Field courses on distance
Written by Erik Sturkell
In mid March 2020 all teaching had to be done on distance, because of the pandemic situation. This was a week before I was about to start a five week long practical geophysical course. In May the sequential idol geophysics or “the real world course” was scheduled. These two courses are on the master’s level. In addition, I helped Mark Peternell in the method course (the so called G4) for one and a half week in May. The latter course introduces first year students to different research methods.
This course comprises two and a half weeks with intervolving lectures and practical exercises. During this time the students learn how to use the instruments, process data and use modeling programs. The students are trained in using the instruments so they know what to do in the field. To be in the real world you need to know how to operate the instruments. It doesn’t look good if you need to consult the manual in front of the people who ordered (paying for) the survey. This has worked very well in the past during the field-work an assistant and I can take care of twenty students. The students come to the car at the rendezvous point and take the instruments and start directly. They will be ready after the basic training for one and a half weeks of field-work in an area decided in advance. The field area is chosen so it contains some exciting anomalies. In the field all students use all the different instruments and in addition they do bedrock and soil mapping (fig. mapping). The mapping constrains what exists on the surface which is important in the interpretation of the sub surface. The final week the students are divided into different groups; each group will work with a data set from one method. So they will not only use the data they collected but mostly data from their fellow students. This means they need to understand the documentation from the other groups. Not everyone produces excellent documentation of the measurements and therefore questions will arise. This course intended to teach the students the need for clear and correct field notes and also the need for standards. The finale day each group gives a presentation of the results of the measurements. Everyone can see the results of what they did. As there often are quite many students attending the course and the basic practice sessions can not host many students there can be up to four parallel exercises. To be able to plan this, all the teaching assistants and I use aliases with colors. In the planning spread sheet, the same color should not appear on the same line. I apply the names from the movie “Reservoir Dogs” so I am Mr. White, Axel Sjöqvist is Mr. Brown and the rest of the teaching assistants are Mr. Blonde, Mr. Blue, Mr. Orange, Mr. Pink and I have to use more colors.
Over the years I have used the same field areas so I know the location of interesting anomalies. The bedrock training area is located in Billdal 20 km south of Gothenburg, and the area with superficial sediments is located in the Mölndal on an empty industrial lot in “Forsåker” (see figure map).
Located 20 km south of Gothenburg, a large granite intrusion and associated gabbro is located. This is a part of the so called Kungsbacka suite with an intrusion age 1335 Ma. The granite came first but was almost directly intruded by the gabbro. At 935 Ma several E–W trending dykes intruded. The granite and gabbro have a large density contrast so gravity works really well. However, the susceptibility values are low for both the granite and gabbro in general. On the other hand, the late (935 Ma) dykes have a high susceptibility value and comes out well in the magnetometer. In places with little infrastructure VLF measurements works. In addition to the measurements, bedrock mapping is also conducted.
This is an empty lot in the central part of the Mölndal municipality. In this area along the stream Kvarnbäcken emanating from the lake Stensjön at 49.5-meter elevation. The center of the valley has an elevation of 7 meters so it was a perfect place for industries. This was the one of the first industrial areas in Mölndal and it dates back to the late middle ages. The serious industrialization really kicks off in the 17th-cenuary. The Kvarnbäcken stream cuts through the so called Gothenburg terminal moraine (age 14500 BP) and has made a delta and later an alluvial fan in the valley below. This circumstance with a delta / alluvial fan, which contains sand that rests on top of marine clays. The valley is filled with up to 70 meters of sediments mainly clay, but interlaid with sand layers. This is a good set up for geophysical surveys such as resistivity, seismic and ground penetrating radar. This lot was acquired by Mölndal municipality in 2004, and has been subject to several surveys to determined the contamination level of the soil. Now it is planed to develop the property and to build housing for 3000 persons and work places for 4000 persons. In spring 2020, the construction had not started yet and I hope we can use the Forsåker lot at least next year before the development gets started. The Forsåker area has been used for several master is and bachelor theses.
Idol geophysics or the real world
In this course the students will experience how it is to be at a consulting company in the real world. They will learn how to make the economic part of a job and also how to do the hazard assessments. In this course the student’s achievements will be judged by professionals from consulting companies. The original idea was that one team would be voted out each week. It is from this exciting (pedagogical?) idea the name idol derives. But, the organization at the department did not allow this reality show approach. So now all teams are in the course (game) to the end. The student consulting company will get a task, such as: depth to the bed rock, the density of a drumline (fig Sandsjöbacka) and find the monastery (archeological geophysics). This is more or less all the information they get, except the area and the resolution asked for in the results. The small consulting companies will get several jobs and they will produce a report. Before the job, they calculate the bid for the project. Currently the bid is just recorded and is used to compare with the end result. As they record the time spent on the project as they conduct the work. The actual cost (time) at the end is compared with the estimation (bid) made before. All this will be put on front of this course and the student’s achievements will be judged by professionals who will deliver a judgement. Some students are especially good and could get a job directly if they would ask! This is the normal course procedure.
Methods course (G4)
This is a ten weeks course in which I take care of 1 – 1½ weeks. It varies between years due to different course leaders. The students are given five lectures spanning general geophysical methods and in particular refraction seismic, resistivity and gamma spectrometry. These three methods they do in the field collecting data to be processed. The gamma spectrometry they use during their bedrock mapping exercise.
How this was done during covid-19
To carry out a field course program on distance is not easy as the students were not allowed to be at the university nor outside in the field. But I was fortunate that Mr. Brown (Axel) was around. This PhD student enjoyed to film and to edit, so instructions videos could be produced. Mr. Brown (fig Brown) and I (Mr. White) made eleven videos covering all the methods addressed in the course. The videos contain a full explanation about the method, how to do use the instruments and to document the measurements (fig GPR Gulldhedstorget). This was complemented with exercises and instruction videos we made about the processing and modelling. In this major effort several of the master’s student took an active part, in particular Mr. Blue (Erik W.), who was making instruction videos and in performing measurements. Also Mr. Green (Alexander), Mr. Gray (Thomas), M (Erik), and the master students: Mr. Blue, Mr. Pink (Jesper), Mr. Orange (Filip) and Mr. Yellow (Yamen) took part in the production of instructive videos.
Mr. Brown, Mr. Blue, Mr. Orange, Mr. Yellow and I, collected data for the students in particular the applied and for the sequential idol geophysics course. Some of the data will be used in future master theses. Mr. Blue, Mr. Orange, and Mr. Yellow helped to collect data, resistivity and ground penetration radar in the vicinity of the department.In the idol geophysics (or the real world) course I got a fantastic help and support from the consultant companies AFRY (former ÅF) and COWI. They came and helped in the finale judgements sessions creating a link between the university and the real world. This year they also provided data from completed projects for the students. This turned out very well as it was possible to compare the results and cost estimates from the consulting company and the students. This is a part that will be included in the future.
In Billdal, Mr. Brown and I measured 213 gravity points mainly along an east – west profile. From west the profile starts at the sea at Örsviken and runs for 4 km along Örsviksvägen and Lindomevägen to Hälleås bus stop (fig student map). We did precise levelling, gravity measurements and performed the terrain correction. The students calculated the gravity anomalies and with the result they could do some simple models. Also the students got the bedrock observation we have collected over the years. They produced a bedrock map using existing data.
But they realized more gravity and mapping data were needed to understand the area. As you always need more data the students should decide where to ask for additional data. For the gravity they know the location of the measured sites and the distribution of height point. The could ask for four kilometer of measurements from the most important (one km in red on the map) to the least (one km yellow in the map). They delivered maps with the suggestions in red, blue, green and yellow (fig student map). The same principle was applied for additional bedrock mapping. The students could place for 100×100 m boxes in the area where they desired additional mapping, with the same color code.The idea was that we would collect the additional gravity and bedrock data and to evaluate the improvements. We would collect the data in the order of importance lined out by the students. But there was no time for this in 2020, perhaps in the future.
In Forsåker located in Mölndal where the geophysical course had been a refraction seismic survey was performed and filmed (fig seismic). In this participated Mr. Brown, Mr. Green, M and Mr. White. Material was collected for three different courses: the applied geophysics, idol geophysics and the “methods” – course. Two 24 geophone array was set out and a total of twenty shots were made. We made a survey to collect data for the plus – minus method, to be processed with the IXrefrax program and for an array with two end shots. The data collected was used for the next course there.
This is a huge drumlin (an elongated land form formed during the glaciation) just south of Gothenburg. The question for the students in the idol course was what density has it. A drumlin could have a bedrock core or just consist of gravel (Figure Sandsjöbacka). If the density could be determined the contents of the drumline core can be established. The students were presented with the problem and they reached to the conclusion from the set parameters of the area that the gravity method should work. The Nettleton technique that is an indirect method for density determination. There a closely spaced gravity traverse is run over some topographic feature and by using the Bouguer correction to extract the likely density of the (in this case) drumline. Mr. Brown and I found a suitable bench mark from the Mölndal municipality with a well determined height. From this we lay out a 1km long profile with 35 gravity points, perpendicular to the strike of the drumlin. Each point was levelled (in both directions) and measured with the gravimeter. The terrain correction was made before the data was given to the students. It turned out the task was slightly more complicated than anticipated.
Mr. Blue (Erik W.) who worked on a Master these in the topic “archeological geophysics” exploring a buried monastery in Lödöse. As some additional resistivity measurements were needed we decided to make an idol project to unravel some question marks. In addition, our hardware lock for the 3D processing program re-surfaced. So we decided to collect data suitable for 3D processing. This was beyond the scope for Mr. Blue’s project, but useful for the next master these in the topic archeological geophysics. An array of electrodes spaced by one meter and 25 parallel profiles one meter apart produced a fantastic data set. Some master students under the leadership of Mr. Blue collected the data during two long days. In the idol course each student processed (in 2D) two profiles. The walls of the monastery appeared clearly in the resistivity data as they have higher resistivity when the surroundings (Fig. RL). Mr. Blue had prepared a track chart and after the student result was delivered. He marked the location of the subsurface wall (Fig. RL) from the profile on to the track chart map. With each profile added the out line of the monastery appeared om the map. This turned out very well and was an exciting project and it will be thrilling to see the results of the future 3D model.