G. S. Kent, K. H. Sage, C. R. Trepte, and P.-H. Wang, "Stratospheric Aerosol and Gas Experiment III cloud data product," Appl. Opt. 46, 1261-1278 (2007)
The latest in a series of solar occultation satellite instruments, Stratospheric Aerosol and Gas Experiment (SAGE) III, was placed into orbit in December 2001, and data were obtained until March 2006. Measurements were made of the extinction attributable to aerosols and cloud at a number of wavelengths between 290 and
. The analysis of data obtained by its predecessor, SAGE II, has shown that an intercomparison of such data at two or more wavelengths may be used to separate the effects of cloud and aerosol. This analysis has been done on a routine basis for many years using SAGE II data at 525 and
and applied extensively to global studies of tropospheric cloud and aerosol. Here we describe the aerosol–cloud separation algorithm developed for use with the SAGE III data, which uses the extinction at 525, 1020, and
. This algorithm is now being used to produce vertical profiles of cloud presence as a standard SAGE III data product. These profiles have a vertical resolution of 0.5 km and cover the altitude range from 6.0 to 30.0 km, and data are presently available from March 2002 onward. An outline is given of the development of this algorithm, the nature of the SAGE III data, and the algorithm performance. To maintain continuity with SAGE II cloud data, the relative performances of the SAGE II and SAGE III algorithms are also examined. An example of the application of the algorithm to SAGE III tropospheric data is shown and discussed.
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A living document describing the algorithm background and its rationale. The document is updated as changes are made to the algorithm; the most recent update is Version 2.3, 8 July 2004.
A guide for SAGE III data users containing a detailed description of the output data format. Sections of the guide describe the nature and format of the cloud product.
A manual describing the postprocessing sequence. It contains details of the data management, file formats, and examples of various types of aerosol and cloud data.
Table 5
Comparison of the Results of the Application of the SAGE II and SAGE III Cloud Algorithms to Northern Hemisphere Tropospheric Data for November 2003a
Insf. Data SAGE III
Aerosol SAGE III
N-Op. Cld. SAGE III
Op. Cld. SAGE III
Total, SAGE III
Insf. Data, SAGE II
502
0
0
0
502
Aerosol, SAGE II
10
1041
52
0
1103
N-Op. Cld., SAGE II
23
102
271
0
396
Op. Cld., SAGE II
3
0
0
73
76
Total, SAGE II
538
1143
323
73
2077
Each box shows the number of event–altitudes with a given interpretation by each algorithm.
Table 6
Agreement Between the Results of the SAGE II and SAGE III Cloud Algorithms and the Relative Number of Cases Handled by Each Algorithma
May 2003 N. Hemisphere
May 2003 S. Hemisphere
November 2003 N. Hemisphere
November 2003 S. Hemisphere
Agreement between SAGE II and III
0.81
0.92
0.90
0.92
(SII∕SIII) case number ratio
0.97
0.99
0.98
0.99
Data are for the troposphere above an altitude of 6 km.
Table 7
Comparison of the Results of the Application of the SAGE II and SAGE III Cloud Algorithms to Northern Hemisphere Dataa
Insf. Data, SAGE III
Aerosol, SAGE III
N-Op. Cld., SAGE III
Op. Cld., SAGE III
Total, SAGE III
Insf. Data, SAGE II
514
0
0
0
514
Aerosol, SAGE II
159
8123
241
0
8523
N-Op. Cld., SAGE II
0
73
90
0
163
Opq. Cld., SAGE II
0
0
0
0
0
Total, SAGE II
673
8196
331
0
9200
The data are for 15–27 km altitude for December 2002. Each box shows the number of event–altitudes with a given interpretation by each algorithm.
Table 8
Statistics for the July 2003 Aerosol and Cloud Histograms Shown in Figure 6(b)
Event Type and Altitude
Number of Aerosol Data Points
Median Aerosol Extinction (10−6 m−1)
rms Log. Deviation
Number of Cloud Data Points
Median Cloud Extinction (10−6 m−1)
rms Log. Deviation
SR 6 km
108
0.12
0.54
23
2.77
0.75
SR 8 km
176
0.13
0.37
42
2.10
0.47
SR 10 km
301
0.19
0.23
32
2.97
0.55
SR 12 km
385
0.17
0.18
5
1.02
0.31
SS 6 km
100
0.76
0.37
15
2.91
0.46
SS 8 km
137
0.65
0.27
31
5.79
0.21
SS 10 km
201
0.49
0.36
60
5.83
0.49
SS 12 km
344
0.23
0.34
43
1.41
0.52
Tables (8)
Table 1
Surface Measurements of Atmospheric Dust: Equivalent Large Particle Mode Radius [dN∕d(logR)]
A living document describing the algorithm background and its rationale. The document is updated as changes are made to the algorithm; the most recent update is Version 2.3, 8 July 2004.
A guide for SAGE III data users containing a detailed description of the output data format. Sections of the guide describe the nature and format of the cloud product.
A manual describing the postprocessing sequence. It contains details of the data management, file formats, and examples of various types of aerosol and cloud data.
Table 5
Comparison of the Results of the Application of the SAGE II and SAGE III Cloud Algorithms to Northern Hemisphere Tropospheric Data for November 2003a
Insf. Data SAGE III
Aerosol SAGE III
N-Op. Cld. SAGE III
Op. Cld. SAGE III
Total, SAGE III
Insf. Data, SAGE II
502
0
0
0
502
Aerosol, SAGE II
10
1041
52
0
1103
N-Op. Cld., SAGE II
23
102
271
0
396
Op. Cld., SAGE II
3
0
0
73
76
Total, SAGE II
538
1143
323
73
2077
Each box shows the number of event–altitudes with a given interpretation by each algorithm.
Table 6
Agreement Between the Results of the SAGE II and SAGE III Cloud Algorithms and the Relative Number of Cases Handled by Each Algorithma
May 2003 N. Hemisphere
May 2003 S. Hemisphere
November 2003 N. Hemisphere
November 2003 S. Hemisphere
Agreement between SAGE II and III
0.81
0.92
0.90
0.92
(SII∕SIII) case number ratio
0.97
0.99
0.98
0.99
Data are for the troposphere above an altitude of 6 km.
Table 7
Comparison of the Results of the Application of the SAGE II and SAGE III Cloud Algorithms to Northern Hemisphere Dataa
Insf. Data, SAGE III
Aerosol, SAGE III
N-Op. Cld., SAGE III
Op. Cld., SAGE III
Total, SAGE III
Insf. Data, SAGE II
514
0
0
0
514
Aerosol, SAGE II
159
8123
241
0
8523
N-Op. Cld., SAGE II
0
73
90
0
163
Opq. Cld., SAGE II
0
0
0
0
0
Total, SAGE II
673
8196
331
0
9200
The data are for 15–27 km altitude for December 2002. Each box shows the number of event–altitudes with a given interpretation by each algorithm.
Table 8
Statistics for the July 2003 Aerosol and Cloud Histograms Shown in Figure 6(b)