Fodar updates USGS maps

Today our paper on determining the highest peak in the US Arctic was published in The Cryosphere Discussions and we also released our final results in a talk at the 2015 Fall American Geophysical Union Meeting in San Francisco.  You can find a copy of the paper here.  Note that this is a Discussion paper, which is the first step in peer-review, so the results and findings in that paper are still preliminary, but we wouldn’t have submitted it if we thought they were wrong…  Papers like these have their purpose, but they are limited by space and format, so here you can find more details and a multimedia gallery of the peaks which includes an online 3D interactive visualization, still images of visualizations, and several movie animations.  Please see also Kit DesLauriers’ blog describing the climbing part of the trip.

What did we do and what did we learn?

We measured the heights of the tallest peaks in the US Arctic for two reasons. First was simply because we were curious.  Different USGS maps indicate different answers to the question of which is the talllest mountain, plus 60 years of climate change since those maps were made adds further mystery.  We put GPS on the peaks and made airborne maps to conclusively show that Mt Isto is the tallest peak and that none of the peaks are over 9000′, as indicated on the USGS maps.  Further, we found it plausible that the height ranking of the top five peaks has changed since the maps were made, and may still change due to climate impacts.  Second was because we have a new airborne topographic mapping technique that we wanted to test in steep mountain terrain.  This technique, called fodar, is a type of SfM photogrammetry that creates maps with quality equal or superior to existing technologies, but at a fraction of the price.  At the heart of our system is a $3000 prosumer Nikon camera, compared to $500k or more for a comparable lidar or standard photogrammetric system.  Our results show that fodar is capable of measuring changes in topography on the order of centimeters, in steep or gentle terrain.  Given that building or purchasing such systems is within reach of most academic research budgets now, fodar is likely to revolutionize our understanding of earth surface dynamics because we can now afford to map enormous areas at low cost to detect tiny changes.  For example, fodar can measure snow depth in the mountain ranges by subtracting a snow free map from a snow covered one, and such measurements can aid in management of water resources that serve millions of citizens.

Here is the abstract to that paper, which gives an overview of the primary results:

“Which are the highest peaks in the US Arctic?  Fodar settles the debate”, by Matt Nolan and Kit DesLauriers

Abstract  While creation of the United States Geological Survey’s topographic maps of the eastern Alaska Arctic were an outstanding accomplishment for their time, they nonetheless contained significant errors when made in the late 1950s. One notable discrepancy relates to the tallest peak in the US Arctic: USGS maps of dierent scale alternate between Mt Chamberlin and Mt Isto. Given that many of the peaks here are close in height and covered with glaciers, recent climate change may also have changed their height and their order. We resolved these questions using fodar, a new airborne photogrammetric technique that utilizes Structure-from-Motion (SfM) software and requires no ground control, and validated it using GPS measurements on the peaks and using airborne lidar. Here we show that Mt Chamberlin is currently the 3rd tallest peak and that the order and elevations of the five tallest mountains in the US Arctic are Mt Isto (2735.6 m), Mt. Hubley (2717.6 m), Mt. Chamberlin (2712.3 m), Mt.Michelson (2698.1 m), and an unnamed peak (2694.9 m); these orthometric heights relative to the NAVD88 vertical datum, established with use of GEOID12B. We find that it is indeed plausible that this ranking has changed over time and may continue to change as summit glaciers continue to shrink, though Mt Isto will remain the highest under current climate trends. Mt Isto is also over 100m higher than the highest peak in Canadian Arctic, making it the highest peak in the North American Arctic. Fodar elevations compared to within a few centimeters of our ground-based GPS measurements of the peaks made a few days later and our complete validation assessment indicates a measurement uncertainty of better than 20 cm (95% RMSE). By analyzing time-series of fodar maps, we were able to detect topographic change on the centimeter-level on these steep slopes, indicating that fodar can be used to measure mountain snow packs for water resource availability or avalanche danger, to measure glacier volume change and slope subsidence, and many other applications of benefit to society. Compared to lidar, the current state-of-the-art in airborne topographic mapping, we found this SfM technique as accurate, more scientifically useful, and significantly less expensive, suggesting that fodar is a disruptive innovation that will enjoy widespread usage in the future.

he USGS maps indicate Mt Isto or Mt Chamberlin as being the highest mountain in the US Arctic — which is it?

This discrepancy had been known for some time, but when Kit saw it she decided to do something about it.  

it DesLauriers, of The North Face’s Professional Athlete team, led an effort to directly measure the elevation of Mt Isto and Mt Chamberlin using GPS.  I led the effort to map these same peaks within a few days of the climbs using airborne fodar.  This image shows the climbing team’s GPS tracks overlaid onto a 3D visualization of fodar data of Mt Isto.

Here is the USGS topographic data for Mt Isto.  Mouse-over to see what 60 years of technological improvements have done for photogrammetry.  The advantage here is not simply resolution but accuracy as well.

We have previously shown how well fodar works on shallow topography, such as to measure snow depth or coastal erosion.  In the paper published today, we demonstrated that it works equally well in steep mountain topography.  We believe our measurement uncertainty of peak heights is less than 20 cm, such as can be seen in our repeated measurements in the fourth column of the table below.  The table also  shows that the peaks are meters apart in height, well beyond our measurement uncertainty.

ere are the final results from our paper.  As can be seen Mt Isto is the tallest mountain in the US Arctic (second to last column), and Mt Chamberlin is not #2 but rather #3.  The measurement uncertainty here is less than 20 cm, so there is no ambiguity in results.  Given that 4 out of 5 mountains are within a few meters of the original USGS 1:63,360 maps (an outstanding accomplishment for the USGS 60 years ago given their challenges!), it seems clear that the 1:250,000 value for Mt Isto was simply a mistake.  The 120′ difference between our fodar measurements and the USGS maps for Mt Chamberlin could have been caused by an actual change in elevation due to avalanche, as described below.  

Here you can see a large pile of debris at the base of Mt Chamberlin directly below its peak (red pushpin).  We do not know when this avalanche occurred, but given it lies on top of the glacier below, it could have been in the last 60 years, after the USGS maps were made, suggesting that the maps were correct at the time.

Besides the ability to accurately measure mountain topography once, we demonstrated in the paper that by making several maps we can measure change in mountain topography.

Here is the climbing team skiing down from the summit of Mt Isto, a few meters behind the photographer, Andy Bardon.  Note the heavily corniced ridge to the left and rocks in the foreground.

Here is that same ridge as a 3D visualization of fodar data from July 2015.  The red pushpin is the peak of Mt Isto, and the rocks seen to the right are the same as seen in the photo above.  Note how well the cornices are resolved.  Mouse-over to see the same topography, but with an image created by subtracting the April 2014 elevations from the July 2015 elevations.  Here elevation gain is colored red and loss is colored blue, and the yellow-green color means < 10 cm change.  Because the two data sets are so accurate and precise, most of the image is yellow-green, meaning that we can pull out subtle changes (and large ones).  In this case, we can see that these large cornices formed sometime between the two mapping dates (big red blobs) and many have already fallen off taking some extra ice with it (blue pits).  The plot below shows a profile extracted from the transect shown on the images– here a cornice 5 m wide and 6 m deep has formed.  Based on the crack behind it seen in the July 2015 image, it is about to break off.

Here we can see the difference between the 2015 elevations (red) and the 2014 elevations (black) in the transect seen in the previous image.  A cornice about 5 m wide and 6 m deep formed in between mapping dates, perhaps as a result of a single storm.  Based on the 2015 image above, the cornice is about to fall off, as have many nearby.  Based on this and many other such analyses as well as our paper, we believe fodar is capable of measure snow depth down the to centimeter scale in steep mountain terrain.  For example, this technique could be used to measure water supplies contained in mountain snow packs, avalanche danger along roads or ski areas, and glacier volume change.

Here is another example of how fodar is able to measure change in topography by comparing two maps. Here we have subtracted the March 2014 topography from the April 2014 topography and found that a lot of snow avalanching has occurred. The plot below shows the actual measurements.  Here red color means that elevation has been lost, and the green/blue means no change at all.  Mouse-over to see the April 2014 image overlain on topography.

Here is a plot of the difference between the March and April 2014 fodar elevation maps — they show that up to 8 m of snow was avalanched out of these gullies.  More importantly, it shows that we can now measure snow depth in steep mountain terrain.

Here is the same sort of image as the previous one, focusing on a single gully with more minor change.  The plot below indicates that we can measure centimeter-to-decimeter snow thickness on steep mountain terrain.


Here is a screenshot of our 3D visualization tool, powered by Cesium.  Cesium allows us to share our fodar data online in a 3D environment similar to Google Earth and embed these windows directly into web pages, as we have done below.  Our data are kindly hosted and served by AGI, the creators of Cesium who share it as open source software.

You can explore our fodar data in full detail here.  Click on the links in the drop down menu at upper left to be flown to a peak, or use the mouse to navigate yourself there (see control help at upper right).  You can also change the background imagery using options at upper right. NOTE: I inadvertently left out Mt Okpilak’s fodar terrain from this app, but will add it as soon as I return from AGU.

Mt Isto

The west face of Mt Isto, tallest mountain in the US Arctic.  This was the face our team skied up and down with GPS.

Green pushpins are our GPS tracks.  The closely spaced points are walking up, the widely spaced ones are skiing down.

Northeast face of Mt Isto.

Summit detail of Mt Isto.  While Kit was making the GPS measurement at the summit, the others hunkered down behind the rocks near the top.

Northwest face of Mt Isto.

Southeast face of Mt Isto.

Southwest face of Mt Isto

isto_top_peakLooking down on the summit of Mt Isto.  Unlike Mt Chamberlin, there is no evidence that large chunks of Mt Isto have peeled off recently.

Mt Hubley

hubley_southfaceView of Mt Hubley’s south face from Schwanda Glacier.

Mt Hubley’s east face from Hubley Glacier.

hubley_mccallviewMt Hubley’s north face from McCall Glacier.

hubley_northfaceMt Hubley’s north face.

he west side of Mt Hubley over Contact Glacier, with McCall Glacier in the background.

hubley_westridgeThe west ridge of Mt Hubley.

hubley_southwestface2The west face of Mt Hubley.

hubley_southwestfaceThe west face of Mt Hubley.

The red pushpin is at the peak of Mt Hubley.  It is the only peak that is not corniced.

Another view of the peak of Mt Hubley.

Mt Chamberlin

The Northwest face of Mt Chamberlin.  The climbing team first tried taking the left ridge up the snow slope, but changed course due to safety and gained the right ridge at the corner where it flattens out.

The southwest face of Mt Chamberlin.  The climbing team skied down this face from the summit.

A view of the northeast side of Mt Chamberlin.

The southeast face of Mt Chamberlin.

The north ridge of Mt Chamberlin.

A top view on Mt Chamberlin.

Mt Michelson

michelson_southfaceSouth face of Mt Michelson

Southwest face of Mt Michelson

Southeast face of Mt Michelson

Looking south towards Mt Michelson

The northwest face of Mt Michelson

The north ridge of Mt Michelson

There is at least 3 m of ice beneath the peak of Mt Michelson, which is only about 3 m higher than Mt Okpilak.

Mt Okpilak

South face of Mt Okpilak

okpilak_eastfaceEast face of Mt Okpilak

West face of Mt Okpilak

West face of Mt Okpilak

Northeast face of Mt Okpilak


This is not Mt Okpilak, but is a small, pretty peak just across the valley from it.

t Okpilak’s peak is on a broad flat ridge.  Between May and July 2015, the “peak” moved laterally 15 m but only changed about 20 cm in height, simply due to cornice development.  There is about 3 m of ice beneath that corniced ridge.

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