Determining if a fine resolution lat/lon point lies in a coarse resolution lat/lon grid box?

Question

I have two datasets, each with two differing resolutions. The first dataset is a coarser resolution data set that has 0.5 x 0.625 degree resolution and contains values of MERRA-2 boundary layer thickness. The second, finer resolution dataset has 0.1 x 0.1 degree resolution and contains values of IMERG rainfall rate. I want to find the boundary layer thickness at every point where the rainfall rate exceeds 10 mm/hr. Since the MERRA-2 boundary layer thickness dataset is coarser, I figured that I could create a grid from the latitude and longitude values in the MERRA-2 dataset and check if the IMERG data points lie within any of the MERRA-2 grid boxes. I'm having trouble figuring out where to start with this, and any help is greatly appreciated.

Here is the formatting of the latitude and longitude for each dataset:

MERRA-2 Latitude: [[1.3500000e+01  1.3500000e+01  1.3500000e+01  1.3500000e+01]
MERRA-2 Longitude: [[-51.875 -51.25  -50.625 -50.    -49.375 -48.75  -48.125 -47.5   -46.875]
IMERG Latitude: [-0.05  0.05  0.15  0.25  0.35  0.45  0.55  0.65  0.75  0.85  0.95  1.05]
IMERG Longitude: [-49.95 -49.85 -49.75 -49.65 -49.55 -49.45 -49.35 -49.25 -49.15 -49.05]

EDIT: I have created a regridded dataset from Nemesi's first methodology (cdo remapcon), and they can be found below. The top image is the regridded data, and the bottom is the original data. Although the number of points in the newly regridded dataset increased from 59,040 to 5,475,600, the image seems to have lower resolution than the original image. The IMERG data also seems to have higher resolution even though both datasets have the same amount of points. Is this due to an error with the data formatting?

Answer 1

Note: I'm assuming that the original data are provided in NetCDF format.

There are two (OK, there are more, but I'll focus on these two) relatively quick ways to deal with this issue. Which one to prefer is very much depending on your preference and ability to use the different tools involved.

The fastest approach that comes to my mind is using the Climate Data Operator (CDO): you can find a detailed documentation here and an overview here.

The approach should be to get the grid description from the highest resolution file:

cdo -griddes imerg.nc

Then, take the description of the grid and put it in a .txt file and remap the coarser resolution file to match this grid. In this case, you may want to use a conservative remapping methodology to maintain the original values unaltered.

cdo remapcon,imerggrid.txt merra_coarse.nc merra_imerggrid.nc

In this way you would have the MERRA-2 data in a resolution matching your IMERG grid.

The second approach uses R. Steps (very quickly):

1. load the two NetCDF files as raster;
2. make a raster to point transformation (or just extract the coordinates and transform them in a Point Spatial object) of the imerg raster (in this way you would obtain the centroids of the imerg cells);
3. extract the data from the merra object overlaying the imerg points. All these passages are well documented in stackoverflow or gis.stackexchange.

This last methodology, however, may result in a very slow process in case of large datasets.