Preliminary validation of GLASS-DSSR products using surface measurements collected in arid and semi-arid regions of China

Figures & data

Figure 1. Schematic diagram explaining why the spatial collocation effect happens when MTSAT images are used to retrieve surface solar irradiance over China (the surface is considered the referenced plane).

Table 1. Basic summary of the meteorological sites used to validate GLASS-DSSR products.

Site name	Location	Latitude (°)	Longitude (°)	Altitude (m)	Climate	Periods (YYYYMM)
A'rou	Qilian mountains	38.044	100.465	3033	Plateau cold climate	200801–200812
Changwu	Loess plateau	35.200	107.667	1220	Temperate continental climate	200807–200808
Daxing	North China plain	39.621	116.427	30	Temperate monsoon climate	200906–200910
Dingxi	Loess plateau	35.556	104.594	1896	Temperate continental climate	200807–200809
Dongsu	Mongolian plateau	44.089	113.574	970	Temperate continental climate	200807–200809; 200906–200909
Guantao	North China Plain	36.515	115.127	20	Temperate monsoon climate	200809–200810; 200906–200909
Huazhaizi	Northwest China	38.767	100.317	1726	Temperate desert climate	200806–200810; 200906–200909
Jinzhou	Northeast China	41.184	121.211	22.3	Temperate monsoon climate	200807–200809; 200906–200909
Maqu	Tibetan plateau	33.887	102.141	3423	Plateau cold climate	200807–200809; 200906–200909
Miyun	North China plain	40.630	117.320	350	Temperate monsoon climate	200801–200812
Naqu	Tibetan plateau	31.369	91.899	4509	Plateau cold climate	200801–200812
Neiman	Mongolian plateau	42.929	120.698	361	Temperate continental climate	200807–200809
Tongyu farmland	Northeast China	44.591	122.928	184	Temperate monsoon climate	200807–200809; 200906–200909
Tongyu meadow	Northeast China	44.567	122.917	184	Temperate monsoon climate	200807–200809; 200906–200909
Yingke	Northwest China	38.857	100.410	1519	Temperate oasis climate	200801–200812
Yuzhong	Northwest China	35.950	104.133	1965	Temperate continental climate	200807–200809; 200906–200909

Figure 2. Spatial collocation effect at the Daxing site. Contour/intensity map of explained variance (in%) between the atmospheric transmittance series derived by surface observed irradiance and the corresponding MTSAT VIS TOA reflectance series from June to October 2009. The black cross denotes the location of the Daxing site and also the origin of the coordinates.

Figure 3. Comparison of the GLASS-DSSR products and 12 sites’ measurements from ASRCOP data with the validating scheme described in this paper. Color represents the number in each unit bin that the (DSSR_Measured, DSSR_GLASS) pair falls into (10 W/m² increment).

Figure 4. Performance of GLASS-DSSR products at six sites in temperate continental climate.

Table 2. Statistics of the comparison between GLASS DSSR and observed DSSR at individual site during summer of 2008 and/or 2009.

Site name	N	Mean observation	R^2	Bias	RMSE
Temperate continental climate
Changwu	785	390.0	0.87	12.6	107.5
Dingxi	920	359.1	0.88	38.7	109.5
Dongsu	2073	481.4	0.86	−54.8	125.3
Neiman	1174	422.9	0.91	−23.2	93.1
Yuzhong	2376	427.3	0.81	−18.0	120.6
Huazhaizi	2477	452.0	0.86	−15.2	119.4
Temperate monsoon climate
Daxing	1873	352.5	0.84	48.45	115.1
Guantao	1896	363.4	0.89	23.3	90.4
Jinzhou	2377	373.3	0.87	25.9	95.6
Tongyu farmland	2500	402.1	0.89	−12.3	92.4
Tongyu meadow	2294	412.6	0.88	−20.0	98.5
Plateau cold climate
Maqu	2263	391.8	0.84	−50.4	130.4

Figure 5. Performance of GLASS-DSSR products at five sites in temperate monsoon climate (from upper left, first five), and one site in plateau cold climate (last).

Figure 6. Inter-comparisons of ISCCP-FD products and GLASS-DSSR products using 2008/2009 summer ASRCOP Pyranometer measurements in temperate continental climate (left) and temperate monsoon climate (right) of China. Black solid line is 1:1 line, red solid line denotes ISCCP-FD fitted line and blue solid line denotes GLASS-DSSR fitted line, respectively.

Figure 7. Histograms of residuals (retrieved DSSR-measured DSSR) distribution at four sites (Naqu, A'rou, Yingke and Miyun) in 2008.

Figure 8. Accumulative percentiles of relative errors at four sites (Naqu, A'rou, Yingke and Miyun).

Figure 9. Frequency scatterplot comparing the GLASS-DSSR products with the observed data at Miyun and Yingke in 2008. Grayscale represents the number in each unit bin that the (DSSR_Measured, DSSR_GLASS) pair falls into (10 W/m² increment).

Table 3. Assessment of GLASS instantaneous DSSR using 2008 measurements at Miyun, Yingke A'rou, and Naqu sites.

Site name	N	Mean observation	R^2	Bias	RMSE	Linear regression equation
Miyun	3836	370.8	0.85	9.39	98.7	Y=0.79x+87.3
Yingke	3767	411.6	0.88	−7.1	97.3	Y=0.85x+53.0
A'rou	3839	434.2	0.81	−38.3	127.8	Y=0.76x+67.0
Naqu	3962	469.5	0.75	−72.9	158.5	Y=0.74x+48.7

Note: y denotes retrieved instantaneous DSSR and x denotes measured DSSR.