Requirements to design traceability

s2_msi_raw_generator reconstructs L1A -> L0plus -> Synthetic L0 by running a S2B L1B backwards through the exact inverse of the operational Synthetic L0->L1B radiometric chain; success is the Synthetic L0 matching the reference ESA L0 img (10/20 m bands <=~4 DN). Each requirement from the SRS (docs/srs.md) is traced to its design component, code, test, verification method (T/A/I/R) and status. Verification details and quantitative results are in the V&V report (docs/vv/report.md).

Functional requirements

The rows below trace the reverse radiometric reverse chain: descending a S2 L1B through the exact inverse of the operational Synthetic L0->L1B chain (invert gain/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 intentionally not re-applied (REQ-FUNC-014 and REQ-FUNC-021 retired below).

REQ ID	Requirement	Design (module)	Code	Test	Method	Status
REQ-FUNC-001	Accept L1A/L1B inputs	io	io.read_l1b_band, read_l1a_raw	test_roundtrip_atbd, test_esa_adf_data	T	realized
REQ-FUNC-003	Per-unit (S2A/B/C) support	sensor	sensor.unit_from_platform	test_esa_adf_data	T	realized
REQ-FUNC-005	Reject unsupported inputs	sensor	sensor.band (KeyError)	test_esa_adf_data	T	realized
REQ-FUNC-010	Invert absolute calibration (DN-domain gain/offset) — radiometric entry of the reverse chain	reverse, sensor	reverse.s1_radiance_to_dn, Band.cal_gain	test_reverse, test_esa_adf_data	T	realized
REQ-FUNC-011	Reverse scene framing (S3)	reverse	reverse.s3_undo_framing	test_inc3_steps	T	realized
REQ-FUNC-012	Remove radiometric offset (S4)	reverse, gipp	reverse.s4_undo_radiometric_offset	test_inc3_steps	T	realized
REQ-FUNC-013	Reverse 60 m binning (S5)	reverse	reverse.s5_unbin	test_inc3_steps	T	realized
REQ-FUNC-014	PSF re-blur — retired (reverse chain runs with MTF-deconvolution OFF; PSF is not re-applied)	—	—	—	—	retired
REQ-FUNC-015	Re-apply relative response / PRNU when descending L1B->Synthetic L0	reverse, adf, gipp	reverse.s7_impress_relative_response, adf.from_gipp, gipp	test_gipp, test_esa_adf_data	T	realized
REQ-FUNC-016	Restore SWIR arrangement (S8)	reverse	reverse.s8_restage_swir	test_inc3_steps, test_integration	T	realized
REQ-FUNC-017	Re-apply crosstalk (S9)	reverse, gipp	reverse.s9_apply_crosstalk, gipp.read_r2crco	test_inc3_steps, test_gipp	T	realized
REQ-FUNC-018	Re-insert blind/defective (S10)	reverse, gipp	reverse.s10_inject_defects, gipp.read_r2depi/read_blindp	test_inc3_steps, test_integration	T	realized
REQ-FUNC-019	Re-apply dark signal (S11)	reverse, gipp	reverse.s11_reapply_dark, GIPP COEFF_D	test_gipp, test_calibration	T	realized
REQ-FUNC-020	Reverse onboard equalization (S12)	reverse	reverse.s12_reapply_onboard_eq	test_reverse	T	realized
REQ-FUNC-021	Add sensor noise — retired (noise is not re-introduced in the reverse chain)	—	—	—	—	retired
REQ-FUNC-022	Cast Synthetic L0 to 12-bit DN (final integer cast, part of L0 assembly)	reverse	reverse.s14_quantize	test_reverse	T	realized
REQ-FUNC-030	Synthetic L0 RAW EOProduct (Zarr)	l0product	l0product.write_l0_product	test_l0product	T	realized
REQ-FUNC-031	156 measurement arrays	l0product	write_l0_product	test_l0product::test_full_156_array_contract	T	realized
REQ-FUNC-032	156 quality masks	l0product	write_l0_product	test_l0product	T	realized
REQ-FUNC-033	STAC discovery metadata	l0product	build_root_metadata	test_l0product, test_integration	T	realized
REQ-FUNC-034	Sensor-configuration metadata	l0product, sensor	build_root_metadata, sensor.spectral_band_info	test_l0product, test_integration	T	realized
REQ-FUNC-044	Synthetic fallback ADFs	adf	adf.synthesize	test_reverse, test_esa_adf_data	T	realized
REQ-FUNC-045	ADF provenance	l0product	build_root_metadata (adf_provenance)	test_l0product, test_integration	I	realized
REQ-FUNC-046	Operational GIPP ingest	gipp, adf	gipp.load_gipp_set, adf.from_gipp	test_gipp	T	realized
REQ-FUNC-047	Calibration sub-set	calibration	calibration.calibrate, estimated_adf	test_calibration	T	realized
REQ-FUNC-039	ESUN spectral ADF	sensor, adf_writer	sensor.esun, adf_writer.write_calibration_db (spectral.zarr)	test_adf_writer	T	realized
REQ-FUNC-035	GPS/OBT line datation	datation, isp, l0product	datation.Datation, isp.parse_cuc_time, build_root_metadata (band_time_stamp)	test_datation, test_isp	T	realized
REQ-FUNC-038	STAC geometry & orbit	l0product	build_root_metadata (bbox/geometry/sat:orbit/datastrip)	test_l0product	T	realized
REQ-FUNC-040	Quality-flag taxonomy	quality, l0product	quality.l0_flags, to_msk_qualit, from_s10_qa	test_quality, test_integration	T	realized
REQ-FUNC-041	EOQC quality report	quality_report, l0product	quality_report.build_qc_report, write_qc_report	test_quality_report	T	realized
REQ-FUNC-036	Orbit/attitude ephemeris	sad, l0product	sad.orbit_ephemeris, synth_orbit_attitude	test_sad	T	realized
REQ-FUNC-037	SAD content (ISP)	sad, l0product	sad.synth_orbit_attitude, pack_sad_isp, scan_ccsds_packets	test_sad	T	realized
REQ-FUNC-042	Open-container L0 handoff	l0product, scripts	l0product.write_l0_opencontainer, nominal ground-decode phase	test_l0_handoff	T/I	realized
REQ-FUNC-048	Calibration-campaign Synthetic L0 products (DASC/ABSR)	calibration, caldb, l0product, scripts	phase_cal_acquire/phase_cal_package/caldb.derive_from_acquisitions; PSFD S02MSIDCA/S02MSISCA	test_cal_mode	T	realized
REQ-FUNC-091	PSFD §3 product naming (ICD-IF-NAME)	naming.py	test_naming, test_s2_l1b_e2e_driver	realized
REQ-FUNC-092	CCSDS-122 compressed ISP payloads + ground decode	ccsds122.py, isp.py, l0product.py	test_ccsds122, test_isp_packetize, test_isp, test_integration	realized
REQ-FUNC-093	S2 L1B reverse-chain E2E: reconstruct L1A->L0plus->Synthetic L0 from S2B L1B and validate against the reference ESA L0 img (10/20 m bands <=~4 DN); L0plus codec round-trip (decode(L0plus)==L1A) kept as an internal check	scripts/run_pipeline.py, s3fetch.py	test_s2_l1b_e2e_driver; SDE run (docs/vv/s2_l1b_e2e.md)	realized
REQ-FUNC-043	Credentialed ADF API	—	—	—	—	deferred
REQ-FUNC-053	Configurable PU orchestration	—	—	—	—	deferred
REQ-FUNC-062	Dask distribution	—	—	—	—	deferred
REQ-FUNC-090	L1C entry + geometry reverse	—	—	—	—	cancelled

Performance requirements

REQ ID	Requirement	Design	Code	Test	Method	Status
REQ-PERF-001	Noise \(\sigma\) within ±5 % — retired (no noise model is impressed in the reverse chain)	—	—	—	—	retired
REQ-PERF-002	SNR@Lref fidelity — retired (measured against the injected noise model; noise not re-applied)	—	—	—	—	retired
REQ-PERF-003	Round-trip exactness (RMSE \(\to 0\)) — retired (L1A forward exact-inverse round-trip; superseded by reverse-chain Synthetic L0 validation, REQ-PERF-005)	—	—	—	—	retired
REQ-PERF-004	Calibration recovery accuracy	calibration	calibrate	test_calibration	T	realized
REQ-PERF-005	Synthetic L0 DN agrees with the reference ESA L0 img within <=~4 DN on the 10/20 m bands	reverse, l0product	reverse chain + write_l0_product	test_s2_l1b_e2e_driver; docs/vv/s2_l1b_e2e.md	T,A	realized

Interface requirements

REQ ID	Requirement	Design	Code	Test	Method	Status
REQ-IF-001	EOPF L1A/L1B input interface	io	read_l1b_band, read_l1a_raw	test_roundtrip_atbd	I,T	realized
REQ-IF-002	L0 output interface (ICD-IF-Synthetic L0)	l0product	write_l0_product	test_l0product, test_integration	I,T	realized
REQ-IF-003	GIPP JSON interface	gipp	gipp.read_*	test_gipp	I	realized

Quality requirements

REQ ID	Requirement	Design	Code	Test	Method	Status
REQ-QUAL-001	Minimal dependencies	(packaging)	pyproject.toml	—	I	realized
REQ-QUAL-002	Test coverage & CI	(all)	tests/, .gitlab-ci.yml	201 tests (v0.3.0)	T	realized
REQ-QUAL-003	Originality (no external-processor source)	(all)	repo	grep	I,R	realized
REQ-QUAL-004	Reproducibility (deterministic output; crc32 checks)	reverse, calibration	crc32 determinism checks	test_*	T	realized