lsst.afw g093c4c12c6+3f22ab7721
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Functions | Variables
lsst.afw.coord._refraction Namespace Reference

Functions

def refraction (wavelength, elevation, observatory, weather=None)
 
def differentialRefraction (wavelength, wavelengthRef, elevation, observatory, weather=None)
 
def deltaN (wavelength, weather)
 
def densityFactorDry (weather)
 
def densityFactorWater (weather)
 
def humidityToPressure (weather)
 
def extractTemperature (weather, useKelvin=False)
 
def defaultWeather (altitude)
 

Variables

float deltaRefractScale = 1.0E8
 

Function Documentation

◆ defaultWeather()

def lsst.afw.coord._refraction.defaultWeather (   altitude)
Set default local weather conditions if they are missing.

Parameters
----------
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation
altitude : `astropy.units.Quantity`
    The altitude of the observatory, in meters.

Returns
-------
default : `lsst.afw.coord.Weather`
    Updated Weather class with any `nan` values replaced by defaults.

Definition at line 293 of file _refraction.py.

◆ deltaN()

def lsst.afw.coord._refraction.deltaN (   wavelength,
  weather 
)
Calculate the differential refractive index of air.

Parameters
----------
wavelength : `float`
    wavelength is in nanometers
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation

Returns
-------
deltaN : `float`
    The difference of the refractive index of air from 1.,
    calculated as (n_air - 1)*10^8

Notes
-----
The differential refractive index is the difference of
the refractive index from 1., multiplied by 1E8 to simplify
the notation and equations. Calculated as (n_air - 1)*10^8

This replicates equation 14 of [1]_

References
----------
.. [1] R. C. Stone, "An Accurate Method for Computing Atmospheric
   Refraction," Publications of the Astronomical Society of the Pacific,
   vol. 108, p. 1051, 1996.

Definition at line 123 of file _refraction.py.

◆ densityFactorDry()

def lsst.afw.coord._refraction.densityFactorDry (   weather)
Calculate dry air pressure term to refractive index calculation.

Parameters
----------
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation

Returns
-------
densityFactor : `float`
    Returns the relative density of dry air
    at the given pressure and temperature.

Notes
-----
This replicates equation 15 of [1]_

References
----------
.. [1] R. C. Stone, "An Accurate Method for Computing Atmospheric
   Refraction," Publications of the Astronomical Society of the Pacific,
   vol. 108, p. 1051, 1996.

Definition at line 160 of file _refraction.py.

◆ densityFactorWater()

def lsst.afw.coord._refraction.densityFactorWater (   weather)
Calculate water vapor pressure term to refractive index calculation.

Parameters
----------
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation

Returns
-------
densityFactor : `float`
    Returns the relative density of water vapor
    at the given pressure and temperature.

Notes
-----
This replicates equation 16 of [1]_

References
----------
.. [1] R. C. Stone, "An Accurate Method for Computing Atmospheric
   Refraction," Publications of the Astronomical Society of the Pacific,
   vol. 108, p. 1051, 1996.

Definition at line 195 of file _refraction.py.

◆ differentialRefraction()

def lsst.afw.coord._refraction.differentialRefraction (   wavelength,
  wavelengthRef,
  elevation,
  observatory,
  weather = None 
)
Calculate the differential refraction between two wavelengths.

Parameters
----------
wavelength : `float`
    wavelength is in nm (valid for 230.2 < wavelength < 2058.6)
wavelengthRef : `float`
    Reference wavelength, typically the effective wavelength of a filter.
elevation : `lsst.geom.Angle`
    Elevation of the observation, as an Angle.
observatory : `lsst.afw.coord.Observatory`
    Class containing the longitude, latitude,
    and altitude of the observatory.
weather : `lsst.afw.coord.Weather`, optional
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation
    If omitted, typical conditions for the observatory's elevation will be calculated.

Returns
-------
differentialRefraction : `lsst.geom.Angle`
    The refraction at `wavelength` minus the refraction at `wavelengthRef`.

Definition at line 94 of file _refraction.py.

◆ extractTemperature()

def lsst.afw.coord._refraction.extractTemperature (   weather,
  useKelvin = False 
)
Thin wrapper to return the measured temperature from an observation.

Parameters
----------
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation
useKelvin : bool, optional
    Set to True to return the temperature in Kelvin instead of Celsius
    This is needed because Astropy can't easily convert
    between Kelvin and Celsius.

Returns
-------
temperature : `astropy.units.Quantity`
    The temperature in Celsius, unless `useKelvin` is set.

Definition at line 269 of file _refraction.py.

◆ humidityToPressure()

def lsst.afw.coord._refraction.humidityToPressure (   weather)
Convert humidity and temperature to water vapor pressure.

Parameters
----------
weather : `lsst.afw.coord.Weather`
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation

Returns
-------
pressure : `astropy.units.Quantity`
    The water vapor pressure in Pascals
    calculated from the given humidity and temperature.

Notes
-----
This replicates equations 18 & 20 of [1]_

References
----------
.. [1] R. C. Stone, "An Accurate Method for Computing Atmospheric
   Refraction," Publications of the Astronomical Society of the Pacific,
   vol. 108, p. 1051, 1996.

Definition at line 232 of file _refraction.py.

◆ refraction()

def lsst.afw.coord._refraction.refraction (   wavelength,
  elevation,
  observatory,
  weather = None 
)
Calculate overall refraction under atmospheric and observing conditions.

Parameters
----------
wavelength : `float`
    wavelength is in nm (valid for 230.2 < wavelength < 2058.6)
elevation : `lsst.geom.Angle`
    Elevation of the observation, as an Angle.
observatory : `lsst.afw.coord.Observatory`
    Class containing the longitude, latitude,
    and altitude of the observatory.
weather : `lsst.afw.coord.Weather`, optional
    Class containing the measured temperature, pressure, and humidity
    at the observatory during an observation
    If omitted, typical conditions for the observatory's elevation will be calculated.

Returns
-------
refraction : `lsst.geom.Angle`
    The angular refraction for light of the given wavelength,
    under the given observing conditions.

Notes
-----
The calculation is taken from [1]_.

References
----------
.. [1] R. C. Stone, "An Accurate Method for Computing Atmospheric
   Refraction," Publications of the Astronomical Society of the Pacific,
   vol. 108, p. 1051, 1996.

Definition at line 36 of file _refraction.py.

Variable Documentation

◆ deltaRefractScale

float lsst.afw.coord._refraction.deltaRefractScale = 1.0E8

Definition at line 33 of file _refraction.py.