53 lines
1.7 KiB
Python
53 lines
1.7 KiB
Python
from __future__ import annotations
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from dataclasses import dataclass
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from math import exp
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from app.config import get_settings
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@dataclass(frozen=True)
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class P833Coefficients:
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gamma_db_per_m: float
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max_attenuation_db: float
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WORLDCOVER_P833: dict[str, P833Coefficients] = {
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"tree_cover": P833Coefficients(gamma_db_per_m=0.20, max_attenuation_db=30.0),
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"mangroves": P833Coefficients(gamma_db_per_m=0.22, max_attenuation_db=32.0),
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"shrubland": P833Coefficients(gamma_db_per_m=0.10, max_attenuation_db=12.0),
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"grassland": P833Coefficients(gamma_db_per_m=0.05, max_attenuation_db=6.0),
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"cropland": P833Coefficients(gamma_db_per_m=0.04, max_attenuation_db=5.0),
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"herbaceous_wetland": P833Coefficients(gamma_db_per_m=0.08, max_attenuation_db=10.0),
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"unknown": P833Coefficients(gamma_db_per_m=0.15, max_attenuation_db=25.0),
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}
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def p833_coefficients_for_class(class_name: str) -> P833Coefficients:
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if class_name in WORLDCOVER_P833:
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return WORLDCOVER_P833[class_name]
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settings = get_settings()
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return P833Coefficients(
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gamma_db_per_m=settings.p833_gamma_db_per_m,
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max_attenuation_db=settings.p833_max_attenuation_db,
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)
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def p833_attenuation(
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depth_m: float,
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freq_hz: float,
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forest_type: str,
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coefficients: P833Coefficients | None = None,
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) -> float:
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if depth_m <= 0:
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return 0.0
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if freq_hz <= 0:
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raise ValueError("freq_hz must be positive")
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coeff = coefficients or p833_coefficients_for_class(forest_type)
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if coeff.max_attenuation_db <= 0:
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raise ValueError("max_attenuation_db must be positive")
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return coeff.max_attenuation_db * (
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1 - exp(-(depth_m * coeff.gamma_db_per_m) / coeff.max_attenuation_db)
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)
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