Radiometric calibration evaluation for RSBs of Suomi-NPP/VIIRS and Aqua/MODIS based on the 2015 Dunhuang Chinese Radiometric Calibration Site in situ measurements

Figures & data

Figure 1. The spectral response functions of NPP/VIIRS and Aqua/MODIS solar reflectance bands (red is for VIIRS and blue is for MODIS). The VIIRS DNB SRF is the version after 4 April 2013.

Figure 2. Coordinate map of 11 spot measurements.

Figure 3. Ground view from 30 m height tower crane at site No.1.

Table 1. Atmospheric parameters and sensor angles information.

Sensor	Date	τa(550)	Time difference (min)^a	WV (g cm^−2)	Ozone (cm atm^−a)	SolZ (°)	SenZ (°)	SolA (°)	SenA (°)
VIIRS	16 August	0.1290	33	0.5632	0.2887	29.38	7.15	−149.56	−100.31
	21 August	0.1722	8	1.2895	0.2846	31.59	16.95	−147.67	−100.69
MODIS	21 August	0.1824	16	1.2895	0.2932	30.07	25.62	−154.95	76.58

^aThe difference time between the time of surface reflectance measurements in the centre of site (No. 6) and the time of satellite overpass. τ_a(550): aerosol optical depth at 550 nm. WV: water vapour. SolZ: solar zenith angle. SenZ: sensor zenith angle. SolA: solar azimuth angle. SenA: sensor azimuth angle.

Figure 4. The aerosol optical depth at 550 nm, measured on 14, 16, 20, and 21 August 2015 at Dunhuang site No. 1.

Figure 5. The surface reflectance of measurement spot No. 6 on 21 August 2015, before (black line) and after (red line) BRDF correction, and their relative bias (blue line).

Figure 6. (a) Radiometric calibration bias results for NPP/VIIRS solar reflectance bands (except M6 and M9 bands) on 16 August (red dot) and 21 August (black square) and the bar for the standard deviation (SD); (b) the 2-day mean bias for each band (black square) and the difference between the 2-day results (based on the result on 16 Aug) (red dot).

Figure 7. The evaluation results of Aqua/MODIS band 1 to band 7. The red square is the mean bias and the red bar is the 1-σ SD for each band.

Table 2. The radiometric calibration consistency for VIIRS and MODIS.

VIIRS band	MODIS band	Bias of VIIRS (%)	Bias of MODIS (%)	Consistence of VIIRS and MODIS (%)
I1	B1	−1.8	0.7	−2.5
I2	B2	1.7	1.7	0.0
I3	B6	3.2	0.9	2.3
M4	B4	−1.9	0.1	−2.0
M5	B1	1.1	0.7	0.4
M7	B2	2.0	1.7	0.3
M8	B5	0.6	−1.0	1.6
M10	B6	2.2	0.9	1.3
M11	B7	1.4	−5.5	6.9

Table 3. Two-way gas transmittance in MODIS B7, VIIRS M11, and VIIRS DNB calculated by 6S and MODTRAN.

	MODIS B7	VIIRS M11	VIIRS DNB
6S	0.947	0.910	0.940
MODTRAN	0.965	0.894	0.960
Bias	−0.0179	0.0162	−0.0194

Table 4. The radiometric calibration evaluation for VIIRS and MODIS and their consistency in M11 and B7 before and after gas transmittance correction.

Band	Before correction (%)	After correction (%)	Consistence of VIIRS and MODIS before correction (%)	Consistence of VIIRS and MODIS after correction (%)
M11	1.4	−0.2	6.9	3.5
B7	−5.5	−3.7
DNB	−4.8	−2.9	NA	NA

Table A1. Radiometric calibration bias results for NPP/VIIRS solar reflectance bands (except M6 and M9 bands) on 16 August and 21 August.

Date	Site	I1	I2	I3	M1	M2	M3	M4	M5	M7	M8	M10	M11	DNB	Mean
16 Aug.	1	0.13	2.79	3.49	−1.91	−2.29	−1.27	−0.33	2.94	3.12	0.83	2.30	3.73	−3.23	0.79
	2	1.15	5.43	6.35	−0.91	−1.34	−0.56	0.31	3.81	5.31	4.17	4.97	6.43	−3.13	2.46
	3	−3.02	0.61	3.19	−3.08	−4.06	−3.44	−2.75	0.62	2.05	1.16	3.35	2.61	−3.03	−0.45
	4	−1.17	3.08	5.36	−1.75	−2.60	−1.76	−1.01	2.43	3.91	3.21	4.84	4.19	−3.03	1.21
	5	−0.47	2.77	2.30	−2.70	−3.64	−2.78	−1.77	2.12	2.65	−1.06	0.97	3.62	−5.88	−0.30
	6	−2.18	1.03	0.92	−2.15	−3.14	−2.86	−2.63	0.32	1.07	−1.66	0.28	1.03	−6.06	−1.23
	7	−1.96	0.58	−0.09	−2.43	−3.07	−2.70	−2.35	0.28	0.66	−1.96	−1.25	−1.34	−6.06	−1.67
	8	−4.70	−0.61	4.04	−5.04	−6.16	−5.87	−5.51	−1.84	−0.04	1.75	3.51	0.25	−6.06	−2.02
	9	−0.81	3.44	8.22	−2.48	−3.04	−1.94	−1.25	2.47	3.97	5.35	7.33	2.49	−3.03	1.59
	10	1.86	5.23	5.19	−0.90	−1.51	−0.56	0.39	4.11	4.65	1.23	3.48	5.34	−2.94	1.97
	11	−2.65	−1.21	−2.26	−2.25	−3.11	−2.59	−2.48	−0.23	−1.35	−5.98	−3.56	−1.13	−8.82	−2.89
	Mean	−1.26	2.43	3.90	−2.33	−3.08	−2.37	−1.69	1.73	2.74	1.30	2.98	2.83	−4.66	0.19
	SD	1.82	2.10	2.88	1.07	1.25	1.42	1.61	1.76	2.00	3.04	2.95	2.42	1.91	2.02
21 Aug.	1	−1.64	1.97	4.01	−1.83	−2.41	−2.06	−1.94	1.12	2.08	1.83	2.62	1.74	−3.23	0.17
	2	−3.13	−0.18	−1.02	−2.22	−2.91	−2.35	−2.78	−0.60	−0.33	−3.32	−2.22	−3.11	−6.06	−2.33
	3	−2.72	0.11	−1.65	−1.58	−2.09	−1.11	−1.48	1.13	1.69	−2.50	−1.71	−0.21	−3.03	−1.17
	4	−2.42	0.69	4.30	−0.99	−1.49	−0.98	−1.23	−0.04	0.87	1.31	3.37	0.69	−5.88	−0.14
	5	−2.50	0.46	0.21	−2.09	−2.82	−1.98	−2.67	−0.29	−0.35	−3.71	−1.68	0.07	−5.88	−1.79
	6	−1.51	1.13	0.89	−2.01	−2.62	−1.88	−1.50	1.51	1.35	−2.15	0.15	3.05	−3.13	−0.52
	7	−3.13	−0.19	3.24	−1.76	−2.50	−2.02	−2.23	−0.31	0.76	1.04	2.51	−2.68	−6.06	−1.03
	8	−2.12	1.71	5.67	−1.61	−2.22	−1.81	−1.65	1.17	2.89	3.14	4.91	−1.06	−3.13	0.45
	9	−3.38	−0.18	2.63	−1.69	−2.47	−2.33	−3.12	−1.66	−0.85	−1.15	0.83	−3.77	−5.88	−1.77
	10	−2.32	1.90	5.22	−3.09	−3.95	−3.26	−3.16	0.33	1.94	2.78	4.54	2.79	−5.71	−0.15
	11	−0.12	3.23	3.77	−0.47	−1.01	−0.63	−0.56	2.75	3.46	0.94	2.70	2.37	−6.06	0.80
	Mean	−2.27	0.97	2.48	−1.76	−2.41	−1.85	−2.03	0.46	1.23	−0.16	1.46	−0.01	−4.91	−0.68
	SD	0.57	0.77	2.53	0.36	0.43	0.45	0.54	0.79	1.06	2.48	2.53	1.95	1.42	1.22

Table A2. Radiometric calibration bias results for Aqua/MODIS solar reflectance bands (B1–B7) on 21 August.

Date	Site	B1	B2	B3	B4	B5	B6	B7	Mean
21 Aug.	1	2.42	4.69	−1.42	0.61	3.04	3.61	−2.88	1.44
	2	0.04	0.58	−1.22	−0.34	−3.31	−1.76	−6.49	−1.79
	3	1.67	2.49	0.87	1.45	−2.36	−1.02	−5.17	−0.29
	4	0.17	1.14	−0.05	0.58	−0.19	2.18	−4.98	−0.16
	5	−0.17	0.00	−0.15	−0.10	−4.76	−2.35	−5.83	−1.91
	6	1.98	2.28	−0.46	0.88	−2.60	−1.54	−3.43	−0.41
	7	0.27	1.49	−0.92	−0.05	0.40	2.80	−7.03	−0.44
	8	1.41	3.34	−1.09	0.40	2.17	5.00	−5.28	0.85
	9	−2.15	−1.63	−1.85	−1.88	−2.69	−0.47	−8.33	−2.72
	10	−0.08	1.63	−1.70	−0.99	0.59	2.08	−5.41	−0.55
	11	2.03	2.75	−0.10	0.78	−1.00	1.08	−5.35	0.03
	Mean	0.69	1.71	−0.74	0.12	−0.97	0.87	−5.47	−0.54
	SD	1.29	1.63	0.79	0.90	2.30	2.33	1.45	1.53