nsidc0756-scripts

Scripts related to NSIDC-0756: MEaSUREs BedMachine Antarctica, Version 2. This repository is a work in progress!

The scripts that are currently in this repository can be used to convert between geographic lat/lon and polar stereographic coordinates, and for interpolating BedMachine Antarctica data onto user-defined coordinates.

For example, one could interpolate bedrock elevation values from BedMachine Antarctica onto a latitude/longitude grid. First, use the ll2xy script to convert lat/lon coordinates to polar stereographic coordinates. Then these coordinates can be used as input for the interpBedmachineantarctica script which will interpolate BedMachine Antarctica values onto the input coordinates. The scripts are available both as Matlab and python scripts, for further details please see below.

Level of Support

• This repository is fully supported by NSIDC. If you discover any problems or bugs, please submit an Issue. If you would like to contribute to this repository, you may fork the repository and submit a pull request.

See the LICENSE for details on permissions and warranties. Please contact nsidc@nsidc.org for more information.

Scripts

xy2ll.m | xy2ll.py

Converts polar stereographic (x, y) coodinates to geodetic (latitude, longitude) coordinates.

Usage example for xy2ll.py:

from netCDF4 import Dataset

from xy2ll import xy2ll

ds = Dataset('BedMachineAntarctica_2019-11-05_v01.nc')
xs = ds.variables['x'][:]
ys = ds.variables['y'][:]

# cast xs and ys as float. `xy2ll` will not return correct results
# otherwise.
xs = xs.astype(float)
ys = ys.astype(float)

lats, lons = xy2ll(
    xs,
    ys,
    -1,  # -1 is a flag indicating the southern hemisphere.
)

ll2xy.m | ll2xy.py

Converts geodetic (latitude, longitude) coordinates to polar sterographic (x, y) coordinates.

interpBedmachineantarctica.m | interp_bedmachine_antarctica.py

Interpolates values from the BedMachineAntarctica netcdf file onto requested (x, y) polar stereographic coordinates.

NOTE:

interp_bedmachine_antarctica.py does not provide a perfect re-implementation of interpBedMachineAntarctica.m! When used with a to_x array of <1000, this code should perform in roughly the same way. When interpolating onto larger grids, interpBedMachineAntarctica.m uses a custom interpolation algorithm that has not yet been implemented in Python.

Outputs from interpBedMachineAntarctica.m have not been directly compared to interp_bedmachine_antarctica.py yet. Results may differ.

Setup

To use interp_bedmachine_antarctica.py, the requirements listed under environment.yml must be installed.

To create an environment with conda:

$ conda env create -f environment.yml
$ conda activate interp_bedmachine

Example usage (Python):

$ python
>>> from interp_bedmachine_antarctica import interp_bedmachine_antarctica
>>> import numpy as np
>>> to_x = np.linspace(-1666500.0, 1666500.0, 13332)
>>> to_y = np.linspace(-1666500.0, 1666500.0, 13332)
>>> variable = 'bed'
>>> bedmachine_nc_path = './BedMachineAntarctica_2019-11-05_v01.nc'
>>> interpolated = interp_bedmachine_antarctica(
        to_x,
        to_y,
        variable,
        bedmachine_nc_path=bedmachine_nc_path
)
>>> interpolated
array([[-4442.84863281, -4442.40963504, -4441.97063731, ...,
          386.82238055,   388.31525668,   389.80810547],
       [-4442.15570974, -4441.8033949 , -4441.45106056, ...,
          385.1755937 ,   386.62244517,   388.06926655],
       [-4441.46270859, -4441.19708971, -4440.93143181, ...,
          383.52890537,   384.92973833,   386.33053843],
       ...,
       [-4019.93213131, -4021.66220741, -4023.39202323, ...,
          241.79977309,   241.0239085 ,   240.24799334],
       [-4018.98273722, -4020.62648272, -4022.27007854, ...,
          264.8464815 ,   262.60142472,   260.35621881],
       [-4018.03344727, -4019.59069298, -4021.14789963, ...,
          287.89288765,   284.17862334,   280.46411133]])

Example usage (MATLAB):

% Input lat. and lon. and they can be an array or a list.
lat = [-84.72, -82.03; -83.96, -79.07];
lon = [92.41 ,85.11; 65.65, 77.67];

% For each lat., lon. calculate the stereographic coordinates
[x,y] = ll2xy(lat, lon, -1);

% Interpolate the Bedmachine values onto the coordinates
bed = interpBedmachineAntarctica(x,y,'bed');

disp(bed)

License

See LICENSE.

Code of Conduct

See Code of Conduct.

Credit

This software was developed by the National Snow and Ice Data Center with funding from multiple sources.