Atmosphere

The Soapy module used to simulate the atmosphere.

This module contains an atmos object, which can be used to create or load a specified number of phase screens corresponding to atmospheric turbulence layers. The layers can then be moved with the moveScrns method, at a specified wind velocity and direction, where the screen is interpolated if it does not fall on an integer number of pixels. Alternatively, random screens with the same statistics as the global phase screens can be generated using the randomScrns method.

The module also contains a number of functions used to create the phase screens, many of these are ported from the book Numerical Simulation of Optical Propagation, Schmidt, 2010. It is possible to create a number of phase screens using the makePhaseScreens() function which are saved to file in a format which can be read by the simulation.

Examples

To get the configuration objects:

from soapy import confParse, atmosphere

config = confParse.loadSoapyConfig("configfile.yaml")

Initialise the amosphere (creating or loading phase screens):

atmosphere = atmosphere.atmos(config)

Run the atmosphere for 10 time steps:

for i in range(10):
    phaseScrns = atmosphere.moveScrns()

or create 10 sets of random screens:

for i in range(10):
    randomPhaseScrns = atmosphere.randomScrns()

Atmosphere Class

class soapy.atmosphere.atmos(soapyConfig)[source]

Class to simulate atmosphere above an AO system.

On initialisation of the object, new phase screens can be created, or others loaded from .fits file. The atmosphere is created with parameters given in ConfigObj.sim and ConfigObj.atmos. These are soapy configuration objects, which can be created by the :ref:confParse module, or could be created manually. If created manually, check the :ref: confParse section to see which attributes the configuration objects must contain.

If loaded from file, the screens should have a header with the parameter R0 specifying the r0 fried parameter of the screen in pixels.

The method moveScrns can be called on each iteration of the AO system to move the scrns forward by one time step. The size of this is defined by parameters given in

The method randomScrns returns a set of random phase screens with the smame statistics as the atmos object.

Parameters:soapyConfig (ConfigObj) – The Soapy config object
moveScrns()[source]

Moves the phase screens one time-step, defined by the atmosphere object parameters.

Returned phase is in units of nana-meters

Returns:a dictionary containing the new set of phase screens
Return type:dict
randomScrns(subHarmonics=True, l0=0.01)[source]

Generated random phase screens defined by the atmosphere object parameters.

Returned phase is in units of nana-meters

Returns:a dictionary containing the new set of phase screens
Return type:dict
saveScrns(DIR)[source]

Saves the currently loaded phase screens to file, saving the r0 value in the fits header (in units of pixels). Saved phase data is in radians @500nm

Parameters:DIR (string) – The directory to save the screens

Phase Screen Creation and Saving

soapy.atmosphere.makePhaseScreens(nScrns, r0, N, pxlScale, L0, l0, returnScrns=True, DIR=None, SH=False)[source]

Creates and saves a set of phase screens to be used by the simulation.

Creates nScrns phase screens, with the required parameters, then saves them to the directory specified by DIR. Each screen is given a FITS header with its value of r0, which will be scaled by on simulation when its loaded.

Parameters:
  • nScrns (int) – The number of screens to make.
  • r0 (float) – r0 value of the phase screens in metres.
  • N (int) – Number of elements across each screen.
  • pxlScale (float) – Size of each element in metres.
  • L0 (float) – Outer scale of each screen.
  • l0 (float) – Inner scale of each screen.
  • returnScrns (bool, optional) – Whether to return a list of screens. True by default, but if screens are very large, False might be preferred so they aren’t kept in memory if saving to disk.
  • DIR (str, optional) – The directory to save the screens.
  • SH (bool, optional) – If True, add sub-harmonics to screens for more accurate power spectra, though screens no-longer periodic.
Returns:

A list containing all the screens.
Return type:

list