# Data Sources — Petrel Fuel Layer v1.0 Global FM40 Crosswalk

All input data used to build the v1.0 vintage, with citations and licensing
notes. v1.0 is a **deterministic crosswalk**, not a trained model: there is no
labelled training set, only two gridded inputs and one published fuel-model
reference. **Every input is CC-BY-4.0**, so the derived layer is fully CC-BY-4.0
/ commercially redistributable — no CC-BY-NC, no LANDFIRE, and no share-alike
(ODbL) sources are included. This is the defining property of v1.0.

## Crosswalk inputs

### 1. ESA WorldCover 2021 v200

Global 10 m land-cover classification (tree cover, shrubland, grassland,
cropland, built-up, bare/sparse, snow/ice, permanent water, herbaceous wetland,
mangrove, moss/lichen) derived from Sentinel-1 and Sentinel-2.

- **Citation:** Zanaga, D., Van De Kerchove, R., Daems, D., De Keersmaecker, W.,
  Brockmann, C., Kirches, G., Wevers, J., Cartus, O., Santoro, M., Fritz, S.,
  Lesiv, M., Herold, M., Tsendbazar, N.-E., Xu, P., Ramoino, F., & Arino, O.
  (2022). ESA WorldCover 10 m 2021 v200.
  https://doi.org/10.5281/zenodo.7254221
- **License:** **CC-BY-4.0** (attribution: "© ESA WorldCover 2021")
- **Used as:** the land-cover class that sets the FM40 family (tree cover / shrub
  / grass / cropland / built / water / bare / snow).

### 2. Beck et al. (2018) Köppen-Geiger climate classification

High-resolution present-day Köppen-Geiger climate classes, ~1 km.

- **Citation:** Beck, H. E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N.,
  Berg, A., & Wood, E. F. (2018). Present and future Köppen-Geiger climate
  classification maps at 1-km resolution. *Scientific Data*, 5, 180214.
  https://doi.org/10.1038/sdata.2018.214
- **License:** **CC-BY-4.0** (attribution: "Beck et al. (2018) Köppen-Geiger")
- **Used as:** the biome context that refines FM40 family and in-family code
  (e.g. Mediterranean Cs shrub → SH5; tropical Af/Am tree cover → TL9; boreal
  D/E tree cover → TU5; grass load by climate zone), and the fallback climate
  used where WorldCover has nodata gaps (Greenland ice sheet).

## Method reference (no data, published fuel models)

### 3. Scott & Burgan (2005) FM40 fuel models

- **Citation:** Scott, J. H., & Burgan, R. E. (2005). Standard fire behavior
  fuel models: a comprehensive set for use with Rothermel's surface fire spread
  model. *USDA Forest Service, RMRS-GTR-153.*
  https://doi.org/10.2737/RMRS-GTR-153
- **Used as:** the target fuel-model vocabulary (the 40-model NB / GR / GS / SH
  / TU / TL family set) that the crosswalk assigns.

## Geographic mask (post-processing)

### 4. GSHHG v2.3.7 full-resolution shoreline (`gshhg_f`)

Petrel's canonical land mask — the Wessel & Smith Global Self-consistent,
Hierarchical, High-resolution Geography database at full resolution (~100 m
native).

- **Citation:** Wessel, P., & Smith, W. H. F. (1996). A global,
  self-consistent, hierarchical, high-resolution shoreline database. *Journal of
  Geophysical Research*, 101(B4), 8741–8743.
- **License:** LGPL (internal masking use only; not redistributed as data).
- **Used as:** the coast clip applied to the class raster (`all_touched` — any
  cell touching real land keeps its value). GSHHG L1 only, so Antarctica is
  excluded by standard.

## Used for validation only (NOT an input)

### 5. LANDFIRE 2022 FBFM40 (CONUS)

- **Citation:** LANDFIRE (2022). Scott and Burgan Fire Behavior Fuel Model 40
  (FBFM40), CONUS. USGS / USFS. https://landfire.gov/
- **Role:** the independent US ground-truth against which the crosswalk's FM40
  **family** assignment is checked (see [`validation_report.md`](validation_report.md)).
  LANDFIRE is **not** used to build the product — it never touches the shipped
  raster — precisely so the derived layer stays CC-BY-clean and globally
  consistent.

## Inputs deliberately excluded from v1.0

- **Meta / WRI global canopy height (CC-BY-NC).** The earlier ML fuel line used
  it; its CC-BY-NC terms are what forced that line to CC-BY-NC. Excluded here so
  v1.0 is CC-BY-4.0. Real per-pixel canopy from the **CC-BY ETH global
  canopy-height** layer is the v1.1 route.
- **LANDFIRE as an input.** Used only for validation (above); splicing it into
  the product would create a US-border method seam and re-introduce a
  redistribution question.
- **OpenStreetMap (ODbL).** Share-alike terms are incompatible with a clean
  CC-BY output; not used.

## Reproducibility

The exact source paths, crosswalk rules, and promote configuration for v1.0 are
versioned in `configs/fuel_layer.yaml` (PetrelML) and
`pgflib/models/fuel_crosswalk.py` (petrel-global-fuel). Those files are the
source of truth — if anything here disagrees with them, they win.