106 lines
4.2 KiB
Matlab
106 lines
4.2 KiB
Matlab
%This Function approximate Ionospheric Group Delay 这个函数近似电离层群延迟
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%CopyRight By Moein Mehrtash
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%************************************************************************
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% Written by Moein Mehrtash, Concordia University, 3/21/2008 *
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% Email: moeinmehrtash@yahoo.com *
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%************************************************************************
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% ***********************************************************************
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% Function for computing an Ionospheric range correction for the *
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% GPS L1 frequency from the parameters broadcasted in the GPS *
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% Navigation Message.功能:根据GPS导航信息中广播的参数计算电离层距离修正的GPS L1频率。 *
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% ==================================================================
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% References: *
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% Klobuchar, J.A., (1996) "Ionosphercic Effects on GPS", in *
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% Parkinson, Spilker (ed), "Global Positioning System Theory and *
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% Applications, pp.513-514. *
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% ICD-GPS-200, Rev. C, (1997), pp. 125-128 *
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% NATO, (1991), "Technical Characteristics of the NAVSTAR GPS", *
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% pp. A-6-31 - A-6-33 *
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% ==================================================================
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% Input : *
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% Pos_Rcv : XYZ position of reciever (Meter) *
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% Pos_SV : XYZ matrix position of GPS satellites (Meter) *
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% GPS_Time : Time of Week (sec) *
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% Alfa(4) : The coefficients of a cubic equation *
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% representing the amplitude of the vertical *
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% dalay (4 coefficients - 8 bits each) 表示垂直dalay振幅的三次方程的系数(4个系数，每个8位) *
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% Beta(4) : The coefficients of a cubic equation *
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% representing the period of the model *
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% (4 coefficients - 8 bits each) 表示模型周期的三次方程的系数(4个系数-各8位) *
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% Output: *
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% Delta_I : Ionospheric slant range correction for *
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% the L1 frequency电离层L1频率的倾斜距离校正(Sec) *
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% ==================================================================
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function [ delay ]=iono_correction(RP, SP, alpha, beta, gpst)
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% RP: 接收机位置
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% SP: 卫星位置
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% Alpha Beta 电离层校准参数
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% GPS Time
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% delay 单位为m
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if norm(RP) < 1
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delay = 0;
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return;
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end
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[lat, lon, ~] = ch_ECEF2LLA(RP);
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lat = lat/pi;
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lon =lon/pi; % semicircles unit Lattitdue and Longitude
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[el, az] = satellite_az_el(SP, RP);
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E = az/pi; %SemiCircle Elevation
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A = el; %SemiCircle Azimoth
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% Calculate the Earth-Centered angle, Psi
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Psi = 0.0137/(E+.11)-0.022; %SemiCircle
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%Compute the Subionospheric lattitude, Phi_L
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Phi_L = lat+Psi*cos(A); %SemiCircle
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if Phi_L>0.416
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Phi_L=0.416;
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elseif Phi_L<-0.416
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Phi_L=-0.416;
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end
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%Compute the subionospheric longitude, Lambda_L
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Lambda_L = lon+(Psi * sin(A)/cos(Phi_L*pi)); %SemiCircle
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%Find the geomagnetic lattitude ,Phi_m, of the subionospheric location
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%looking toward each GPS satellite:
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Phi_m = Phi_L+0.064*cos((Lambda_L-1.617)*pi);
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%Find the Local Time ,t, at the subionospheric point
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t=4.32*10^4*Lambda_L+gpst; %GPS_Time(Sec)
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t= mod(t,86400);
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if t>86400
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t = t-86400;
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elseif t<0
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t=t+86400;
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end
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%Convert Slant time delay, Compute the Slant Factor,F
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F=1+16*(.53-E)^3;
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%Compute the ionospheric time delay T_iono by first computing x
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Per=beta(1)+beta(2)*Phi_m+beta(3)*Phi_m^2+beta(4)*Phi_m^3;
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if Per <72000 %Period
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Per=72000;
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end
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x=2*pi*(t-50400)/Per; %Rad
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AMP=alpha(1)+alpha(2)*Phi_m+alpha(3)*Phi_m^2+alpha(4)*Phi_m^3;
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if AMP<0
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AMP=0;
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end
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if abs(x)>1.57
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T_iono=F*5*10^(-9);
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else
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T_iono=F*(5*10^(-9)+AMP*(1-x^2/2+x^4/24));
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end
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delay = T_iono*299792458;
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