This package provides a Python interface to running the CALC delay modeling tool by providing parameters as astropy objects.
CALC has a long history, originally written in Fortran 77 with parts updated into Fortran 90 over time. CALC aims to compute VLBI baseline delays to picosecond precision by incorporating general relativistic deflection from the Sun, Earth, and other planets, and including baseline shifts due to solid Earth and ocean tide loading, and deflection due to atmospheric contributions [EUBANKS91].
This repository carries a modified version of the CALC source code. The modifications enable easier operation as a library, rather than as a standalone program, and support dynamic array allocation for some arrays that were previously fixed-size.
[EUBANKS91] Eubanks, Marshall, et al. Proceedings of the U.S. Naval Observatory Workshop on Relativistic Models for Use in Space Geodesy. 1991.
Install directly from the repository with pip:
pip install git+https://github.com/aelanman/pycalc11.git
The source code for CALC is in the repository and will be built and added as an extension to the pycalc11 module.
The interface to running CALC11 is provided by the Calc class. A Calc instance may be initialized
with lists of stations, sources, a start time, and a duration, with the station locations given as
astropy EarthLocation instances, source locations given as astropy SkyCoord, start time as an astropy Time
instance, and duration as a float representing the length of the scan in minutes.:
from pycalc11 import Calc
import numpy as np
from astropy import coordinates as ac
from astropy import units as un
from astropy.time import Time
# ------------
# First, create parameters as astropy objects.
# ------------
# Times
time = Time("2020-10-02T15:30:00.00", format="isot", scale='utc')
duration_min = 10
# Names of sites in astropy
anames = ['gbt', 'vla', 'ALMA', 'mwa', 'chime']
site_locs = [ac.EarthLocation.of_site(nm) for nm in anames]
# Names of sites in ocean loading data
site_names = ['GBT-VLBA', 'VLA_E9', 'ALMA', 'MWA', 'CHIME']
n_srcs = 500 # Arbitrarily many. Previously limited to 300.
source_coords = ac.SkyCoord(
ra=np.random.uniform(0, 360, n_srcs),
dec=np.random.uniform(-90,90, n_srcs),
unit='deg',
frame='icrs',
)
# ------------
# Initialize the Calc object.
# ------------
ci = Calc(
station_names=site_names,
station_coords=site_locs,
source_coords=source_coords,
time=time,
duration_min=duration_min,
)
# ------------
# Run the driver
# ------------
ci.run_driver()
To include ocean loading effects, the provided station_names must match entries in the ocean loading (OL) and ocean pole tide loading (OPTL) data sets. The OceanFiles class gives more information on these.
Alternatively, a .calc file may be given via the calc_file keyword. If both a calc file and keywords are set, the keywords will override settings from the file.
Once the Calc object is initialized, the method run_driver will run the main function of CALC11. The results of this (delays, delay rates, partial derivatives) are then set in the attributes Calc.delay, Calc.delay_rate, and Calc.partials, respectively. Those properties' docstrings define the array axes.
