Testing electrical resistivity tomography (ERT) on ice and debris

Exciting! A guest blog post from Dr Sarah Thompson who spent 6 months working with us here during summer 2016. Although it wasn’t even her main project while in Innsbruck, discussions about field data and confusing results meant that we cooked up a plan to use the cold room here in ACINN to do some laboratory tests of geophysical measurements. This meant that Sarah ended up spending a lot of time battling technical difficulties in a walk-in freezer, which is never that much fun. Here is what she was up to in there:

We wanted to test the difference in resistivity signal between temperate and cold ice beneath debris layers of varying characteristics to allow us to interpret field data collected from the debris-covered Ngozumpa Glacier in Nepal.

Electrical resistivity tomography (ERT) is a geophysical tool used to image subsurface properties by measuring the electrical conductance properties of different materials. Electrical resistivity is largely controlled by the presence of water held in fractures and pores. As a result, a marked increase in resistivity occurs at freezing point. ERT techniques have been used successfully for hydrological and permafrost investigations, detecting and areas of ice and frozen ground and to identify the presence (or absence) of ice in glacial moraines. The mechanisms of electrical conduction in natural ice, such as that contained in polar ice sheets, mountain glaciers or frozen ground, are still not fully understood but measurements typically vary over several orders of magnitude, with temperate ice having a much higher resistivity than cold ice.

In late autumn of 2010 and 2014, ERT surveys were carried out on Ngozumpa Glacier to locate the ice margin at the debris-covered glacier terminus. Inversion and interpretation of ERT data collected in 2010 gave resistivity values more commonly associated with cold glacier ice. Very little is known about the thermal regime of large Himalayan debris-covered glaciers but isolated studies have suggest some glacier in the region may be polythermal. While it is feasible that the ice imaged may be cold, the ERT data are a 2-D representation of an actually 3-D distribution of electrical subsurface properties, this leads to an uncertainty in the data which is not generated by data error or noise. Also, the high contrast in resistivity within the profiles can cause the equivalence problem, specifically, the signal of the highly resistive ice could be suppressed by the thin, more conductive surface layer.

We set out to test the hypothesis a ‘debris layer of sufficient thickness and conductivity masks the highly resistive signal of glacier ice beneath reducing the resistivity to values commonly associated with cold ice or frozen sediments’.

To do this we froze a block of ice (0.8 x 1.2 m) in a plastic water butt and installed a string of temperature sensors (encased in green tubing) through the middle and edge of the block to monitor ice temperature during a series of miniaturized geophysical surveys:

A scaled electrode array was created using stainless steel nails, complete with saltwater sponges and attached to the electrode points of the cable used in the full-size field measurements:

We carried out surveys using surface debris layers of different characteristics, including coarse (left) and fine (right) grained debris:
Surveys were also conducted over cold (< -15º C) and temperate ~ 0º C bare ice, for which holes were drilled into the ice and a very small amount of salt water added to allow elected connection:

As far a possible all surveys were carried out using both cold and the temperate ice. A combination of different debris characteristics were added to the ice surface to test the effect of debris thickness, grain size, saturation and freezing on the resistivity signal from underlying temperate or cold ice.

Sarah did a phenomenal job in tedious and testing conditions and we will use the results of these hard-won laboratory studies to hopefully unravel the meaning of the field data, but as its not a side project for both of us it may take some time!

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Alpine glaciers in context

I live in the European Alps. People here are concerned about the glaciers in this region (e.g. this www.insideclimatenews.org article) and want them to stick around, for tourism, skiing, climbing, enjoyment and scenery, amongst other reasons. Unfortunately for those holding these wishes, the data on glacier change in the region, and projections of their response to foreseen Alpine temperature changes suggest that their survival outlook is gloomy (e.g. Zemp et al., 2006).

My colleagues Dr Kristin Richter and Dr Wolfgang Gurgiser put these Alpine glacier in context in an outreach exercise for school children in which the participants are given a lump of playdough and asked to distribute it across a world map according to how the glaciers and acetates of the earth are currently distributed. The last lot of students did a pretty good job as you can read in Kristins blog on the matter, and in the end the division of ice mass between the major ice sheets of Antarctic (left) and Greenland (middle) and the mountain glaciers (right) that are closer to home for most of us looks like this:

As Kristin says: “Though only small amounts of ice are stored in glaciers compared to the ice sheets, they still have been one of the main contributors to sea level rise during the last centuries. However, the glaciers in the European Alps are but a tiny fraction (less than 1%) of the small ball that represents the glaciers. Literally just a drop in the ocean.”

So, while we may miss our Alpine glaciers when they are gone, if we are concerned about how glacier melt will affect global sea level rise our eyes should be elsewhere.

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JIRP presence at AGU

The American Geophysical Union (AGU) annual Fall Meeting later this month is one of the biggest earth science meetings of the year. This year the student research projects from the Juneau Icefield Research Program (JIRP) have each prepared a poster on their scientific projects and findings to be presented t this meeting by a student representative of the group. Its a great achievement and I hope those who can attend the meeting have a great time there. If you are visiting the AGU please try to visit the posters being presented by our teams of students, which I have listed below. The name of the person presenting the poster is given in brackets after the poster title although the posters were prepared by a whole team, whose names can be found my following the title link to the abstract.

C33A-0756: Gravimetric determination of the Thickness of Taku Glacier: Impact of Glacier Thickness on Subglacial Hydrology and Potential Erosion (Hamm, Tae)

H13A-1334: Chemical Weathering on the Llewellyn Glacier, Juneau Icefield (Zaccarin, Annie)

PP31D-2330: Spatio-temporal Variation of Water Isotopes on the Juneau Icefield (Semnacher, Cezanna)

GC31C-1133: Vascular Vegetation and Soil Microbiota of Juneau Icefield Nunataks (Collins, Deirdre)

C41C-0688: Evaluating Interannual Variability of Accumulation Gradients on the Juneau Icefield (Koncewicz, Evan)

C53D-0777: Temporal Changes of Surface Elevation and Velocity of Taku Glacier, Juneau Icefield (Ooman, Brittany)

sanfran

Many JIRP faculty are also presenting at the AGU Fall Meeting, including Jason Amundson, Anthony Arendt, Billy Armstrong, Matt Beedle, Kiya Riverman, Eric Klein, Jeremy Littell, Brad Markle, Chris McNeil, Twila Moon, Allen Pope, Shad O’Neel and Martin Truffer. Have a talk to any of our former students of these faculty members to learn more about the program. Or indeed, check out the JIRP blog, which continues to post students reflections and continuing news on the website.

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Ngozumpa glacier runoff

In April this year, Costanza and I went to try and download some data from a water level guage on the Dudh Kosi Phanka and Nha, in front of the Ngozumpa glacier, operated by the Department of Hydrology and Meteorology. Unfortunately, we found that it had been dismantled – looks like someone decided they could make better use of the solar panel and the battery. To be fair, that is likely to be true!

Anyway it made me think about what data was ever collected from this guage and all I could find was  data from 2007, though there may well be more. I don’t know the full history of its installation, maintenance and data download history.

You can see some of the data below but first some information on the sensor and some caveats.

  • The sensor is a sonic ranger so it measures a distance to the water level, by using the speed of soun, and the travel time for a sonic pulse to bounce back from the water surface to the sensor.
  • This will obviously be noisy as the water surface is choppy and variable, even though its mounted over a backwash pool.
  • Readings were saved for 15 minute, 60 minute and daily values – I have not seen the program for this but I assume these are averaged values in order to filter out some of the noise.
  • This location captures runoff from the connected lakes and cathcments on the west side of the glacier, as well a the glacier.

First, I wanted to remove some of the outliers as there are some big jumps in the apparent water level in the dataset which are unlikely to be true. So, I made a very crude filter by determining the mean distance to the water level (calculated on all data including those that I think are probably erroneous), which was 2.01m, and removed all data points that deviated from this by more than 1.50m. I chose this threshold just by eyeballing the data and its a pretty generous filter in that it definitely lets through some remaining noise, but I thought thats better that excluding some valid data.

Here is the daily mean water level for the available data bracketed by the daily maximum and minimum in grey. Clearly there are still some values that are most probably errors and they will be affecting the calculated mean values, but you can see the general pattern of peak water level during the core monsoon months which is as expected.

phanka_dailywaterlevelThen I used the 15 minute data to plot the hour of the day when the high and low water occurred. Becasue of limitations in the size of the memory of teh datalogger (which overwrites its data once its full), this covers only the latter part of 2007. I think the plot is kind of interesting as it looks like during the core summer monsoon months of July, August and September that the river level is highest around the middle of the night, whereas outside of these three summer monsoon months the river is highest in the middle of the day.

phanka-flow-timingTo be honest I’m not totally sure how to interpret this. Is this because the monsoon rain comes in the afternoon/evening here and by the time it all comes downstream its late into the night? Or does this tell us something about the efficiency of the glacier drainage system varying between these two seasons? I’d need to analyse the precipitation data at the same time to start exploring this, and I do not have that data to hand just now. Watch this space.

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Sketchfab

Check this out – I can embed sketchfab visuals here on my website!

We made 0.5cm resolution surface models of penitentes on the Tapado Glacier in Chile for our last paper in The Cryopshere.

This is site B on Tapado glacier on the 3rd of January. The are shown above is about 2m x 2m (the corner stakes are 2m apart). For the analysis in the paper this are was trimmed down to 1.5 x 1.5 m.

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Glacier mass balance infographic

Allie Strel is studying cartography and is one of the staff partly responsible for the student mass balance measurements of the Juneau Icefield during JIRP each summer. She has made this infographic of the Juneau icefield mass balance measurement program:

tackling-the-taku-mass-balance-infographic-allie-strel

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East African Glaciers on GlacierHub

Georg Kaser just brought to my attention that our work on Mt Kenya was features on GlacierHub and the Mountain Partnership websites:

East African Glaciers at Risk from “Global Drying”

 

 

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Why use professional blogging/tweeting/webpages?

I recently spent a delightful few days wandering around Grindelwald with my friend (and paleclimatologist) Brad Markle. Isn’t it nice?

Grindelwald

On one particularly fine sunny day we got to talking about websites, blogging, tweeting and so on. I am quite a proponent of this actually, even though initially it seems its going to take way too much time away from the more important science activities that we actually are judged on, get jobs on, and feel pressured to produce more of.

That is writing papers of course.

I have mixed feelings about this heavy weighting of success on the number of papers published by scientists, as I think it has some negative consequences for the integrity of the science being produced, as well as being responsible for making a glut of incremental papers instead of a smaller number of more complete, well thought out, and well-reviewed papers. However, that topic is not for this blog, and also its a hard thing for me to take a stance on as my own publication list is generally too short, low impact, and of marginal interest, so I need to be careful not to sound bitter and like I am just making excuses for my own shortcomings.

So, on to the business at hand. Let me first tell you a story about how I began to develop my own small web presence, then I will follow up with what I get out of it, and why I have grown to appreciate what it offers far more than I did at my cynical outset.

I made this website as I thought it might increase my chances of getting a grant from the FWF. I googled what would be the easiest way to do this, and concluded: WordPress. I decided if I could not make a webpage in half a day then it was too much time to invest. With WordPress I managed to meet this tight time constraint and had the bare bones of my website by 11am. I was however a bit annoyed to see that (at least at that time) you could not avoid having a blog page with WordPress. I thought “Curses! I’ve not time for that! I can’t even get my own papers written”. But I was stuck, as to start again with a package that did not require a blog component would mean going over my half-day time rule. For some months before this, a friend of mine who works in sustainability had been trying to get be to join Twitter. She advised me that you can use it as a filtered news feed to keep up to data on thing of interest to you. I realised that I could link a Twitter feed onto my website thereby making some updates to the page even if I was too lazy to write real blogs. So I joined Twitter as well.

Yes, I was pretty cynical. But now I like it a lot, and here are some reasons why.

I chose my website content to serve my own interests. It helps me:

  • Keep a clean record of my achievements in my online CV, which saves me time when I need to do annoying tasks like complete my annual achievement reports to my own University, apply for jobs, find my own papers/posters if I want to share them with colleagues
  • Have a feed of journal contents of potential interest to me in one place (admittedly this partly broke when the EGU changed their RSS feed and it took me more than half a day to try and fix it so it is not fixed – sorry, but it was really useful to me for a while)
  • Easily provide useful background on me and my work if I am contacted by colleagues, media or anyone else, and also if I am approaching someone for help I use it to offer background on me

My blog helps me in even more ways:

  • I write up the small bits of analysis that we all have to do to check quality, process out data, understand its meaning. The kind of things that take 3 days of data analysis and then become one or two lines in a publication, like how do my measurements compare to earlier or other measurements. These posts are super-useful when colleagues come with questions about the basic science of my projects. Many times I have avoided a long email answer to a valid questions by being able to say: “Check out this blog which answers all your questions”. I find this useful as its like keeping an online lab book of the small analysis step we make, s it costs little time to do and saves lots of time if someone asks you details about something you did months ago (and you can’t remember everything off the top of your head, so would have to spend time going back to your analysis notes). I see these types of blog as saving me time in the long run.
  • I also write up small studies carried out as part of a teaching field trip, and its never going to feature in a publication, but time was invested and there might be something cool to show from it. I see these types of blogs as adding value to the time already invested, by allowing me to easily share methods, small findings and so on with students, and the wider public if anyone reads it!
  • I also write some opinion pieces. These blogs help me clear up my thinking on a certain topic and help me develop a (hopefully) clear,  straightforward writing style.
  • Also some days when everything is going wrong, I write a short, fun blog post just to trick myself into believing I have achieved something. I see these types of blog as serving an important role in making me feel I can round off a hitherto unsatisfactory work day on a positive note.
  • I blog short summaries of my own papers, and also papers that I have just struggled to understand. I think this is valuable to developing a simple lost of key findings from published studies, and helping me to remember them (yes, sometimes I even forget my own arguments).
  • I guess the outreach impact of my blogging is very small as I do not ‘advertize’ the  things I write via other channels and I suppose the traffic to my site is low. I feel uncomfortable with self-promotion, so I am happy with this, but it means I cannot really assess the potential  impact of blogging. Certainly, I do try and use my blog if I am contacted by the media, in my face-to-face outreach, my teaching, and my research partners are glad to have something to put in a web outreach box in the annual reports to the funding agencies.

Tweeting helps me in different ways:

  • I tweet things that I’ve read, and find valuable sources of information that I might need to look up later – so basically its like a public internet reading list for my own personal use. How selfish. But at least I share it, right? It might be useful to you too?
  • It makes it look like I update my website even if I’m too lazy/ have no time to write a blog post. I guess this actually fools no-one.
  • The people I follow give me filtered news on imprint glaciological topics that I am not directly involved in. For example, I do no research on the large icesheets, and these are a hot bed for new glaciological understanding, are of great relevance to understanding past climate, and future sea levels, and I think its important that I know whats going on in this sphere. However, I’ve hardly the time to read all the papers on icesheets as well as all the papers coming out each week on mountain glaciers and topics I am actually engaged in researching in. So. Twitter gives me soundbite updates and points me towards things that I really must make the time to read. In doing this it makes me a better, broader, scientist.
  • Linking Twitter to a Facebook page lets me update my community page on research on glaciers in the Khumbu Himal, without actually having to look at Facebook very often. Phew! Dodged a procrastination bullet there! Yes, thats right, I actually have TWO webpages, twitter accounts and Facebook pages. Never thought that would happen.

So there you have it. My first rule of my web and social media presence is that I don’t let it take too much of my time. That means if its hard to do something technical with the webpage, or some potentially interesting blog topic would take a weeks worth of otherwise un-necessary research, then it won’t get done. My second rule is that I don’t let Twitter get me depressed by the onslaught of achievement that it delivers to my screen. Rule #1 is easier than rule #2, but I hope this blog helps convince some people to get involved. The public deserve that we learn to communicate our science better. Have fun!

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Structure from Motion

There are always so many things to do and learn about! Its fun having Jordan Mertes here in Innsbruck for a while, as he is expert in using Structure from Motion tools to develop surface terrain models. I’ve dabbled in this a fair bit but usually feel a bit out of my depth and am not always sure if I have generated models of the best possible quality.

The principle is that you take a bunch of photos of an object or surface of interest, from a variety of angles and distances and specialized software can be used to identify a large number of common features in the images, perform a suite of positional calculations on these and determine where the photos was taken from and also the 3D form of the surface being photographed. Its pretty cool stuff. Anyone can do it! Like many colleagues of mine, I use Agisoft Photoscan software, which you must pay for, but there are other freeware versions using the same principles such as Visual Structure from Motion. All you need is a camera and a computer and a natty idea …

Ben Partan and I took a bunch of images and videos in 2013/2014 to see how well we could use this  kind of photogrammetry and software to create surface models of snow penitentes in Chile to compare with the models we generated using the Microsoft Kinect as a close range 3D camera (see Nicholson et al., 2016).

Penitentes are a hard challenge for terrestrial photography as the contrast is poor and the surface is complex and shadowed. It was a very good learning ground for us – we could see how well different configurations of photo vantage points compared to extracting frames from videos, and we tried both cheap and high quality cameras.

Below is an example model of snow penitentes in a river bed, where we tested all our equipment and set up. The image is a screenshot from Agisoft Photoscan software. You can see from the camera positions indicated in blue that we were trying two approaches: (1) taking an array of photos from a single location and moving on to do the same at another, and (2) taking a single photo, and then moving along a meter to take the next one.

SfM_penitentesYou can read much more about Structure from Motion (SfM) applications in earth science in this new book: Structure from Motion in the Geosciences by Jon Carrivick, Mark Smith and Duncan Quincey, and in Westoby and others (2012). A very timely publication indeed as these techniques are booming in earth science and perhaps especially in glaciology at present. You can read more about the penitentes we measured in our publication in the Cryosphere.

Westoby, M. J., Brasington, J., Glasser, N. F., Hambrey, M. J., & Reynolds, J. M. (2012). “Structure from-Motion” photogrammetry: A low-cost, effective tool for geoscience applications. Geomorphology, 179, 300–314. doi:10.1016/j.geomorph.2012.08.021

Nicholson, L. I., Petlicki, M., Partan, B., and MacDonell, S. (2016) 3D surface properties of glacier penitentes over an ablation season, measured using a Microsoft Xbox Kinect, The Cryosphere, 10, 1897-1913, doi:10.5194/tc-10-1897-2016, 2016.

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Attribution of sea level rise

I like to follow the work of my colleagues and office mates, and both Ben Marzeion and Kristin Richter were recently involved in publishing a paper in Nature Climate Change that demonstrates that human activities dominate the recent sea level rise.

The key findings are that in the first half of the 20th century, only about 15 % of sea-level rise were of anthropogenic origin, but human emissions caused about 70 % of sea-level rise between 1970 and 2005, as summarized in the infographic below.

Sea level rise graphicFor further information you can read the original article (Slangen et al., 2016) or a  News & Views story by Sönke Dangendorf.

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