Compare different DEMs for individual glaciers

For most glaciers in the world there are several digital elevation models (DEM) which cover the respective glacier. In OGGM we have currently implemented 10 different open access DEMs to choose from. Some are regional and only available in certain areas (e.g. Greenland or Antarctica) and some cover almost the entire globe. For more information, visit the rgitools documentation about DEMs.

This notebook allows to see which of the DEMs are available for a selected glacier and how they compare to each other. That way it is easy to spot systematic differences and also invalid points in the DEMs.

Input parameters

This notebook can be run as a script with parameters using papermill, but it is not necessary. The following cell contains the parameters you can choose from:

# The RGI Id of the glaciers you want to look for
# Use the original shapefiles or the GLIMS viewer to check for the ID: https://www.glims.org/maps/glims
rgi_id = 'RGI60-11.00897'

# The default is to test for all sources available for this glacier
# Set to a list of source names to override this
sources = None
# Where to write the plots. Default is in the current working directory
plot_dir = f'outputs/{rgi_id}'
# The RGI version to use
# V62 is an unofficial modification of V6 with only minor, backwards compatible modifications
prepro_rgi_version = 62
# Size of the map around the glacier. Currently only 10 and 40 are available
prepro_border = 10
# Degree of processing level.  Currently only 1 is available.
from_prepro_level = 1

Check input and set up

# The sources can be given as parameters
if sources is not None and isinstance(sources, str):
    sources = sources.split(',')
# Plotting directory as well
if not plot_dir:
    plot_dir = './' + rgi_id
import os
plot_dir = os.path.abspath(plot_dir)
import pandas as pd
import numpy as np
from oggm import cfg, utils, workflow, tasks, graphics, GlacierDirectory
import xarray as xr
import rioxarray as rioxr
import geopandas as gpd
import salem
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import AxesGrid
import itertools

from oggm.utils import DEM_SOURCES
from oggm.workflow import init_glacier_directories
# Make sure the plot directory exists
utils.mkdir(plot_dir);
# Use OGGM to download the data
cfg.initialize()
cfg.PATHS['working_dir'] = utils.gettempdir(dirname='OGGM-DEMS', reset=True)
cfg.PARAMS['use_intersects'] = False
2022-04-04 15:00:32: oggm.cfg: Reading default parameters from the OGGM `params.cfg` configuration file.
2022-04-04 15:00:32: oggm.cfg: Multiprocessing switched OFF according to the parameter file.
2022-04-04 15:00:32: oggm.cfg: Multiprocessing: using all available processors (N=2)
2022-04-04 15:00:32: oggm.cfg: PARAMS['use_intersects'] changed from `True` to `False`.

Download the data using OGGM utility functions

Note that you could reach the same goal by downloading the data manually from https://cluster.klima.uni-bremen.de/~oggm/gdirs/oggm_v1.4/rgitopo/

# URL of the preprocessed GDirs
gdir_url = 'https://cluster.klima.uni-bremen.de/~oggm/gdirs/oggm_v1.4/rgitopo/'
# We use OGGM to download the data
gdir = init_glacier_directories([rgi_id], from_prepro_level=1, prepro_border=10, 
                                 prepro_rgi_version='62', prepro_base_url=gdir_url)[0]
2022-04-04 15:00:32: oggm.workflow: init_glacier_directories from prepro level 1 on 1 glaciers.
2022-04-04 15:00:33: oggm.workflow: Execute entity tasks [gdir_from_prepro] on 1 glaciers
2022-04-04 15:00:33: oggm.utils: /github/home/OGGM/download_cache/cluster.klima.uni-bremen.de/~oggm/gdirs/oggm_v1.4/rgitopo/RGI62/b_010/L1/RGI60-11/RGI60-11.00.tar verified successfully.

Read the DEMs and store them all in a dataset

if sources is None:
    sources = [src for src in os.listdir(gdir.dir) if src in utils.DEM_SOURCES]
print('RGI ID:', rgi_id)
print('Available DEM sources:', sources)
print('Plotting directory:', plot_dir)
RGI ID: RGI60-11.00897
Available DEM sources: ['NASADEM', 'MAPZEN', 'AW3D30', 'ASTER', 'DEM3', 'TANDEM', 'SRTM']
Plotting directory: /__w/tutorials/tutorials/notebooks/outputs/RGI60-11.00897
# We use xarray to store the data
ods = xr.Dataset()
for src in sources:
    demfile = os.path.join(gdir.dir, src) + '/dem.tif'
    with rioxr.open_rasterio(demfile) as ds:
        data = ds.sel(band=1).load() * 1.
        ods[src] = data.where(data > -100, np.NaN)
    
    sy, sx = np.gradient(ods[src], gdir.grid.dx, gdir.grid.dx)
    ods[src + '_slope'] = ('y', 'x'),  np.arctan(np.sqrt(sy**2 + sx**2))

with rioxr.open_rasterio(gdir.get_filepath('glacier_mask')) as ds:
    ods['mask'] = ds.sel(band=1).load()
# Decide on the number of plots and figure size
ns = len(sources)
x_size = 12
n_cols = 3
n_rows = -(-ns // n_cols)
y_size = x_size / n_cols * n_rows

Raw topography data

smap = salem.graphics.Map(gdir.grid, countries=False)
smap.set_shapefile(gdir.read_shapefile('outlines'))
smap.set_plot_params(cmap='topo')
smap.set_lonlat_contours(add_tick_labels=False)
smap.set_plot_params(vmin=np.nanquantile([ods[s].min() for s in sources], 0.25),
                     vmax=np.nanquantile([ods[s].max() for s in sources], 0.75))

fig = plt.figure(figsize=(x_size, y_size))
grid = AxesGrid(fig, 111,
                nrows_ncols=(n_rows, n_cols),
                axes_pad=0.7,
                cbar_mode='each',
                cbar_location='right',
                cbar_pad=0.1
                )

for i, s in enumerate(sources):
    data = ods[s]
    smap.set_data(data)
    ax = grid[i]
    smap.visualize(ax=ax, addcbar=False, title=s)
    if np.isnan(data).all():
        grid[i].cax.remove()
        continue
    cax = grid.cbar_axes[i]
    smap.colorbarbase(cax)
    
# take care of uneven grids
if ax != grid[-1]:
    grid[-1].remove()
    grid[-1].cax.remove()

plt.savefig(os.path.join(plot_dir, 'dem_topo_color.png'), dpi=150, bbox_inches='tight')
../_images/dem_comparison_19_0.png

Shaded relief

fig = plt.figure(figsize=(x_size, y_size))
grid = AxesGrid(fig, 111,
                nrows_ncols=(n_rows, n_cols),
                axes_pad=0.7,
                cbar_mode='none',
                cbar_location='right',
                cbar_pad=0.1
                )
smap.set_plot_params(cmap='Blues')
smap.set_shapefile()
for i, s in enumerate(sources):
    data = ods[s].copy().where(np.isfinite(ods[s]), 0)
    smap.set_data(data * 0)
    ax = grid[i]
    smap.set_topography(data)
    smap.visualize(ax=ax, addcbar=False, title=s)
    
# take care of uneven grids
if ax != grid[-1]:
    grid[-1].remove()
    grid[-1].cax.remove()

plt.savefig(os.path.join(plot_dir, 'dem_topo_shade.png'), dpi=150, bbox_inches='tight')
../_images/dem_comparison_21_0.png

Slope

fig = plt.figure(figsize=(x_size, y_size))
grid = AxesGrid(fig, 111,
                nrows_ncols=(n_rows, n_cols),
                axes_pad=0.7,
                cbar_mode='each',
                cbar_location='right',
                cbar_pad=0.1
                )

smap.set_topography();
smap.set_plot_params(vmin=0, vmax=0.7, cmap='Blues')

for i, s in enumerate(sources):
    data = ods[s + '_slope']
    smap.set_data(data)
    ax = grid[i]
    smap.visualize(ax=ax, addcbar=False, title=s + ' (slope)')
    cax = grid.cbar_axes[i]
    smap.colorbarbase(cax)
    
# take care of uneven grids
if ax != grid[-1]:
    grid[-1].remove()
    grid[-1].cax.remove()

plt.savefig(os.path.join(plot_dir, 'dem_slope.png'), dpi=150, bbox_inches='tight')
../_images/dem_comparison_23_0.png

Some simple statistics about the DEMs

df = pd.DataFrame()
for s in sources:
    df[s] = ods[s].data.flatten()[ods.mask.data.flatten() == 1]

dfs = pd.DataFrame()
for s in sources:
    dfs[s] = ods[s + '_slope'].data.flatten()[ods.mask.data.flatten() == 1]
df.describe()
NASADEM MAPZEN AW3D30 ASTER DEM3 TANDEM SRTM
count 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000
mean 3028.332505 3023.202610 3023.871970 3031.316346 3061.494096 3066.819092 3032.272219
std 247.615467 254.144292 253.597569 250.883864 241.860064 258.874115 246.447678
min 2430.000000 2413.000000 2417.000000 2428.000000 2501.000000 2469.287598 2450.000000
25% 2855.000000 2850.000000 2851.000000 2865.000000 2886.000000 2889.410828 2857.000000
50% 3054.000000 3051.000000 3052.500000 3058.000000 3076.000000 3097.242310 3060.000000
75% 3202.000000 3201.750000 3201.750000 3203.000000 3233.750000 3249.972717 3203.000000
max 3691.000000 3723.000000 3720.000000 3693.000000 3706.000000 3738.977051 3684.000000

Comparison matrix plot

# Table of differences between DEMS
df_diff = pd.DataFrame()
done = []
for s1, s2 in itertools.product(sources, sources):
    if s1 == s2:
        continue
    if (s2, s1) in done:
        continue
    df_diff[s1 + '-' + s2] = df[s1] - df[s2]
    done.append((s1, s2))
# Decide on plot levels
max_diff = df_diff.quantile(0.99).max()
base_levels = np.array([-8, -5, -3, -1.5, -1, -0.5, -0.2, -0.1, 0, 0.1, 0.2, 0.5, 1, 1.5, 3, 5, 8])
if max_diff < 10:
    levels = base_levels
elif max_diff < 100:
    levels = base_levels * 10
elif max_diff < 1000:
    levels = base_levels * 100
else:
    levels = base_levels * 1000
levels = [l for l in levels if abs(l) < max_diff]
if max_diff > 10:
    levels = [int(l) for l in levels]
levels
[-50, -30, -15, -10, -5, -2, -1, 0, 1, 2, 5, 10, 15, 30, 50]
smap.set_plot_params(levels=levels, cmap='PuOr', extend='both')
smap.set_shapefile(gdir.read_shapefile('outlines'))

fig = plt.figure(figsize=(14, 14))
grid = AxesGrid(fig, 111,
                nrows_ncols=(ns - 1, ns - 1),
                axes_pad=0.3,
                cbar_mode='single',
                cbar_location='right',
                cbar_pad=0.1
                )
done = []
for ax in grid:
    ax.set_axis_off()
for s1, s2 in itertools.product(sources, sources):
    if s1 == s2:
        continue
    if (s2, s1) in done:
        continue
    data = ods[s1] - ods[s2]
    ax = grid[sources.index(s1) * (ns - 1) + sources[1:].index(s2)]
    ax.set_axis_on()
    smap.set_data(data)
    smap.visualize(ax=ax, addcbar=False)
    done.append((s1, s2))
    ax.set_title(s1 + '-' + s2, fontsize=8)
    
cax = grid.cbar_axes[0]
smap.colorbarbase(cax);

plt.savefig(os.path.join(plot_dir, 'dem_diffs.png'), dpi=150, bbox_inches='tight')
../_images/dem_comparison_30_0.png

Comparison scatter plot

import seaborn as sns
sns.set(style="ticks")

l1, l2 = (utils.nicenumber(df.min().min(), binsize=50, lower=True), 
          utils.nicenumber(df.max().max(), binsize=50, lower=False))

def plot_unity(xdata, ydata, **kwargs):
    points = np.linspace(l1, l2, 100)
    plt.gca().plot(points, points, color='k', marker=None,
                   linestyle=':', linewidth=3.0)

g = sns.pairplot(df.dropna(how='all', axis=1).dropna(), plot_kws=dict(s=50, edgecolor="C0", linewidth=1));
g.map_offdiag(plot_unity)
for asx in g.axes:
    for ax in asx:
        ax.set_xlim((l1, l2))
        ax.set_ylim((l1, l2))

plt.savefig(os.path.join(plot_dir, 'dem_scatter.png'), dpi=150, bbox_inches='tight')
../_images/dem_comparison_32_0.png

Table statistics

df.describe()
NASADEM MAPZEN AW3D30 ASTER DEM3 TANDEM SRTM
count 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000
mean 3028.332505 3023.202610 3023.871970 3031.316346 3061.494096 3066.819092 3032.272219
std 247.615467 254.144292 253.597569 250.883864 241.860064 258.874115 246.447678
min 2430.000000 2413.000000 2417.000000 2428.000000 2501.000000 2469.287598 2450.000000
25% 2855.000000 2850.000000 2851.000000 2865.000000 2886.000000 2889.410828 2857.000000
50% 3054.000000 3051.000000 3052.500000 3058.000000 3076.000000 3097.242310 3060.000000
75% 3202.000000 3201.750000 3201.750000 3203.000000 3233.750000 3249.972717 3203.000000
max 3691.000000 3723.000000 3720.000000 3693.000000 3706.000000 3738.977051 3684.000000
df.corr()
NASADEM MAPZEN AW3D30 ASTER DEM3 TANDEM SRTM
NASADEM 1.000000 0.999643 0.999553 0.999131 0.997409 0.999342 0.998544
MAPZEN 0.999643 1.000000 0.999819 0.999455 0.996358 0.999687 0.998217
AW3D30 0.999553 0.999819 1.000000 0.999315 0.996423 0.999633 0.998216
ASTER 0.999131 0.999455 0.999315 1.000000 0.995739 0.999344 0.998518
DEM3 0.997409 0.996358 0.996423 0.995739 1.000000 0.996175 0.997038
TANDEM 0.999342 0.999687 0.999633 0.999344 0.996175 1.000000 0.998315
SRTM 0.998544 0.998217 0.998216 0.998518 0.997038 0.998315 1.000000
df_diff.describe()
NASADEM-MAPZEN NASADEM-AW3D30 NASADEM-ASTER NASADEM-DEM3 NASADEM-TANDEM NASADEM-SRTM MAPZEN-AW3D30 MAPZEN-ASTER MAPZEN-DEM3 MAPZEN-TANDEM ... AW3D30-ASTER AW3D30-DEM3 AW3D30-TANDEM AW3D30-SRTM ASTER-DEM3 ASTER-TANDEM ASTER-SRTM DEM3-TANDEM DEM3-SRTM TANDEM-SRTM
count 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 ... 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000
mean 5.129894 4.460534 -2.983841 -33.161591 -38.487375 -3.939714 -0.669360 -8.113735 -38.291485 -43.617270 ... -7.444375 -37.622126 -42.947910 -8.400249 -30.177750 -35.503534 -0.955873 -5.325784 29.221877 34.547661
std 9.360127 9.588316 10.892745 18.533220 14.527865 13.380009 4.859039 8.953622 24.467068 7.972539 ... 9.720664 24.010492 8.722370 16.555147 24.464741 12.211383 14.247553 27.721822 19.342194 19.220421
min -51.000000 -48.000000 -55.000000 -92.000000 -80.386475 -69.000000 -35.000000 -46.000000 -123.000000 -85.858154 ... -44.000000 -121.000000 -82.822998 -79.000000 -112.000000 -79.663330 -69.000000 -131.650635 -47.000000 -21.226807
25% -1.000000 -2.000000 -9.000000 -43.000000 -48.055481 -10.000000 -3.000000 -14.000000 -50.000000 -48.300476 ... -13.000000 -49.000000 -47.949890 -20.000000 -42.000000 -43.959106 -10.000000 -21.998291 22.000000 22.963257
50% 3.000000 3.000000 -4.000000 -34.000000 -42.692627 -4.000000 -1.000000 -8.000000 -38.000000 -45.182861 ... -7.000000 -36.000000 -43.253540 -9.000000 -29.000000 -37.429810 0.000000 -6.978149 32.000000 35.271484
75% 10.000000 8.000000 3.000000 -25.000000 -33.745605 1.000000 1.000000 -2.000000 -25.000000 -40.532715 ... -1.000000 -25.000000 -38.227905 1.000000 -20.000000 -28.404724 7.000000 7.438965 40.000000 45.801941
max 40.000000 38.000000 40.000000 91.000000 16.636475 59.000000 28.000000 30.000000 100.000000 -1.023926 ... 33.000000 109.000000 -2.486084 75.000000 94.000000 0.389160 59.000000 79.397461 84.000000 106.757324

8 rows × 21 columns

df_diff.abs().describe()
NASADEM-MAPZEN NASADEM-AW3D30 NASADEM-ASTER NASADEM-DEM3 NASADEM-TANDEM NASADEM-SRTM MAPZEN-AW3D30 MAPZEN-ASTER MAPZEN-DEM3 MAPZEN-TANDEM ... AW3D30-ASTER AW3D30-DEM3 AW3D30-TANDEM AW3D30-SRTM ASTER-DEM3 ASTER-TANDEM ASTER-SRTM DEM3-TANDEM DEM3-SRTM TANDEM-SRTM
count 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 ... 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000 3218.000000
mean 7.451212 7.379117 8.758856 34.688626 38.762453 10.136109 3.354257 9.781231 40.133623 43.617270 ... 9.678682 39.443754 42.947910 14.691734 33.658173 35.503776 10.924798 21.395372 32.021753 35.206708
std 7.641868 7.574302 7.128573 15.486716 13.776885 9.580093 3.578254 7.093540 21.310154 7.972539 ... 7.498083 20.882402 8.722370 11.346579 19.397900 12.210679 9.193391 18.411083 14.233504 17.984406
min 0.000000 0.000000 0.000000 0.000000 0.005859 0.000000 0.000000 0.000000 0.000000 1.023926 ... 0.000000 0.000000 2.486084 0.000000 0.000000 0.389160 0.000000 0.001709 0.000000 0.166016
25% 2.000000 2.000000 3.000000 25.000000 33.745605 3.000000 1.000000 4.000000 26.000000 40.532715 ... 4.000000 26.000000 38.227905 5.000000 21.000000 28.404724 4.000000 7.188965 24.000000 22.963257
50% 4.000000 5.000000 7.000000 34.000000 42.692627 7.000000 2.000000 9.000000 38.000000 45.182861 ... 8.000000 36.000000 43.253540 13.000000 30.000000 37.429810 9.000000 16.839111 32.000000 35.271484
75% 10.000000 10.000000 12.000000 43.000000 48.055481 15.000000 4.000000 14.000000 50.000000 48.300476 ... 14.000000 49.000000 47.949890 22.000000 43.000000 43.959106 16.000000 30.157959 41.000000 45.801941
max 51.000000 48.000000 55.000000 92.000000 80.386475 69.000000 35.000000 46.000000 123.000000 85.858154 ... 44.000000 121.000000 82.822998 79.000000 112.000000 79.663330 69.000000 131.650635 84.000000 106.757324

8 rows × 21 columns

What’s next?