5.4.1 CCIR Model

The CCIR algorithm (CCIR Report 719, Annex 2.1) is based on a linear relationship between the total attenuation A at a given frequency f and direction (elevation angle θ) and the contribution of the different atmospheric constituents water vapour content V(θ), liquid water content L(θ) and other gasses. Starting again with equation:

Leads to the following retrieval algorithms for V(θ) and L(θ).

Calculation of Water Vapour CCIR Model

Calculated at zenith value with

• d_0, d_1, d_2: values from MODEL.TXT, calculated with a(f), b(f), c(f,θ,Z_0) from basic equation
• f_1: 31,75GHz
• f_2: 23,8GHz or 21,3GHz
• r(f,90): zenith opacity af frequency f

• With m(θ): correction for actual look angle

• And r(f,θ): opacity af frequency f and El θ

• T_eff (f,θ): effective medium temperature
• T_S (f,θ): Measured Sky Noise Temp
• T_C : Cosmic Temperature

• a_1 (f), a_2 (f): values from MODEL.TXT
• T_0 [K] : actual ground temperature
• m(θ): correction for actual look angle

Calculation of Liquid Water CCIR Model

Calculated at zenith value

• d_0, d_1, d_2: values from MODEL.TXT, calculated with a(f), b(f), c(f,θ,Z_0) from basic equation
• f_1: 31,75GHz
• f_2: 23,8GHz or 21,3GHz
• r(f,90): zenith opacity af frequency f

• With m(θ): correction for actual look angle

• And r(f,θ): opacity af frequency f and El θ

• T_eff (f,θ): effective medium temperature
• T_S (f,θ): Measured Sky Noise Temp
• T_C : Cosmic Temperature

• a_1 (f), a_2 (f): values from MODEL.TXT
• T_0 [K] : actual ground temperature
• m(θ): correction for actual look angle