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

[Zia Ahmed]

This is might help you:

https://zia207.github.io/geospatial-r-github.io/netCDF-data-processing.html

Zia

On Wed, Mar 18, 2020, 9:34 AM Frederico Faleiro <fvfaleiro using gmail.com> wrote:

> Hi Miluji,
>
> the R in general do not handle very well with netCDF. However I
> recommend you use the netcdf4 package before try others.
> This link is a good start:
>
> http://geog.uoregon.edu/bartlein/courses/geog490/week04-netCDF.html#get-coordinate-including-time-variables
> .
> The coordinates of this file is not in longitude and latitude, it use
> "number_of_lines" for X Axis and "number_of_pixels" for Y Axis. This way
> the difference between the cells is always one and raster package
> interprete the difference as one degree and return an warning about it.
> I open the file in the software Panoply (design to work with netCDF)  and
> everything is OK apparently.
> Check bellow some exploration of the data in R.
>
> library(raster)
> library(ncdf4)
> library(rgdal)
>
> # netcdf4 package
> netcdf_file <- "VNP02DNB_NRT.A2020069.1048.001.nc"
> nc <- nc_open(netcdf_file)
> print(nc)
> # check your variable is structured as:
> observation_data/DNB_observations[number_of_pixels,number_of_lines]
> # variables available
> names(nc[["var"]])
> # properties from your variable
> ncatt_get(nc, "observation_data/DNB_observations")
> # get the variables values and check the structure
> obs_matrix <- ncvar_get(nc, "observation_data/DNB_observations")
> str(obs_matrix)
>
> # raster package
> nc_r <- brick(netcdf_file, lvar=0, values=TRUE,
> varname="observation_data/DNB_observations")
> # [1] "vobjtovarid4: **** WARNING **** I was asked to get a varid for
> dimension named number_of_pixels BUT this dimension HAS NO DIMVAR! Code
> will probably fail at this point"
> # [1] "vobjtovarid4: **** WARNING **** I was asked to get a varid for
> dimension named number_of_lines BUT this dimension HAS NO DIMVAR! Code will
> probably fail at this point"
>
> Best regards,
>
> Frederico Faleiro
> Postdoctoral Researcher in the INCT-EECBio (https://www.eecbio.ufg.br/)
> Federal University of Goiás | Brazil
> RG: https://www.researchgate.net/profile/Frederico_Faleiro
>
> On Tue, Mar 17, 2020 at 11:39 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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> >
>
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