[R-sig-Geo] Extract VIIRS data in R

[Michael Sumner]

You won't find much on this kind of file in the R community, this is
relatively new NetCDF-4 with "groups", and contains a satellite "granule" -
a kind of pre-mapping raw data array with only technical information about
where the scanning occurred.

In short, raster and stars package (and RNetCDF and ncdf4) will read the
data from this file, but give very little or no help for how to treat it
like a map. The spatial resolution and extent are purely nominal as shown
by raster, a spacing of 1 in two dimensions and extending from 0 to nrows,
0 to ncols (with a  half cell shift). There aren't any coordinate arrays in
the file, or any simple way to transform from this matrix-space to
geography as far as I know.  (Would love to be corrected on how to do
that).

You'd need to pursue domain-specific expertise to discover the mapping of
this, unless some kind soul turns up to help here. I expect you'll want to
find a product that has been converted into simpler form for these data.

Cheers, Mike.


On Wed, Mar 18, 2020 at 1:39 AM Miluji Sb <milujisb using gmail.com> wrote:

> Dear all,
>
> Hope everyone is keeping safe.
>
> I am trying to extract/read VIIRS nighttime lights data but the output
> seems rather strange.
>
> I have uploaded the file here
> <https://drive.google.com/open?id=1zpqXJ8AlEcnk6ApRb75tfQc4-Y8AfK5h> so as
> not exceed the size limit of the email.
>
> ## Code ##
> library(ncdf4)
> library(rgdal)
>
> netcdf_file <- c("VNP02DNB_NRT.A2020069.1048.001.nc")
> nl <- brick(netcdf_file, lvar=0, values=TRUE,
> varname="observation_data/DNB_observations")
>
> ## Detail ##
> class      : RasterLayer
> dimensions : 3232, 4064, 13134848  (nrow, ncol, ncell)
> resolution : 1, 1  (x, y)
> extent     : 0.5, 4064.5, 0.5, 3232.5  (xmin, xmax, ymin, ymax)
> crs        : NA
> source     : C:/Users/shour/Desktop/VNP02DNB_NRT.A2020069.1048.001.nc
> names      : DNB.observations.at.pixel.locations
> zvar       : observation_data/DNB_observations
>
> The spatial resolution is supposed to be 750m but this shows 1°. What am I
> doing wrong? Any help will be greatly appreciated. Thank you.
>
> Sincerely,
>
> Millu
>
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>
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-- 
Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsumner using gmail.com

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