Notations and conventions

Block diagram symbols

Symbol	Meaning
S#	A reverse-chain processing step (S1–S15), one per ATBD §5 block.
rounded box	A processing step (a function in s2_msi_raw_generator.reverse / forward_radiometric_atbd).
cylinder	A data store — input product, ADF, or output product.
solid arrow	Data flow between steps (a 2-D (lines, detector_columns) array).
\(X\)	raw focal-plane digital number (L0 domain).
\(L\)	at-sensor band radiance (L1B input), \(\mathrm{W \cdot m^{-2} \cdot sr^{-1} \cdot \mu m^{-1}}\).
\(A\)	per-band absolute-calibration gain (Band.cal_gain).
\(G\)	per-pixel relative response (PRNU), GIPP R2EQOG.
\(D\)	per-pixel dark signal, GIPP R2EQOG COEFF_D.
\(\alpha, \beta\)	per-band noise-model coefficients, \(\sigma = \sqrt{\alpha^2 + \beta \cdot \mathrm{DN}}\).

Units & types. Radiance in \(\mathrm{W \cdot m^{-2} \cdot sr^{-1} \cdot \mu m^{-1}}\); DN dimensionless uint16 in \([0, 4095]\); wavelengths in nm; line period in ms. Arrays are (along-track lines, across-track detector columns). Detector index 01–12; bands B01…B12, B8A (no panchromatic). Per-unit data keyed S2A/S2B/S2C.

Determinism. All stochastic steps (noise, synthetic ADF/calibration) use a seeded numpy.random.Generator; a fixed seed yields a reproducible product (REQ-QUAL-004).