Nitrate concentration

## ============================================================================
## NIOZ westerschelde image plot of nitrate
## data are in OceanView, called WSnioz
## implemented by Karline Soetaert
## ============================================================================
library(OceanView)
Long <- WSnioz[as.character(WSnioz$VariableName) == "WNO3",
            c("SamplingDateTimeREAL", "Station", "DataValue")]
Long$year <- Long$SamplingDateTimeREAL / 365 + 1900

# cross table; samples taken within 5 days are assumed to be = campaign
Cross <- db2cross(Long, row = "year", df.row = 5/365, 
  col = "Station", val = "DataValue")

# image plot; increase resolution  
image2D(x = Cross$x, y = Cross$y, z = Cross$z, 
  resfac = 3, ylim = c(0, 17), log = "", 
  main = "Nitrate", xlab = "year", ylab = "station", clab = "mmol/m3")