Compact 3-level U-Net that segments built-up / impervious surface from
multi-band Sentinel-2 tiles. Trained on US spaceport scenes with ESA WorldCover
(class 50) as labels; validated on held-out sites (unseen geography).
Purpose: annual built-up maps to track spaceport buildout over time —
WorldCover covers only 2020/2021; this model extends the signal to all Sentinel-2 years.
