Alert, 10 April, 2006
Received from Ron Verral and Trine Dahl-Jensen
Edited by Henrik Højmark Thomsen, GEUS
Action on the inner line, first data in the hand
7 April, 2006
Weather in Alert: -26, in the morning, sunny, no wind (mid afternoon -14)
The weather was perfect, and we started the work on the inner 200 km long line, stretching south-north from land and out in the Arctic Ocean. It is a complicated manoeuvre. First we shall load 11 shots equally distributed along the line. Following this we shall deploy 150 instruments on the ice, which shall record the signals from the blastings. These shall also be distributed equally along the 200 km long line. Then we shall do the blasting, one at a time with a proper time interval, and finally we shall recover all the instruments and fly them to Alert to download and save the data.
We started at the northern end of the line, where the helicopter could fuel and pick up explosives from the cache at the ice camp. The range of the helicopters is limited, when they are loaded with equipment, because they can not at the same time carry so much fuel.
The first team to go were the drilling team, who was drilling the holes in the ice and marking the positions with black garbage bags filled with snow. They show up quit well in the white landscape. The next to follow was the ferry team. They were bringing all the blasting equipment and were installing a beacon, which sends its position continuous to Alert. And finally the loading team took off to load the charges and leave the site ready for blasting. The work went well, and we succeed to load the charges at the six northernmost positions, which in local LORITA-slang are called IS6-11. I for inner line, S for shot and the number of the blasting position.
Meanwhile the Twin Otter went on a reconnaissance flight along the southern part of the line to search for a landing strip for a fuel and explosives cache to be used for the loading the next day. They found a suitable location and started soon after to ferry out fuel and explosives.
8 April, 2006
Weather in Alert: -29, in the morning, sunny, no wind
As of today we have midnight sun
Another perfect day. All three teams took off to the southerly fuel cache, and after fuelling and loading of the three helicopters, the teams continued the loading of charges at the last five positions at the southern end of the line. Again every thing went well and mid afternoon the explosives were ready at positions IS1-5. By that time the Twinn Otter had ferried out a load with instruments, and soon after the helicopters took off along the southern part of line with three teams installing the first instruments.
Each of the 150 instruments to be deployed on the ice is made up by a seismometer connected to batteries and a recording unit to store the data. The whole installation is in local slang called a “receiver” The recording unit and the batteries are not supposed to be cooled below – 20 degree, so they are placed in an insulated “cooler” to keep them warm. In a further effort to keep them warm, they are surrounded by six “icepacks” English needs a few new words; “cooler” and “icepacks” just do not have the right connotation for this job.
It was a long day, and the last helicopter arrived to Alert around 21. But it was a successful day. A total of 66 receivers had been installed on the southern part of the line. The receivers are spaced only about 1,3 km apart, so the helicopter has just nicely taken off when it has to land again.
During the day the Twin Otter took Morten Sølvsten and Arne Olesen out to the ice camp together with Jon Biggar from Canadian Hydrographic Service, where they should test their equipment before, they start the measurements of water depths and gravity along the seismic lines. Locally they are called the BG-team. B for bathymetry and G for Gravity. The test was successful, and Arne succeeded to install a GPS tidewater gauge on the ice, which will measure the changes in the elevations of the sea ice due to the tide. The tide movements create noise in the gravity measurements, and the data from the GPS-station should be used to filter this out. The three inhabitants in the ice camp are still doing well, and they are enjoying a life that is much more simple than life in Alert. But maybe it starts getting a bit too busy out there for their taste of life. The BG-team could report, that the three locals looked at least as happy when the team left as when they arrived. The drifting seismic station at the camp is now in operation.
9 April, 2006
Weather in Alert: -29, in the morning, sunny, wind, picked up in the evening
From the morning we knew that the weather, in the northern part of the line was going to be not so good. All three helicopters started out from Alert each with two man on board to start deploying the remaining 84 receivers. We planned to work as far north as we could reach and around noon the next 33 receivers where installed. Here we had to abort the activities due to low clods and fog on the ice, and on top of that the bad weather was moving south with increasing wind.
Now with two thirds of the receivers on the ice, we had to decide, if we wanted to wait on better weather to finish the deployment and get all the data, or we should start blasting on the southern part of the line with receivers and get some of the data. The forecast was for the bad weather to last several days. The predicted high winds could certainly cause the ice to move. And this could displace the shots and the receivers away from their intended positions, and the line might well end up in an area that was completely useless for the experiment. We decided to start the blasting, and we succeeded to detonate the six southernmost shots. And soon after we started to recover the receivers as far north as we could come. We recovered the first 57 receivers and ferried them back to Alert. We will watch the weather closely and retrieve the other 43 as soon as the weather permits.
As to the five undetonated shots, there are a couple of possibilities. If the ice does not move very much, we could use them on the outer – more northerly – line. If the ice does carry the charges away from the useful area, we will just detonate them to get rid of them. Remember that each shot location has a beacon on site. The beacon regularly sends its position to Alert, and we pick up that position on the web.
A few hours after the first load of receivers were back in Alert, Isa Asudeh had data off the first 25 instruments and we could see, that we have data in the can. Some of it has been plotted out for a quick look, ant it look very good. This called for a small celebration.
It has been a day spent in a race with incoming bad weather, and in this race there has been no clear winner. Although we do have data, we do not have as much, as we had planned.
10 April, 2006
Weather in Alert: -20, snow, light wind
Today has been a weather day – no flying. The whole day, we have been busy downloading the data from the instruments and making back ups. The weather forecast indicates that noon tomorrow will be the earliest, we can expect flying weather. The receivers out on the ice will just have to wait for us.