Graham McIntire
6d69989599
First HF prediction building block. GIRO publishes MUFD — the F2-layer maximum usable frequency at the 3000 km reference distance — directly from station measurements, already calibrated against CCIR M(3000)F2 climatology. Rather than recomputing MUF from scratch (which would require the ~2 MB CCIR coefficient tables), this module treats the measured MUFD as the anchor and scales it to the actual path distance using a thin-layer secant-of-incidence ratio. That keeps the measurement calibration (~3.3× foF2 at our fixture, vs ~5.1× from a naive thin-layer formula) and only uses the thin-layer math for the relative distance correction. * adjust_mufd/2 — scales MUFD(3000) to an arbitrary hop distance. At D=3000 it's a no-op; shorter paths get lower MUF (near-vertical), longer paths within the single-hop window get higher MUF. * fot/1 — standard 0.85 × MUF Frequency of Optimum Traffic. * hf_score/2 — 0-100 band-vs-MUF score with 5-tier curve: 100 (≤ 0.75×MUF) / 80 (FOT) / 50 (≤ MUF) / 20 (fringe) / 0 (dead). Limitations are in the moduledoc: single-hop only, nearest-station bias, no LUF/D-layer absorption, no Kp geomagnetic storm modeling. Those are separate commits once this has bake time. Not yet wired into PathLive — follow-up commit will add HF bands to BandConfig and wire the panel.
93 lines
3.4 KiB
Elixir
93 lines
3.4 KiB
Elixir
defmodule Microwaveprop.Propagation.HfMuf do
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@moduledoc """
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HF / F2-layer MUF scoring from GIRO-measured MUFD(3000).
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GIRO ionosondes publish `MUFD` — the maximum usable frequency for a
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specific reference ground distance D (we request 3000 km). That is a
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*measured* value incorporating the true F2-layer profile and the CCIR
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M(3000)F2 climatology, not a thin-layer approximation.
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This module treats the measured MUFD as the anchor and scales it to
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the actual path distance using a thin-layer secant-of-incidence ratio
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(h ≈ 300 km). That preserves the calibration from the measurement and
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only uses the thin-layer formula for a *relative* distance correction,
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which is much more accurate than recomputing MUF from scratch.
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Limitations:
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- Single-hop only; paths beyond ~4000 km need multi-hop logic we
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don't implement here.
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- Uses the nearest ionosonde's MUFD regardless of how far away it is
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— for CONUS paths outside New England the F2 layer can look quite
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different from Millstone Hill / Alpena. Good enough for a first
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pass; a proper solution needs CCIR coefficient tables.
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- Ignores D-layer absorption, so low-frequency cutoff (LUF) is not
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modelled. The scoring curve is MUF-only.
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- Ignores geomagnetic disturbance (Kp) effects. A storm-elevated Kp
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can collapse daytime MUF without touching MUFD if the storm
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post-dates the nearest observation.
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"""
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@f2_layer_height_km 300.0
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@ref_distance_km 3000.0
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# FOT (Frequency of Optimum Traffic) is the standard 85 % of MUF that
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# ITU-R / NOAA quote as the reliable working frequency below the MUF.
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@fot_ratio 0.85
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@doc """
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Scale a measured MUFD(3000) value to a different ground-range
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distance using thin-layer secant obliquity. Returns a MUF in MHz.
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At D = 3000 km this is a no-op (returns the input unchanged).
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"""
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@spec adjust_mufd(number() | nil, number() | nil) :: float()
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def adjust_mufd(nil, _), do: 0.0
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def adjust_mufd(_, nil), do: 0.0
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def adjust_mufd(mufd, _) when mufd <= 0, do: 0.0
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def adjust_mufd(_, distance_km) when distance_km <= 0, do: 0.0
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def adjust_mufd(mufd_ref_mhz, distance_km) do
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ratio = sec_i_factor(distance_km) / sec_i_factor(@ref_distance_km)
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mufd_ref_mhz * ratio
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end
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@doc """
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Frequency of Optimum Traffic — the standard 85 % of MUF used as the
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reliable working frequency below the MUF ceiling.
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"""
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@spec fot(number() | nil) :: float()
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def fot(nil), do: 0.0
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def fot(muf) when muf <= 0, do: 0.0
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def fot(muf_mhz), do: muf_mhz * @fot_ratio
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@doc """
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Score an HF band on a path with the given MUF, in the 0–100 scale
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used by the rest of the propagation engine.
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- band ≤ 0.75 × MUF → 100 (reliable, comfortably below FOT)
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- band ≤ 0.85 × MUF (FOT) → 80 (optimal working band)
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- band ≤ 1.00 × MUF → 50 (marginal, pushing the MUF ceiling)
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- band ≤ 1.15 × MUF → 20 (fringe, intermittent)
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- band > 1.15 × MUF → 0 (dead, well above MUF)
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"""
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@spec hf_score(number() | nil, number()) :: integer()
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def hf_score(nil, _band), do: 0
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def hf_score(muf, _band) when muf <= 0, do: 0
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def hf_score(muf_mhz, band_mhz) do
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ratio = band_mhz / muf_mhz
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cond do
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ratio <= 0.75 -> 100
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ratio <= 0.85 -> 80
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ratio <= 1.00 -> 50
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ratio <= 1.15 -> 20
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true -> 0
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end
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end
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defp sec_i_factor(distance_km) do
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:math.sqrt(1 + :math.pow(distance_km / (2 * @f2_layer_height_km), 2))
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end
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end
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