EarthTidalGravity

A python wrapper for ETGTAB (Earth Tidal Gravity TABle) - a program to predict Earth tidal gravity accelerations and other tidal components.

ETGTAB computes Earth tide components (tidal potential, acceleration, tilt, displacements, strains, etc.) at any location for time intervals of 5 or 60 minutes. Tidal components can be computed using different tidal potential developments (DOODSON 1921 with 378 waves, CARTWRIGHT-TAYLER-EDDEN 1973 with 505 waves, TAMURA 1987 with 1200 waves, or BUELLESFELD 1985 with 665 waves) for a rigid or elastic Earth.

Note that ETGTAB has been superseeded by PREDICT - a module in the ETERNA software package (version 3.4). ETGTAB and PREDICT were originally written in FORTRAN by the late Prof. H.-G. Wenzel, Geodetic Institute, Karlsruhe University.

Basic usage

• The user specifies location parameters (coordinates, local gravity, timezone, etc) and tide model parameters (tide components, time intervals, potential model, etc). The code separates these parameters into dictionaries Location and TidePars to allow for simple comparisons between locations or tide models. A basic example is shown below:

from ETGTAB import *

etg   = Earth_Tidal_Gravity
utils = Utilities

Location = {
  'Latitude':  45.9500,           ## Latitude  (deg North)
  'Longitude': 66.6411,           ## Longitude (deg East)
  'Elevation': 45.,               ## Elevation above sea level (m)
  'Gravity':   9.8067624,         ## Local gravity (m/s^2)
  'Timezone':  'Canada/Atlantic', ## Local timezone (e.g. 'Europe/Paris', 'Canada/Atlantic', 'UTC', see pytz.common_timezones)
  'City':      'Fredericton, NB', ## City description
}

TidePars = {
  'Azimuth':    0.,              ## [deg]
  'TidalComps': ['Vertical_Acceleration', 'Vertical_Displacement'], ## List of tidal components to compute.
  'PrintLevel': 'None',          ## 'None', 'Some', 'All'
  'TimeStart':  [2024, 8, 1, 0], ## [YYYY,MM,DD,HH] in UTC timezone
  'TimeSpan':   24*31,           ## [hrs]
  'TimeStep':   3600,            ## [s] (300 or 3600 only)
  'TidalModel': 'Tamura1987',    ## 'Doodson1921', 'CTE1973', 'Tamura1987', 'Buellesfeld1985'
  'EarthModel': 'Elastic'        ## 'Rigid', 'Elastic'
}

utils.Time_Series('Example', Location, TidePars)

• Possible tidal components are: 'Tidal_Potential', 'Vertical_Acceleration', 'Horizontal_Acceleration', 'Vertical_Displacement', 'Horizontal_Displacement', 'Vertical_Strain', 'Horizontal_Strain', 'Areal_Strain', 'Shear_Strain', 'Volume_Strain', 'Ocean_Tides'

• This code produces the following plot:

• In the folder Output, this code produces a CSV file called Example.csv containing all requested tidal components, along with copies of the dictionaries Location and TidePars in json format called Example_Location.json and Example_TidePars.json.

File Descriptions

• Main.py: main the entry point for generating model output.

• ETGTAB/Earth_Tidal_Gravity.py: contains the Python wrapper for ETGTAB, sets default plot options, configures the logger, and defines the class EarthTidalGravity. The class has the following methods:

  • __init__(): Initializes class attributes.
  • Export_Model_Parameters(): Exports model parameters to files.
  • Import_Model_Parameters(): Import model parameters from files.
  • Parse_Tidal_Components(): Parses current tidal component from list and assigns ETGTAB index, plot labels, and units.
  • Write_Input_File(): Write ETGTAB input parameters to a formatted file.
  • Run_ETGTAB(): Python wrapper for ETGTAB. This method overwrites the input file, deletes any existing raw output file, and runs the ETGTAB executable as a subprocess. It then reads the new raw output file.
  • Read_Raw_Output_File(): Read raw ETGTAB output into a dataframe.
  • Move_Raw_Output_File(): Move and rename raw ETGTAB output file into 'Output' directory.
  • Write_CSV_File(): Write dataframe to CSV file.
  • Read_CSV_File(): Read CSV file into dataframe.
  • Generate_Model_Output(): Generate Earth tidal gravity model output in the form of raw text files and a CSV file in the Output folder.
  • Plot_Tidal_Component(): Plot output from the ETGTAB computation.
  • Plot_All_Tidal_Components(): Plot all Earth tidal model components stored in data frame.

• ETGTAB/Utilities.py: Utilities and helper functions that manipulate Earth tidal gravity data.

  • TimeSeries(): Generate time series of tidal components at one location and plot the result.
  • Compare_Locations(): Compare time series of tidal component at two locations.
  • Interpolate(): Compute tidal gravity anomaly at times specified by a list of timestamps. Here, ETGTAB is used to compute the veritical tidal gravity on a grid with 300 s resolution. Then an interpolant is used to predict values between these grid points at times in the list.
  • Interpolate_Example(): Example implementation of ETG_Interpolate().