Module: TCD::Inference

Defined in:
lib/tcd/inference.rb

Overview

Computes inferred constituents when M2, S2, K1, and O1 are given. This fills remaining unfilled constituents based on article 230 of “Manual of Harmonic Analysis and Prediction of Tides”, Paul Schureman, C & GS special publication no. 98, October 1971.

This is useful for stations with short observation periods that only have a few major constituents developed. The inferred constituents can improve tide predictions.

Constant Summary collapse

INFERRED_SEMI_DIURNAL =

Semi-diurnal constituents that can be inferred from M2 and S2

%w[N2 NU2 MU2 2N2 LDA2 T2 R2 L2 K2 KJ2].freeze
SEMI_DIURNAL_COEFF =

Coefficients for semi-diurnal inference (relative to M2)

[
    0.1759,  # N2
    0.0341,  # NU2
    0.0219,  # MU2
    0.0235,  # 2N2
    0.0066,  # LDA2
    0.0248,  # T2
    0.0035,  # R2
    0.0251,  # L2
    0.1151,  # K2
    0.0064   # KJ2
].freeze
INFERRED_DIURNAL =

Diurnal constituents that can be inferred from K1 and O1

%w[OO1 M1 J1 RHO1 Q1 2Q1 P1 PI1 PHI1 PSI1].freeze
DIURNAL_COEFF =

Coefficients for diurnal inference (relative to O1)

[
    0.0163,  # OO1
    0.0209,  # M1
    0.0297,  # J1
    0.0142,  # RHO1
    0.0730,  # Q1
    0.0097,  # 2Q1
    0.1755,  # P1
    0.0103,  # PI1
    0.0076,  # PHI1
    0.0042   # PSI1
].freeze
M2_COEFF =

Reference coefficients for M2 and O1

0.9085
O1_COEFF = 
0.3771

Class Method Summary collapse

Class Method Details

.infer_constituents(station, constituent_data) ⇒ Boolean

Infer missing constituents for a reference station.

Requires the station to have non-zero values for M2, S2, K1, and O1. Modifies the station’s amplitudes and epochs arrays in place.

Parameters:

  • station (Station) —

    A reference station with amplitudes/epochs arrays

  • constituent_data (ConstituentData) —

    The constituent data from the reader

Returns:

  • (Boolean) —

    true if inference was performed, false if not enough data



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# File 'lib/tcd/inference.rb', line 59

def self.infer_constituents(station, constituent_data)
    return false unless station.reference?
    return false unless station.amplitudes && station.epochs

    # Find the required constituents
    m2 = constituent_data.find("M2")
    s2 = constituent_data.find("S2")
    k1 = constituent_data.find("K1")
    o1 = constituent_data.find("O1")

    return false unless m2 && s2 && k1 && o1

    m2_idx = m2.index
    s2_idx = s2.index
    k1_idx = k1.index
    o1_idx = o1.index

    # Check that all four required constituents have non-zero values
    return false if station.amplitudes[m2_idx] == 0.0
    return false if station.amplitudes[s2_idx] == 0.0
    return false if station.amplitudes[k1_idx] == 0.0
    return false if station.amplitudes[o1_idx] == 0.0

    # Get the epochs, handling wrap-around
    epoch_m2 = station.epochs[m2_idx]
    epoch_s2 = station.epochs[s2_idx]
    epoch_k1 = station.epochs[k1_idx]
    epoch_o1 = station.epochs[o1_idx]

    # Build lookup from constituent name to index
    constituent_lookup = {}
    constituent_data.each_with_index do |c, idx|
        constituent_lookup[c.name] = idx
    end

    # Infer semi-diurnal constituents
    INFERRED_SEMI_DIURNAL.each_with_index do |name, j|
        idx = constituent_lookup[name]
        next unless idx
        next unless station.amplitudes[idx] == 0.0 && station.epochs[idx] == 0.0

        constituent = constituent_data[idx]
        next unless constituent

        # Compute amplitude
        station.amplitudes[idx] = (SEMI_DIURNAL_COEFF[j] / M2_COEFF) *
                                  station.amplitudes[m2_idx]

        # Compute epoch with wrap-around handling
        e_m2 = epoch_m2
        e_s2 = epoch_s2
        if (e_s2 - e_m2).abs > 180.0
            if e_s2 < e_m2
                e_s2 += 360.0
            else
                e_m2 += 360.0
            end
        end

        speed_diff_ratio = (constituent.speed - m2.speed) / (s2.speed - m2.speed)
        station.epochs[idx] = e_m2 + speed_diff_ratio * (e_s2 - e_m2)
    end

    # Infer diurnal constituents
    INFERRED_DIURNAL.each_with_index do |name, j|
        idx = constituent_lookup[name]
        next unless idx
        next unless station.amplitudes[idx] == 0.0 && station.epochs[idx] == 0.0

        constituent = constituent_data[idx]
        next unless constituent

        # Compute amplitude
        station.amplitudes[idx] = (DIURNAL_COEFF[j] / O1_COEFF) *
                                  station.amplitudes[o1_idx]

        # Compute epoch with wrap-around handling
        e_k1 = epoch_k1
        e_o1 = epoch_o1
        if (e_k1 - e_o1).abs > 180.0
            if e_k1 < e_o1
                e_k1 += 360.0
            else
                e_o1 += 360.0
            end
        end

        speed_diff_ratio = (constituent.speed - o1.speed) / (k1.speed - o1.speed)
        station.epochs[idx] = e_o1 + speed_diff_ratio * (e_k1 - e_o1)
    end

    true
end