number of bytes in the record, checking for the correct header byte, and 

 adding data bytes to confirm that the checksum byte is correct. Because some 

 bytes in each record do not correspond to actual data, it is possible to replace 

 these bytes with place holders if it is determined that the missing bytes 

 occurred in those places. 



Along with examining each byte of a data record, it is possible to track the 

 bytes allotted to keep track of time. Each data record has a few bytes allotted 

 to count the actual clock time or to keep track of the record number which 

 would be referenced to the time from the microprocessor which is sending the 

 data. Again, because these bytes can be tracked, they can be replaced if 

 found to be missing by referring to previous records. If any ACP acoustic 

 intensity bytes, BASS velocity bytes, or pressure sensor bytes are lost, these 

 cannot be replaced and the time of the occurrence of such a data record must 

 be noted and a tally kept of such records for each data file. 



The next order of analysis includes examining some basic statistics of the 

 raw data. Because BASS data and pressure sensor data are directly converted 

 algebraically, the best way to examine these data is to convert them to their 

 final form. Data obtained from the ACP, however, can be examined for 

 statistical regularity before conversion, and this process is described in a later 

 section. Other analysis and interpretation focuses on the final converted data 

 and includes determining a proper averaging time and using that averaging 

 time to construct average profiles of ACP concentration data and BASS 

 velocity data. 



Data file format 



ACP/Pressure sensor. To implement a completed ARMS data collection 

 system including the BASS array, two separate data streams were used for the 

 laboratory version of the system at SUPERTANK. The format for the ACP 

 data stream is the same as that used for previous ARMS deployments and 

 includes data from the pressure sensor. The data file format from the BASS, 

 including some bytes allocated to keep track of the clock time, was designed 

 to be used specifically for SUPERTANK. 



The ACP data file for each 1-sec record of data contains a total of 

 128 bytes of 2 hexadecimal digits each, of which there are 110 bytes used for 

 the reflected acoustic intensity. At the beginning of each data record there are 

 16 bytes allocated for data from other instruments, and the first and last bytes 

 contain a constant valued header byte and a checksum byte. The format has 

 the form 



H XRRBXXXXPXXXXXPX CCC.CCC S C 9 " 1 ) 



where H represents the header byte, R's represent the record number, B is the 

 block number, P's are the two pressure measurements, C's correspond to the 

 1 10 reflected acoustic intensities, S is the checksum byte, which is the sum of 



Chapter 9 The Ohio State University Measurements 



169 



