THEME: Snow and Glaciers
SATELLITE: Sentinel-2 L2A
SUBJECT: True color optimized
IMAGES:
SUBJECT ANALYTICALLY:
This optimized True color
script uses the visible light bands red, green and blue in the corresponding
red, green and blue color channels, resulting in a product with natural colours
that represents the Earth as humans would naturally see it. The visualisation
uses highlight compression and improves the contrast and color vividness
through minor contrast and saturation enhancement.
When comparing the two
satellite images with True Color index, differences in snow and ice coverage
are observed. The image on the right, corresponding to 2024, shows
significantly greater snow cover, especially in the mountainous parts of the
island, in contrast to the 2016 image (left), where the presence of snow is
limited. This may indicate more intense winter weather conditions or changes in
the climate patterns of the region.
INDEX: false color
SUBJECT: false color optimized
IMAGES:
SUBJECT ANALYTICALLY:
A false color composite uses
at least one non-visible wavelength to image Earth. The false color composite
using near infrared, red and green bands is very popular (a band is a region of
the electromagnetic spectrum; a satellite sensor can image Earth in different
bands). The false colour composite is most commonly used to assess plant
density and health, since plants reflect near infrared and green light, while
they absorb red. Cities and exposed ground are grey or tan, and water appears
blue or black.
Comments-observations:
In the comparison of the two
images, strong differences in snow cover are observed. In the 2024 image, the
white and blue shades indicate the extensive presence of snow and ice in the
mountainous parts, which is not so evident in the 2016 image (left). At the
same time, the red shades, which correspond to vegetation, appear more intense
in 2016, which may indicate changes in climatic conditions or land use.
INDEX: Highlight optimized natural color
IMAGES:
SUBJECT
ANALYTICALLY:
This script aims to display the Earth in beautiful
natural color images. It uses highlight optimization to avoid burnt out pixels
and to even out the exposure.
Comments-observations:
In the comparison between the
two images, a significant decrease in snow-covered areas and glaciers is
observed in 2016 compared to 2024. The areas shown in white or light color in
the 2024 image are more extensive compared to those in 2016, which indicates a
retreat of snow-covered areas. This change can be attributed to natural climate
fluctuations
INDEX: Normalised Difference Snow Index (NDSI)
IMAGES:
The Sentinel-2 normalised
difference snow index can be used to differentiate between cloud and snow cover
as snow absorbs in the short-wave infrared light, but reflects the visible
light, whereas cloud is generally reflective in both wavelengths. Snow cover is
represented in bright vivid blue.
In comparing the two images, a
significant increase in the area covered by snow and ice in 2024 is observed
compared to 2016. The 2024 image shows many more areas with light color,
indicating more intense snow cover on a larger scale. This increase may be due
either to unusually low temperatures that year or to other environmental
factors that deserve further investigation. This observation indicates that the
climate in the region may be experiencing increased variability.
GROUND DATA:
Thassos is an island in the northeastern Aegean Sea with a rich geological history. It is characterized by a pronounced relief, mountainous massifs and rich vegetation. The highest point of the island is Mount Ypsario, with an altitude of 1,204 meters, where snow cover appears during the winter. Its geological history affects the relief and drainage of the island, contributing to the retention of water and the formation of microclimatic conditions. In general, Thassos does not have glaciers due to the Mediterranean climate, but it does have seasonal snow cover at the highest altitudes.
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