Source code for SMBcorr.mar_extrap_mean
#!/usr/bin/env python
u"""
mar_extrap_mean.py
Written by Tyler Sutterley (09/2024)
Interpolates mean MAR products to times and coordinates
Uses fast nearest-neighbor search algorithms
https://scikit-learn.org/stable/modules/generated/sklearn.neighbors.BallTree.html
https://scikit-learn.org/stable/modules/generated/sklearn.neighbors.KDTree.html
and inverse distance weighted interpolation to extrapolate spatially
INPUTS:
DIRECTORY: full path to the MAR data directory
<path_to_mar>/MARv3.11/Greenland/ERA_1958-2019-15km/daily_15km
<path_to_mar>/MARv3.11/Greenland/NCEP1_1948-2020_20km/daily_20km
<path_to_mar>/MARv3.10/Greenland/NCEP1_1948-2019_20km/daily_20km
<path_to_mar>/MARv3.9/Greenland/ERA_1958-2018_10km/daily_10km
EPSG: projection of input spatial coordinates
tdec: dates to interpolate in year-decimal
X: x-coordinates to interpolate in projection EPSG
Y: y-coordinates to interpolate in projection EPSG
OPTIONS:
XNAME: x-coordinate variable name in MAR netCDF4 file
YNAME: x-coordinate variable name in MAR netCDF4 file
TIMENAME: time variable name in MAR netCDF4 file
VARIABLE: MAR product to interpolate
RANGE: start year and end year of mean file
SIGMA: Standard deviation for Gaussian kernel
SEARCH: nearest-neighbor search algorithm (BallTree or KDTree)
NN: number of nearest-neighbor points to use
POWER: inverse distance weighting power
FILL_VALUE: output fill_value for invalid points
PYTHON DEPENDENCIES:
numpy: Scientific Computing Tools For Python
https://numpy.org
https://numpy.org/doc/stable/user/numpy-for-matlab-users.html
scipy: Scientific Tools for Python
https://docs.scipy.org/doc/
netCDF4: Python interface to the netCDF C library
https://unidata.github.io/netcdf4-python/netCDF4/index.html
pyproj: Python interface to PROJ library
https://pypi.org/project/pyproj/
scikit-learn: Machine Learning in Python
https://scikit-learn.org/stable/index.html
https://github.com/scikit-learn/scikit-learn
UPDATE HISTORY:
Updated 09/2024: use wrapper to importlib for optional dependencies
Updated 08/2022: updated docstrings to numpy documentation format
Updated 01/2021: using conversion protocols following pyproj-2 updates
https://pyproj4.github.io/pyproj/stable/gotchas.html
Written 08/2020
"""
from __future__ import print_function
import sys
import os
import re
import warnings
import numpy as np
import scipy.spatial
import scipy.ndimage
import scipy.interpolate
import SMBcorr.spatial
import SMBcorr.utilities
# attempt imports
netCDF4 = SMBcorr.utilities.import_dependency('netCDF4')
pyproj = SMBcorr.utilities.import_dependency('pyproj')
# PURPOSE: read and interpolate a mean field of MAR outputs
[docs]def extrapolate_mar_mean(DIRECTORY, EPSG, VERSION, tdec, X, Y,
XNAME=None, YNAME=None, TIMENAME='TIME', VARIABLE='SMB',
RANGE=[2000,2019], SEARCH='BallTree', NN=10, POWER=2.0,
SIGMA=1.5, FILL_VALUE=None):
"""
Spatially extrapolates the temporal mean of MAR products
Parameters
----------
DIRECTORY: str
Working data directory
EPSG: str or int
input coordinate reference system
VERSION: str
MAR Version
- ``v3.5.2``
- ``v3.9``
- ``v3.10``
- ``v3.11``
tdec: float
time coordinates to interpolate in year-decimal
X: float
x-coordinates to interpolate
Y: float
y-coordinates to interpolate
VARIABLE: str, default 'SMB'
MAR product to interpolate
- ``SMB``: Surface Mass Balance
- ``PRECIP``: Precipitation
- ``SNOWFALL``: Snowfall
- ``RAINFALL``: Rainfall
- ``RUNOFF``: Melt Water Runoff
- ``SNOWMELT``: Snowmelt
- ``REFREEZE``: Melt Water Refreeze
- ``SUBLIM``: Sublimation
XNAME: str or NoneType, default None
Name of the x-coordinate variable
YNAME: str or NoneType, default None
Name of the y-coordinate variable
TIMENAME: str or NoneType, default 'TIME'
Name of the time variable
RANGE: list, default [2000,2019]
Start and end year of mean
SEARCH: str, default 'BallTree'
nearest-neighbor search algorithm
NN: int, default 10
number of nearest-neighbor points to use
POWER: int or float, default 2.0
Inverse distance weighting power
SIGMA: float, default 1.5
Standard deviation for Gaussian kernel
FILL_VALUE: float or NoneType, default None
Output fill_value for invalid points
Default will use fill values from data file
"""
# regular expression pattern for MAR dataset
rx = re.compile('MAR_SMBavg(.*?){0}-{1}.nc$'.format(*RANGE))
# find mar mean file for RANGE
FILE, = [f for f in os.listdir(DIRECTORY) if rx.match(f)]
# Open the MAR NetCDF file for reading
with netCDF4.Dataset(os.path.join(DIRECTORY,FILE), 'r') as fileID:
nx = len(fileID.variables[XNAME][:])
ny = len(fileID.variables[YNAME][:])
# python dictionary with file variables
fd = {}
# create a masked array with all data
fd[VARIABLE] = np.ma.zeros((ny,nx),fill_value=FILL_VALUE)
fd[VARIABLE].mask = np.zeros((ny,nx),dtype=bool)
# python dictionary with gaussian filtered variables
gs = {}
# use a gaussian filter to smooth each model field
gs[VARIABLE] = np.ma.zeros((ny,nx), fill_value=FILL_VALUE)
gs[VARIABLE].mask = np.ones((ny,nx), dtype=bool)
# Open the MAR NetCDF file for reading
with netCDF4.Dataset(os.path.join(DIRECTORY,FILE), 'r') as fileID:
# surface type
SRF=fileID.variables['SRF'][:]
# indices of specified ice mask
i,j=np.nonzero(SRF == 4)
# Get data from netCDF variable and remove singleton dimensions
tmp=np.squeeze(fileID.variables[VARIABLE][:])
# combine sectors for multi-layered data
if (np.ndim(tmp) == 3):
# ice fraction
FRA=fileID.variables['FRA'][:]/100.0
# create mask for combining data
MASK = np.zeros((ny,nx))
MASK[i,j] = FRA[i,j]
# combine data
fd[VARIABLE][:,:] = MASK*tmp[0,:,:] + \
(1.0-MASK)*tmp[1,:,:]
else:
# copy data
fd[VARIABLE][:,:] = tmp.copy()
# verify mask object for interpolating data
fd[VARIABLE].mask[:,:] |= (SRF != 4)
# combine mask object through time to create a single mask
fd['MASK']=1.0 - np.array(fd[VARIABLE].mask,dtype=np.float64)
# MAR coordinates
fd['LON']=fileID.variables['LON'][:,:].copy()
fd['LAT']=fileID.variables['LAT'][:,:].copy()
# convert x and y coordinates to meters
fd['x']=1000.0*fileID.variables[XNAME][:].copy()
fd['y']=1000.0*fileID.variables[YNAME][:].copy()
# use a gaussian filter to smooth mask
gs['MASK']=scipy.ndimage.gaussian_filter(fd['MASK'],SIGMA,
mode='constant',cval=0)
# indices of smoothed ice mask
ii,jj = np.nonzero(np.ceil(gs['MASK']) == 1.0)
# replace fill values before smoothing data
temp1 = np.zeros((ny,nx))
i,j = np.nonzero(~fd[VARIABLE].mask)
temp1[i,j] = fd[VARIABLE][i,j].copy()
# smooth spatial field
temp2 = scipy.ndimage.gaussian_filter(temp1, SIGMA,
mode='constant', cval=0)
# scale output smoothed field
gs[VARIABLE].data[ii,jj] = temp2[ii,jj]/gs['MASK'][ii,jj]
# replace valid values with original
gs[VARIABLE].data[i,j] = temp1[i,j]
# set mask variables for time
gs[VARIABLE].mask[ii,jj] = False
# convert MAR latitude and longitude to input coordinates (EPSG)
crs1 = pyproj.CRS.from_string(EPSG)
crs2 = pyproj.CRS.from_epsg(4326)
transformer = pyproj.Transformer.from_crs(crs1, crs2, always_xy=True)
direction = pyproj.enums.TransformDirection.INVERSE
# convert projection from model coordinates
xg,yg = transformer.transform(fd['LON'], fd['LAT'], direction=direction)
# construct search tree from original points
# can use either BallTree or KDTree algorithms
xy1 = np.concatenate((xg[i,j,None],yg[i,j,None]),axis=1)
tree = SMBcorr.spatial.build_tree(xy1, SEARCH=SEARCH)
# number of output data points
npts = len(tdec)
# output interpolated arrays of output variable
extrap = np.ma.zeros((npts),fill_value=FILL_VALUE,dtype=np.float64)
extrap.mask = np.ones((npts),dtype=bool)
# query the search tree to find the NN closest points
xy2 = np.concatenate((X[:,None],Y[:,None]),axis=1)
dist,indices = tree.query(xy2, k=NN, return_distance=True)
# normalized weights if POWER > 0 (typically between 1 and 3)
# in the inverse distance weighting
power_inverse_distance = dist**(-POWER)
s = np.sum(power_inverse_distance)
w = power_inverse_distance/s
# variable for valid points
var1 = gs[VARIABLE][i,j]
# spatially extrapolate using inverse distance weighting
extrap.data[:] = np.sum(w*var1[indices],axis=1)
# complete mask if any invalid in data
invalid, = np.nonzero((extrap.data == extrap.fill_value) |
np.isnan(extrap.data))
extrap.mask[invalid] = True
# return the interpolated values
return extrap