PISM Drainage basin delineation tool

Overview

Regional modeling of outlet glacier flows using PISM requires isolating a drainage basin.

Our goal was to develop a tool using surface topography to divide an ice sheet into smaller basins. On the one hand, we do not want to use measured ice surface velocities because they may not be available in some cases (for example, paleo-glacial applications). On the other hand, we observe that existing hydrologic drainage basin generators (for example, topotoolbox) generate poor outlines to their drainage basins because (ironically) of the smooth surface topography of ice sheets.

Please see doc/method.tex (unfinished) for further details of our numerical strategy, and some references to the literature of the ice sheet drainage basin problem.

Requirements

The C code that does the heavy lifting uses an ODE solver from GSL, although hand-coding one of standard time-stepping methods would probably result in code that performs about as well.

This code can be used separately (i.e. in a C-only program).

In addition to using GSL, some functions are parallelized using OpenMP, so a compiler supporting OpenMP 2.5 or later is needed (GCC 4.2 and later is OK.)

Cython is used to make the C code mentioned above available from Python.

The wrapper script pism_regional.py uses several Python modules, notably

• netcdf4-python for NetCDF I/O
• NumPy for 2D arrays, etc
• matplotlib for plotting
• Tkinter for the GUI

All these libraries and packages are available via a package manager on Linux systems.

Installation

To install for the current user, run

python setup.py install --user

To build and use from the current directory, run

python setup.py build_ext --inplace

To disable OpenMP, run

NO_OPENMP=1 python setup.py ...

If you have GSL in a non-standard location, run

GSL_PREFIX=/path/to/gsl python setup.py ...

On systems where the default compiler does not support OpenMP you can specify the compiler to use like this:

CC=gcc-4.2 CXX=g++-4.2 python setup.py ...

Usage

• Run pism_regional.py. Select a NetCDF file containing variables x, y, usurf, and thk.
• Select the terminus region using the mouse.
• Click "Compute the drainage basin mask"
• Repeat the terminus region selection and re-generate the mask if necessary
• Save the mask to a file.
• Quit the script by closing all windows.