86 lines
2.2 KiB
Matlab
86 lines
2.2 KiB
Matlab
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function [corr] = tropo_correction(el, h)
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% SYNTAX:
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% [corr] = tropo_error_correction(el, h);
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%
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% INPUT:
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% el = satellite elevation (rad)
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% h = receiver ellipsoidal height (m)
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%
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% OUTPUT:
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% corr = tropospheric error correction
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%
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% DESCRIPTION:
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% Computation of the pseudorange correction due to tropospheric refraction.
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% Saastamoinen algorithm.
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%----------------------------------------------------------------------------------------------
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% goGPS v0.4.3
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%
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% Copyright (C) 2009-2014 Mirko Reguzzoni, Eugenio Realini
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%
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% Portions of code contributed by Laboratorio di Geomatica, Polo Regionale di Como,
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% Politecnico di Milano, Italy
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%----------------------------------------------------------------------------------------------
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global tropo_model
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%Saastamoinen model requires positive ellipsoidal height
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h(h < 0) = 0;
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% If in ATM_model section in config file tropo is set to 0 it does not use tropospheric model
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% [ATM_model]
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% tropo=0
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if (tropo_model == 0)
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corr = zeros(size(el));
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else
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if (h < 5000)
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%conversion to radians
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el = abs(el);
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%Standard atmosphere - Berg, 1948 (Bernese)
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%pressure [mbar]
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Pr = 1013.25;
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%temperature [K]
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Tr = 291.15;
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%numerical constants for the algorithm [-] [m] [mbar]
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Hr = 50.0;
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P = Pr * (1-0.0000226*h).^5.225;
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T = Tr - 0.0065*h;
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H = Hr * exp(-0.0006396*h);
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%----------------------------------------------------------------------
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%linear interpolation
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h_a = [0; 500; 1000; 1500; 2000; 2500; 3000; 4000; 5000];
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B_a = [1.156; 1.079; 1.006; 0.938; 0.874; 0.813; 0.757; 0.654; 0.563];
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t = zeros(length(T),1);
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B = zeros(length(T),1);
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for i = 1 : length(T)
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d = h_a - h(i);
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[dmin, j] = min(abs(d));
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if (d(j) > 0)
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index = [j-1; j];
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else
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index = [j; j+1];
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end
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t(i) = (h(i) - h_a(index(1))) ./ (h_a(index(2)) - h_a(index(1)));
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B(i) = (1-t(i))*B_a(index(1)) + t(i)*B_a(index(2));
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end
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%----------------------------------------------------------------------
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e = 0.01 * H .* exp(-37.2465 + 0.213166*T - 0.000256908*T.^2);
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%tropospheric error
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corr = ((0.002277 ./ sin(el)) .* (P - (B ./ (tan(el)).^2)) + (0.002277 ./ sin(el)) .* (1255./T + 0.05) .* e);
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else
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corr = zeros(size(el));
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end
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end
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