THEME: OCEAN and WATER BODIES - Copernicus Browser

 

THEME: Ocean and Water Bodies

SATELLITE: Sentinel-2 L2A

 

INDEX: True color

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.

COMMENTS – OBSERVATION:

In the left image we can see areas depicted in dark brown, in December 2016, these are areas with abundant drought. In contrast, in the right image, in December 2024 respectively, the areas that had suffered this devastating fire appear to be now overgrown.

INDEX: false color

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 – OBSERVATION:

In the left image, in December 2016, the plants of the burned areas do not absorb the red color. In other words, in the image these areas are depicted in dark brown, while all the other areas in various tones of red. This is due to the drought. On the contrary, in the right image, in the same month of 2024, respectively, the plants have acquired their natural color and absorb the red, since reforestation has occurred. Thus, now all of Thassos is depicted in various tones of red.

 

INDEX: Normalized Difference Water Index (NDWI)

SUBJECT ANALYTICALLY:

The normalized difference water index is most appropriate for water body mapping. Values of water bodies are larger than 0.5. Vegetation has smaller values. Built-up features have positive values between zero and 0.2.

COMMENTS – OBSERVATION:

In the left image, we can see embedded features in the areas that have suffered fire. In December 2016, these appear with an index less than 0.2 and greater than 0 and are depicted in the images with very light shades of green. In contrast, in the right image, December 2024, the burned areas have returned to their natural vegetation.

 

INDEX:  Ulyssys Water Quality Viewer (UWQV)

SUBJECT ANALYTICALLY:

The script aims to dynamically visualise the chlorophyll and sediment conditions of water bodies, which are primary indicators of water quality. The chlorophyll content ranges in colors from dark blue (low chlorophyll content) through green to red (high chlorophyll content). Sediment concentrations are colored brown; opaque brown indicates high sediment content.

 INDEX:  Short wave infrared composite (SWIR)

SUBJECT ANALYTICALLY:

Short wave infrared (SWIR) measurements can help scientists estimate how much water is present in plants and soil, as water absorbs SWIR wavelengths. Short wave infrared bands (a band is a region of the electromagnetic spectrum; a satellite sensor can image Earth in different bands) are also useful for distinguishing between cloud types (water clouds versus ice clouds), snow and ice, all of which appear white in visible light. In this composite vegetation appears in shades of green, soils and built-up areas are in various shades of brown, and water appears black. Newly burned land reflects strongly in SWIR bands, making them valuable for mapping fire damages. Each rock type reflects shortwave infrared light differently, making it possible to map out geology by comparing reflected SWIR light.

COMMENTS – OBSERVATION:

In the left image, December 2016, the lack of water in the burned areas is depicted in dark brown, while the overgrown areas are depicted in green. In contrast, in the right image, December 2024, all areas are now depicted in green.