How to Replace Raster Values Less than 0 to NA in R code

Question

I am working with Landsat imagery to calculate net radiation. There are very low negative values (ex: -0.000003) that are in my converted reflectance raster layers. I want to make sure that my reflectances are 0 - 1 in order to reduce error in my future calculations.

How can I replace raster values less than 0 to "NA" in R. Similar to a raster calc function. I'm unsure how to provide an example, but I'm certain one of you could help me, yes?

Here is my equation for the reflectivity derived from Bastiaanssen et al. (1998)

Assuming, the pb1 indicates the reflectance for band 1 of Landsat, pi = 3.14..., lb1 = radiance for band 1, ESUN = exoatmospheric value for band 1, dr = the relative earth sun distance for the day of year.

#Calculate reflectivity per band. QC: Always 0 to 1
pb1 = (pi * lb1)/(ESUN1 * cos(solzen) * dr)

After this raster is created, all I want to do is set the pb1 values that are less than 0 to NA.

Help?

Answer 1

With the raster package, the memory-safe way to do this is to use reclassify or clamp

library(raster)
r <- raster(ncol=10, nrow=10)
values(r) <- rnorm(100)
x <- clamp(r, useValues=FALSE)
y <- reclassify(r, cbind(-Inf, 0, NA), right=FALSE)

Note the right=FALSE to not set cells that are zero to NA.

These methods are memory-safe and you can also provide a filename argument so that you do not need to call writeRaster afterwards.

Answer 2

library(raster)

values(pb1)[values(pb1) < 0] = NA

Or, as suggested by @jbaums:

pb1[pb1 < 0] <- NA

If you want to keep the original raster object, remember to assign the original raster to a new object name before running the code above.