5.4.2 SIGMA-A Model
The SIGMA A algorithm was developed by Sigma Consultand, Sweden and utilizes additional information on actual local meteorological conditions, here ambient temperature and pressure. Starting again with equation:
Leads to the following retrieval algorithms for V(θ) and L(θ).
Calculation of Water Vapour SIGMA A Model
Calculated at zenith value with
- c_eff, a_1, a_2, a_3: values from MODEL.TXT, calculated with a(f), b(f), c(f,θ,Z_0) from basic equation
- P_0 [mbar]: Pressure at Radiometer Site
- P_avg [mbar]: Mean Pressure from MODEL.TXT
- T_0 [K]: Temperature at Radiometer Site
- T_avg [K]: Mean Temperature from MODEL.TXT
- X_12 (θ=90): value determined by by sky noise temperatuer f1, f2
The variable X_12 is found as
- f_1: 31,75GHz
- f_2: 23,8GHz or 21,3GHz
- r(f,90): zenith opacity af frequency f
- r_OX (f,θ=90): opacity caused by oxygen at frequency f
- r_OX (19): opacity caused by oxygen
- P_0 [mbar]: Pressure at Radiometer Site
- T_0 [K]: Temperature at Radiometer Site
And again the calculation of r(f,90):
- 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 SIGMA A Model
Calculated at zenith value
- a_0, a_1, a_2, a_3, a_4: values from MODEL.TXT, calculated with a(f), b(f), c(f,θ,Z_0) from basic equation
- P_0 [mbar]: Pressure at Radiometer Site
- T_0 [K]: Temperature at Radiometer Site
- 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