PNB

This false-color image can also be referred to as a land cover type false-color image. It combines the calculated water body index (NDPI), near-infrared reflectance (NIR), and blue light (Blue). Specifically, the calculated NDPI data is mapped to the red channel of the visible spectrum, NIR data to the green channel, and blue spectrum data to the blue channel.

This map layer is available year-round, but it is most applicable and informative during the active vegetation period. In Figure 1, the color tone changes are visualized across different seasons. Generally, the map layer appears red in early spring, transitions to colorful tones as different land cover types become distinct in summer, and gradually reverts to reddish hues in autumn and withering vegetation. In winter, when the ground is bare, the reddish tone remains, but with snow cover, the map layer shifts to bluish tones. Snow appears as light blue on this false-color layer, while open water bodies without ice appear dark blue.

Figure 1. PNB false-color views across seasons. From top left: spring, summer, autumn, winter.

Chlorophyll in plants reflects near-infrared light well but reflects significantly less blue light. The near-infrared information is displayed through the green channel, and healthy plants typically have low NDPI values. As a result, areas with high chlorophyll content appear green in the PNB false-color combination. It can be generalized that neon greens represent areas with high chlorophyll content and low NDPI values, such as lush, unmown fields, deciduous forests, and green spaces (Figure 2). Coniferous trees, which reflect slightly less near-infrared light compared to deciduous trees, appear brownish-green in the images (Figure 3). However, due to potential exceptions, detailed analysis of specific areas is necessary to draw accurate conclusions.

Figure 2. On the left, the PNB false-color image highlights optimal vegetation in bright green; on the right, a comparison with the vegetation index (NDVI).

Figure 3. On the left, coniferous forests appear dark brownish-green, while deciduous forests are lighter textured green. On the right, a forestry orthophoto for comparison.

Wetlands and peatlands are well distinguished in the PNB images. Satellite imagery taken in late spring or summer shows these areas as distinctly red compared to their surroundings (Figure 4). These areas reflect little blue and near-infrared light and have high NDPI values, which, when displayed through the red channel, give them their red hue.

Figure 4. Wetlands and peatlands stand out in red tones, with the Satilao sub-1m mask activated (reference to Satilattu).

Mown grasslands and plowed fields appear bright pink (Figure 5). Bare soil surfaces have high NDPI values and reflect less near-infrared light. The pink color is due to the increased contribution of the blue channel in the false-color image. High values in both the red and blue channels produce this pink tone. Depending on the proportion of the blue channel, the tone can vary from pink to bluish-purple.

Figure 5. Plowed fields and areas with minimal vegetation appear pink in tone (left). On the right, an RGB image for comparison.

Water bodies absorb near-infrared light well and reflect little blue light. Water bodies generally have low NDPI values. As a result, in the PNB spectral combination, water bodies appear dark blue or black. Clouds reflect both near-infrared light and blue light and have low NDPI values. Thus, clouds (and snow, among others) appear light blue.

Figure 7. Different types of clouds and their impact on the PNB false-color image. In the upper left corner, Pärnu Bay is visible.