Author Contributions
Qiaozhen Mu programed the code for the DCC technique, carried out all the experiments, participated in the sensitivity experiment designing, performed the data analyses, wrote the major part of the manuscript. Aisheng Wu participated in the entire process including code testing, MODIS RSB selection, data analyses, and manuscript writing. Xiaoxiong Xiong supervised and participated in data analyses, sensitivity experiment designing, and manuscript writing. David R. Doelling instructed designing the sensitivity test experiments, helped in the data analyses, and participated in the manuscript writing. Amit Angal participated in experiment designing, data analyses, and manuscript writing. Tiejun Chang participated in the sensitivity experiment designing, parameter selection, data analyses, and manuscript writing. Rajendra Bhatt helped in the BRDF corrections, data analyses, and manuscript writing.
Figure 1.
Spatial patterns of 11-µm brightness temperature (BT11) for Terra Level 1B (L1B) granule 2014305.0125 using: all valid frames (a); potential deep convective cloud (DCC) frames (b) and actual DCC frames (c) with BT11 less than 210 K before and after the spatial uniformity test with solar zenith angle (SZA) and view zenith angle (VZA) less than 40°, and their corresponding histograms of BT11 (d–f), respectively.
Figure 1.
Spatial patterns of 11-µm brightness temperature (BT11) for Terra Level 1B (L1B) granule 2014305.0125 using: all valid frames (a); potential deep convective cloud (DCC) frames (b) and actual DCC frames (c) with BT11 less than 210 K before and after the spatial uniformity test with solar zenith angle (SZA) and view zenith angle (VZA) less than 40°, and their corresponding histograms of BT11 (d–f), respectively.
Figure 2.
Monthly probability distribution functions of reflectance over DCCs for Terra with: no Bidirectional Reflectance Distribution Function (BRDF) correction (a); and Hu-BRDF correction (b); and for Aqua with: no BRDF correction (c); and Hu-BRDF correction (d) for band 1 in each July during 2002 and October 2016.
Figure 2.
Monthly probability distribution functions of reflectance over DCCs for Terra with: no Bidirectional Reflectance Distribution Function (BRDF) correction (a); and Hu-BRDF correction (b); and for Aqua with: no BRDF correction (c); and Hu-BRDF correction (d) for band 1 in each July during 2002 and October 2016.
Figure 3.
The diagram of MODIS DCC technique (DCCT) showing the flowchart of MODIS DCCT, indicating the parameters to be optimized and the Hu-BRDF correction for reflectance in MODIS DCCT. BT11: ~11-µm brightness temperature from band 31; B1: band 1; Ref: reflectance; STD: standard deviation.
Figure 3.
The diagram of MODIS DCC technique (DCCT) showing the flowchart of MODIS DCCT, indicating the parameters to be optimized and the Hu-BRDF correction for reflectance in MODIS DCCT. BT11: ~11-µm brightness temperature from band 31; B1: band 1; Ref: reflectance; STD: standard deviation.
Figure 4.
Standard deviations (STD) of monthly DCC mode reflectances versus bin size for RSB 1, 3–7, 18, and 26 for Terra and Aqua: without (a); and with (b) Hu-BRDF correction. Both Terra and Aqua data cover time periods from July 2002 to October, 2016. Results are in black for Terra and in red for Aqua. The unit is percentage of STDs to their corresponding fitted mode reflectance values in July 2002. Bin size is in reflectance units.
Figure 4.
Standard deviations (STD) of monthly DCC mode reflectances versus bin size for RSB 1, 3–7, 18, and 26 for Terra and Aqua: without (a); and with (b) Hu-BRDF correction. Both Terra and Aqua data cover time periods from July 2002 to October, 2016. Results are in black for Terra and in red for Aqua. The unit is percentage of STDs to their corresponding fitted mode reflectance values in July 2002. Bin size is in reflectance units.
Figure 5.
(a) Standard deviations (STDs) of mode reflectances normalized to their corresponding fitted mode reflectances at the first data point versus collection time interval for Terra and Aqua RSB 1, 3–7, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus collection time interval for Terra and Aqua RSB 1, 3–7, 18, and 26. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage. Time interval is in month.
Figure 5.
(a) Standard deviations (STDs) of mode reflectances normalized to their corresponding fitted mode reflectances at the first data point versus collection time interval for Terra and Aqua RSB 1, 3–7, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus collection time interval for Terra and Aqua RSB 1, 3–7, 18, and 26. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage. Time interval is in month.
Figure 6.
Spatial patterns and histograms of 11-µm brightness temperature for Terra granule 2014305.0125 over DCC frames after the spatial uniformity test with a core size of: 5 by 5 (
a,
b); 7 by 7 (
c,d); and 9 by 9 (
e,f). The same figures for the same granule with a core size of 3 by 3 are shown in
Figure 1c,f.
Figure 6.
Spatial patterns and histograms of 11-µm brightness temperature for Terra granule 2014305.0125 over DCC frames after the spatial uniformity test with a core size of: 5 by 5 (
a,
b); 7 by 7 (
c,d); and 9 by 9 (
e,f). The same figures for the same granule with a core size of 3 by 3 are shown in
Figure 1c,f.
Figure 7.
Monthly probability distribution functions of Hu-BRDF reflectances over DCC samples for: Terra (
a–
c); and Aqua (
d–
f) RSB 1 in each July during 2002 and October 2016 after the spatial uniformity test with a core size of: 5 by 5 (
a,
d); 7 by 7 (
b,
e); and 9 by 9 (
c,
f). The same figures for the same granule with a core size of 3 by 3 are shown in
Figure 2.
Figure 7.
Monthly probability distribution functions of Hu-BRDF reflectances over DCC samples for: Terra (
a–
c); and Aqua (
d–
f) RSB 1 in each July during 2002 and October 2016 after the spatial uniformity test with a core size of: 5 by 5 (
a,
d); 7 by 7 (
b,
e); and 9 by 9 (
c,
f). The same figures for the same granule with a core size of 3 by 3 are shown in
Figure 2.
Figure 8.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus core size for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus core size for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage. The core size refers to 1-km pixels.
Figure 8.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus core size for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus core size for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage. The core size refers to 1-km pixels.
Figure 9.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus criteria for STDs of brightness temperature and RSB 1 reflectance for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus criteria for STDs of brightness temperature and RSB 1 reflectance for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage.
Figure 9.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus criteria for STDs of brightness temperature and RSB 1 reflectance for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus criteria for STDs of brightness temperature and RSB 1 reflectance for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage.
Figure 10.
(a) Average monthly DCC frequency versus BT11 (K) threshold values for Terra and Aqua RSB 1 over the study time period from July 2002 to October 2016. (b) The percentage of change in average monthly DCC number relative to that from the baseline experiment versus BT11 threshold values for Terra and Aqua RSB 1 over July 2002–October 2016. Results are in black for Terra and in red for Aqua. Units: (a) count; and (b) percentage.
Figure 10.
(a) Average monthly DCC frequency versus BT11 (K) threshold values for Terra and Aqua RSB 1 over the study time period from July 2002 to October 2016. (b) The percentage of change in average monthly DCC number relative to that from the baseline experiment versus BT11 threshold values for Terra and Aqua RSB 1 over July 2002–October 2016. Results are in black for Terra and in red for Aqua. Units: (a) count; and (b) percentage.
Figure 11.
The percentage of change in: (a) average mean reflectance; and (b) average monthly mode reflectance relative to that from the baseline experiment versus brightness temperature threshold values for Terra and Aqua RSB 1 over July 2002–October 2016. The reflectance for RSB 1, 3–4, and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. The change is normalized to the corresponding value from baseline at BT11 threshold 205 K. Results are in black for Terra and in red for Aqua.
Figure 11.
The percentage of change in: (a) average mean reflectance; and (b) average monthly mode reflectance relative to that from the baseline experiment versus brightness temperature threshold values for Terra and Aqua RSB 1 over July 2002–October 2016. The reflectance for RSB 1, 3–4, and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. The change is normalized to the corresponding value from baseline at BT11 threshold 205 K. Results are in black for Terra and in red for Aqua.
Figure 12.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus brightness temperature thresholds for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus brightness temperature thresholds for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage.
Figure 12.
(a) Standard deviations (STDs) of monthly mode reflectances normalized to their corresponding fitted mode reflectances in July 2002 versus brightness temperature thresholds for Terra and Aqua RSB 1, 3–7, 18, and 26. (b) Changes in STDs relative to those derived from the baseline experiment versus brightness temperature thresholds for Terra and Aqua RSB 1, 3–7, 18, and 26. Both Terra and Aqua data cover time period from July 2002 to October 2016. The reflectance for RSB 1, 3–4 and 18 is Hu-BRDF corrected and non-BRDF corrected for RSB 5–7 and 26. Results are in black for Terra and in red for Aqua. The units are in percentage.
Table 1.
Wavelengths of the nine Solar Diffuser Stability Monitor (SDSM) detectors and their corresponding MODIS bands in nm. The MODIS bands in gray are the selected reflective solar bands in this study.
Table 1.
Wavelengths of the nine Solar Diffuser Stability Monitor (SDSM) detectors and their corresponding MODIS bands in nm. The MODIS bands in gray are the selected reflective solar bands in this study.
SDSM Detector | Center Wavelength (nm) | MODIS Bands | SDSM Detector | Center Wavelength (nm) | MODIS Bands |
---|
D1 | 411.8 | 8 | D6 | 746.6 | 15 |
| 442.1 | 9 | D7 | 856.5 | 2 |
D2 | 465.7 | 3 | | 866.3 | 16 |
| 487.0 | 10 | D8 | 904.2 | 17 |
D3 | 529.7 | 11 | | 935.7 | 18 |
| 546.9 | 12 | D9 | 936.2 | 19 |
D4 | 553.7 | 4 | | 1242.3 | 5 |
D5 | 646.3 | 1 | | 1382.3 | 26 |
| 665.6 | 13 | | 1629.4 | 6 |
| 677.0 | 14 | | 2114.2 | 7 |
Table 2.
Parameter values in the baseline experiment and parameter value ranges in the sensitivity test experiments using the DCC technique (DCCT). BT: ~11-µm brightness temperature; Ref: 0.65-µm reflectance.
Table 2.
Parameter values in the baseline experiment and parameter value ranges in the sensitivity test experiments using the DCC technique (DCCT). BT: ~11-µm brightness temperature; Ref: 0.65-µm reflectance.
All Channels | BT11 Threshold (K) | Uniformity Filter Thresholds | PDF Bin (Ref) | Time Interval (Month) | BRDF |
---|
BT11 (K) | Ref STD (%) | Extent (Pixel × Pixel) |
---|
Baseline DCCT | 205 | 1 | 3 | 3 × 3 | 0.001 | 1 | Hu |
Sensitivity Tests | 189–210 | 0.5–3 | 1, 3, 5 | 3 × 3, 5 × 5, 7 × 7, 9 × 9 | 0.0005–0.005 | 1, 3, 6, 12 | Hu |
Table 3.
The minimum DCC sample collection time intervals in in the long-term stability monitoring for Terra and Aqua RSB 1, 3–7, 18, and 26 over July 2002–October 2016. The unit is in month.
Table 3.
The minimum DCC sample collection time intervals in in the long-term stability monitoring for Terra and Aqua RSB 1, 3–7, 18, and 26 over July 2002–October 2016. The unit is in month.
| B1 | B3 | B4 | B18 | B5 | B6 | B7 | B26 |
---|
Terra | 3 | 6 | 6 | 12 | 6 | 12 | 12 | 3 |
Aqua | 3 | 6 | 12 | 12 | 12 | 12 | 6 | 12 |
Table 4.
The recommended ranges of brightness temperature threshold values (BT11) for Terra and Aqua MODIS RSB 1, 3–7, 18, and 26 (B1, B3–B7, B26).
Table 4.
The recommended ranges of brightness temperature threshold values (BT11) for Terra and Aqua MODIS RSB 1, 3–7, 18, and 26 (B1, B3–B7, B26).
| Terra BT11 | Aqua BT11 | Terra and Aqua BT11 |
---|
B1 | 198–210 | 198–210 | 198–210 |
B3 | 195–210 | 195–210 | 195–210 |
B4 | 197–210 | 197–210 | 197–210 |
B18 | 197–206 | 189–206 | 197–206 |
B5 | 202–210 | 202–210 | 202–210 |
B6 | 203–210 | 203–210 | 203–210 |
B7 | 203–210 | 203–210 | 203–210 |
B26 | 190–206 | 189–205 | 190–205 |
All | 203–206 | 203–205 | 203–205 |
Table 5.
Optimal parameter values as recommended for all the RSB.
Table 5.
Optimal parameter values as recommended for all the RSB.
Baseline DCCT | BT Threshold (K) | Uniformity Filter Thresholds | PDF Bin (Ref) | Time Interval | BRDF |
---|
BT11 (K) | Ref (%) | Extent (Pixel × Pixel) |
---|
B1 | 205 | 1 | 3, 5 | 5 × 5 | 0.002 | monthly | Hu |
B3 | 205 | 1 | 3, 5 | 5 × 5 | 0.002 | monthly | Hu |
B4 | 205 | 1 | 3, 5 | 5 × 5 | 0.002 | monthly | Hu |
B18 | 205 | 1 | 3, 5 | 5 × 5 | 0.002 | Monthly | Hu |
B5 | 205 | 1 | 3, 5 | 3 × 3 | 0.002 | Monthly | none |
B6 | 205 | 1 | 3, 5 | 3 × 3 | 0.001 | monthly | none |
B7 | 205 | 1 | 3, 5 | 3 × 3 | 0.001 | monthly | none |
B26 | 205 | 1 | 3, 5 | 3 × 3 | 0.002 | monthly | none |
Table 6.
Terra (T) and Aqua (A) standard deviations of the monthly reflectances from DCCT, Libya-4 and Dome-C in percentage for (DCCT) baseline, optimized DCC (O-DCCT), Libya-4 and Dome-C over July 2002–October 2016 for all the RSB. The optimized parameters in DCCT are listed in
Table 5. The unit is percentage of STDs to their corresponding fitted reflectance values in July 2002.
Table 6.
Terra (T) and Aqua (A) standard deviations of the monthly reflectances from DCCT, Libya-4 and Dome-C in percentage for (DCCT) baseline, optimized DCC (O-DCCT), Libya-4 and Dome-C over July 2002–October 2016 for all the RSB. The optimized parameters in DCCT are listed in
Table 5. The unit is percentage of STDs to their corresponding fitted reflectance values in July 2002.
Terra | Band | Aqua |
---|
DCCT | O-DCCT | Libya-4 | Dome-C | | DCCT | O-DCCT | Libya-4 | Dome-C |
---|
0.54 | 0.50 | 1.15 | 2.59 | B1 | 0.56 | 0.49 | 1.00 | 2.15 |
0.59 | 0.51 | 1.51 | 1.70 | B3 | 0.53 | 0.45 | 1.74 | 1.22 |
0.59 | 0.59 | 1.15 | 2.72 | B4 | 0.57 | 0.47 | 1.33 | 2.34 |
0.72 | 0.67 | | | B18 | 0.77 | 0.78 | | |
0.52 | 0.51 | 0.92 | | B5 | 0.58 | 0.54 | 0.87 | |
1.37 | 1.30 | 1.00 | | B6 | 1.74 | 1.64 | | |
1.79 | 1.70 | 2.33 | | B7 | 2.60 | 2.50 | 1.85 | |
1.28 | 1.18 | | | B26 | 1.77 | 1.50 | | |