during the evening. Site named 90A. Ice had about 30 mm of snow and was 1.9 m thick. Freeze in thermistor array. Some thermistors were found to be not working. Full survival course for Vanessa.|
|October 17 Wednesday||Weather not so good, no travel. Main part of camp arrived at midday, spent rest of the afternoon and evening setting up camp - no experiments. Slept in NZ8.|
|October 18 Thursday Transmission and backscattering experiments at 90A. Took a salinity ice core and temperature profile. Slept in NZ3. Vanessa arrived, general celebration throughout camp.|
|October 19 Friday||Try time resolved experiment, measure salinity. Time resolved experiment indicates that the sensitivity is on the low side and will have to look at short separations only. Can improve things however. Made measurements at two separations and spectra look different. There is a pick up problem from the RF of the laser. This varies from scan to scan. Need to do more careful experiments in good weather. Getting windy towards the end of the experiment. Did the first density experiment - gear worked well.|
|October 20 Saturday||Very windy but sunny. Filled in top of array with salt water/ice and undertook a calibration of the visible source. 5204 lock-in failed! Finished with 220. Did a salinity and temperature core. Greenpeace and Helo called, both with fresh bread! Problems getting ice core out. Still windy and thus cold.page 7|
|October 21 Sunday||Cold wind. Measured transmission and backscattering at 90A in the morning. Measured density at 90A, reduced background in time experiment - detector out of box, used slower detector and covered it with aluminium foil to reduce pickup. This produced a 100-fold improvement.|
|October 22 Monday||Repeat salinity density and temperature measurements at 90B. A very good day, no wind. Tried the time resolved experiment with the new setup at 2 sites, 90B and 90C. 90B was a very milky site that had overflowed from the ice edge/crack. 90C was a snow free site of "normal" columnar ice in appearance. The experiment worked very well. The S/N was much better than on the October 19 RF pickup down and signal up - the big improvement. Detector was placed in a plastic bag. The data collected was very good. Observed a shift in the position of the peak to longer times with increasing separation. No change in tail. Greenpeace and surveyors came over in the evening. New loo hole cut and shifted into place.|
|October 23 Tuesday||Transmission at 90A both through snow and without on the wide detector. Clear that wide detector was used on October 21. Backscattering at both sites 90B and 90C. Vanessa and Joe went to Cape Evans/Scotts Hut. Seems clear that we do not have enough petrol to last the full time - 60 litre is about ½ our requirements. We will need more by the weekend. Should have enough 50:1 however.|
|October 24 Wednesday||Time resolved experiment at site 90C, looking at long collection times. Did salinity and density of full cores at 90C. Having trouble getting core up - still cold and windy −17°C.|
|October 25 Thursday||Did transmission and backscattering at site 90A and density and salinity at 90A. Did transmission at 90B also. JS made a really neat saw handle!|
|October 26 Friday||No work, snow and wind, wind drop in afternoon. Greenpeace leave for their trip. No work.|
|October 27 Saturday||Blowing snow all night, cold −14°C and 18 knots. Little chance of work.|
|October 28 Sunday||Still blowing snow, although not first time −15°C and 16 knots from the south at 11am.|
|October 29 Monday||Clear sky, temp −19°C. Very little wind. Helo trip on at 2pm. New loo hole. Helo trip went very well. Measured temp. salinity and ice depth at 3 sites in McMurdo Sound. Two in sound, and one near the ice edge. Very sunny.page 8|
|October 30 Tuesday||Overcast −15°C. Time resolved experiment at 90C. Density and salinity at 90A. Blowing snow and colder in mid-afternoon. Halo and glory appeared.|
|October 31 Wednesday||Blowing snow again as yesterday afternoon, −18°C good visibility however. Confirm that Joe T goes. Markus is expected for tea. Forecast is for no change in weather for a while. David B now expected on normal date.|
|November 1 Thursday||Transmission at site 90A. Time resolved at 90C. Salinity measured on core taken on 31 October at 90C. Joe T left at 7pm in ASV, parry of four came out! Mechanic tried to fix 15 kVA generator. Talked to Malcolm. Journalist from NZ Herald. Very good time resolved data including backgrounds. Joe S undertaking subtractions on time resolved data. Mail came. Restarted array measurements.|
|November 2 Friday||−18.5°C but 5 knots blowing. Ice crystals in sky so halo/glory was visible again. At least as good, if not better than on 30/10. Made a density measurement at 90A but core gave problems again poles to get it up. Penguin seen sliding on its belly moving slowly into a strong wind. Also took a salinity core. Analyse the density results. Site 90A appears to be changing but not 90C? Ice appears to be getting thicker and less dense at the surface - not apparent at C, could be understood in terms of growth at top with snow/ice. Site 90A has a lot of snow on it, could be as much as 80 mm and growing. Site C has snow on it but a lot less than 90A and it has not increased by the same fraction. Joe got subtractions going, looks very good. Continuing with array measurements again - a lot of snow on top. Measured density and salinity at 90A.|
|November 3 Saturday||Clear sky again −19°C, no wind, sunny, measured conductivity of samples collected 2 November. Set up time resolved experiment site 90C 2 hr scans and background (1) 400 mm; (2) 600 mm - should be able to look more closely at the tail; (3) 200 mm for 1.25 hrs only. Did salinity and density at 90C. Had time resolved system going from 9am~8pm. Climb Inaccessible Island after tea. Malcolm called to say we may need to leave Wednesday. Voltage on Victoria generator max at 220 V.|
|November 4 Sunday||Blowing snow −15°C, 15 knots. No work outside. Measured conductivity of core taken 3/11. Subtract files. Backscartering 90C. Tea with Markus, very nice. Recalculated all salinity with new standard.page 9|
|November 5 Monday||Time resolved at C all day, looking at small separations with high voltage resolutions. Transmission at 90A for last time. 12 volt supply gave out! Continued with battery. Used almost all the fuel for generators, ie, 2 × 60S, should get 3 × 60S in future. Temperatures on array continue to decrease. Ross and Ken arrived by ski-doo, David and Grant at 7pm. Did density and salinity at 90A. Need new saw.|
|November 6 Tuesday||Ken and Ross leave, day starts clear, but by midday wind and blowing snow. Did not work, packed up gear. Joe worked on data. Tim and Chris arrived. Stopped reading the array. Need screw drivers, hack-saws, longer metal files, ring spanners, more computers - generators to run in boxes.|
|November 7 Wednesday||Finished packing up last items. Weather deteriorated but John, Dave etc came out at about 3 and picked us up. Drove back to Scott Base in blowing snow and very poor visibility. Called Liz. Organising to leave. Talked to Ken and Ross about their experiment.|
|November 8 Thursday||Weather began poorly, but by 11am had come right. Nevertheless flight cancelled! Still preparing to go. Using Macintosh SE - very good - analyse some transmission data.|
|November 9 Friday||Bags to Hill Cargo. More analysis of transmission data - can see transmission decreasing. Fly to Christchurch, leave at 8.30pm.|
|November 10 Saturday||Arrive in Christchurch at 3.30am. Fly to Wellington at 10.45am.|