Category Archives: Greenland

Sea Ice from Satellite at 20-m Resolution

I am a self-taught amateur on remote sensing, but it tickled my pride when a friend at NASA asked me, if I could tell a friend of his at NOAA on how I got my hands on data to produce maps of radar backscatter to describe how the sea ice near Thule Air Base, Greenland changes in time and space.

Wolstenholme Fjord, Greenland Feb.-5, 2017 from Sentinel-1 radar. The data are at 20-m resolution

Wolstenholme Fjord, Greenland Feb.-5, 2017 from Sentinel-1 radar. The data are at 20-m resolution

In about 4 weeks from today I will be working along a line near the red dots A, B, and C which are tentative locations to place ocean sensors below the sea ice after drilling through it with ice fishing gear. The colored line is the bottom depth as it was measured by the USCG Healy in 2003 when I was in Thule for the first time. Faint bottom contours are shown in gray.

I discovered the 20-m Sentinel-1 SAR-C data only 3 weeks ago. They are accessible to me (after making an account) via

https://scihub.copernicus.eu/dhus/#/home

where I then search for a specific geographic area and time frame using the following “product”

Product Type: GRD
Sensor Mode: IW
Polarization: HH

Screenshot on how I search for the Sentinel-1 SAR-C DATA.

Screenshot on how I search for the Sentinel-1 SAR-C DATA.

The more technical detail can be found at

https://sentinel.esa.int/web/sentinel/user-guides/sentinel-1-sar

where one also finds wonderful instructional videos on how to work the software.

The data file(s) for a typical scene are usually ~800 MB, however, for processing I use the free SNAP software (provided by European Space Agency) via a sequence of steps that result in a geotiff file of about 7 MB.

Screenshot of SNAP software and processing with [1] input and [2] output of the Feb.-5, 2017 data from Wolstenholme Fjord.

Screenshot of SNAP software and processing with [1] input and [2] output of the Feb.-5, 2017 data from Wolstenholme Fjord.

This .tiff file I then read with Fortran codes to tailor my own (quantitative or analyses) purposes.

Start of Fortran code to covert the SNAP output geotiff file into an ascii file with latitude, longitude, and backscatter as columns. The code has 143 lines plus 80 lines of comment.

Start of Fortran code to covert the SNAP output geotiff file into an ascii file with latitude, longitude, and backscatter as columns. The code has 143lines plus 80 lines of comment.

The final mapping is done with GMT – General Mapping Tools which I use for almost all my scientific graphing, mapping, and publications.

Please note that I am neither a remote sensing nor a sea-ice expert, but consider myself an observational physical oceanographer who loves his Unix on a MacBook Pro.

Working the Night shift aboard CCGS Henry Larsen in the CTD van in Aug.-2012. [Photo Credit: Renske Gelderloos]

Working the Night shift aboard CCGS Henry Larsen in the CTD van in Aug.-2012. [Photo Credit: Renske Gelderloos]

If only my next problem, working in polar bear country with guns for protection, had as easy a solution.

Polar bear as seen in Kennedy Channel on Aug.-12, 2012. [Photo Credit: Kirk McNeil, Labrador from aboard the Canadian Coast Guard Ship Henry Larsen]

Polar bear as seen in Kennedy Channel on Aug.-12, 2012. [Photo Credit: Kirk McNeil, Labrador from aboard the Canadian Coast Guard Ship Henry Larsen]

North Greenland Sea Ice: Wolstenholme Fjord and Thule Air Base

Greenland hunters, seals, and polar bears all need sea ice atop a frozen ocean to eat, breath, or live. The sea ice around northern Greenland changes rapidly by becoming thinner, more mobile, and less predictable as a result of warming ocean and air temperatures. I will need to be on the sea ice to the north and west of Thule Air Base in March and April about 6 weeks from to conduct several connected science experiments. The ice should be “land fast,” that is, it should be a solid, not moving plate of ice. The work is funded by the National Science Foundation who asked me to prepare a sea ice safety plan to keep the risk to people working with me to a minimum. In a science plan I included this satellite image of what the ice and land looked like in march of 2016:

Optical satellite image of Wolstenholme Fjord, Greenland on March-21, 2016 with Thule Air Base in bottom right. Darker areas show thin ice.

Optical satellite image of Wolstenholme Fjord, Greenland on March-21, 2016 with Thule Air Base in bottom right. Darker areas show thin ice.

This LandSat image captures the reflection of sun light during a cloud-free day at ~15 m pixel size. No such imagery exists for 2017 yet, because the sun does not set until late February with this US satellite overhead. The European Space Agency (ESA), however, flies a radar on its Sentinel satellite. This radar sends out its own radio waves that are then reflected back to its antenna. The radar sees not only during the polar night, it can also see through clouds. And ESA provides these data almost instantaneous to anyone who wants it and knows how to deal with large data files. If you think your 8 mega pixels are sharp, these images are closer to 800 mega pixels. Here are three such images from January 3, 24, and 28 (yesterday):

The lighter white tones indicate that lots of radar signals return to the satellite. The many tiny white specks to the south of the Manson Islands are grounded icebergs. The different shades of gray indicate different types of ice and snow. The Jan.-24 and Jan.-28 images show a clear boundary near longitude of -70 degrees to the north of the island (Saunders Island) that separates land-fast ice to the east from thinner and mobile ice in Baffin Bay to the west.

I plan to work from Thule Air Base (red dot bottom right) out along points C, B, towards A. The color of line near these points is a section where I have very accurate bottom depth from a 2003 US Coast Guard Icebreaker that was dropping off scientists at Thule on August 15, 2003. I was then one of the scientist dropped off after a 3 week excursion into Nares Strait and Petermann Fjord. Along this section I hope to test and deploy and under-water acoustic network that can send data via whispers from C to A via B. First, however, we will need to know how sound moves along this track and before that, for my ice safety plan, I will need to know how thick or thin the ice is. The imagery does not tell me ice thickness.

Flying to Thule Greenland with US Air force Air Mobility Command delivering cargo and people.

Flying to Thule Greenland with US Air force Air Mobility Command delivering cargo and people.

Arriving in Thule on Mar.-8, we will first need to measure ice thickness along this A-B-C section with a sharp ice-cutting Kovacs drill and a tape measure. The US National Snow and Ice Data Center (NSIDC) distributes a “Handbook for community-based sea ice monitoring” that we will follow closely. This first ice survey will also give us a feel and visual on how the radar satellite imagery displays a range of ice and snow surfaces. One of my PhD students, Pat Ryan, will process and send us the ESA Sentinel-1 radar data while a small University of Delaware and Woods Hole Oceanographic Institution group will work on the ice in early April.

The mental preparation for this scientific travel to Thule and the sea ice beyond gives me the freedom and pleasure to explore new data such as Sentinel-1 imagery and perspectives on tremendous local traditional knowledge of the Inugguit who have lived with the sea ice for perhaps 4000 years. The town of Qaanaaq is 45 minutes by helicopter to the north of Thule Air Base (TAB) at Pituffik. The town was established in 1953 when local populations living in the TAB area were forcibly removed. Despite these challenges the displaced people have prospered throughout the Cold War, but a less predictable and rapidly changing sea ice poses a severe threat to the community whose culture, health, and livelihood still depends on hunting and traveling on sea ice. Stephen Leonard is an anthropological linguist at the University of Cambridge who lived in Qaanaaq for a year in 2010/11 when he made this video:

P.S.: If possible, I would very much like to work with a local person who knows sea ice and wild life that we would need protection from. Danish contacts are reaching out on my behalf to people they know in Siorapaluk, Qaanaaq, and Savissivik.

Petermann Gletscher and Greenland Climate Change

Multi-media story of two old-style scientists on a Greenland data rescue mission. Keith (Nicholls) and I were joined by Chris Mooney and Whitney Shefte of the Washington Post who just posted

Testifying before the US Congress back in 2010, I refused to endorse the view that a first large calving at Petermann Gletscher in North Greenland was caused by global warming. Additional events and analyses of new data and old data, however, convinced me that climate change forces Petermann Gletscher into a new and unknown state.

Polar Bears and Guns and Politics

Polar bears are endangered and need protection. They hunt and eat meat to survive. Seals are such meat as are scientists walking and working on the sea ice. I am planing an experiment in polar bear habitat. Do I need a gun to protect myself and my students working with me? About 10 people told me “YES” last week, all with experience working in polar bear habitat. Who am I to say no? Encounters between bears and people happen, but only rarely. None of the 10 people advising me to carry a shotgun or rifle ever discharged their weapon or had a bear encounter.

Polar bear as seen in Kennedy Channel on Aug.-12, 2012. [Photo Credit: Kirk McNeil, Labrador from aboard the Canadian Coast Guard Ship Henry Larsen]

Polar bear as seen in Kennedy Channel on Aug.-12, 2012. [Photo Credit: Kirk McNeil, Labrador from aboard the Canadian Coast Guard Ship Henry Larsen]

In 3 month’s time I hope to do ~20 day trips from Thule Air Base near Pituffik, Greenland to explore the oceanography and acoustics of the local fjord covered by sea ice. The US National Science Foundation supports this work, maintains a dormitory where we sleep, and provides us with two snowmobiles. We will use these motorcycles on skies to reach science stations on the ice covering Wolstenholme Fjord. We will drill 10” holes through 3-5 feet of sea ice, set-up an electric winch connected to a small generator, and probe the ocean’s temperature, salinity, bottom depth, and ice thickness to prepare for a quiet acoustic communication system to move data under water from the outer fjord to the pier at Thule and the internet.

Thule-NSF2017

Leading this science effort, I will have to estimate and manage potential risks which include encounters with polar bears. I will have to decide how much money to allocate to each risk that then may not be available for other activities such as to support students, buy better sensors, or return in the summer. The first and almost always best response is to hire a local hunter who knows the area along with its bears, ice, and weather. There are about 600 people living in Qaanaaq about 100 miles to the north. Most of them are children and grand-children who were forcibly removed from Pituffik in 1952 when more than 13,000 Americans built a large air field during the height of the Cold War. The local llanguage spoken in remote Qaanaaq is the Inuktitut dialect of north-west Greenland, the first foreign language learnt in school is Danish, and English is not widely spoken, however, Qaanaaq has two non-Inuit villagers who originate from Denmark and Japan.

Relations between Qaanaaq and Thule Air Base are complex and sensitive with regard to politics and finances. One of many perspective is that of Kim Petersen who writes in Dissident Voice about “The Struggle against Colonialism and Imperialism in Kalaallit Nunaat.” Kalaallit Nunaat refers to Greenland in the local language. While the forced removal of native populations from Pituffik to Qaanaaq in 1952 and the crash of a nuclear armed B-52 bomber into Wolstenholme Fjord in 1968 are not in dispute, the political arguments presented seem to me rather narrow, one-dimensional, and rooted in a tired ideological Left-Wing mode of conspiracy-thinking. Does this perspective represent the community of Qaanaaq? Perhaps I need to ask someone who may know:

Working on the sea ice off northern Greenland [Photo credit, Steffen Olsen]

Working on the sea ice off northern Greenland [Photo credit, Steffen Olsen]

It is not straight-forward to bring a gun to Greenland as it requires a large amount of paper work. Another layer of regulations relates to bringing a gun to an US military installation. Shooting a polar bear is a burocratic and political nightmare, because strict quotas exist for the “taking” of polar bears. International complications include Canada, because the quotas are assigned to Canadian and Greenlandic hunters from the same bear population. It is a sensitive topic in many dimensions, a riddle for which I have no solution.

How much time do I spent to prepare for an unlikely event such as a fatal polar bear encounter? Could I not argue with ethics that were instilled into me when hiking in the back-country of Denali National Park (no guns there). Park rangers then told me that I enter bear habitat and should do so respectfully with minimal impact. They gave me useful pointers on how to lower contact and I saw no bears hiking for 4 days alone without a gun, but grizzlies eat berries while polar bears do not.

So, should I carry a gun, if I am not ready to kill a bear while working in bear country? I can accept the consequences of injury and death for myself, however, I cannot do so for those who are with me. Perhaps this then is a path to a solution: Discuss this with all who will be with me on the ice.

Oceanography below Petermann Gletscher for 400 Days

Ocean data from 810 meters below sea level under one of Greenland’s last remaining ice shelves arrives every 3 hours at my laptop via a 3-conductor copper cable that passes through 100 meter thick ice to connect to a weather station that via a satellite phone system connects to the rest of the world. This Ocean-Weather station on the floating section of Petermann Gletscher has reported for 400 days today. I am still amazed, stunned, and in awe that this works.

The station started 20th August of 2015 as a small part of a larger joint US-Swedish expedition to North Greenland after friends at the British Antarctic Survey drilled holes through the Empire-State-Building thick ice shelf. It is powered by two 12 Volt car batteries that are recharged by two solar panels. When the sun is down, the car batteries run the station as in winter when temperatures reached -46 C. When the sun is up, the solar cells run the station and top off the batteries. The voltage during the last 400 days shows the “health” of the station:

Battery voltage at the Petermann Ocean-Weather Station from Aug.-20, 2015 through  Sept.-23, 2016. The polar night is indicated by slowly declining voltage near 12 V while during the polar day voltage is near 14 V with oscillations in spring and fall during the transition from 24 hours of darkness to 24 hours of sun light.

Battery voltage at the Petermann Ocean-Weather Station from Aug.-20, 2015 through Sept.-23, 2016. The polar night is indicated by slowly declining voltage near 12 V while during the polar day voltage is near 14 V with oscillations in spring and fall during the transition from 24 hours of darkness to 24 hours of sun light.

There is an unexplained outage without data from February 12-25 (Day 175-189) which happened a day after the first data logger shut down completely without ever recovering. Our station has 2 data loggers: A primary unit controls 2 ocean sensors, atmospheric sensors, and the Iridium satellite communication. The secondary unit controls 3 ocean sensors and the GPS that records the moving glacier. Remote access to the secondary logger is via the primary, however, each logger has its own processors, computer code, and back-up memory card.

Inside of University of Delaware command and control of five ocean sensors and surface weather station. Two data loggers are stacked above each other on the left.

Inside of University of Delaware command and control of five ocean sensors and surface weather station. Two data loggers are stacked above each other on the left.

The primary logger failed 11th February 2016 when we received our last data via Iridium satellites until Keith Nicholls and I visited the station 27th and 28th August 2016 via helicopter from Thule, Greenland. Since I could not figure out what went wrong sitting on the ice with the helicopter waiting, I spent a long night without sleep to swap the data logger with a new and tested unit. I rewired sensors to new data logger, switched the Iridium modem, transceiver, and antenna, changed the two car batteries, and now both data loggers with all five ocean sensors have since reported faithfully every 3 hours as scheduled as seen at

http://ows.udel.edu

Lets hope that the station will keep going like as it does now.

The major discovery we made with the ocean data are large and pronounced pulses of fresher and colder melt waters that swosh past our sensors about 5 and 25 meters under the glacier ice. These pulses arrive about every 14 days and this time period provides a clue on what may cause them – tides. A first descriptive report will appear in December in the peer-reviewed journal Oceanography. Our deeper sensors also record increasingly warmer waters, that is, we now see warm (and salty) waters under the glacier that in 2015 we saw more than 100 km to the west in Nares Strait. This suggests that the ocean under the glacier is strongly coupled to the ambient ocean outside the fjord and vice versa. More on this in a separate future posting.

Time series of salinity (top) and potential temperature (bottom) from four ocean sensors deployed under the ice shelf of Petermann Gletscher from 20th of August 2015 through 11th of February 2016. Temperature and salinity scales are inverted to emphasize the vertical arrangements of sensors deployed at 95m (black), 115 (red), 300 m, and 450 m (blue) below sea level. Note the large fortnightly oscillations under the ice shelf at 95 and 115 m depth in the first half of the record. [From Muenchow et al., 2016]

Time series of salinity (top) and potential temperature (bottom) from four ocean sensors deployed under the ice shelf of Petermann Gletscher from 20th of August 2015 through 11th of February 2016. Temperature and salinity scales are inverted in order to emphasize the vertical arrangements of sensors deployed at 95m (black), 115 (red), 300 m, and 450 m (blue) below sea level. Note the large fortnightly oscillations under the ice shelf at 95 and 115 m depth in the first half of the record. [From Muenchow et al., 2016]

P.S.: The installation and year-1 analyses were supported by a grants from NASA and the Jet Propulsion Laboratory, respectively, while the current work is supported by NSF for the next 3 years. Views and opinions are mine and do not reflect those of the funding agencies.