Introduction

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Introduction#

This Data Processing Model (DPM) describes the processing chain of the Sentinel-2 MSI Synthetic Raw Data Generator (s2_msi_raw_generator) — the reverse chain that runs a Sentinel-2B L1B product backwards through the exact inverse of the operational L0→L1B radiometric chain (invert offset, relative-response/PRNU, dark, un-bin, SWIR re-stage, defective, crosstalk, on-board equalization) to reconstruct L1A → L0plus (CCSDS-122 ISP) → Synthetic L0. MTF-deconvolution is OFF, so PSF and noise are not re-applied. Success is the Synthetic L0 compared against the reference ESA L0 img (10/20 m bands ≤ ~4 DN). It complements the ATBD (docs/atbd/atbd.md, the per-step physics) and the SDD (docs/sdd/, the software structure). DRD: ECSS-E-ST-40C Rev.1, tailored for EOPF processor.

Processing chain#

The chain inverts the operational L0→L1B radiometric chain of the msi-processor, step by step, to reconstruct focal-plane counts from a S2 L1B. It is radiometric-only (input is already in per-detector sensor geometry). Because MTF-deconvolution is off, no PSF re-blur and no noise are re-applied; the reverse chain runs the ordered inversion steps that reconstruct L1A → L0plus → Synthetic L0 (ATBD §5):

        flowchart TD
    IN["S2 L1B at-sensor radiance<br/>(per-detector geometry)"]
    S1["S1 · radiance → equalized signal DN (X = A·G·L + D, A = cal_gain)"]
    S3["S3 · undo scene framing / round-clamp"]
    S4["S4 · invert radiometric offset (−100, GIPP R2PARA)"]
    S5["S5 · un-bin 60 m bands (B01/B09/B10)"]
    S7["S7 · invert relative response / PRNU (GIPP R2EQOG, cubic VNIR / bilinear SWIR)"]
    S8["S8 · SWIR re-arrangement, reverse (B10/B11/B12)"]
    S9["S9 · invert inter-band crosstalk (GIPP R2CRCO ≈ 0 for S2A)"]
    S10["S10 · re-insert blind/defective pixels (GIPP R2DEPI / BLINDP)"]
    S11["S11 · invert per-pixel dark signal (GIPP R2EQOG COEFF_D)"]
    S12["S12 · invert onboard equalization"]
    S14["S14 · quantize to 12-bit uint16 [0, 4095] → Synthetic L1A"]
    S15a["S15a · assemble L0plus · CCSDS-122 lossless compress (onboard step; ccsds122)"]
    S15b["S15b · L0 · ISP packetize (SEQ flags + CUC) + SAD telemetry + STAC/PSFD naming"]
    GD["L0plus codec round-trip:<br/>decode(L0plus) == L1A bit-exact (read_l0_isp_dn)"]
    VAL["validate: Synthetic L0 vs reference ESA L0 `img`<br/>(10/20 m bands ≤ ~4 DN)"]
    IN --> S1 --> S3 --> S4 --> S5 --> S7 --> S8 --> S9 --> S10 --> S11 --> S12 --> S14 --> S15a --> S15b
    S15a -.-> GD
    S15b -.-> VAL

Realized execution order. reverse.reverse_mvp runs S1 → S7 → S11 → S12 → S14 — the DN-domain inversion steps that reconstruct the L1A focal-plane counts; no PSF re-blur and no noise are re-applied (MTF-deconvolution off). reverse.reverse_full additionally inserts S8 (SWIR re-arrangement, reverse) and S10 (defects) as genuine reverse chain steps. Verification is the L0plus codec round-trip — decode(L0plus) reproduces the Synthetic L1A bit-exactly (read_l0_isp_dn) — and the comparison of the reconstructed L0 against the reference ESA L0 img (10/20 m bands ≤ ~4 DN).

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