35 lines
899 B
Python
35 lines
899 B
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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@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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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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if coefficients is None:
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raise NotImplementedError(
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"P.833 coefficients must be supplied from ITU-R tables for "
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f"forest_type={forest_type}"
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)
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coeff = coefficients
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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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