# Petrel Flow Accumulation — Layers — release notes

Rolling version history for the Petrel Flow Accumulation **Layer** — DEM-derived
drainage structure at ~278 m (9 arcsec) globally: distance-to-drainage and the
topographic wetness index (TWI). Newest release first.

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## v0.1 · 2026
> **Status: not yet live.** Initial release under preparation; publishes once the
> global build and previews are signed off.

- **Initial release.** Flow accumulation and its drainage sub-layers derived
  entirely from the **Copernicus GLO-30 DEM** (pysheds fill → flow-direction →
  accumulation), so the product is Petrel-owned and carries no third-party
  redistribution obligations. Ships two sub-layers at **~278 m (9 arcsec)**
  globally: **distance-to-drainage** (metres to the nearest channel, ≥1000
  accumulated cells) and the **topographic wetness index** (TWI). Raw
  accumulation is held as an internal intermediate for this vintage.
- **A commercially-clean replacement for HydroSHEDS/HydroRIVERS.** Built as a
  drop-in drainage layer whose single permissive input lets it be both given
  back to the community (CC-BY-NC-4.0) and embedded cleanly inside Petrel's paid
  hazard models — the copyleft-flavoured HydroSHEDS licence never touches them.
- **Native-honest resolution.** Ships at the true 9 arcsec derivation grid
  (`_278m`), not an interpolated 90 m; the filenames carry the real resolution.
- **v0.1 caveat — drainage structure, not absolute basin totals.** Derivation is
  halo-tiled (~110 km overlap) so channel geometry, distance-to-drainage and TWI
  are correct, but absolute accumulation for major rivers crossing far beyond the
  halo is under-counted at tile interiors. A Barnes-style global two-pass
  accumulation is the planned v1 upgrade. Antarctica is excluded by standard.
- **Free, non-commercial Layer.** Distributed under CC-BY-NC-4.0; a derived input
  data product rather than a paid Hazard. Commercial use is licensed separately.