Data management and recording

Survey activities

Datasheets (Fig. 21) should be used to document activities that occur during an acoustic survey.  Transect turns, CTD measurements, trawl deployment, or interesting echoes should be noted with time and/or file name.  Some groups use consecutive “event numbers” to delineate deployments and other occurrences.

 

Date:                                                              Vessel:                                               
Survey Location:                                                                                                     

Time	Transect	Event	Comment

Figure 21.  Example datasheet for an acoustic survey. 

Inserting breaks into data files at key events is a useful technique.  For systematic surveys, file breaks at the end of a transect and the beginning of the next will allow data from the turn to be quickly excluded in post-processing.  This may be especially helpful if data analysis will utilize individual transects.  Similarly, this approach simplifies the identification of survey sections (e.g., specific transect, data collected during a trawl) of interest.  Be sure to note the significance of any inserted file breaks in the acoustic log. 

Although not currently used in the Great Lakes, Simrad commercial ES60 systems have a periodic “dither” that must be removed post-processing.  This dither alters (increases or decreases) backscatter values in a predictable pattern. As dither removal is based on establishing the sequence of pings between each introduced error, the process is made more complicated by inserted file breaks. Open source software (ES60Adjust, Keith et al. 2005) is available to remove this dither.

Data archiving

All acoustic and associated meta-data should be routinely archived during the survey.  If a break in the survey occurs, data should be backed-up to shore-based computers as well.  We recommend bringing a high capacity portable hard drive in the field and backing up all data after each day of data collection.