Fig. 1. Fitting curves and surfaces of diffuse fraction Sigmoid model. (a) S0 model fitting curve based on 1 h training data; (b) S0 model fitting curve based on 10 min training data; (c) S0 model fitting curve based on 1 min training data; (d) S1 model fitting surface based on 1 h training data; (e) S1 model fitting surface based on 10 min training data; (f) S1 model fitting surface based on 1 min training data

Fig. 2. Validation comparison diagrams for S0 models with different parameters. (a) Validation comparison diagram for S0 model using 1 h radiation data collected in May, 2012 at Lijiang station; (b) validation comparison diagram for S0 model using 10-min radiation data collected in May, 2012 at Lijiang station; (c) validation comparison diagram for S0 model using 1 h radiation data collected in July, 2012 at Kazuo station; (d) validation comparison diagram for S0 model using 10-min radiation data collec

Fig. 3. Validation comparison diagrams for S1 models with different parameters. (a)--(c) Validation comparison diagrams for S1 model using 1-h data collected in May, 2012 at Lijiang station; (d)--(f) validation comparison diagrams for S1 model using 10-min data collected in May, 2012 at Lijiang station; (g)--(i) validation comparison diagrams for S1 model using 1-h data collected in July, 2012 at Kazuo station; (j)--(l) validation comparison diagrams for S1 model using 10-min data collected in December,

Table 1. Parameters of diffuse fraction sigmoid models S0 and S1

Table 2. Statistical results of diffuse fraction calculated by S0 and S1 models