// Multiplies two Spectrums together, by multiplying the spectral powers at each wavelength sample.
//static Spectrum Multiply(Spectrum a, Spectrum s)
//{
// Spectrum result = new Spectrum();
// for (int i = 0; i < NumberOfSamples; i++)
// {
// result.Powers[i] = a.Powers[i] * s.Powers[i];
// }
// return result;
//}
///// <summary>
///// Multiplies the <see cref="Spectrum"/> by a scalar.
///// </summary>
///// <param name="s">The scalar.</param>
//public void Multiply(float s)
//{
// for (int i = 0; i < NumberOfSamples; i++)
// Powers[i] = Powers[i] * s;
//}
/// <summary>
/// Computes direct and indirect light information when this spectrum passes through the earth's
/// atmosphere.
/// </summary>
/// <param name="zenithAngle">
/// The angle between the zenith and the direction of the light source emitting the simulated
/// spectrum in radian.
/// </param>
/// <param name="turbidity">
/// The simulated atmospheric turbidity in the range [1.8, 20.0]. A turbidity of 2 describes a
/// clear day whereas a turbidity of 20 represents thick haze. A commonly used value is 2.2.
/// </param>
/// <param name="altitude">The simulated altitude in meters above mean sea level.</param>
/// <param name="directIrradiance">
/// Output: The spectral energy directly from the light source that survives transmission
/// through the atmosphere.
/// </param>
/// <param name="scatteredIrradiance">
/// Output: The spectral energy scattered by the atmosphere, which makes up "skylight" (ambient
/// light from the sky).
/// </param>
/// <remarks>
/// <para>
/// This method simulates the passage of this spectrum through earth's atmosphere, employing the
/// National Renewable Energy Lab's "Bird model". Two new spectra, representing the direct and
/// scattered irradiance resulting from passage through the atmosphere, are returned.
/// </para>
/// <para>
/// If the light source is below the horizon, this model returns 0. Thus, it cannot be used to
/// compute twilight.
/// </para>
/// </remarks>
public void ApplyAtmosphericTransmittance(double zenithAngle, double turbidity, double altitude,
Spectrum directIrradiance, Spectrum scatteredIrradiance)
{
// For more info, see the reference in the notes of this class.
double[] Ao =
{
0, 0, 0, 0, // 380 - 395
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.003, // 400 - 450
0.004, 0.006, 0.007, 0.009, 0.011, 0.014, 0.017, 0.021, 0.025, 0.03, // 455 - 500
0.035, 0.04, 0.044, 0.048, 0.055, 0.063, 0.071, 0.075, 0.08, 0.085, // 505 - 550
0.091, 0.12, 0.12, 0.12, 0.12, 0.12, 0.12, 0.12, 0.119, 0.12, // 555 - 600
0.12, 0.12, 0.10, 0.09, 0.09, 0.085, 0.08, 0.075, 0.07, 0.07, // 605 - 650
0.065, 0.06, 0.055, 0.05, 0.045, 0.04, 0.035, 0.028, 0.25, 0.023, // 655 - 700
0.02, 0.018, 0.016, 0.012, 0.012, 0.012, 0.012, 0.01, 0.01, 0.01, // 705 - 750
0.008, 0.007, 0.006, 0.005, 0.003, 0
};
double[] Au =
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 380 - 500
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 505 - 550
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 550 - 600
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 605 - 650
0, 0, 0, 0, 0, 0, 0, 0.15, 0, 0, // 655 - 700
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 705 - 750
0, 4.0, 0, 0, 0, 0, // 755 - 780
};
double[] Aw =
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 380 - 500
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 505 - 550
0, 0, 0, 0, 0, 0, 0, 0.075, 0, 0, // 550 -600
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 605 - 650
0, 0, 0, 0, 0, 0, 0, 0.016, 0.015, 0.014, // 655 - 700
0.013, 0.0125, 1.8, 2.3, 2.5, 2.3, 1.8, 0.061, 0.003, 0.0008, // 705 - 750
0.0001, 0.00001, 0.00001, 0.0001, 0.0003, 0.0006, // 755 - 780
};
double beta = 0.04608 * turbidity - 0.04586;
double cosZenith = Math.Cos(zenithAngle);
double zenithDeg = MathHelper.ToDegrees(zenithAngle);
const double modelLimit = 90.0; //93.885
if (zenithDeg < modelLimit)
{
// NREL air mass model
//double m = 1.0 / (cosZenith + 0.15 * pow(93.885 - zenithDeg, -1.253));
// International Comet Quarterly air mass model
//double m = 1.0 / (cosZenith + 0.025 * exp(-11 * cosZenith));
// SPECTRL2 air mass model (also adopted by CIE)
double m = 1.0 / (cosZenith + 0.50572 * Math.Pow(93.885 - zenithDeg, -1.6364));
// Account for high altitude. As you lose atmosphere, less scattering occurs.
const double H = 8435.0; // pressure scale height
double isothermalEffect = Math.Exp(-(altitude / H));
m *= isothermalEffect;
// ozone mass
const double O3 = 0.35; // ozone amount, atm-cm
double Mo = 1.003454 / Math.Sqrt(cosZenith * cosZenith + 0.006908);
const double W = 2.5; // precipitable water vapor (cm)
const double omega = 0.945; // single scattering albedo, 0.4 microns
const double omegap = 0.095; // Wavelength variation factor
const double asym = 0.65; // aerosol asymmetry factor
double alg = Math.Log(1.0 - asym);
double afs = alg * (1.459 + alg * (0.1595 + alg * 0.4129));
double bfs = alg * (0.0783 + alg * (-0.3824 - alg * 0.5874));
double fsp = 1.0 - 0.5 * Math.Exp((afs + bfs / 1.8) / 1.8);
double fs = 1.0 - 0.5 * Math.Exp((afs + bfs * cosZenith) * cosZenith);
for (int i = 0; i < NumberOfSamples; i++)
{
double um = 0.380 + (i * 0.005);
// Rayleigh scattering
double Tr = Math.Exp(-m / (Math.Pow(um, 4.0) * (115.6406 - (1.335 / (um * um)))));
// Aerosols
double a = um < 0.5 ? 1.0274 : 1.2060;
double c1 = beta * Math.Pow(2.0 * um, -a);
double Ta = Math.Exp(-c1 * m);
// Water vapor
double aWM = Aw[i] * W * m;
double Tw = Math.Exp(-0.2385 * aWM / Math.Pow(1.0 + 20.07 * aWM, 0.45));
// Ozone
double To = Math.Exp(-Ao[i] * O3 * Mo);
// Mixed gas is only important in infrared
double Tm = Math.Exp((-1.41 * Au[i] * m) / Math.Pow(1.0 + 118.3 * Au[i] * m, 0.45));
// Aerosol scattering
double logUmOver4 = Math.Log(um / 0.4);
double omegl = omega * Math.Exp(-omegap * logUmOver4 * logUmOver4);
double Tas = Math.Exp(-omegl * c1 * m);
// Aerosol absorptance
double Taa = Math.Exp((omegl - 1.0) * c1 * m);
// Primed Rayleigh scattering (m = 1.8)
double Trp = Math.Exp(-1.8 / (um * um * um * um) * (115.6406 - 1.3366 / (um * um)));
// Primed water vapor scattering
double Twp = Math.Exp(-0.4293 * Aw[i] * W / Math.Pow((1.0 + 36.126 * Aw[i] * W), 0.45));
// Mixed gas
double Tup = Math.Exp(-2.538 * Au[i] / Math.Pow((1.0 + 212.94 * Au[i]), 0.45));
// Primed aerosol scattering
double Tasp = Math.Exp(-omegl * c1 * 1.8);
// Primed aerosol absorptance
double Taap = Math.Exp((omegl - 1.0) * c1 * 1.8);
// Direct energy
double xmit = Tr * Ta * Tw * To * Tm;
directIrradiance.Powers[i] = (float)(Powers[i] * xmit);
// diffuse energy
double c2 = To * Tw * cosZenith * Taa;
double c4 = 1.0;
if (um <= 0.45)
{
c4 = Math.Pow((um + 0.55), 1.8);
}
double rhoa = Tup * Twp * Taap * (0.5 * (1.0 - Trp) + (1.0 - fsp) * Trp * (1.0 - Tasp));
const double rho = 0.3; // ground albedo. Set less for ocean, more for snow.
double dray = c2 * (1.0 - Math.Pow(Tr, 0.95)) / 2.0;
double daer = c2 * Math.Pow(Tr, 1.5) * (1.0 - Tas) * fs;
double drgd = (directIrradiance.Powers[i] * cosZenith + dray + daer) * rho * rhoa / (1.0 - rho * rhoa);
scatteredIrradiance.Powers[i] = (float)(Powers[i] * (dray + daer + drgd) * c4);
if (scatteredIrradiance.Powers[i] < 0)
scatteredIrradiance.Powers[i] = 0;
}
}
else
{
for (int i = 0; i < NumberOfSamples; i++)
{
directIrradiance.Powers[i] = 0;
scatteredIrradiance.Powers[i] = 0;
}
}
}
// Multiplies two Spectrums together, by multiplying the spectral powers at each wavelength sample.
//static Spectrum Multiply(Spectrum a, Spectrum s)
//{
// Spectrum result = new Spectrum();
// for (int i = 0; i < NumberOfSamples; i++)
// {
// result.Powers[i] = a.Powers[i] * s.Powers[i];
// }
// return result;
//}
///// <summary>
///// Multiplies the <see cref="Spectrum"/> by a scalar.
///// </summary>
///// <param name="s">The scalar.</param>
//public void Multiply(float s)
//{
// for (int i = 0; i < NumberOfSamples; i++)
// Powers[i] = Powers[i] * s;
//}
/// <summary>
/// Computes direct and indirect light information when this spectrum passes through the earth's
/// atmosphere.
/// </summary>
/// <param name="zenithAngle">
/// The angle between the zenith and the direction of the light source emitting the simulated
/// spectrum in radian.
/// </param>
/// <param name="turbidity">
/// The simulated atmospheric turbidity in the range [1.8, 20.0]. A turbidity of 2 describes a
/// clear day whereas a turbidity of 20 represents thick haze. A commonly used value is 2.2.
/// </param>
/// <param name="altitude">The simulated altitude in meters above mean sea level.</param>
/// <param name="directIrradiance">
/// Output: The spectral energy directly from the light source that survives transmission
/// through the atmosphere.
/// </param>
/// <param name="scatteredIrradiance">
/// Output: The spectral energy scattered by the atmosphere, which makes up "skylight" (ambient
/// light from the sky).
/// </param>
/// <remarks>
/// <para>
/// This method simulates the passage of this spectrum through earth's atmosphere, employing the
/// National Renewable Energy Lab's "Bird model". Two new spectra, representing the direct and
/// scattered irradiance resulting from passage through the atmosphere, are returned.
/// </para>
/// <para>
/// If the light source is below the horizon, this model returns 0. Thus, it cannot be used to
/// compute twilight.
/// </para>
/// </remarks>
public void ApplyAtmosphericTransmittance(double zenithAngle, double turbidity, double altitude,
Spectrum directIrradiance, Spectrum scatteredIrradiance)
{
// For more info, see the reference in the notes of this class.
double[] Ao =
{
0, 0, 0, 0, // 380 - 395
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.003, // 400 - 450
0.004, 0.006, 0.007, 0.009, 0.011, 0.014, 0.017, 0.021, 0.025,0.03, // 455 - 500
0.035, 0.04, 0.044, 0.048, 0.055, 0.063, 0.071, 0.075, 0.08,0.085, // 505 - 550
0.091, 0.12, 0.12, 0.12, 0.12, 0.12, 0.12, 0.12, 0.119,0.12, // 555 - 600
0.12, 0.12, 0.10, 0.09, 0.09, 0.085, 0.08, 0.075, 0.07,0.07, // 605 - 650
0.065, 0.06, 0.055, 0.05, 0.045, 0.04, 0.035, 0.028, 0.25,0.023, // 655 - 700
0.02, 0.018, 0.016, 0.012, 0.012, 0.012, 0.012, 0.01, 0.01,0.01, // 705 - 750
0.008, 0.007, 0.006, 0.005, 0.003, 0
};
double[] Au =
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 380 - 500
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 505 - 550
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 550 - 600
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 605 - 650
0, 0, 0, 0, 0, 0, 0, 0.15, 0, 0, // 655 - 700
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 705 - 750
0, 4.0, 0, 0, 0, 0, // 755 - 780
};
double[] Aw =
{
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 380 - 500
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 505 - 550
0, 0, 0, 0, 0, 0, 0, 0.075, 0, 0, // 550 -600
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 605 - 650
0, 0, 0, 0, 0, 0, 0, 0.016, 0.015,0.014, // 655 - 700
0.013, 0.0125, 1.8, 2.3, 2.5, 2.3, 1.8, 0.061, 0.003,0.0008, // 705 - 750
0.0001, 0.00001, 0.00001, 0.0001, 0.0003,0.0006, // 755 - 780
};
double beta = 0.04608 * turbidity - 0.04586;
double cosZenith = Math.Cos(zenithAngle);
double zenithDeg = MathHelper.ToDegrees(zenithAngle);
const double modelLimit = 90.0; //93.885
if (zenithDeg < modelLimit)
{
// NREL air mass model
//double m = 1.0 / (cosZenith + 0.15 * pow(93.885 - zenithDeg, -1.253));
// International Comet Quarterly air mass model
//double m = 1.0 / (cosZenith + 0.025 * exp(-11 * cosZenith));
// SPECTRL2 air mass model (also adopted by CIE)
double m = 1.0 / (cosZenith + 0.50572 * Math.Pow(93.885 - zenithDeg, -1.6364));
// Account for high altitude. As you lose atmosphere, less scattering occurs.
const double H = 8435.0; // pressure scale height
double isothermalEffect = Math.Exp(-(altitude / H));
m *= isothermalEffect;
// ozone mass
const double O3 = 0.35; // ozone amount, atm-cm
double Mo = 1.003454 / Math.Sqrt(cosZenith * cosZenith + 0.006908);
const double W = 2.5; // precipitable water vapor (cm)
const double omega = 0.945; // single scattering albedo, 0.4 microns
const double omegap = 0.095; // Wavelength variation factor
const double asym = 0.65; // aerosol asymmetry factor
double alg = Math.Log(1.0 - asym);
double afs = alg * (1.459 + alg * (0.1595 + alg * 0.4129));
double bfs = alg * (0.0783 + alg * (-0.3824 - alg * 0.5874));
double fsp = 1.0 - 0.5 * Math.Exp((afs + bfs / 1.8) / 1.8);
double fs = 1.0 - 0.5 * Math.Exp((afs + bfs * cosZenith) * cosZenith);
for (int i = 0; i < NumberOfSamples; i++)
{
double um = 0.380 + (i * 0.005);
// Rayleigh scattering
double Tr = Math.Exp(-m / (Math.Pow(um, 4.0) * (115.6406 - (1.335 / (um * um)))));
// Aerosols
double a = um < 0.5 ? 1.0274 : 1.2060;
double c1 = beta * Math.Pow(2.0 * um, -a);
double Ta = Math.Exp(-c1 * m);
// Water vapor
double aWM = Aw[i] * W * m;
double Tw = Math.Exp(-0.2385 * aWM / Math.Pow(1.0 + 20.07 * aWM, 0.45));
// Ozone
double To = Math.Exp(-Ao[i] * O3 * Mo);
// Mixed gas is only important in infrared
double Tm = Math.Exp((-1.41 * Au[i] * m) / Math.Pow(1.0 + 118.3 * Au[i] * m, 0.45));
// Aerosol scattering
double logUmOver4 = Math.Log(um / 0.4);
double omegl = omega * Math.Exp(-omegap * logUmOver4 * logUmOver4);
double Tas = Math.Exp(-omegl * c1 * m);
// Aerosol absorptance
double Taa = Math.Exp((omegl - 1.0) * c1 * m);
// Primed Rayleigh scattering (m = 1.8)
double Trp = Math.Exp(-1.8 / (um * um * um * um) * (115.6406 - 1.3366 / (um * um)));
// Primed water vapor scattering
double Twp = Math.Exp(-0.4293 * Aw[i] * W / Math.Pow((1.0 + 36.126 * Aw[i] * W), 0.45));
// Mixed gas
double Tup = Math.Exp(-2.538 * Au[i] / Math.Pow((1.0 + 212.94 * Au[i]), 0.45));
// Primed aerosol scattering
double Tasp = Math.Exp(-omegl * c1 * 1.8);
// Primed aerosol absorptance
double Taap = Math.Exp((omegl - 1.0) * c1 * 1.8);
// Direct energy
double xmit = Tr * Ta * Tw * To * Tm;
directIrradiance.Powers[i] = (float)(Powers[i] * xmit);
// diffuse energy
double c2 = To * Tw * cosZenith * Taa;
double c4 = 1.0;
if (um <= 0.45)
{
c4 = Math.Pow((um + 0.55), 1.8);
}
double rhoa = Tup * Twp * Taap * (0.5 * (1.0 - Trp) + (1.0 - fsp) * Trp * (1.0 - Tasp));
const double rho = 0.3; // ground albedo. Set less for ocean, more for snow.
double dray = c2 * (1.0 - Math.Pow(Tr, 0.95)) / 2.0;
double daer = c2 * Math.Pow(Tr, 1.5) * (1.0 - Tas) * fs;
double drgd = (directIrradiance.Powers[i] * cosZenith + dray + daer) * rho * rhoa / (1.0 - rho * rhoa);
scatteredIrradiance.Powers[i] = (float)(Powers[i] * (dray + daer + drgd) * c4);
if (scatteredIrradiance.Powers[i] < 0)
{
scatteredIrradiance.Powers[i] = 0;
}
}
}
else
{
for (int i = 0; i < NumberOfSamples; i++)
{
directIrradiance.Powers[i] = 0;
scatteredIrradiance.Powers[i] = 0;
}
}
}