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transmitting low volume environmental data from remote sites for various institutions and government 
agencies. 
Each station on the GOES and METEOSAT networks has been assigned a transmission window 
allowing approximately 30 kbytes per day in twenty four individual transmissions at hourly intervals. 
During each transmission, a packet of data and status information are time stamped by the radiometer, the 
DCP and the central receiving station (Wallops Island, VA, USA for GOES, Darmstadt, Germany for 
METEOSAT and Tokyo, Japan for GMS). Typically the data are maintained in the receiving station 
computers for 3 to 5 days before they are overwritten. We retrieve the data daily from the central receiving 
station which we term near real-time. 
3 PROCESSING SYSTEM 
The third fundamental component of a sun photometer network is a friendly software package that provides 
near real-time information on the health and calibration of the instruments, provides state of the art 
processing of the data, provides an orderly archive of the data and provides easy access for all users to that 
data base. The automatic radiometer and DCS transmissions allow these software goals to be developed. 
We shall discuss these aspects of the current operational state of the software and future directions. 
3.1. Instrument and Network Health 
The radiometer data stream includes date, time, temperature, battery voltage, wet sensor status and time of 
transmission as well as several levels of identification numbers. The DCP adds a time stamp at the time of 
transmission as does the DCS receiving station plus checks for parity errors and signal strength of the 
transmission. When the data are downloaded from the central receiving station, these data and information 
are used to automatically generate a status report and a trouble shooting report both of which are 
automatically emailed to appropriate system managers. The status report provides a comprehensive 
assessment of the operation of the radiometer and DCP for the data transmitted with the current download. 
Network managers then have sufficient information to assess the operation of individual stations. To more 
quickly identify trouble spots, a troubleshooting report is generated that lists by instrument only 
information that fails to meet normal operating thresholds i.e.. low battery voltage, transmission time 
error, missed transmission etc. This approach can identify problems with a remote station often leading to 
same day resolution. Previously this would have been possible at only the most sophisticated sun 
photometer facilities. 
3.2. Data Processing 
Data processing includes both the Beer’s Law of standard sun photometry and rather sophisticated aureole 
inversions required for the present day radiometer instrument. Standardization is complicated by the lack of 
agreement on corrections, calibration procedures etc. often caused by divergent error tolerances or 
requirements of various investigators. We have assembled a series of processing algorithms running under 
X-WINDOWS that meets simple criteria which are that the algorithms have been published in the open 
literature and are generally accepted in the scientific community. We have assembled these algorithms into 
one primary program called "demonstrattttt". The algorithms are accessed in the program under three 
principle categories, calibration, time dependent sun retrievals, and sky radiance retrievals. There are a 
growing number of sub processing algorithms from each of these. 
3.2.1. Calibration. Calibration of sun photometers historically has limited the wide scale 
deployment and long term reliability of these data. A number of strategies exist which have been 
implemented for calibrating the direct sun observation most of which are a variation of the Langley method. 
Other methods rely on a combination of direct sun and aureole langleys. A third method is a simple inter- 
comparison. 
The radiometer makes a langley data collection each morning and afternoon between an optical 
airmass of 2 and 7. The interactive calibration routines allow deselection of points and tabled Vo's 
recomputed and displayed with each deletion. The Vo’s may be applied to the original langley data and 
aerosol optical thickness plotted as a function of time or airmass in two additional windows for further 
inspection of the quality of the langley. The calibration for the modified langley for water vapor (Bruegge