OBSERVER: Monitoring Glaciers from Space

OBSERVER: Monitoring Glaciers from Space

OBSERVER: Monitoring Glaciers from Space

Thu, 03/11/2022 – 11:46

A warming climate

European Union, Copernicus Sentinel-2 imagery of the Alpine glaciers in 2022

Glaciers are essential to enabling life on Earth. As frozen towering giants, they act as freshwater reservoirs providing potable water for human consumption. Meltwater that is released by the melting of the ice helps irrigate crops and fields as is the case for farmers in Switzerland’s Rhone Valley. In Norway, scientists and engineers have been able to tap into glacial resources and generate electricity thanks to the damming of glacial meltwater. In addition to the benefits which can be directly appreciated by humans, glaciers are crucial to the hydrological cycle as they have a central role in regulating climate change.  

European Union, Copernicus Sentinel-2 imagery of the first significant melt event of 2021 in Greenland

Between 1992 and 2017, the Greenland and Antarctic ice sheets have together lost 6,400 gigatonnes (Gt) of ice, causing global sea levels to rise by nearly 2 centimetres (European State of the Climate Report 2019). The Greenland ice sheet loss rate has exponentially increased over time with almost half of the ice lost between 1992 and 2018 having occurred between 2006 and 2012. As for the Antarctic ice sheet, it is now losing ice faster than ever before. Prior to 2012, Antarctica lost ice at a steady rate of 76 Gt per year. However, there has since been a threefold increase with more than half the total ice loss of the last 28 years occurring between 2012 and 2017.

From 1993 to 2020, the global sea level has increased by about 3.1 centimetres (The Copernicus Marine Environmental Monitoring Service’s Ocean State Report 5).  This report further states that the warming of the world’s oceans and melting land ice caused sea levels to rise by 2.5 mm per year in the Mediterranean; 4.5 mm per year in Baltic Sea; 4.2 mm per year in western Pacific Islands; 1.7 mm per year in the Black Sea; 3.6 mm per year in the Iberian Biscay Ireland Seas; 2.9 mm per year in the North West Shelf; 3.5 mm per year Central Pacific Islands and 3.4 mm per year in Pacific Islands 30% of this global rise is directly attributable to ocean thermal expansion and 70% to land ice melt. Monitoring the Earth’s polar ice sheets is therefore hugely important to determining their past, current, and future contributions to sea level rise and to mitigate the resulting impact on coastal populations.

Cumulative total mass change of the Greenland Ice Sheet, and its corresponding contribution to sea level rise. The shading represents the cumulative uncertainty. Data source: IMBIE. Credit: IMBIE/ESA/NASA.

How can Copernicus help?

Thanks to its stable sensing geometry and high resolution, Copernicus Sentinel-2, helps monitor spatial changes over time, with a high revisit time of minimum 5 days. For instance, Sentinel-2 can track snow distribution and how fast it is melting or monitor the terminus where a glacier meets a lake or an ocean and enable the understanding of its dynamics over time. The high resolution of the data obtained allows monitoring at an individual glacier level. Thus, it is possible to link the changes undergone by each glacier to its type and its lithology, as well as its surrounding environment with its interacting elements, like fjord circulation (how ice and water move and coexist inside fjords) or ice buttressing (the stabilizing effect of ice sheets on the grounded parts of glaciers). Furthermore, the constant recording accomplished by the Sentinel satellites enables the accurate analysis of the monthly or weekly precursor motions of disasters such as landslides or mountain creeps which in turn allows for a better understanding of the mechanics of such natural hazards.

­­ Cumulative mass changes in Europe from 1967 to 2021 for glaciers with long-term records in nine different regions. Mass balance values are given in the unit ‘metre water equivalent (m w.e.)’ relative to 1997. Data source: WGMS (2021, updated). Credit: C3S/WGMS.

Moreover, Copernicus Sentinel satellites provide accurate data on ice parameters such as the mass balance of the glacier or the total change in ice-thickness, which are critical to understand the current dynamics of the melting of glaciers, the shrinkage of ice sheets and the rise of sea levels. For example, sea level indicators such as maps of sea level anomalies are based on the data provided by Sentinel-6 (dedicated to sea level rise monitoring) and Sentinel-3. Many of the datasets mentioned above are freely available, in the Climate Data Store (CDS) of the Copernicus Climate Change Service (C3S), monitored monthly in the Copernicus Marine Service (CMEMS,  sea level maps) and annually published in the annual ocean state report (5th edition, June 2022).

Figure 2: Sea level trends (mm/year) from January 1993 to July 2021 in shades of blue (from -4 mm) to red (to +7 mm). The data have not been adjusted for glacial isostatic adjustment nor for the TOPEX-A instrumental drift. Data source: CMEMS Ocean Monitoring Indicator based on the C3S sea level product. Credit: C3S/ECMWF/CMEMS.

Copernicus Glacier Projects

A cooperation between the Norwegian water resources and energy directorate (NVE), the Norwegian Polar Institute (NPI) and the University of Oslo, the Project, Copernicus Glacier Service, uses Copernicus Sentinel satellite data to closely track the glacier environment on Earth. The CGS aims to monitor glaciers in mainland Norway and in Svalbard. Among others, they track glacier velocity which can be determined by from repeat optical or radar images. The velocities are derived from two pairs of images with 12-day intervals taken from Sentinel-1 or Sentinel-2, resulting in displacement fields that can be processed considering expected magnitude and direction of movement. The data is used for detecting surge, to study glacier dynamics or assess ice discharge to the ocean.

European Union, Copernicus Sentinel-2 imagery

The Copernicus Climate Change Service uses the estimations of the mass balance of glaciers to evaluate their contribution to sea-level rise. The mass balance of a glacier is the difference between snow accumulation (mass gain) and melt of ice and snow (mass loss). The measurements of specific reference glaciers’ mass balance are compiled by the World Glacier Monitoring Service (WMGS) thanks to a scientific collaboration counting more than 40 countries worldwide that dates back more than 30 years. As an example, since 1997 the monitored glaciers in Europe are estimated to have lost between 9 and 26 metres water equivalent (m.w.e) of mass, which corresponds to between 10 and 29 meters of ice thickness loss. Calculating the contribution of this mass balance to the rise of sea-level is a complicated task, which requires various methods and sources of measurements to obtain estimations, such as in-situ data, DEM differentiating, altimetry or gravimetry. Furthermore, the measurements for one region generally come from a small sample of glaciers, which are not always representative enough of the overall regional trend. The C3S estimates the contribution of the glaciers to the rise of the sea-level through the different techniques mentioned above and further works to obtain scaling factors of the measurements for several regions, to correct the estimations made from the small samples of glaciers to match their real situation.

Outlook onto the future

Regarding the melting ice of glaciers all over the world, closely monitoring icesheets and glaciers parameters is becoming critical. By 2030, the 6 current Copernicus Sentinel missions will be supported by new missions which will expand Copernicus capacities. Among the Copernicus Expansion missions foreseen, CRISTAL, the Copernicus Polar Ice and Snow Topography Altimeter, will help provide more timely and spatially accurate measurements of the ice sheets and glaciers worldwide thanks to its dual frequency radar altimeter and its microwave radiometer.

Thu, 03/11/2022 – 12:00

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