tpl2go / nequickg

Python Implementation of European Space Agency's Galileo Ionospheric Model

Nequick-G

This is a python implementation of the Nequick-G ionospheric correction model described in European Space Agency's Galileo Ionospheric Model. Ionospheric disturbance flags are not implemented

Reference: Ionospheric correction Algorithm for galileo single frequency users (2016) https://www.gsc-europa.eu/system/files/galileo_documents/Galileo_Ionospheric_Model.pdf

Installation

This module depends on numpy for computation, and matplotlib and Basemap for plotting. In ubuntu they can be installed via:

sudp apt-get install python-numpy
sudo apt-get install python-matplotlib
sudo apt-get install python-mpltoolkits.basemap

This module doesn't require installation to your python environment's site-packages. Simply write scripts in the same directory as this project and import the necessary classes

Main classes

NequickG_global:

The global ionosphere's electron density, as described by the Nequick model, is fully defined by two types of inputs: time (month and universal time) and broadcast coefficients (a01, a02, a03). Once the NequickG_global object is instantiated, it can be used to calculate slant TECs and act as a factory for "local" NequickG objects

NequickG:

NequickG objects are models of the ionosphere localised to a particular longitude and latitude. It is generated by giving a position input to the Nequick_global's get_Nequick_local method. Internally, it contains the topside and bottomside models that constitutes the NequickG model. NequickG objects allows calculation of vertical electron density profiles and vertical TEC

Ray:

Ray objects specify a straight line propagation path. Used mainly with NequickG_global objects for slant TEC calculations. Relevant routines, such as determining the validity of the propagation path or the altitude along the path, are contained in this class.

NEQTime / Position / GalileoBroadcast:

These classes wrap and group the input parameters of the Nequick-G model into meaningful concepts. Also used to implement "approximate equality" just in case it is needed.

Example of approximate equality: [40.2N 0.3W] == [40N 0E]

Usage

Example usages of these classes are provided in the task folder.

If you need any more information, have any suggestions or noticed any bugs, do open a new Issue on this repository

Known issues

For low solar activities, like that listed in the validation table. F1 critical frequency can become negative. This is unphysical and likely to mean that there is a bug in the implementation.

nequickg's Issues

aux.py

Not a big issue but consider changing the aux.py file name. See: https://www.howtogeek.com/fyi/windows-10-still-wont-let-you-use-these-file-names-reserved-in-1974/

compling errors visual studio

I installed visual studio 2022 community with c/c++ core.
I open the solution file, debug it, get lots of errors , some of them are below, would anyone help me? thanks.

Severity Code Description Project File Line Suppression State
Severity Code Description Project File Line Suppression State
Error C2054 expected '(' to follow 'P' NeQuickJRC C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.34.31933\include\vadefs.h 61

Severity Code Description Project File Line Suppression State
Error C2054 expected '(' to follow 'P' NeQuickJRC C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.34.31933\include\vadefs.h 61

Severity Code Description Project File Line Suppression State
Error C2081 'uintptr_t': name in formal parameter list illegal NeQuickJRC C:\Program Files (x86)\Windows Kits\10\Include\10.0.22621.0\ucrt\corecrt.h 368

Severity Code Description Project File Line Suppression State
Error C2081 'va_list': name in formal parameter list illegal NeQuickJRC C:\Program Files (x86)\Windows Kits\10\Include\10.0.22621.0\ucrt\corecrt_wstdio.h 277

Issue with NequickG for altitudes under 100km

The NequickG python code closely follows the European GNSS (Galileo) Open Service Ionospheric Correction Algorithm for Galileo Single Frequency Users, specifically the equations for Electron Density Computations.

Line 864 of the NequickG code computes the exponential arguments for each layer, starting with the condition:
h[h < 100] = 100

This follows the documentation, however its implementation sets h values of 100 or greater for the rest of the code that follows. This means that h values less than 100 are ignored, and the electron density calculation calculates a constant density at these values. A proposed fix for this issue is to simply copy the contents of h into a different variable (i.e. m) for the exponential argument calculation. This ensures that h is unchanged in the rest of the code. Below is an example of this new logic starting at line 864:

Compute the exponential arguments for each layer

    m = h.copy()

    m[m<100] = 100



    # thickness parameter with fade out exponent for E and F1 layer

    thickF2 = self.B2bot

    thickF1 = BF1 / np.exp(10 / (1 + np.abs(m - self.hmF2)))

    thickE = BE / np.exp(10 / (1 + np.abs(m - self.hmF2)))

    

    # suppress small values in epstein layer

    diffF2 = (m - self.hmF2)

    diffF1 = (m - self.hmF1)

    diffE = (m - self.hmE)



    EpstF2 = epstein(self.AmpF2, self.hmF2, thickF2, h)

    EpstF1 = epstein(self.AmpF1, self.hmF1, thickF1, h)

    EpstE = epstein(self.AmpE, self.hmE, thickE, h)

   

    alphaF2 = diffF2 / thickF2

    alphaF1 = diffF1 / thickF1

    alphaE = diffE / thickE

This fix allows for values of h less than 100 to be calculated with the appropriate corrective terms.

Kyle Johnston & Sarah Thomas

Wrong solar declination

Computation of the quotient must be float devision, not int devision:
https://github.com/tpl2go/NequickG/blob/master/NequickG.py#L361

Also, the cosine function in
https://github.com/tpl2go/NequickG/blob/master/NequickG.py#L364

has to be replaced with a sine function (see https://en.wikipedia.org/wiki/Position_of_the_Sun)