{
  "schema_id": "IceExtentChange",
  "version": "0.1",
  "description": "Detect changes in glacier or ice-sheet margins, seasonal snow cover, or ice-shelf calving between before/after Sentinel-2 tiles.",
  "class_match": "GL",
  "bands_required": ["B03", "B04", "B11"],
  "band_rationale": "Visible (B03/B04) separates snow/ice albedo from bare ground; SWIR1 (B11) discriminates snow from cloud and ice from water.",
  "predicate": "Have glacier, ice-sheet, snow-cover, or ice-shelf boundaries changed (retreat, advance, calving, seasonal melt) between the before and after tiles?",
  "fields": {
    "severity": {"type": "enum", "values": ["low", "moderate", "high", "extreme"]},
    "direction": {"type": "enum", "values": ["retreat", "advance", "calving", "seasonal_melt", "seasonal_accumulation"]},
    "area_fraction": {"type": "number", "range": [0.0, 1.0]},
    "vlm_explanation": {"type": "string"},
    "confidence": {"type": "number", "range": [0.0, 1.0]}
  },
  "negative_output": null,
  "negative_instruction": "If ice/snow boundaries look unchanged, return null."
}