3.2.4. Down welling Flux. In addition to aerosol properties and concentrations we have 
incorporated an empirical spectral cloud free flux model (Bird and Riordan, 1986) to compute from the 
measured aerosol and water vapor measurements the total, direct and diffuse down welling flux in the total 
solar spectrum and photosynthetically active radiation (PAR) bands. Single scattering albedo and ground 
reflectance are the only parameters which the instrument does not measure and which are required inputs. 
The interactive computations are made for any instantaneous or time dependent measurements. The window 
displays the spectral flux curves for the total, direct and diffuse irradiance and a summary box gives 
integrated values for each component of the broad band and PAR. The model is applied to the time 
dependence creating a data set of integrated fluxes. Options exist to compute coincident fluxes for user 
specified background conditions. Ratios of ambient vs background conditions are computed and displayed in 
a summary box. 
Incorporation of more rigorous radiative transfer models is planned. 
3.3. Cloud Screening 
Data are taken by the automatic instruments under all non precipitation conditions causing significant cloud 
contamination in the raw data. The philosophy for using the data base within "demonstrattttt" is to provide 
primitive cloud screening based on the variability of the triplets that allows some cloud contaminated data 
to be displayed. Further refinements to the screening process may be made by manual deselection of the 
contaminated data through cursor control on the time dependent window allowing the data set to be cleaned 
and downloaded if desired. 
Automatic cloud screening of the almucantar and principal plane data are by symmetry and 
smoothness checks respectively of the data about the solar disc as explained in section 3.2.3. 
3.4. Downloading Data 
Labeled spreadsheet export files may be created of all data in the data base and all data generated in the 
"demonstrattttt" processing program. Data for export may be selected by location, time, and the type of raw 
or processed data desired. The data may be downloaded to any computer with internet access using a guest 
account. For further access information send a request to sunphoto@kratmos.gsfc.nasa.gov. 
3.5. Data Accuracy 
The data accuracy of the aerosol optical thickness and water vapor retrievals is a function of the knowledge 
of the calibration accuracy, cloud contamination and the variability of the instrument. From section 2.3 the 
instrument variability is for all practical purposes insignificant and will not be displayed as error bars. The 
variability of the atmosphere is characterized by the variability of the triplet optical thicknesses which may 
at times be cloud contaminated. This variability will be plotted as error bars on the time dependence. The 
uncertainty due to calibration will be tracked with all time dependent data through a second set of error bars 
plotted on request and a dialogue box that tracks the calibration sequence to a time dependence between 
and/or to the nearest mountain top langley. 
The uncertainty of the sky radiance data is more difficult to ascertain since these only constitute 
single observations and no absolute self-calibration procedure is implemented between the sphere 
calibrations. Based on the sphere calibration the uncertainty in the sky radiance is ±0.05 (iw/cm^p.m/str for 
all four channels at the time of calibration. 
4 ■ CONCLUSION 
We believe that a successful system for long term monitoring of aerosols requires automatic low 
maintenance radiometers, real time data reception and processing as well as an easily accessible data base for 
the scientific community. We have developed a system of commercially available hardware and public 
domain software that has yielded regionally based aerosol amounts and properties in North and South 
America. Systems will come on-line in 1994 what will accommodate global monitoring and intensive field 
campaigns. The philosophy of an open interactive data base is expected to promote research and 
collaboration among investigators 
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