Monitoring Polar Ice Melt with Tip and Cue Technologies
Scientists use Tip and Cue strategies to monitor and assess ongoing changes in the elevation of arctic ice sheets - giving new insight into the ongoing threat of climate change.
The effects of climate change are increasing at unprecedented rates, with the average global temperature rising by more than one degree C since the late 1800s.
While regions around the globe are experiencing fluctuating and increasing average temperatures, the world’s arctic areas are witnessing the most significant changes.
According to the World Wildlife Foundation (WWF), temperatures in the Arctic are rising twice as fast as anywhere else on Earth - reducing sea ice by more than 10% every decade. The rapid loss of ice is causing global sea levels to rise, putting numerous coastal nations worldwide in jeopardy of land loss and natural disasters.
Based on sea ice data from the NOAA and as stated by the WWF, “Even if we significantly curb emissions in the coming decades, more than a third of the world’s remaining glaciers will melt before the year 2100. When it comes to sea ice, 95% of the oldest and thickest ice in the Arctic is already gone.”
The melting of glaciers doesn’t just affect global sea levels, either.
Melting glaciers can significantly impact the world’s weather systems, creating unpredictable weather patterns and changes in ocean currents that threaten everything from maritime safety to agricultural and fisheries production.
Background: Monitoring Ice Sheets in the Antarctic
Due to the sharp rise and devastating potential that arctic ice loss has on the world, scientists have focused on monitoring polar ice sheets and ice loss over the past couple of decades.
Today, monitoring ice loss is typically carried out by collecting physical ice data from satellites and aerial sensors using altimeter radars. Altimeter radars collect data on the absolute altitude, which is measured by the Above Ground Level (AGL) of ice sheets.
However, certain types of satellites and sensors are costly and resource-dependent to operate and can also deliver varying results based on the type of sensor, so a two-step approach called ‘Tip and Cueing’ is often utilized to make the process more efficient, more accurate, and more affordable.
Materials and Methods: Tip and Cue Strategies Employed
In a recent study conducted by a team from the Chinese Academy of Sciences, researchers used the ‘Tip and Cue’ approach to combine elevation data of an arctic ice sheet from two different satellites and sensors - evaluating the accuracy of the methodology using separate datasets from highly accurate earth observation satellites.
Data for the study was obtained between 2016 to 2019 from sensors in the CryoSat-2 and Sentinel-3 - two satellites developed and operated by the European Space Agency (ESA).
The CryoSat-2 is equipped with a lower-resolution sensor with wide-range coverage that can monitor large regions and areas, including the complex edge regions of arctic ice sheets. The Sentinel-3, on the other hand, is equipped with a higher-resolution sensor that provides far better accuracy under specific environmental parameters like dense cloud cover.
The team of researchers needed to ensure their estimates were accurate, so they decided to first filter the ice sheet data using a clustering algorithm. Simply put, the algorithm divided two sets of data by their values, rejecting the clusters that contained outliers and potentially significant measurement errors.
The team also used a “fitting model” to pinpoint and extract ice sheet elevation changes from both satellites - correcting data points for measurement bias. To validate the results, the team compared the data with elevation change data using other altimeters not used by the two satellites.
The aim of the study was to gain a more defined and time-accurate map of sea ice elevation changes in the region and validate the Tip and Cue methodology for accurately monitoring and assessing polar ice loss.
Findings and Validation: Study-Specific Accuracy Achieved
Analysis of the data showed a rate decrease in the average ice sheet elevation in the region of 4.3 +/- 0.9 cm per year between 2016 and 2019.
The findings did vary based on the area of the ice sheet, with data showing that the inner continental ice sheet (the area where the sheet is mostly flat) decreased at a slower rate than the edges.
The rate of ice loss for the inner continental sheet was measured at only 1.1 +/- 0.3 cm per year on average - a significantly lower rate than at or near the edges.
Findings from the study were then validated with LiDAR altimeter data from the OIB and ATLAS/ICESAT-2 satellites using their land ice height to validate the data in the findings. These satellites are known to deliver highly-accurate ice sheet elevation data and have been monitoring the polar regions since 2009. The data included geolocation estimates of ice-surface elevation and ancillary parameters that could help interpret elevation change estimates.
Based on comparisons of the datasets, the methodology used to monitor the Arctic ice sheet between 2016 and 2019 proved accurate and affordable.
As stated by Professor Jingjuan Liao, “We derived a correlation between elevation changes and the surface slope, with rapid elevation changes occurring more often in areas with large terrain undulations, such as mountainous and marginal ice shelves… Our study presents an effective method for improving the measurement accuracy [of ice sheet loss] by combining elevation information from new radar altimeters. This could enable long-term monitoring of global climate change in the Antarctic region.”
The study results have given a hopeful outlook to researchers looking to curb the impacts of climate change on the world’s polar regions and ice sheets, opening doors to new monitoring potentials that include the adoption and deployment of various optical and high-resolution satellite sensors.
The Tip and Cue strategy could allow more affordable and accurate long-term monitoring of some of the world’s most remote regions, providing valuable insights to global officials and policymakers tasked with putting the brakes on the effects of climate change in the Arctic regions.