working on bottom-tracking biosonic files

Test code:

    library(oce)
    source('~/src/R-kelley/oce/R/echosounder.R')
    source('~/src/R-kelley/oce/R/oce.R')
    source('~/src/R-kelley/oce/R/processingLog.R')
    d <- read.oce('03-BottomStructure.dt4', debug=dd)
    str(d)
    x11()
    plot(d)
    lines(d[['time']], -d[['range']]) # odd ... also, times wrong