Fishery Bay, D.Shefi 12 Feb. 2006

Transcription

1 Fishery Bay, D.Shefi 12 Feb Flinders University Maritime Archaeology Field School Arch 8103 Mount Dutton Bay, Eyre Peninsula, South Australia 1-15 February 2006 Dianna Zwart

2 Table of contents 1 Introduction History Site Location Site description Equipment Methodology Downloading Magnetometer data Constraints Results Conclusion References

3 1 Introduction During the Maritime archaeology Field School every one had to do a personal project. My first idea was to do an underwater magnetometer survey, but the equipment was not working properly, so decided to do a land survey. It is basically the same and I wanted to learn how to use a magnetometer. This project was done at Fishery Bay. The rest of my team assisted me with my project. 2 History Fishery bay was used as a whaling station. They would drag the whale onto the rocks and cook the blubber of the whale into big pots to retrieve the oil. The actual whaling site with the try works was excavated in 2001 and parts of the try works and barrel hoops were found. About 300 meter further is a site where the whalers probably lived. Whaling was as seasonal activity and they only used this site for a short time. 3 Site Location The Sleaford bay Whaling station is in Fishery Bay. Fishery bay is located in Sleaford Bay. It is approximately 30km from Port Lincoln on the Eyre Peninsula (see Fig. 1). Position using the Australian map grid WGS 84 Position: Easting and Northing Fig. 1 Fishery Bay location on a map 3

4 4 Site description The site is situated close to the beach. The actual survey area was situated past the dunes in a sort of valley. It was surrounded by two clifs and the dunes (see fig. 2). The area was covered by bushes and the actual house sites were not visible anymore. Taking a closer look under the bushes the stones of the building could still be seen there. Fig. 2 Fishery Bay mud map and survey pattern 4

5 5 Equipment GPS Garmin Magnetometer Geometrix G-856 Tapemeasures Camera Nikon D70s Digital Portable radio 6 Methodology The first thing to do when conducting a mag survey is setting the parameters of the area to survey. In this case there were already three natural boundaries that could be used. Dunes on the south side, cliff on the north side and a cliff on the eastside. The western parameter was set parallel to the cliff and from the dunes a line to a distinctive stone on the other cliff. Normally you would take a grid spacing of 1m, but for this a spacing of 5m. was used. The reason for this was that the terrain was really rough and the GPS usually has an accuracy of 5m. This way you still have enough data for this area. The starting point was next to the dunes in the SW corner of the area. The first line to walk went parallel with the dunes to the East cliff. All the lines would run parallel to the dunes. After the first line would move over 5 meters to start with the next line. To maintain the 5 meter spacing between the lines a person would stand on the East cliff and another one at the opposite side. They had a tape measure to measure out the 5 meters. In Fig. 2 a survey pattern can be found. Fig. 3 Magnetometer track with person as marker on the cliff, D.Shefi, 12 Feb

6 Before starting with the survey the magnetometer had to be set. The first thing to do is to tune the magnetometer to the background magnetic intensity. The value for South Australia is 6000nT. Next step is to set the time and date. The time changes if you don t use the magnetometer for a while. You have to synchronize the time of the magnetometer and the GPS. The GPS retrieves the time from the satellite, so that is the correct time. During the survey you want to acquire the data automatically, so the next step is to set the GPS and Magnetometer. For this survey an interval of 5 seconds is enough. The GPS makes a track on the screen and takes a waypoint every 5 seconds. You can follow this track on the screen of the GPS. All settings are correct, so the survey can start. The magnetometer and the GPS are set on automatically so you don t really have to do anything during the survey. The few things that are important are: the sensor should always point north, the tracks should be as straight as possible and check if the magnetometer and the GPS are collecting data. Fig. 4 Pointing the sensor north, D. Shefi, 12 Feb Downloading Magnetometer data The data can be downloaded onto the computer by using the MagMap2000 software. The GPS and Magnetometer data have to be combined and synchronized. In this report not details are give how to do this. To create a grid map out of the data the Magpick survey is used. Both programs can be downloaded for free from the Geometrix website ( 6

7 8 Constraints For this survey the biggest constraint were the bushes. Most of the times it was possible to go trough the bushes, but sometimes not. This resulted in not really straight lines. Near the eastern cliff there was a pretty big slope. Sometimes it was hard to keep the sensor pointing north during the climbing of this slope. It was also hard to see the person at the other side of the line. Using another person to stand in the middle of the line as guidance solved this. Another difficulty is the interpretation of the data. As an archaeologist you are not really trained in interpreting the data. To have a really good interpretation of the data you need a geophysicist to do this. 9 Results Figure 4 shows the grid map of the GPS and Magnetometer data from the survey. The red lines show the pattern walked with the GPS. The different colours represent the magnetometer intensity. In this map blue is the lowest intensity and green the highest. See also the scales bar on the map. When there is a big difference in intensity this means there is an anomaly there. In this map there are two spots of interest these are marked in the map with green circles. 7

8 Fig.5 Un-interpreted grid map Fig.5 Interpreted grid map with four anomalies

9 10 Conclusion In figure 5 the interpreted map can be seen that there are four anomalies. With a magnetometer survey it is impossible to say what they are, so the anomalies have to be further investigated. Position of the anomalies: Nr Easting Northing In the part where the remains of the houses are no anomalies were found. This indicates that probably only the stone structures are left and that the Whalers took all the others items back home. It was not possible to put the GPS track on the map, because the software for that is not available at the moment of writing the report. The parts on the map were there are no data labels is not surveyed. This was a really good learning experience, although especially the interpretation of the data is really hard, so this definitely needs some more practice. 9

10 11 References Moffat, I. (2006). Introduction to archaeological Geophysics. University of Adelaide. Paterson A. (2004). Understanding the Sleaford Bay tryworks: an interpretive approach to the industrial archaeology of shore based whaling. Maritime archaeology monograph and report series no.3. Flinders University. 10