Prior to my Iceland fieldwork earlier this year, I put together a simple spreadsheet to input my Vertical Electrical Sounding (VES) resistivity data into whilst in the field. VES for me is a tried and test back to basics geophysical technique. I needed a vertical profile through my fields sites to gain insight into how thick the ground ice is and how thick the sediment cover was above it. Logistically and economically collecting VES data to augment the previous year’s conductivity dataset was a good solution.
The VES system used in this case was the Megger DET4TD2 configured using a wenner array. The acquisition is fairly simple; insert the 4 probes at equal spacings with a constant centre point, click measure, record/write down the resistance, increase the spacing, click measure, record the resistance, “wash, rinse, repeat”.
Traditionally I have always just written the data down in my yellow notebook, and transcribed them when back in the office. The transcribed data is then run through software such as IPI2Win or R-VES for those of you who like to dabble in R.
I made this fairly simple spreadsheet to allow me to visualise the data in the field and ground truth (e.g. collect data over a ground ice exposure). I’ve made the spreadsheet available to download, it works particularly well on a phone or tablet in the field especially if you link excel to cloud storage such as google drive, Then you can’t lose your data.
It’s very simple to use, you will need Excel on your phone/tablet.
- Email the spreadsheet to the device.
- Open the spreadsheet using the excel app.
- Save the spreadsheet with your fieldsite name.
- Copy the template sheet and rename with the site number
- Insert probes at spacings p values represent where on the tape to insert each probe (tweak these if you want different spacings/depths).
- If needed water the probed with saline water.
- Click measure
- Enter the resistance given by the Megger DET4TD2 into the grey column next to the appropriate spacing.
- Move the probes and repeat steps 5-8 until you have finished collecting data at that point.
- As you enter data you will see it plot on the log graphs below, you can use these to identify changes in subsurface materials.
I’ve been working on mounting the new Flir Vue Pro R to the phantom over the last few weeks. The wooden prototype worked reasonably well but was a bit off balance, the new 3D printed design flys much better and has mounting slots for the battery and for better securing of the camera and battery. I did a few tests using video, timelapse and photos but need to tinker with the settings a bit more before taking it out to Iceland.
The mount flys well, and doesn’t inhibit the use of the phantoms inbuilt camera, I’ve also worked out how to georeference the thermal images.
Things I’ll be looking into in the coming weeks include…
- Tweaking the settings
- Optimum height for acquisition
- Stitching together thermal images
Looking forward to an exciting few weeks ahead.
I’ll be heading out to Iceland again in Easter 2019 to carry out some repeat UAV surveys of my field sites, fortunately, the equipment is a little more portable this year. I’m looking forward to seeing the topography change over the last year. I’ll also be carrying out a thermal imaging survey from the drone at dawn/dusk to help identify areas of ground ice. In addition to this, I will be building on the geophysics (EM-31) collected last year, by using resistivity to collect resistivity sounds to help constrain cover and ice thickness. Depending on how the preliminary tests go next week I may also collect some 2D transects using a different configuration of the resistivity equipment. As mentioned before this fieldwork is kindly supported by the NSGG.
Some more great news, my submission (see above) to the BGA photograph competition won second prize, first prize went to an amazing photograph taken offshore retrieving equipment from between icebergs as if it were a giant hook a duck (really impressive, both the activity and the photo). The photographs were judged by the BGA committee at the Postgraduate Research in Progress Meeting in the University of Cardiff. The prize money will be put towards the next field season which will hopefully yield more photographs of geophysical surveys being carried out among the beautiful scenery of Iceland.
Thanks again to the British Geophysical Association
Following a successful funding application, the Near Surface Geophysics Group (NSGG) are funding part of my next field season in Iceland. The Field season is planned for Easter 2019. I plan to carry out repeat flights over my current sites to identify any subtle changes in topography, take resistivity readings to identify cover and ice thickness and collect thermal imaging at dawn and dusk to help identify any potential ground ice.
This is great news and I’m looking forward to the planning and execution of the fieldwork early next year.
A big thankyou to all concerned at the NSGG.