Thousands of historical aerial photos received a new life in 3D models
Recently, a Danish-Norwegian research team re-processed thousands of aerial photos into 3D Digital Elevation Models (DEM) surrounding the entire coastline of Greenland. The new data extends the precise geometric record of Greenland glacier margins to the late 1970s and 80s and can be used to quantify the decline in the ice mass, for example. The data is freely available to the public domain.
3D visualation in research: A 3D representation of the glacier elevation changes around Daugaard Jensen glacier from 1987 to 2014. The image is the 1987 orthophoto and the elevation change color scale ranges from 1 to 0.5 meters per year. Data and differences as described in Scientific Data (Korsgaard, Nuth et. al. 2016)
On Greenland, we find an ice sheet so large that it covers 85% of the island. In addition, there is a large amount of ice stored in smaller glaciers and ice caps that surround the ice sheet. It is estimated that Greenland ice contains up to 10% of the fresh water in the world.
The ice sheet is about 250,000 years old, with recent ice loss accelerating during the past 10-15 years. Researchers are interested in quantifying the ice melt, but also understanding the delicate feedbacks between glacier change, with ice dynamics, ocean currents and atmospheric forcings.
A treasure of 3,500 aerial photos
In the archive for aerial photos from Denmark`s Agency for Data Supply and Efficiency, SDFE, Danish researchers got access to 3,500 aerial photos taken from various places around Greenland.
Aerial photography was often acquired before the use of satellite observations in monitoring the island located between the Arctic and Atlantic Oceans. The island covers an area of 2,130,800 km2 and is the world´s largest island.
The team wanted to use the historical aerial photographs to quantify the decline of ice mass of the ice sheet the latest years.
But first they had to convert the images to digitalized form, then the digitalized data had to be processed together into 3D Digital Elevation Models (DEM). A DEM model is a 3D representation of a terrain's surface.
One of the researchers Christopher Nuth, Postdoctoral Fellow at Department of Geosciences, UiO, who has worked on the dataset, explains;
- DEM models are important for studying and modelling glacier change, and reference data for other cryological and remote sensing research.
In addition to the Digital Elevation Models the research team generated high resolution (2m) orthophotographs of the photo material. An orthophotograph is an aerial photo geometrically corrected such that the scale is uniform and it is adjusted to Earth`s distance and corrected for differences in angles.
Unique insight of a melting ice sheet
- This particular dataset and DEMs is unique as it extends the precisely and accurately known glacier geometry of the entire Greenland margin with a temporal snapshot that is now 30 years old, this is long enough to serve as a benchmark for climatic studies, says Chris.
The re-processing of the data was lead by a research group at The Danish Research institute; GeoGenetik, The Natural History Museum of Denmark, University of Copenhagen.
A main article from the research project was published last year in December 2015 in the prestigious scientific journal Nature. The article received a lot of media attention from international press after release.
Into the public domain
The research team has now released the dataset into the public domain, and the data is available for all interested researchers and others interested in the Artic region. The data is freely for download from NOAA's National Centers for Environmental Information (US), which hosts and provide access to one of the most significant archives on earth, with comprehensive oceanic, atmospheric, and geophysical data
- The material is open for researchers and others who are interested, the knowledge about this enourmous ice sheet response to a warmer climate are not fully understood, says Chris Nuth and he and the others hope that researchers in climate change, cryosphere and ocean research pay interest to the new dataset.
The dataset contains a high resolution 3D model of the entire surroundings and margins and coastline of Greenland and the Greenland Ice Sheet from the late 70s and 80s.
In addition the dataset and findings are described in an article recently published in the journal Nature Scientific Data (April 2016), reference to article below.
Korsgaard, NJ., Nuth, C., Khan, SA., Kjeldsen, KK., Bjørk, AA, Schomacker, A. & KH. Kjær. 2016. Digital elevation model and orthophotographs of Greenland based on aerial photographs from 1978–1987. Scientific Data 3, Article number: 160032 (2016). doi:10.1038/sdata.2016.32