ska_ost_senscalc.mid_utilities

Module holding functions useful to the MidCalculator

class ska_ost_senscalc.mid_utilities.Beam(*, frequency=None, zoom_frequencies=None, array_configuration, weighting, robustness=None, dec, taper=0.0, calculator_mode, telescope=Telescope.MID)

Beam class

Parameters:

• frequency (astropy.units.Quantity or number) – the observing frequency (Hz)

• zoom_frequencies (iterable astropy.units.Quantity or list) – the frequencies of the line zooms (Hz)

• array_configuration (ArrayConfiguration) – the subarray configuration

• weighting (Weighting) – the type of uv-weighting used (robust or uniform)

• robustness (float) – the Briggs robustness parameter

• dec (astropy.units.Quantity or number) – the target declination (deg)

• taper (astropy.units.Quantity or number) – the Gaussian taper to apply (arcsec)

• calculator_mode (CalculatorMode) – the calculator mode being used

Returns:

Beam object

Return type:

object

beam_size()

method to return list of beam sizes.

confusion_noise()

method to calculate the confusion noise of beam

surface_brightness_conversion_factor() → Quantity

method to calculate the factor the sensitivity returned by calculator must be multiplied by to obtain the surface brightness sensitivity in units of K/Jy.

weighting_factor()

method to calculate the beam weighting factor of the observation

class ska_ost_senscalc.mid_utilities.BeamSize(beam_maj, beam_min, beam_pa)

Class for returning a BeamSize object.

Parameters:

• beam_maj (astropy.units.Quantity or number) – the beam major axis in degrees

• beam_min (astropy.units.Quantity or number) – the beam minor axis in degrees

• beam_pa (astropy.units.Quantity or number) – the beam position angle in degrees

Returns:

BeamSize object

Return type:

object

class ska_ost_senscalc.mid_utilities.CalculatorMode(value)

Enumeration for calculator modes

class ska_ost_senscalc.mid_utilities.Limit(value)

Enumeration for different types of limit

ska_ost_senscalc.mid_utilities.Tgal(target, obs_freq, dish_type, alpha)

Brightness temperature of Galactic background in target direction at observing frequency.

Parameters:

• target (astropy.SkyCoord) – target direction

• obs_freq (astropy.units.Quantity) – the observing frequency

• dish_type (DishType) – the type of dish

• alpha (float) – spectral index of emission

Returns:

the brightness temperature of the Galactic background

Return type:

astropy.units.Quantity

ska_ost_senscalc.mid_utilities.Trcv(obs_freq, obs_band, dish_type)

Receiver temperature for specified freq, band and dish.

Parameters:

• obs_freq (astropy.units.Quantity) – the observing frequency

• obs_band (str) – the observing band

• dish_type (DishType) – the type of dish

Returns:

the receiver temperature

Return type:

astropy.units.Quantity

ska_ost_senscalc.mid_utilities.Tsky(Tgal, obs_freq, elevation, weather)

Brightness temperature of sky in target direction.

Parameters:

• Tgal (astropy.units.Quantity) – brightness temperature of Galactic background

• obs_freq (astropy.units.Quantity) – the observing frequency

• elevation (astropy.units.Quantity) – the observing elevation

• weather (float) – the atmosphere PWV

Returns:

the brightness temperature of the sky

Return type:

astropy.units.Quantity

ska_ost_senscalc.mid_utilities.Tspl(dish_type)

Spillover temperature for specified dish type.

Parameters:

dish_type (DishType) – the type of dish

Returns:

the spillover temperature

Return type:

astropy.units.Quantity

ska_ost_senscalc.mid_utilities.Tsys_dish(Trcv, Tspl, Tsky, obs_freq)

System temperature.

Parameters:

• Trcv (astropy.units.Quantity) – the receiver temperature

• Tspl (astropy.units.Quantity) – the spillover temperature

• Tsky (astropy.units.Quantity) – the sky temperature

• obs_freq (astropy.units.Quantity) – the observing frequency

Returns:

the dish system temperature

Return type:

astropy.units.Quantity

class ska_ost_senscalc.mid_utilities.Weighting(value)

Enumeration for different weighting

ska_ost_senscalc.mid_utilities.eta_bandpass()

Efficiency factor for due to the departure of the bandpass from an ideal, rectangular shape. For now this is a placeholder.

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_coherence(obs_freq)

Efficiency factor for the sensitivity degradation due to the incoherence on a baseline.

Parameters:

obs_freq (astropy.units.Quantity) – the observing frequency

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_correlation()

Efficiency factor due to imperfection in the correlation algorithm, e.g. truncation error.

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_digitisation(obs_band)

Efficiency factor due to losses from quantisation during signal digitisation. This process is independent of the telescope and environment, but only depends on the ‘effective number of bits’ (ENOB) of the system, which depends in turn on digitiser quality and clock jitter, and on band flatness.

Parameters:

obs_band (str) – the observing band

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_dish(obs_freq, dish_type)

Efficiency factor due to losses for specified dish type.

Parameters:

• obs_freq (astropy.units.Quantity) – the observing frequency

• dish_type (DishType) – the type of dish

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_point(obs_freq, dish_type)

Efficiency factor at the observing frequency due to the dish pointing error.

Parameters:

• obs_freq (astropy.units.Quantity) – the observing frequency

• dish_type (DishType) – the type of dish

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_rfi()

Efficiency factor due to Radio Frequency Interference (RFI)

Returns:

the efficiency, eta

Return type:

float

ska_ost_senscalc.mid_utilities.eta_system(eta_point, eta_coherence, eta_digitisation, eta_correlation, eta_bandpass)

System efficiency for SKA interferometer

Parameters:

• eta_point (float) – efficiency loss due to pointing errors

• eta_coherence (float) – efficiency due to loss of coherence

• eta_digitisation (float) – efficiency loss due to errors in the digitisation process

• eta_correlation (float) – efficiency loss due to errors in the correlation process

• eta_bandpass (float) – efficiency loss due to the bandpass not being rectangular

Returns:

the system efficiency

Return type:

float

ska_ost_senscalc.mid_utilities.read_table(file_name, columns=None)

function to read in the lookup tables