The Google Earth Engine Digitisation Tool (GEEDiT) and the Margin change Quantification Tool (MaQiT) – simple tools for the rapid mapping and quantification of changing Earth surface margins

Abstract

Abstract. Changes in margins derived from satellite imagery are quantitative indicators of the environmental processes and drivers acting on the Earth's surface, for example retreating ice margins or coastal changes with rising sea level. However, the large-scale rapid visualisation and analysis of the satellite record is often impractical due to factors such as computer processing power, software availability, internet connection speed and/or user expertise in remote sensing. Here are presented three new, freely accessible tools that together can be used to process, visualise and review data from the full Landsat 4–8 and Sentinel 1–2 satellite records in seconds, enabling efficient mapping (through manual digitisation) and automated quantification of margin changes. These tools are highly accessible for users from a range of remote-sensing expertise (from academics to high school students), with minimal computational, licensing and knowledge-based barriers to access. The Google Earth Engine Digitisation Tool (GEEDiT) allows users to define a point anywhere on the planet and filter data from each satellite for user-defined time frames, maximum acceptable cloud cover extent, and options of predefined or custom image band combinations via a simple graphical user interface (GUI). GEEDiT allows georeferenced vectors to be easily and rapidly mapped from each image, with image metadata and user notes automatically appended to each vector, which can then be exported for subsequent analysis. The GEEDiT Reviewer tool allows users to quality control their own/others' data and also filter existing datasets based on the spatial/temporal requirements for their particular research question. The Margin change Quantification Tool (MaQiT) is complementary to GEEDiT and GEEDiT Reviewer, allowing the rapid quantification of these margin changes by utilising two well-established methods that have previously been used to measure glacier margin change and two new methods via a similarly simple GUI. A case study of the lake-terminating glacier Breiðamerkurjökull, Iceland, is used to demonstrate the complementary functionality of GEEDiT, GEEDiT Reviewer and MaQiT, though it should be noted that MaQiT is also suitable for the (re-)analysis of existing datasets not generated by GEEDiT. MaQiT has been developed with the original aim of quantifying tidewater glacier terminus change, though the methods included within the tool have potential for wide applications in multiple areas of Earth surface science (e.g. coastal and vegetation extent change). It is hoped that these tools will allow a wide range of researchers and students across the geosciences to efficiently map, analyse and access volumes of data that would have previously proven prohibitive.

‘Detachment’ of icefield outlet glaciers: catastrophic thinning and retreat of the Columbia Glacier (Canada)

“…Our investigations of glacier margin change were carried out using the Google Earth Engine Digitisation Tool (GEEDiT), developed by Lea (2018), to explore all optical imagery for the period between July 2009 and June 2019. Our investigations of glacier margin change were carried out using the Google Earth Engine Digitisation Tool (GEEDiT), developed by Lea (2018), to explore all optical imagery for the period between July 2009 and June 2019.…”

“…Our investigations of glacier margin change were carried out using the Google Earth Engine Digitisation Tool (GEEDiT), developed by Lea (2018), to explore all optical imagery for the period between July 2009 and June 2019. This reduced the image selection to 56 sets, but improved visualisation of the data by only exploring change over timescales of greater interest than day-to-day (Lea, 2018). This approach is useful because it enables rapid searching of the image archive, regardless of cloud cover, and for image usefulness to be determined on a case-by-case basis.…”

“…In order to document the changes taking place on the Columbia Glacier, we used freely available optical satellite imagery from Landsat-5, Landsat-7, Landsat-8 (via USGS Earth Explorer) and Sentinel-2 (via ESA Copernicus). Our investigations of glacier margin change were carried out using the Google Earth Engine Digitisation Tool (GEEDiT), developed by Lea (2018), to explore all optical imagery for the period between July 2009 and June 2019. The approach is particularly advantageous since it allows all imagery to be viewed virtually instantaneously and then either rejected or (where the margin is clearly visible) used in assessing glacier change.…”

“…This dataset was subsequently temporally filtered so as to explore images separated by at least 7-day gaps (and a maximum of 400 days). This reduced the image selection to 56 sets, but improved visualisation of the data by only exploring change over timescales of greater interest than day-to-day (Lea, 2018). For all datasets, within GEEDiT, true-colour images were generated by combining bands (3-2-1 for pre-Landsat 8; 4-3-2 for Landsat 8 and 4-3-2 for Sentinel-2).…”

“…Changes in glacier extent were quantified using both a single centreline and a multi-centreline method (Lea, 2018). This is a development of the more traditional single centreline approach, developed by Lea (2018), here generating 42 centrelines, separated by gaps of 10 m, across the glacier tongue, parallel to the centreline shown in Figure 2. The approach offers significant new insights because, by facilitating many one-dimensional measurements of terminus change, spatial variability in the glacier margin position is easily determined.…”