How to change the resolution of your spatial data in R? Here's how! Full article at: https://firsttimeprogrammer.blogspot.com/2017/03/resizing-spatial-data-in-r.html

expand_resolution.R

# We want more resolution for our data!

require(sp)
require(ncdf4)
require(gstat)
require(raster)
require(rasterVis)

# Clear workspace
rm(list=ls())

# Open nc file and get the data
a <- nc_open("qnet_2008.nc")
qnet <- ncvar_get(a, "qnet")
lon <- ncvar_get(a, "lon")
lat <- ncvar_get(a, "lat")
time <- ncvar_get(a, "time")
nc_close(a)

# Generate the expanded grid
grd <- expand.grid(lon, lat, time)
# Set names
names(grd) <- c("lon", "lat", "time")
# Put the data for qnet in a dataframe
vdata <- data.frame(qnet = as.numeric(qnet)) %>% tbl_df()
# Bind with the grid
data_ <- grd %>% 
                tbl_df() %>% 
                        bind_cols(vdata) %>% 
                                    filter(time == 1) %>% 
                                                select_("-time") %>% 
                                                            na.omit()
# Remove variables not needed anymore
rm(a, qnet, lon, lat, grd, vdata, time)

# Set coordinates variables
coordinates(data_) <- ~ lon + lat
gridded(data_) <- TRUE

# Interpolation grid. Set a 161x81 grid.
data.grid <- expand.grid(lon = seq(310, 350, .25), lat = seq(40, 60, .25))
coordinates(data.grid) <- ~ lon + lat
gridded(data.grid) <- TRUE

# IDW interpolation
idw_out <- idw(qnet ~ 1, locations = data_, newdata = data.grid, nmax = 5)

# Plots!
# Full data plot. Just for fun.
spplot(data_, xlab = "Longitude", ylab = "Latitude", main = "Net heat flux")

# Levels for plotting
lvls <- pretty(range(data_$qnet), 50)

# Actual data
r1 <- raster(data_)
levelplot(crop(r1, extent(310, 350, 40, 60)), par.settings = RdBuTheme, xlab = "Longitude", ylab = "Latitude", main = "Net heat flux", at = lvls)
spplot(crop(r1, extent(310, 350, 40, 60)), xlab = "Longitude", ylab = "Latitude", main = "Net heat flux", at = lvls)

# Interpolated data
r <- raster(idw_out)
levelplot(r, at=lvls, par.settings = RdBuTheme, xlab = "Longitude", ylab = "Latitude", main = "Net heat flux")
spplot(r, xlab = "Longitude", ylab = "Latitude", main = "Net heat flux", at = lvls)