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# Software development plan

ECSS-E-ST-40C Rev.1 (with ECSS-Q-ST-80C for product assurance). This SDP defines the development process,
the increment history and the ECSS tailoring for `s2_msi_raw_generator`. The software runs an
Sentinel-2B **L1B** 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-equalisation;
MTF-deconvolution is OFF, so PSF and noise are **not** re-applied) to reconstruct **L1A → L0plus (CCSDS-122
ISP) → Synthetic L0**. Success is the Synthetic L0 measured against the reference ESA L0 'img' (10/20 m bands within
~4 DN); the L0plus codec round-trip `decode(L0plus) == L1A` is bit-exact as a supporting check.

## Process

Increment-based, test-first development. Each increment adds one capability of the reverse chain with its
unit/integration tests, is implemented on a feature branch, reviewed via merge request, and gated on
green continuous integration before merge to `main`. Algorithms are implemented from public
specifications (the ATBD and the Sentinel-2 L1 ATBD) and validated againstS2 data where available.

## Increments

| Inc | Content |
|-----|---------|
| 0 | Scaffold, CI, ATBD + Annex A datasheet |
| 1 | MVP radiometric core (S1, S6, S7, S11–S14) + sensor model + SRF ADFs (PSF loaded for the sensor model only; MTF-deconvolution OFF, so PSF is not re-applied) |
| 2 | Synthetic L0 RAW EOProduct assembly (156-array Zarr + STAC / sensor configuration) |
| 3 | Remaining chain steps S3/S4/S5/S8/S9/S10 (framing, offset, binning, SWIR re-arrangement (reverse), crosstalk, defects) |
| 4 | S15 CCSDS ISP packet generation + SAD telemetry |
| 5 | Radiometric relation $X = A\cdot G\cdot L + D$ (offset/gain/dark) inverted in the DN domain to recover L1A |
| 6 | Operational GIPP → per-pixel dark + relative response (`gipp.py`, `BandADF.from_gipp`) |
| 8 | Calibration sub-set — synthetic CSM sun-diffuser + dark → derived coefficients (inverse-crime cure) |
| Docs | ECSS-E-ST-40C documentation set (SRS, SDD, ICD, DPM, V&V, SUM, SRN, CIDL, SCF, SRF, SDP) |

## ECSS tailoring — Document Requirements List (DRL)

This is a single-CSC (Computer Software Configuration item) E2ES of low criticality. The full DRL
(ECSS-E-ST-40C Rev.1 Annexes B–T + ECSS-Q-ST-80C + M-ST-40C items) is dispositioned as follows; every
DRD is either a standalone document or is tailored with recorded rationale.

| DRD | Disposition |
|---|---|
| SSS (Annex B) | standalone — [sss.md](sss.md) |
| IRD (Annex C) | standalone — [ird.md](ird.md); the interface *requirements* stay single-sourced in the SRS (REQ-IF), the IRD references them |
| SRS (Annex D) | standalone — [srs.md](srs.md) |
| ICD (Annex E) | standalone — [icd.md](icd.md) |
| SDD (Annex F) | standalone — [sdd/](sdd/index.rst) incl. the traceability matrix |
| DJF | standalone — [djf.md](djf.md) |
| SRelD (Annex G) | standalone — [srn.md](srn.md) + `CHANGELOG.md` |
| SUM (Annex H) | standalone — [sum.md](sum.md) |
| SVerP + SValP (Annexes I, J) | **combined** into the [V&V plan](vv/plan.md) — single-CSC scope makes separate plans redundant |
| SUITP (Annex K) | standalone — [vv/suitp.md](vv/suitp.md) |
| SVS (Annex L) | **folded into** the [V&V plan](vv/plan.md) §2 verification matrix + [SUITP](vv/suitp.md) §5 pass/fail criteria — the validation specifications are the executable tests themselves |
| SVR (Annex M) | standalone — [V&V report](vv/report.md) + [S2 L1B E2E validation](vv/s2_l1b_e2e.md) |
| SUITR | standalone — [vv/suitr.md](vv/suitr.md) |
| SRF (Annex N) | standalone — [srf.md](srf.md) |
| SDP (Annex O) | this document |
| SRevP (Annex P) | standalone — [srevp.md](srevp.md) |
| SMP (Annex T) | **folded into this SDP** — maintenance follows the same feature-branch → MR → CI → `main` process; releases recorded in the SRN and `CHANGELOG.md` |
| SPAP (ECSS-Q-ST-80C) | standalone — [spa-plan.md](spa-plan.md) |
| Risk register | standalone — [risk-register.md](risk-register.md) |
| CIDL / SCF (M-ST-40C) | standalone — [cidl.md](cidl.md), [scf.md](scf.md) |
| QR report | standalone — [qr.md](qr.md) |
| ATBD / DPM (mission-specific) | standalone — [atbd/atbd.md](atbd/atbd.md) (issued v1.0), [dpm/](dpm/index.rst) |

## Configuration management

Version control: git, repository `gitlab.eopf` `ipf/s2-msi-raw-generator`. Branching: short-lived feature branches
(`feat/*`, `docs/*`) merged to `main` via merge request after CI passes; `main` is the controlled baseline.
Continuous integration: `.gitlab-ci.yml` runs the test suite on a public Python image (no credentials).
Configuration items and baseline are listed in the CIDL and SCF.