surtgis v0.14.6

Patch release. Advances ROADMAP item L ("Radiometric
calibration chain") from the 2026-06-08 OTB-survey backlog. Ships
the pure-math primitives for DN → reflectance conversion of
Landsat 8/9 and Sentinel-2, plus a simplified DOS1 atmospheric
correction. Metadata parsing (MTL.txt, MTD_MSIL1C.xml) is
intentionally out of scope — the existing STAC pipeline already
exposes the calibration coefficients in item properties and can
pass them straight through.

Added

• imagery::dn_to_toa_landsat — Landsat 8/9 Collection 2
  Level-1: ρ_TOA = (M_p · DN + A_p) / sin(SUN_ELEVATION). Caller
  supplies M_p, A_p, sun_elevation_deg from the MTL file.
  USGS Landsat 8/9 C2 L1 Data Format Control Book reference.

• imagery::dn_to_surface_reflectance_landsat_c2 — Landsat
  Collection 2 Level-2 with the fixed USGS coefficients
  (ρ = 2.75e-5 · DN − 0.2). DN == 0 is treated as "fill" per
  USGS spec and emitted as NaN.

• imagery::dn_to_reflectance_s2 — Sentinel-2 L1C TOA or
  L2A BOA: ρ = (DN + offset) / quantification_value. Default
  params (quantification = 10000, offset = 0) work for
  pre-baseline products. For PSD baseline 04.00+ (post
  2022-01-25) harmonised products pass offset = −1000.

• imagery::dos1 — simplified per-band dark-object
  subtraction (Chavez 1988). Estimates path radiance as the
  configurable quantile of finite cells (default 0.001 — the
  0.1 % darkest pixel, robust to sensor artefacts), subtracts it,
  clamps to non-negative. Full Chavez 1988 DOS1 with E_SUN
  rescaling is out of scope — chain with dn_to_toa_landsat /
  dn_to_reflectance_s2 for an equivalent effect.

• CLI: surtgis imagery calibrate with four subcommands:

  • landsat-toa --mult M --add A --sun-elevation DEG
  • landsat-sr-c2 (no params — fixed C2 coefficients)
  • s2 [--quantification 10000] [--offset 0]
  • dos1 [--quantile 0.001]

All calibrators preserve NaN cells, set output nodata to
Some(NaN), and use the rayon-parallel per-pixel pattern shared
across the imagery module.

Tests

• 3 hand-computed reference values:
  • Landsat TOA: M=2e-5, A=-0.1, elev=60°, DN=10000 → ρ = 0.1 / sin(60°) ≈ 0.11547 (1e-12 tolerance)
  • Landsat C2 SR: DN=20000 → ρ = 0.35 (1e-12 tolerance)
  • S2 TOA: DN=2500, q=10000 → ρ = 0.25 (1e-12 tolerance)
  • S2 post-baseline: DN=2500, q=10000, offset=-1000 → ρ = 0.15
    (1e-12 tolerance)
• NaN passthrough on all four calibrators.
• Sun-elevation domain check, quantification > 0 check.
• DOS1 invariants: dark cell → 0, monotonicity preserved across
  the raster, NaN passthrough, all-NaN raster errors cleanly.

12/12 calibration tests pass.

Backlog status

Survey 2026-06-06 status after this release: G ✓, H ✓, I
trigger-driven, J ✓ (v0.14.4), K ✓ (v0.14.5), L ✓ (this
release). Remaining: M (pansharpening), N (MAD / IR-MAD), O
(mosaic seams + color balance).