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General SNDA description

The SNDA system consists of two subsystems as shown at the picture:

a real time subsystem (RTS) for collection of multichannel data, storing them in a diskloop and pre-processing of the data flow by group filtering (e.g. beamforming) and detecting procedures; an off-line seismic analysis subsystem (SAS) for automated interactive processing of registered seismograms with the help of more sophisticated and time consuming procedures for statistically optimal multichannel data analysis. The main problem in RTS design is to provide reliable execution of application procedures in conditions of varying intensity of data streams and user's activity. This problem is solved in the SNDA by utilizing the advanced structural programming technique. The latter involves implementation of such means as: an "up-to-down design projection", a free asynchronous communication between different system processes based on the "port" method and semaphore facilities, a provision of special System Process Table and Global System Table in which all ports, processes priorities and system "macroses" are defined that guarantee the System handling flexibility and availability of it's easy modification by an uniquely way.

The SAS is designed as an asynchronous dialogue process. It can interact with the RTS that enables users to control on-line data processing, in particular to modify parameters of group filtering and detecting procedures.

The main peculiarity of the SAS is the Data Stack (DS) concept, which had been put forward by the authors of the well known system EP designed by NORSAR for SASA data handling. The DS is a random access memory buffer where multichannel seismic traces are stored altogether with their concomitant parameters. Multichannel data can be written to the DS from the RTS Diskloop or from ordinary disc files. A new feature of the SNDA in comparison with the NORSAR EP is distinguishing of routine data handling operations from sophisticated seismic analysis procedures. Operations of the first group do not require many parameters to be adjusted - we named them the Stack Commands (SC).

The SC set includes data read/write commands; trace and time window handling commands; trace sample arithmetic commands; filter, power spectra, FFT commands; trace display and decoration commands (labels, legends, etc), SNDA service commands. The SC are entered by a user from a special Stack Command Window.

Seismic analysis procedures (SA-procedures) as a rule demand tuning with the help of rather large amount of parameters. SNDA SA-procedures are controlled by its "input file" comprising all parameters (with comment information) needed to tune the procedure for a given processing session.

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