Question

Hello again,

SaasTropModel^? class has a bug. There is a wrong implementation of the formula that computes the wet zenith delay (see line 1527, TropoModel^?.cpp). According to the reference given in the class definition, i.e., Saastamoinen (1972) the formula inside the parentheses should be:

(1255/T + 0.5) * humid

while gpstk implementation is

double delay = 0.0022768 * humid * 1255/(temp+273.20) / (1 - 0.00266 * ::cos(2*latitude*DEG_TO_RAD) - 0.00028 * height/1000.);

Thus, in my opinion the right implementation would be:

double delay = 0.0022768 * humid * (1255/(temp+CELSIUS_TO_KELVIN)+0.5) / (1 - 0.00266 * ::cos(2*latitude*DEG_TO_RAD) - 0.00028 * height/1000.);

References:

• Saastamoinen, J., 1972, “Atmospheric Correction for the Troposphere and Stratosphere in Radio Ranging of Satellites,” Geophysical Monograph 15, Henriksen (ed), pp. 247–251.
• Saastamoinen, J., 1973, “Contributions to the theory of atmospheric refraction,” In three parts, Bull. G`eod., 105, pp. 279–298, 106, pp. 383–397, 107, pp. 13–34.

Best regards, Octavian

-- OctavianAndrei - 23 Jun 2008

Answer

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You are right. Fixed at 1262. Thanks Octavian.

-- BrianTolman - 24 Jun 2008