BRDF correction

Bidirectional Reflectance Distribution Function correction — adjusting imagery so a surface looks the same regardless of the sun-sensor viewing angle.

Why it matters

Without it, the same field looks brighter or darker just because the satellite viewed it from a different angle — which would corrupt any change-over-time analysis. HLS applies BRDF correction so Landsat and Sentinel-2 can be compared directly.

In plain terms

Removing the “glare angle” effect, so a meadow photographed at noon and at dusk reads as the same meadow, not two different ones.