Case study Sentinel-2 reveals the barest Earth

Published:10 March 2022

A snapshot of regular satellite imagery on the left and Sentinel-2 Barest Earth imagery on the right

Researchers from Geoscience Australia and the Australian National University have recently released a new national Barest Earth product that uses the Digital Earth Australia satellite archive.

Satellite imagery can provide useful data for mapping surface mineralogy and geochemistry of soil and rock. However, exposed rock and soil are often masked by vegetation.

In 2019, researchers developed an algorithm to preferentially weight bare earth pixels from Landsat satellite images through time. This work produced a national scale Barest Earth mosaic of the Australian continent with significantly reduced seasonal vegetation cover, to support enhanced mapping of soil and geology.

This release takes advantage of improvements made since 2019 version and uses images from Sentinel-2 satellite observations, up to September 2020.

A snapshot of regular satellite imagery on the left and Sentinel-2 Barest Earth imagery on the right

A snapshot of regular satellite imagery on the left and Sentinel-2 Barest Earth imagery on the right

What is Sentinel-2

Sentinel-2 is part of the European Earth Observation program, with 2 polar-orbiting satellites: Sentinel-2A, launched in 2015, and Sentinel-2B, launched in 2017. The twin satellites provide shorter revisit times, increasing the frequency of observations and the likelihood of observing bare earth pixels that aren't obscured by clouds and shadows.

A significant advantage of the Sentinel-2 images is an improvement in spatial resolution with 4 bands at 10 metres compared to 30 metres for Landsat. This provides a 9 times improvement in spatial resolution with broad application in geological mapping, mineral exploration and natural resource management. In collaboration with the Terrestrial Ecosystems Research Network, the previous Barest Earth products have been used to map soil properties across the nation. These new finer resolution products will allow us to improve the spatial resolution of these soil property maps at the local farm and paddock scale.

Image over part of the township of Temora central NSW (lower left) comparing Sentinel-2 with other Sentinel-2 Barest Earth products

Comparison of (a) Sentinel-2 3-2-1 true colour with seasonal green vegetation cover (b) Sentinel-2 Barest Earth 3-2-1 true colour and (c) Landsat TM 30 year Barest Earth 3-2-1- true colour. Image over part of the township of Temora central NSW (lower left). The Barest Earth products significantly removes the masking of seasonal cropping/vegetation that would otherwise blanket the underlying soil response. Increased spatial resolution of the Sentinel-2 Barest Earth (b) compared with the 30-year Landsat Barest Earth (c)

The Barest Earth images can be used to map regolith that consists mainly of weathered rock and sediments. Soil can be seen as the upper most part of the regolith profile. Australia's surface is mostly regolith, demonstrated by the characteristic red hue of the continent due to the abundance of iron oxides.

The Barest Earth Sentinel-2 bands are available as 1:250 000 map sheet area tiles, each with 10 bands. Each tile has a slight buffer overlap of 60 meters to ensure no pixel is missing between adjacent sheet area boundaries.

More information

Read the Sentinel-2 Barest Earth extended abstract and download the Sentinel-2 Barest Earth tiles.

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