GrOGG on ice

At about 100 km across, the Humboldt Glacier is the widest tidewater glacier in the Northern Hemisphere. A tidewater glacier originates on land, but terminates in water. Terminating in the ocean makes these glaciers very vulnerable to rapid retreat. Calving of the glacier front, essentially large chunks breaking off into the water, dominates the loss of ice. Thinning due to increased melting at the surface, or due to warmer water at the base of the ice, can cause a tidewater glacier to retreat at hundreds of metres a year. Between 2000 and 2008, the Humboldt retreated nearly 20 km in its north where the glacier is fastest flowing.

The glacier is named after German geologist and geographer Alexander von Humboldt. Between 1799–1804 von Humboldt led an expedition to Latin America and collected an enormous amount of data in a systematic and quantitative way with the most advanced instruments of the time, among the first to do so in science. His careful observations of rocks, climate and the distribution of plants, significantly contributed to the rise of the fields of geology, biogeography and meteorology. Humboldt was a prolific publisher, largely the reason for his subsequent fame, producing many essays and a massive multi-volume series called Kosmos. Humboldt popularised scientific illustration of data insisting that these “…speak to the senses without tiring the intellect [and] have the advantage of bringing attention to a large number of important facts”. A lesson for anyone giving a presentation. Humboldt mentored many young scientists including Louis Agassiz, for whom he directly funded and helped secure an academic position. Louis went on to establish the field of glacial geology and the concept of the Ice Age. Humboldt became the rock star scientist of his age. The President of the USA at the time, Thomas Jefferson, himself a scientist, referred to Humboldt as “the most scientific man of the age”. Darwin write that he was the “greatest scientific traveller who ever lived”. In 1869 on the centennial of his birth, festivals were held across America to celebrate the event. Humboldt’s legacy lives on in Humboldtian Science, numerous species named after him such as the Humboldt penguin, and many geographical features such as the name of a major surface ocean current, and this glacier.

The Humboldt glacier was studied in 2011 and 2012 as part of a joint UK-US, Natural Environment Research Council/National Science Foundation named the Greenland Outlet Glacier Geophysics (GrOGG) project. This project aimed to investigate what is happening at the bed of Greenland glaciers at the transition of flow from internal deformation to where it starts sliding at the bed. This is important because changes at the bed can have dramatic consequences for the velocity of the glacier, and hence its discharge at the terminus. The plane carried an ice penetrating radar to see through the ice, a laser altimeter to then infer its thickness and also collected aerial photos of the ice. The position of the plane was recorded by GPS as it flew in sweeping loops over the lower part of the glacier.

My colleague Steve Palmer was a Scientist on Board (SOB on the crew list). When he was showing me these photos, it occurred to me that the aerial images could be used for photogrammetry. The 3D model of Humboldt glacier above was created along one flight line as it flew across the calving margin. The only problem with structure from motion in this setting is that there is little contrast on the ice. This lowers the accuracy of a digital elevation model made from the 3D image. However, the orthophoto (an image corrected for distortion by parallax error) at full 25000 x 25000 pixel resolution is spectacular. The model itself allows you to fly around over the ice as if you were on the original flight. No doubt Humboldt would have taken a drone into the field with him and would have been thrilled by 3D models.


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