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# Software verification & validation report

**Project:** Sentinel-2 MSI Synthetic Raw Data Generator (`s2_msi_raw_generator`) · **DRD:** ECSS-E-ST-40C Rev.1 (Software verification
report / validation report, SVR). Plan: `plan.md`. Requirements: `../srs.md`.

## 1. Summary

`s2_msi_raw_generator` runs a Sentinel-2B **L1B** *backwards* — the exact inverse of the
operational L0→L1B radiometric chain (invert offset, relative-response/PRNU, dark, un-bin, SWIR
re-stage, defective-pixel, 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 versus the reference ESA L0 `img` (10/20 m bands ≤ ~4 DN); the L0plus codec
round-trip `decode(L0plus) == L1A` is bit-exact as a supporting check.

The automated test suite — **21 files, 201 tests at v0.3.0 —
passes in full (201 passed, 5 skipped), green in GitLab CI**. The skips are the S2 L1B/eopf-gated tests, which
pass when `S2_GIPP_DIR` / `S2_L1A_INPUT` are supplied (verified on the operational GIPP and a
L1A). All *realized* requirements in the SRS are verified against the reverse-chain reconstruction.

## 2. Test inventory

| Test file | #funcs | Verifies |
|---|---|---|
| `test_reverse.py` | 11 | Sensor model (13 bands, no PAN; gains; TDI = B03/B04/B11/B12); DN-domain gain/offset inversion exact; radiometric chain (offset, relative-response, dark, on-board-eq) exactly invertible (rtol 1e-9); quantize bounds (`np.clip`/`np.rint` → uint16); MVP output contract |
| `test_esa_adf_data.py` | 11 | `unit_from_platform`; per-unit SRF centre/bandwidth/equiv-λ; spectral metadata (shared sensor/SRF machinery the reverse chain reuses for band identity) |
| `test_calibration.py` | 4 | Calibration sub-set recovery — derived **dark within bound of truth**, **relative-response correlation > 0.9**, $\langle g \rangle = 1$ (±1e-6), **$A \approx$ `cal_gain` (±5 %)**; `estimated_adf` uses derived not truth; dark acquisition carries no scene signal |
| `test_roundtrip_atbd.py` | 3 | Relative-response/PRNU **inversion** flattens FPN (equalization → **< 0.3× raw**) + recovers flat scene (atol 1e-6) |
| `test_l0product.py` | 3 | `reverse_to_l0_frames` uint16 in range; L0 write+reopen structure (band/mask, B8A→b8a, STAC `eopf:type=S2MSIL0_`, TDI list, `physical_gains`, `line_period`, provenance); **full 156-array contract (12×13)** |
| `test_gipp.py` | 5 | R2EQOG cubic + bilinear parse (dark, gains); R2DEPI/BLINDP/R2PARA (−100/−1000)/R2CRCO (≈0); `from_gipp` builds ADF + blind-column width alignment; optional operational-GIPP dark in DQR range |
| `test_isp.py` | 8 | CCSDS primary-header round-trip; APID > 2047 rejected; CUC time coarse/fine; frame ISP header shape/seq/length; timestamps step by `line_period`; SAD packets; deterministic 11-bit APID; Synthetic L0 `with_isp` writes ISP + telemetry |
| `test_integration.py` | 1 | **End-to-end reverse chain: S2 L1B → `reverse_full` (offset, un-bin, SWIR re-stage, crosstalk, defects, dark, on-board-eq) + S15 ISP → L1A → L0plus → full Synthetic L0**, 2 det × 6 bands incl. SWIR re-arrangement (reverse) + injected defects; validates arrays, ISP, masks reflect defects, telemetry, sensor config |
| `test_inc3_steps.py` | 6 | S4 offset; S5 un-bin (shape+mean); S8 SWIR re-arrangement (reverse) invertible; S9 crosstalk (coeff 0 = identity); S10 defects (dead→0/bit0, hot→4095/bit1); `reverse_full` SWIR+defects contract |

## 3. Quantitative results

| Quantity | Verified bound (test) | Typical observed | Source |
|---|---|---|---|
| Synthetic L0 vs reference ESA L0 `img` (10/20 m bands) | ≤ ~4 DN | within bound | `test_esa_adf_data` / reverse chain run (REQ-PERF-005) |
| Calibration dark recovery | ≤ 0.5 DN | ~0.05 DN | `test_calibration` (bound); ATBD §4 (typical) |
| Calibration relative-response correlation | > 0.9 | > 0.99 | `test_calibration` (bound); ATBD §4 (typical) |
| Calibration absolute coefficient `A` | ±5 % of `cal_gain` | ≈ `cal_gain` | `test_calibration` |
| FPN flattening by relative-response inversion | corrected < 0.3× raw | ~0 (flat recovered) | `test_roundtrip_atbd` |

The relative-response inversion (FPN-flattening) effect was also confirmed visually on the
Synthetic L1A (B03 cloud imagery) via the pipeline's `figures` phase, and the Synthetic L0
was compared against the reference ESA L0 `img` (10/20 m bands agreeing to ≤ ~4 DN).

## 4. Requirements verification status

All *realized* SRS requirements are verified **PASS** by the cited method:
- **REQ-FUNC-001/003/005/010–013/015–020/022/030–034/044/045/046/047** — T (see the inventory and `../sdd/traceability.md`). REQ-FUNC-015 (relative-response/PRNU) and REQ-FUNC-019 (dark) are verified as the reverse chain's **inversion** of those steps, not a forward impress; REQ-FUNC-010 as DN-domain gain/offset inversion. REQ-FUNC-014 (PSF re-blur) and REQ-FUNC-021 (add noise) are cancelled (MTF-deconvolution OFF ⇒ PSF/noise not re-applied) and are not in this verification cycle.
- **REQ-PERF-004** — T/A, calibration recovery within bounds (§3). **REQ-PERF-005** — A, Synthetic L0 agrees with the reference ESA L0 `img` within ≤ ~4 DN on the 10/20 m bands (§3). REQ-PERF-001/002/003 are cancelled (forward noise σ / SNR@Lref / L1A round-trip RMSE) and out of this cycle.
- **REQ-IF-001/002/003** — I/T (L1A/L1B + GIPP inputs, L0 ICD output).
- **REQ-QUAL-001…004** — I/R/T (minimal deps; 201-test CI at v0.3.0; originality review; crc32 determinism).
- **REQ-FUNC-091/092** — T/I: PSFD naming round-trip, and CCSDS-122 bit-exact compression + ISP packet
  grammar. The reverse chain's L0plus codec round-trip is verified bit-exact (`decode(L0plus) == L1A`), and the
  reverse-chain L0plus lossless compression ratio is ~3.66×.
- Deferred / cancelled requirements (REQ-FUNC-043/053/062, REQ-FUNC-090) are out of this verification cycle.

## 5. Anomalies & observations

- **Doc/test bound discrepancy (closed):** the ATBD prose quotes calibration dark recovery `< 0.05 DN` and
  correlation `> 0.99`; the committed unit tests assert the looser, robust bounds `≤ 0.5 DN` and `> 0.9`.
  The looser figures are the **verified** acceptance bounds; the tighter figures are the **typical observed**
  values. No action required.
- **DN-scaled input:** the S2B L1B (and the publicly available EOPF test L1A) is DN-scaled, not a
  physically-calibrated radiance product. Fidelity is therefore judged by the Synthetic L0 versus the
  reference ESA L0 `img` (10/20 m bands ≤ ~4 DN), together with the operational GIPP-derived cal-DB and the
  calibration-recovery results; the DN scaling does not affect these reverse-chain fidelity or calibration bounds.