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Image of the Week — An Early Spring via Satellite

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The study of the Earth's natural life cycles is known as phenology. Scientists track the emergence of shoots and leaves, blooming flowers and pollinators as phenological signals every spring. Spring has sprung earlier than usual in much of the United States this year. The USA National Phenology Network notes that much of the country has seen spring come 3 to 4 weeks faster than normal. Parts of the southeast have seen their earliest blooms in 39 years. Phenology is tracked by a network of observers but satellites like Landsat can also highlight the impact of an early spring. This area near the border of North and South Carolina is among those seeing its earliest leaf-outs and blooms on record. There's little difference between the 2020 and 2018 images in natural color, but Landsat's infrared and red bands can tease out the change through a greenness indicator called the Normalized Difference Vegetation Index, or NDVI. The early spring shines through clearly with NDVI. Areas with middling greenness in 2018 have brighter signals in 2020. Lakes, rivers, floodplains and marshes show the most vivid change. This image isolates the areas that saw higher NDVI. The green gradient represents healthier plant life, with the darkest areas showing the highest spikes. Most citizens can't run satellites, but they can contribute their observations to the Phenology Network. The non-profit group welcomes contributions from volunteers of nearly any age, through its Nature's Notebook program.




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