TOA (Top-of-Atmosphere)

TOA reflectance is derived from the sensor measurement and normalizes for illumination, but it still includes atmospheric effects such as aerosols, water vapor, and scattering.

TOA can be useful when you need fast processing, when atmospheric correction is unreliable, or when you want to apply a custom correction method. The downside is that TOA values can vary more across dates due to changing atmosphere.

If your goal is time-series comparability for indices or thresholds, surface reflectance is usually a better baseline, assuming the correction is consistent.