first commit

api/app/core/vegetation.py

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+from __future__ import annotations
+
+from dataclasses import dataclass
+from math import exp
+
+
+@dataclass(frozen=True)
+class P833Coefficients:
+    gamma_db_per_m: float
+    max_attenuation_db: float
+
+
+def p833_attenuation(
+    depth_m: float,
+    freq_hz: float,
+    forest_type: str,
+    coefficients: P833Coefficients | None = None,
+) -> float:
+    if depth_m <= 0:
+        return 0.0
+    if freq_hz <= 0:
+        raise ValueError("freq_hz must be positive")
+
+    if coefficients is None:
+        raise NotImplementedError(
+            "P.833 coefficients must be supplied from ITU-R tables for "
+            f"forest_type={forest_type}"
+        )
+    coeff = coefficients
+    if coeff.max_attenuation_db <= 0:
+        raise ValueError("max_attenuation_db must be positive")
+    return coeff.max_attenuation_db * (
+        1 - exp(-(depth_m * coeff.gamma_db_per_m) / coeff.max_attenuation_db)
+    )