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Define a marine habitat

notebook filename | 07_turtlewatch_xtracto.Rmd

The TurleWatch project investigated the thermal habitat of loggerhead sea turtles in the Pacific Ocean north of the Hawaiian Islands. Research results indicate that most loggerhead turtles stay in water between 17.5°C and 18.5°C. When the 17.5°C to 18.5°C temperature contour is drawn on a map of sea surface temperature conditions, it delineates the boundary of the loggerhead’s preferred habitat.

In this exercise you will plot the thermal boundary of loggerhead sea turtles using satellite sea surface temperature. The exercise demonstrates the following techniques:
* Using xtracto_3D to extract data from a rectangular area
* Masking a data array
* Plotting maps using ggplot

Install required packages and load libraries

# Function to check if pkgs are installed, install missing pkgs, and load
pkgTest <- function(x)
{
  if (!require(x,character.only = TRUE))
  {
    install.packages(x,dep=TRUE,repos='http://cran.us.r-project.org')
    if(!require(x,character.only = TRUE)) stop(x, " :Package not found")
  }
}

list.of.packages <- c( "ncdf4", "rerddap", "plotdap", "RCurl",  
                       "raster", "colorRamps", "maps", "mapdata",
                       "ggplot2", "RColorBrewer", "rerddapXtracto")

# create list of installed packages
pkges = installed.packages()[,"Package"]

for (pk in list.of.packages) {
  pkgTest(pk)
}

Select the Satellite Data

  • Use the MUR SST dataset (ID jplMURSST41mday)
  • Gather information about the dataset (metadata) using rerddap
  • Displays the information
# CHOOSE DATASET and get information about it 


url = "http://coastwatch.pfeg.noaa.gov/erddap/"
dataInfo <- rerddap::info('jplMURSST41mday',url=url)
parameter <- 'sst'

Get Satellite Data

  • Select an area off the coast of California: longitude range of -130 to -115 east and latitude range of 25 to 40 north
  • Set the time range to days withing one month: tcoord=c(‘2018-06-06’,‘2018-06-08’)). The values do have to be different.
# latitude and longitude of the vertices
ylim<-c(25,40)
xlim<-c(-130,-115)

# Choose an area off the coast of California
# Extract the data
SST <- rxtracto_3D(dataInfo,xcoord=xlim,ycoord=ylim,parameter=parameter, 
                   tcoord=c('2018-06-06','2018-06-08'))
## Registered S3 method overwritten by 'httr':
##   method           from  
##   print.cache_info hoardr

## info() output passed to x; setting base url to: http://coastwatch.pfeg.noaa.gov/erddap/

# Drop command needed to reduce SST from a 3D variable to a 2D  one  
SST$sst <- drop(SST$sst)

Make a quick plot using plotBBox

plotBBox(SST, plotColor = 'thermal',maxpixels=100000)
## grid object contains more than 1e+05 pixels

## increase `maxpixels` for a finer resolution

## Warning in raster::projectRaster(r, crs = crs_string): input and ouput crs are
## the same

Define the Thermal niche of Loggerhead Turtles

__ Set the thermal range to 17.5-18.5 degrees C, as determined by the TurtleWatch program.__

## Define turtle temperature range
min.temp <- 17.5
max.temp <- 18.5

Create another variable for habitat temperature

Set the habitat temperature to equal NA

SST2 <- SST
SST2$sst[SST2$sst >= min.temp & SST2$sst <= max.temp] <- NA
plotBBox(SST2, plotColor = 'thermal',maxpixels=100000)
## grid object contains more than 1e+05 pixels

## increase `maxpixels` for a finer resolution

## Warning in raster::projectRaster(r, crs = crs_string): input and ouput crs are
## the same

It would be nicer to color in the turtle habitat area (the NA values) with a different color. If you want to customize graphs its better to use ggplot than the plotBBox that comes with rerrdapXtracto package. Here we will use ggplot to plot the data. But first the data is reformatted for use in ggplot.

Restructure the data

dims <- dim(SST2$sst)
SST2.lf <- expand.grid(x=SST$longitude,y=SST$latitude)
SST2.lf$sst<-array(SST2$sst,dims[1]*dims[2])

Plot the Data using ‘ggplot’

coast <- map_data("worldHires", ylim = ylim, xlim = xlim)

par(mar=c(3,3,.5,.5), las=1, font.axis=10)

myplot<-ggplot(data = SST2.lf, aes(x = x, y = y, fill = sst)) +
  geom_tile(na.rm=T) +
  geom_polygon(data = coast, aes(x=long, y = lat, group = group), fill = "grey80") +
  theme_bw(base_size = 15) + ylab("Latitude") + xlab("Longitude") +
  coord_fixed(1.3,xlim = xlim, ylim = ylim) +
  ggtitle(unique(as.Date(SST2$time))) +
  scale_fill_gradientn(colours = rev(rainbow(12)),limits=c(10,22),na.value = "firebrick4") 

myplot