Satellite images from the Sat4Envi project support agriculture

The photo from December 6, 2019, shows a very clear image of the snow cover in the Tatra Mountains and cultivated fields – shades of cyan and dark blue (the colour depends on the angle of illumination of the areas). Zakopane has a gray colour. As it moves north, the green and brown colours become dominant, these are forest areas. The colour is dark green in coniferous and brown in deciduous, although in this case it is very difficult to capture the differences in the colour composition of the leafless forest and moist, uncovered ground in the background. The range of natural and artificial water reservoirs – for example, Lake Dobczyckie – In dark blue colour is also clearly visible in the RGB Agriculture image. Big cities – including Krakow – are mainly gray and purple. There is not much snow here, but it appears in the uplands, in arable fields north to Krakow (in the vicinity of Skała and Słomniki, as well as near the runways of the Balice airport (east of Krakow). Despite the advanced winter, the grassy apron of the airport is also visible (light green), from which the runways stand out (urbanized areas, purple). A similar, although slightly more intense, green is also adopted by Błonia in Kraków, a large, triangular meadow near the city center. In Krakow itself, you can also see popular bathing areas: Bagry, Kryspinowski Reservoir, and Budzyński Reservoir.

Due to the use of specific properties of radiation reflection in various spectral bands, we obtain the possibility of “extracting” a particular element of the image, which are clouds against the background of snow. In the visible light spectrum, both clouds and snow reflect very well solar radiation with the same wave range. For a person unfamiliar with the terrain’s topography (e.g., distribution of mountain ranges), these elements of the satellite image may be indistinguishable (cloud and snowmelt into a white area). By using RGB colour combinations such as “Agriculture,” we can distinguish the “whiteness” of a water cloud from the “whiteness” of snow by using a medium infrared channel (channel 11 for MSI Sentinel-2). This is possible because snow and ice absorb solar radiation in 1.6 µm band very strongly, while the water cloud reflects it.This specific characteristic distinguishes the low-lying cloud/fog in the mountain valleys (on the border of Poland and Slovakia in the south-eastern part of the characterized area) from areas free from cloudiness but with accumulated snow.

In the photo from April 9, 2020, the lack of snow is most noticeable – It occurs only in the upper mountains. The Tatra vegetation floors are mainly exposed, like the forests around Zakopane and Nowy Targ – dark green. The snow is still between Nowy Targ and Mszana Dolna in the Gorczański National Park (dark green forests and cyan corresponding to snow areas) – It can be seen, among others, on the Turbacz Massif. However, it is not found in the Niepołomice Forest (rotten-green colour); it has also completely disappeared from the vicinity of Krakow. Around Krakow and Proszowice, we can see both heavily built-up areas (purple/gray) and “empty” areas in shades of brown and pink – this is probably the soil lying on arable/cultivated fields. There are numerous areas with the beginning of plant vegetation in light green colours. In Krakow, for example, it is a small green square located north of Błonie – Jordan Park. The Krakow Wolski Forest, just like the Niepołomice Forest, is blooming – It has the colour of green mixed with brown. In this respect, it differs significantly from the dark green coniferous forests, proving that RGB Agriculture images perfectly emphasize the differences between individual plant species, in this case trees that dominate in a given area.

The last colour composition was created from the data recorded on August 2, 2020. It is almost the middle of summer – we can see that there is practically no snow in the Tatras anymore. On the highest peaks of the mountains, there is a characteristic colour – magenta – reflecting the exposed “naked” rocks in this colour composition. On the other hand, individual plant levels of high mountains are clearly visible, as well as single, long and dark shadows, white cumulus clouds over the Tatra Mountains. Clouds also appear over the Gorce and around Tarnów. As in the description of the image concerning the winter period, we can also describe the type of visible cloudiness by its colour. Low-floor water clouds, such as the small cumulus clouds visible over the Tatras, Gorce, and other higher parts of the mountains, are white. Clouds on the high floor, like the clouds visible in the vicinity of Tarnów, made of tiny ice crystals, are cyan.

It is green around Zakopane – there are pastures here, but there are not many cultivated fields. The Niepołomicka Forest and the Wolski Forest have become more mature, more intense colors of green – the trees are covered with leaves. Apparently, the area around Krakow has been affected by drought, the grass at the Balice airport and even in part of Jordan and Błonie Park is brown. Brown and pink stains north of Krakow also attract attention – these are arable fields where crops have already been harvested. There are also many areas with bare soil (light purple) – there is also already after the harvest. Thus, there are not many cultivated plants still growing at this time of the year, but these fields are not hard to find – in the photo, they are shown in light green colours. The gray-purple “veins” are built-up and urban areas, concentrating along the river valleys.