pyEM31

This codebase was initiated by the late Dr. Josh King (see original repository) at Environment and Climate Change Canada (ECCC) with support from Dr. Christian Haas at the Alfred Wegener Institute (AWI). Efforts are being continued by Mike Brady (ECCC) in order to share Josh's work with the general science community.

The EM31 Instrument

The Geonics EM31 sensor is designed to measure changes in conductivity through electromagnetic induction. Offered in two configurations (conventional EM31-MK2 and "short" EM31-SH), the device can be mounted on a trailer/toboggan and towed while traversing a given study area. Further information on the EM31 devices can be found at http://www.geonics.com/html/em31-mk2.html

At ECCC, the EM31-SH version is used (pictured below, mounted on a toboggan) to detect changes in conductivity in sea ice in order to estimate total ice thickness for a given area.

Supplementary Figure 1 from Haas et. al (2017) https://dx.doi.org/10.1002/2017GL075434

What this code does

This codebase takes the raw logger output from the EM31 and converts it into a pandas DataFrame for further analysis. If run as a script, all EM31 data files (*.R31) inside ./data/em31/ are converted into comma-separated value (.csv) text files containing measurement data and total thickness estimates.

Quickstart

Creating the runtime environment

# assumes you have python3.10 installed
# create the environment
python3 -m venv .venv

# activate the environment
## linux
source ./.venv/bin/activate
## windows
.\.venv\Scripts\activate

# install requirements
python3 -m pip install -r requirements.txt

Running the code

python3 em31.py

Using the functions interactively

from em31 import read_r31, thickness
# gps_tol: acceptable gps time separation in seconds
# encoding: the specific encoding for the input data file (default windows-1252)
df = read_r31('./data/em31/datafile.R31', gps_tol=1, encoding='windows-1252')
# inst_height: height of instrument above surface (meters?)
# coeffs: 3-element list of coefficients for estimating thickness from EM31 measurements
df = thickness(df, inst_height=0.15, coeffs=HAAS_2010)

Caveats

This code attempts to recover for NMEA0183 message corruption where EM31 data-logger lines intersect multi-line NMEA0183 GPS messages. If it finds any other problems - whether a parsing or checksum error for GPS data - it logs a message but makes no attempt to recover. Users can set debug-level logging to log the problematic NMEA0183 messages for further analysis:

logger.setLevel(logging.DEBUG)