GREOPy: A General Relativistic Emitter-Observer problem Python algorithm

[irideselby]

Submitting Author: Jan P. Hackstein (@irideselby)
All current maintainers: (@irideselby)
Package Name: GREOPy
One-Line Description of Package: Calculate relativistic light rays sent by an emitter to a receiver in the presence of a gravitational field.
Repository Link: https://codeberg.org/JPHackstein/GREOPy
Version submitted: v0.2.0
EiC: TBD
Editor: TBD
Reviewer 1: TBD
Reviewer 2: TBD
Archive: https://zenodo.org/records/14537866
JOSS DOI: TBD
Version accepted: TBD
Date accepted (month/day/year): TBD

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Description

GREOPy is a Python library for calculating relativistic light rays sent by an emitter to a receiver in the presence of a gravitational field. Finding a light ray connecting two events is sometimes called "Emitter-Observer" problem and is always present when it comes to communication between two observers, e.g. two satellites in orbit. GREOPy allows the emitter and receiver to move along arbitrary curves, making this an initial-value problem to solve from the emitter's perspective, and the gravitational field can be described by a rotating, non-accelerating central mass. Everything is being calculated in the general relativistic framework to include relativistic effects like light bending and the relativistic Doppler effect to be able to quantify their impact on error propagation. While only two spacetimes are implemented at the moment (even though further additions are planned), GREOPy is written in a way to allow the community to easily expand the number of spacetimes to suit their needs.

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Data processing/munging: GREOPy uses parametrised curves, e.g. orbit data, to simulate communication via relativistic light rays between them. This allows analysis of relativistic effects on light and by extension any corresponding observable in some chosen spacetime, giving insights into fundamental properties of the underlying spacetime.

• Who is the target audience and what are scientific applications of this package?

This package is mainly targeted for scientists working in geodesy; it can be used to simulate satellite-satellite or satellite-ground station communication and from this derive, e.g. how the Earth mass distribution changes over time due to for example climate change.

• Are there other Python packages that accomplish the same thing? If so, how does yours differ?

Not the same thing. There exist of course Python packages that implement General Relativity, e.g. to be able to calculate light rays (lightlike/nulllike geodesics) as one can do with EinsteinPy for example. However there appear to be no packages that implement specifically the Emitter-Observer problem (initial-value problem with a variable target boundary) in terms of General Relativity.

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