Boat Lights from the VIIRS: Shedding some light on night-time fishing activity in the Indo-Malayan waters

Light emitted at night due to human activities can easily be seen from space and detected by satellite. Many compelling pictures of the Earth at night have been taken revealing cities, roads, and conurbations. Light emitted at sea has, however, received less attention. Applications relating to fisheries and their management might prove particularly useful. NOAA/NASA and partners have recently developed a boat detection product derived from satellite imagery at high temporal and spatial resolution and the data can be downloaded for free from here as either kml/csv files and processed in R. 

For many years (since 1972 to be precise), global low light night imaging was collected by the US Air Force's Defence Meteorological Satellite Programmes Operational Linescan System (DMSP-OLS). While night-time lights collected from DMSP-OLS has major shortcomings, there were no reasonable alternative products for mapping night-lights of lit fishing boats. This all changed in 2011 with the launch of NASA/NOAA Suomi National Polar Partnership satellite equipped with the Visible Infrared Radiometer Suite (VIIRS) as the primary imaging sensor. You can find out many of the advantages the new VIIRS sensor has over the DMPS-OLS here. One of the most important improvements is that the 'Day/Night band' on the VIIRS that is used for night-time light detection has a detection footprint 45 times smaller than that on the DMSP, which ultimately means it can detect light sources a lot more smaller than what the DMPS-OLS could! The VIIRS also has a better dynamic range and lower detection limits which means it can identify and discern more sources of light at night with less saturation when it gets too bright with surrounding lights. These two improvements are key in enabling better detection of boat lights at night.

Commercial fishermen the world over use very bright light to attract squid and small pelagics to their nets, for example, and these are visible from space. Here we use the NOAA boat light data to animate nightly boat lights during February 2015 (cumulative for entire night) for a part of south-east Asia including Indonesia, Malaysia and the northern tip of Australia. We think that many of these lights reflect fishing activity, but more work needs to be done to detect and isolate shipping etc. A concerted fishers' knowledge/consultation process would be essential for enabling us to understand these data properly. We think it would it would be worth the effort, though, and could yield fascinating insights into fleet behavior and the species targeted.

As usual, we provide the R code below on how we produced the above animation of the boat lights detection product.

##### Code to read and produce animation of boat night light detection data from NGDC site #####
 
# Load required libraries
 
library(RCurl)
library(rvest)
library(dplyr)
library(lubridate)
library(zoo)
library(ggplot2)
library(rgdal)
library(grid)
library(animation)
library(gridExtra)
library(extrafont)
 
# Set working directory
 
setwd("D:/Projects/BoatLights")
 
# Load fonts
 
loadfonts()
 
# Set date range for csv files to be downloaded from NGDC site
 
date.range <- seq.Date(from=as.Date('2015-02-01'),as.Date('2015-02-28'),by='1 day')
 
# Get dates into relevant format
 
date <- as.character(date.range)
date1 <- gsub("-","",date)
 
 
# Get urls to scrape boat light csv files off  NGDC site
 
urls <- sprintf((paste("http://mapserver.ngdc.noaa.gov/viirs_data/indo_boats///",c(date1),"/VNB_npp_d",c(date1),
        "_ssec_v12.csv",sep="")))
 
# Read boat light data files in csv format and bind them
 
boats <- do.call(rbind,lapply(urls,read.csv))
 
# Extract useful columns
 
boats.df <- boats[-c(18,19)]
 
# Reformat date and add other date and time columns
 
boats.df$Date <- as.POSIXct(boats.df$Date_Mscan, format="%Y-%m-%d %H:%M:%S",tz="GMT")
boats.df$Dates <- as.Date(boats.df$Date)
boats.df$Year <- as.numeric(as.POSIXlt(boats.df$Date)$year+1900)
boats.df$Month <- as.numeric(as.POSIXlt(boats.df$Date)$mon+1)
boats.df$Monthf <- factor(boats.df$Month,levels=as.character(1:12),
                 labels=c("Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"),ordered=TRUE)
boats.df$Weekday = as.numeric(format(as.POSIXlt(boats.df$Date),"%u"))
boats.df$Yearmonth <- as.yearmon(boats.df$Date)
boats.df$Yearmonthf <- factor(boats.df$Yearmonth)
boats.df$Week <- as.numeric(format(as.POSIXlt(boats.df$Date),"%W"))
boats.df$Day <- strftime(boats.df$Date,'%A')
boats.df$Jday <- strptime(boats.df$Date, "%Y-%m-%d")$yday+1
boats.df$Hour <- as.numeric(format(strptime(boats.df$Date, format = "%Y-%m-%d %H:%M"),format = "%H"))
 
# Extract only detections that are classified as 'boat' from quality flag for nightboat detection algorithm
 
boats.df1 <- subset(boats.df,QF_Detect==1)
 
# Import shapefiles
 
world <- readOGR(dsn="D:/GeoSpatial/Data/World_Boundaries", layer="TM_WORLD_BORDERS-0.3") # World boundary shp's download from www.thematicmapping.org
 
eez <- readOGR(dsn="D:/Projects/BoatLights", layer="EEZs") # EEZ boundary shp's downloaded from www.marineregions.org
 
mpa <- readOGR(dsn="D:/Projects/BoatLights", layer="MPAs") # MPA boundary shp's downloaded from CT Atlas website - www.ctlas.reefbase.org
 
# Fortify layers for ggplot mapping
 
world.df <- fortify(world)
 
eez.df <- fortify(eez)
 
mpa.df <- fortify(mpa)
 
# Set theme options for map
 
theme_opts <- list(theme(panel.grid.minor = element_blank(),
                         panel.grid.major = element_blank(),
                         panel.background = element_rect(fill="black"),
                         panel.border = element_rect(colour="black"),
                         legend.text = element_text(size = 8,face="bold",family="Myriad Pro"),
                         legend.position = "right",
                         legend.key.width=unit(0.75,"line"),
                         legend.key.height=unit(0.75,"line"),
                         legend.direction="horizontal",
                         axis.line = element_blank(),
                         axis.text.x = element_blank(),
                         axis.text.y = element_blank(),
                         axis.ticks = element_blank(),
                         axis.title.x = element_blank(),
                         plot.title = element_text(size=20,face="bold",family="Graph Black",hjust=0,vjust=-0.5),
                         axis.title.y = element_blank()))
 
 
# Run loop to produce boat light maps for each night in February 2015
 
for (i in date)
 
{
 
 
b <- ggplot(subset(boats.df1,Dates ==i),aes(Lon_DNB,Lat_DNB))+
     geom_polygon(data=mpa.df, aes(long,lat, group=group,fill="MPA"),colour=NA,alpha=0.5)+
     geom_point(color = "gold", size = 0.5, alpha = 0.5) +
     geom_polygon(data=eez.df, aes(long,lat, group=group,colour="EEZ"),fill=NA,size=0.25,linetype="dashed")+
     geom_polygon(data=world.df, aes(long,lat, group=group),fill="black",colour="darkgray",size=0.35)+
     theme_bw()+ ylab("")+ xlab("")+
     ggtitle((paste("Boat Lights detected from VIIRS on ",i,"\n"))) +
     scale_fill_manual(name="",values=c(MPA="forestgreen"))+
     scale_colour_manual(name="",values=c(EEZ="dimgray"))+
     coord_equal(xlim=c(95,140),ylim=c(-15,9))+
     theme_opts
 
b
 
bg <- arrangeGrob(b, sub = textGrob("Source: VIIRS Boat Detection (VBD) Data (PROTOTYPE) - NGDC (2015)\n", hjust = -0.33,
      vjust=-0.3,gp = gpar(fontface = "bold", fontsize = 8, fontfamily="Tw Cen MT Condensed")))
 
bg
 
ggsave(bg,file=paste("D:/Projects/BoatLights/boatlights_",i,".png",sep=""),width=8,height=5,unit="in",type="cairo-png")
 
}
 
# Set path for Image Magick convert program 
 
path.to.convert <- paste0(shortPathName("C:/Program Files/ImageMagick-6.9.0-Q16)/"),"convert.exe")
ani.options(convert=path.to.convert)
 
 
# Convert png files to GIF animation
 
files = sprintf('boatlights_%s.png', c(date))
im.convert(files, output = 'BoatLights_Feb2015.gif')

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