Rnightlights

Nightlights Data Extraction in R

The Rnightlights package extracts country rasters and zonal statistics from satellite nightlight rasters downloaded from the United States National Oceanic and Atmospheric Administration (http://www.noaa.gov) free data repositories.

The package supports DMSP-OLS annual and SNPP-VIIRS daily, monthly and annual (yearly) nightlight raster data. Satellite nightlight raster tiles are downloaded and cropped to the country boundaries using shapefiles from the GADM database of Global Administrative Areas (http://gadm.org). Specified zonal statistics are then calculated at the selected administrative level(s) for the selected country(ies) and cached locally for future retrieval. Finally, a simple data explorer/browser is included that allows one to visualize the cached data e.g. graphing, mapping and clustering regional data.

Installation

R package Rnightlights is available on CRAN and can be installed in R as:

install.packages("Rnightlights")

To install the development version run:

devtools::install_github("chrisvwn/Rnightlights")

NOTE: On Linux the following software pre-requisites are required:

• libcurl

  • deb: libcurl4-openssl-dev (Debian, Ubuntu, etc)
  • rpm: libcurl-devel (Fedora, CentOS, RHEL)
  • csw: libcurl_dev (Solaris)

• openssl

  • deb: libssl-dev (Debian, Ubuntu, etc)
  • rpm: openssl-devel (Fedora, CentOS, RHEL)
  • csw: libssl_dev (Solaris)
  • brew: openssl@1.1 (Mac OSX)

• gdal >= 1.11.4

  • deb: gdal-dev (Debian, Ubuntu, etc) (deb: libgdal-dev)
  • rpm: gdal-devel (Fedora, CentOS, RHEL)
  • csw: gdal_dev (Solaris)

• libxml-2.0

  • deb: libxml2-dev (Debian, Ubuntu, etc)
  • rpm: libxml2-devel (Fedora, CentOS, RHEL)
  • csw: libxml2_dev (Solaris)

• aria2 (Optional) For faster tile downloads

Example

An example to process VIIRS monthly nightlights for Kenya for the year 2014 from the Ishara Data blog post

Notes

1. Change the "ctry" variable to run the example on another country
2. This will not work for countries without admin levels below the country level e.g. ATA (Antarctica)
3. This calculates total radiances per region and so may be biased by area. Normalize by area to see regions with higher radiances per unit area e.g. to estimate areas with higher economic activity

a) In Rnightlights version 0.2.0 and later calculate directly at the county level with one line:

#install.packages(“Rnightlights”)
#install.packages("lubridate")
#install.packages("reshape2")
#install.packages("ggplot2")

library(Rnightlights)
library(lubridate)
library(reshape2)

#(Optional performance enhancement if you have aria2c and gdal installed)
#pkgOptions(downloadMethod = "aria", cropMaskMethod = "gdal", extractMethod = "gdal", deleteTiles = TRUE)

#Optional performance enhancement. If extractMethod="rast" you can specify the number of
#CPU cores to use in parallel
#pkgOptions(extractMethod = "rast", numCores=4)

ctry <- "KEN" #replace to run for any other country

#download and process monthly VIIRS stats at the highest admin level
highestAdmLevelStats <- getCtryNlData(ctryCode = ctry, 
                                     admLevel = "highest",
                                     nlType = "VIIRS.M", 
                                     nlPeriods = nlRange("201401", "201412","VIIRS.M"), 
                                     nlStats = list("sum",na.rm=TRUE),
                                     ignoreMissing=FALSE)

#Optionally plot the data
library(ggplot2)
library(plotly)

#melt the stats into key-value format for easy multi-line plotting with ggplot2
highestAdmLevelStats <- melt(highestAdmLevelStats,
                              id.vars = grep("NL_", names(highestAdmLevelStats), 
                                             invert=TRUE), 
                              variable.name = "nlPeriod", 
                              value.name = "radiancesum")

#extract date from the NL col names
highestAdmLevelStats$nlPeriod <- substr(highestAdmLevelStats$nlPeriod, 12, 17)

#format period as date
highestAdmLevelStats$nlPeriod <- ymd(paste0(substr(highestAdmLevelStats$nlPeriod, 1,4), 
                                               "-",substr(highestAdmLevelStats$nlPeriod, 5,6), "-01"))

#plot admin level sums for the year
g <- ggplot(data = highestAdmLevelStats, 
            aes(x=nlPeriod, y=radiancesum, 
                color=highestAdmLevelStats[[2]])) +
  scale_x_date(date_breaks = "1 month", date_labels = "%Y-%m")+
  geom_line()+geom_point() + labs(color = names(highestAdmLevelStats)[2]) + 
  xlab("Month") + 
  ylab("Sum of Radiances") +
  ggtitle(paste0(unique(names(highestAdmLevelStats)[2]), " sum of radiances for ", ctry))

print(g)

Performance enhancements

Some performance enhancements are available to speed up processing speeds and they fall into 2 classes:

a. Parallel processing: The most straightforward way to speed up processing is by increasing the number of CPU cores used to calculate the zonal statistics. By default only one CPU core is used. This option is available out of the box and is enabled by setting the numCores package option e.g. to process in parallel across 4 CPU cores run pkgOptions(numCores=4) before processing. Note numCores is only used when: pkgOptions(extractMethod="rast") which is the default.

b. GDAL: The GDAL tools provide tools that are often much faster than the usual processing workflow. For example, zonal statistics can be calculated much faster using GDAL than looping over sub-polygons even with a number of CPUs in parallel. GDAL tools are provided by the rgdal and gdalUtils packages, however, they require the GDAL software to be installed in the operating system. GDAL can be enabled at 2 stages: i) when cropping rasters by setting pkgOptions(cropMaskMethod="gdal") and ii) when calculating zonal stats by setting pkgOptions(extractMethod="gdal")

Process multiple countries at once

processNlData is the function to call to process multiple countries or admLevels which getCtryNlData cannot do. The other difference is that processNlData does not return any value - instead all processed data is cached and can then be retrieved using multiple calls to getCtryNlData. For example to process various admLevels in East Africa you could run:

processNlData(ctryCodes = list("KEN","TZA","UGA"), admLevels = list(list("county","constituency","ward"),list("adm0","adm1"), "adm1"), nlTypes = "OLS.Y", nlPeriods = "2013", nlStats = list("sum","na.rm=T"))

Note the matching ctryCodes and admLevels. Also note the nlStats parameter now can pass arguments to the functions and DOES NOT default to na.rm=TRUE.

Browse the cached data with the internal Shiny app

exploreData() #still under construction