Graham McIntire
f632ea83bd
Adds the missing link between the GIRO ionosonde data we just started
ingesting and the VHF/UHF band scoring:
* `Microwaveprop.Propagation.SporadicE` — ITU-R P.534-6 / Davies 1990
thin-layer Es MUF (sec(i) · foEs with h=110 km), plus an `es_score/3`
that maps (foEs, target band, hop distance) into a 0-100 single-hop
propagation likelihood. Calibrated against literature: 50 MHz Es at
2000 km needs foEs ≳ 5.5 MHz (routine summer); 144 MHz needs
foEs ≳ 15.8 MHz (rare Jun/Jul peaks only); 440 MHz Es does not occur
at physical foEs values. Multi-hop Es and Es-scatter are separate
factors and explicitly out of scope.
* `Ionosphere.nearest_foes/3` — given a lat/lon, returns the latest
observation from the nearest polled GIRO station (Millstone Hill or
Alpena for now), with a configurable staleness cutoff (default 2h).
Returns `{:error, :stale}` or `{:error, :no_data}` so callers can
choose whether to apply the Es factor at all.
Neither is wired into the grid scorer yet — that's a separate commit
so the integration can be reviewed on its own.
84 lines
3.1 KiB
Elixir
84 lines
3.1 KiB
Elixir
defmodule Microwaveprop.Propagation.SporadicE do
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@moduledoc """
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Sporadic-E propagation physics for VHF scoring.
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Given foEs (the E-layer critical frequency measured by an ionosonde,
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in MHz) and a ground-range distance in km, computes the single-hop
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Es MUF via the thin-layer obliquity factor from ITU-R P.534-6 /
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Davies 1990 *Ionospheric Radio*, Eq. 6.26:
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MUF_Es = foEs · sec(i)
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where `sec(i) = √(1 + (D / (2h))²)` with the reflection height
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`h = 110 km` (standard thin-E approximation).
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The `es_score/3` function maps a `(foEs, target band, distance)`
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triple into a 0–100 propagation likelihood for **single-hop Es
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only**. Multi-hop Es (which extends the range but needs consecutive
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intense Es patches) and Es-scatter are not modelled here — those
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are separate factors.
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Calibration notes:
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- 50 MHz Es at 2000 km needs foEs ≳ 5.5 MHz (routine summer Es).
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- 144 MHz Es at 2000 km needs foEs ≳ 15.8 MHz (rare, observed during
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major Jun/Jul peaks).
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- 440 MHz Es does not occur at physically observed foEs values.
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- Single-hop Es has a minimum useful range of ~500 km (steeper rays
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escape the layer rather than reflect) and a maximum of ~2500 km
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(the geometric horizon limit for a 110 km reflection height).
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"""
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# Standard E-layer reflection height for the thin-layer approximation.
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@e_layer_height_km 110.0
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@min_hop_km 500
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@max_hop_km 2500
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@doc """
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Single-hop Es MUF in MHz. Returns 0.0 for nil/non-positive inputs.
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"""
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@spec single_hop_muf(number() | nil, number() | nil) :: float()
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def single_hop_muf(nil, _), do: 0.0
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def single_hop_muf(_, nil), do: 0.0
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def single_hop_muf(fo_es_mhz, _) when fo_es_mhz <= 0, do: 0.0
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def single_hop_muf(_, distance_km) when distance_km <= 0, do: 0.0
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def single_hop_muf(fo_es_mhz, distance_km) do
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sec_i = :math.sqrt(1 + :math.pow(distance_km / (2 * @e_layer_height_km), 2))
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fo_es_mhz * sec_i
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end
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@doc """
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Returns a 0–100 score for single-hop Es propagation of `band_mhz`
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over a ground-range `distance_km`, given the measured `fo_es_mhz`.
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- Short paths (< 500 km) and long paths (> 2500 km) are outside the
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single-hop window → 0.
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- `nil` or 0 foEs → 0.
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- Otherwise the score ramps with `MUF_Es / band_mhz`:
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≥ 1.20 → 100 (comfortably above the critical threshold)
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≥ 1.00 → 80 (just above, marginal Es)
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≥ 0.90 → 50 (close, occasional fringe)
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≥ 0.70 → 20 (weak fringe, unreliable)
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below → 0
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"""
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@spec es_score(number() | nil, number(), number() | nil) :: integer()
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def es_score(nil, _band, _distance), do: 0
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def es_score(_fo_es, _band, nil), do: 0
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def es_score(fo_es_mhz, _band, _distance) when fo_es_mhz <= 0, do: 0
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def es_score(_fo_es, _band, distance_km) when distance_km < @min_hop_km or distance_km > @max_hop_km, do: 0
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def es_score(fo_es_mhz, band_mhz, distance_km) do
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muf = single_hop_muf(fo_es_mhz, distance_km)
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ratio = muf / band_mhz
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cond do
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ratio >= 1.20 -> 100
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ratio >= 1.00 -> 80
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ratio >= 0.90 -> 50
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ratio >= 0.70 -> 20
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true -> 0
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end
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end
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end
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