395 lines
18 KiB
Python
395 lines
18 KiB
Python
from .ASensor import ASensor
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from ..IRadiant import IRadiant
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from ..Entry import Entry
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from ...lib.logger import logger
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from ..SpectralQty import SpectralQty
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import numpy as np
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from astropy import units as u
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from astropy.constants import k_B
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from astropy.table import QTable
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from typing import Union
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import os
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class Heterodyne(ASensor):
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"""
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A class for modelling the behaviour of a superheterodyne spectrometer.
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"""
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def __init__(self, parent: IRadiant, aperture_efficiency: float, main_beam_efficiency: float,
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receiver_temp: u.Quantity, eta_fss: float, lambda_line: u.Quantity, kappa: float, common_conf: Entry,
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n_on: float = None, lambda_local_oscillator: u.Quantity = None):
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"""
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Initialize a new heterodyne detector
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Parameters
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----------
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parent : IRadiant
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The parent element of the optical component from which the electromagnetic radiation is received.
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aperture_efficiency : float
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The aperture efficiency of the antenna.
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main_beam_efficiency : float
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The main beam efficiency of the telescope.
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receiver_temp : u.Quantity in Kelvins
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The intrinsic noise temperature of all receiver components.
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eta_fss : float
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The forward scattering efficiency of the antenna.
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lambda_line : u.Quantity
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The wavelength to be used for calculating the SNR.
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kappa : float
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The backend degradation factor.
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common_conf : Entry
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The common-Entry of the configuration.
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n_on : float
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The number of on source observations.
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"""
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self.__aperture_efficiency = aperture_efficiency
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self.__main_beam_efficiency = main_beam_efficiency
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self.__receiver_temp = receiver_temp
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self.__eta_fss = eta_fss
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self.__lambda_line = lambda_line
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self.__lambda_local_oscillator = lambda_local_oscillator
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self.__kappa = kappa
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self.__common_conf = common_conf
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self.__n_on = n_on
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super().__init__(parent)
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@u.quantity_input(exp_time="time")
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def calcSNR(self, background: SpectralQty, signal: SpectralQty, obstruction: float,
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exp_time: u.Quantity) -> u.dimensionless_unscaled:
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"""
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Calculate the signal to background ratio (SNR) for the given exposure time using the CCD-equation.
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Parameters
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----------
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background : SpectralQty
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The received background radiation
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signal : SpectralQty
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The received signal radiation
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obstruction : float
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The obstruction factor of the aperture as ratio A_ob / A_ap
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exp_time : time-Quantity
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The exposure time to calculate the SNR for.
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Returns
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-------
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snr : Quantity
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The calculated SNR as dimensionless quantity
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"""
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# Calculate the signal and background temperatures
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t_signal, t_background = self.calcTemperatures(background, signal, obstruction)
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line_ind = np.where(t_signal.wl == self.__lambda_line)[0][0]
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t_sys = t_background + 2 * self.__receiver_temp + t_signal
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# Calculate the noise bandwidth
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delta_nu = t_signal.wl.to(u.Hz, equivalencies=u.spectral()) / (t_signal.wl / self.__common_conf.wl_delta() + 1)
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snr = []
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for exp_time_ in exp_time if exp_time.size > 1 else [exp_time]:
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# Calculate the RMS background temperature
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if self.__n_on is None:
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t_rms = 2 * t_sys * self.__kappa / np.sqrt(exp_time_ * delta_nu)
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else:
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t_rms = t_sys * self.__kappa * np.sqrt(1 + 1 / np.sqrt(self.__n_on)) / np.sqrt(exp_time_ * delta_nu)
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# Calculate the SNR
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snr_ = t_signal / t_rms
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snr.append(snr_.qty[line_ind])
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# Print details
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self.__printDetails(t_sys.qty[line_ind], delta_nu[line_ind], t_rms.qty[line_ind], t_signal.qty[line_ind],
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"t_exp=%.2f s: " % exp_time_.value)
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self.__output(t_signal, t_background, t_rms, "texp_%.2f" % exp_time_.value, snr=snr_)
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return u.Quantity(snr) if len(snr) > 1 else u.Quantity(snr[0])
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@u.quantity_input(snr=u.dimensionless_unscaled)
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def calcExpTime(self, background: SpectralQty, signal: SpectralQty, obstruction: float, snr: u.Quantity) -> u.s:
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"""
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Calculate the necessary exposure time in order to achieve the given SNR.
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Parameters
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----------
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background : SpectralQty
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The received background radiation
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signal : SpectralQty
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The received signal radiation
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obstruction : float
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The obstruction factor of the aperture as ratio A_ob / A_ap
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snr : Quantity
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The SNR for which the necessary exposure time shall be calculated as dimensionless quantity.
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Returns
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-------
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exp_time : Quantity
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The necessary exposure time in seconds.
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"""
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# Calculate the signal and background temperatures
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t_signal, t_background = self.calcTemperatures(background, signal, obstruction)
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line_ind = np.where(t_signal.wl == self.__lambda_line)[0][0]
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t_sys = t_background + 2 * self.__receiver_temp + t_signal
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# Calculate the noise bandwidth
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delta_nu = t_signal.wl.to(u.Hz, equivalencies=u.spectral()) / (t_signal.wl / self.__common_conf.wl_delta() + 1)
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exp_time = []
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for snr_ in snr if snr.size > 1 else [snr]:
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# Calculate the RMS background temperature
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t_rms = t_signal / snr_
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# Calculate the exposure time
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if self.__n_on is None:
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exp_time_ = ((2 * t_sys * self.__kappa / t_rms) ** 2 / delta_nu)
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else:
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exp_time_ = ((t_sys * self.__kappa / t_rms) ** 2 *
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(1 + 1 / np.sqrt(self.__n_on)) / delta_nu)
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exp_time_ = SpectralQty(exp_time_.wl, exp_time_.qty.decompose())
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exp_time.append(exp_time_.qty[line_ind])
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# Print details
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self.__printDetails(t_sys.qty[line_ind], delta_nu[line_ind], t_rms.qty[line_ind], t_signal.qty[line_ind],
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"SNR=%.2f: " % snr_.value)
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self.__output(t_signal, t_background, t_rms, "snr_%.2f" % snr_.value, exp_time=exp_time_)
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return u.Quantity(exp_time) if len(exp_time) > 1 else u.Quantity(exp_time[0])
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# @u.quantity_input(exp_time="time", snr=u.dimensionless_unscaled,
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# target_brightness=[u.mag, u.mag / u.sr])
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def calcSensitivity(self, background: SpectralQty, signal: SpectralQty, obstruction: float, exp_time: u.Quantity,
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snr: u.Quantity, target_brightness: u.Quantity) -> [u.mag, u.mag / u.sr]:
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"""
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Calculate the sensitivity of the telescope detector combination.
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Parameters
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----------
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background : SpectralQty
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The received background radiation
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signal : SpectralQty
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The received signal radiation
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obstruction : float
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The obstruction factor of the aperture as ratio A_ob / A_ap
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exp_time : Quantity
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The exposure time in seconds.
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snr : Quantity
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The SNR for which the sensitivity time shall be calculated.
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target_brightness : Quantity
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The target brightness in mag or mag / sr.
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Returns
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-------
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sensitivity: Quantity
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The sensitivity as limiting apparent star magnitude in mag.
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"""
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# Calculate the signal and background temperatures
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t_signal, t_background = self.calcTemperatures(background, signal, obstruction)
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line_ind = np.where(t_signal.wl == self.__lambda_line)[0][0]
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t_sys = t_background + 2 * self.__receiver_temp + t_signal
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# Calculate the noise bandwidth
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delta_nu = t_signal.wl.to(u.Hz, equivalencies=u.spectral()) / (t_signal.wl / self.__common_conf.wl_delta() + 1)
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sensitivity = []
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for snr_, exp_time_ in zip(snr, exp_time) if snr.size > 1 else zip([snr], [exp_time]):
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# Calculate the RMS background temperature
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if self.__n_on is None:
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t_rms = 2 * t_sys * self.__kappa / np.sqrt(exp_time_ * delta_nu)
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else:
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t_rms = t_sys * self.__kappa * np.sqrt(1 + 1 / np.sqrt(self.__n_on)) / np.sqrt(exp_time_ * delta_nu)
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# Calculate the limiting signal temperature
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t_signal_lim = t_rms * snr_
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# Calculate the sensitivity
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signal_ratio = t_signal_lim / t_signal
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sensitivity_ = SpectralQty(signal_ratio.wl,
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target_brightness - 2.5 * np.log10(signal_ratio.qty) * target_brightness.unit)
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sensitivity.append(sensitivity_.qty[line_ind])
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# Print details
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self.__printDetails(t_sys.qty[line_ind], delta_nu[line_ind], t_rms.qty[line_ind],
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t_signal_lim.qty[line_ind], "SNR=%.2f t_exp=%.2f s: " % (snr_.value, exp_time_.value))
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self.__output(t_signal, t_background, t_rms, "snr_%.2f_texp_%.2f" % (snr_.value, exp_time_.value),
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sensitivity=sensitivity_)
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return u.Quantity(sensitivity) if len(sensitivity) > 1 else u.Quantity(sensitivity[0])
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@u.quantity_input(t_sys=u.K, delta_nu=u.Hz, t_rms=u.K, t_signal=u.K)
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def __printDetails(self, t_sys: u.Quantity, delta_nu: u.Quantity, t_rms: u.Quantity,
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t_signal: u.Quantity, prefix: str = ""):
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"""
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Print details on the signal and noise composition.
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Parameters
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----------
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t_sys : Quantity
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The system temperature.
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delta_nu : Quantity
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The noise bandwidth.
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t_rms : Quantity
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The RMS antenna temperature.
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t_signal : Quantity
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The antenna temperature.
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prefix : str
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The prefix to be used for printing.
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Returns
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-------
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"""
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logger.info("--------------------------------------------------------------------------")
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logger.info(prefix + "System temperature: %1.2e K" % t_sys.value)
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logger.info(prefix + "Noise bandwidth: %1.2e Hz" % delta_nu.value)
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logger.info(prefix + "RMS antenna temperature: %1.2e K" % t_rms.value)
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logger.info(prefix + "Antenna temperature: %1.2e K" % t_signal.value)
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logger.info("--------------------------------------------------------------------------")
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@u.quantity_input(signal=u.electron, background=u.electron, read_noise=u.electron ** 0.5, dark=u.electron)
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def __output(self, t_signal: SpectralQty, t_background: SpectralQty, t_rms: SpectralQty,
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name: str, snr: SpectralQty = None, exp_time: SpectralQty = None, sensitivity: SpectralQty = None):
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"""
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Write the signal and the noise in electrons to files.
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Parameters
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----------
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t_signal : SpectralQty
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The signal temperature in Kelvins.
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t_background : SpectralQty
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The background temperature in Kelvins.
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t_rms : SpectralQty
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The RMS noise temperature in Kelvins.
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name : str
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The name of the configuration.
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snr : SpectralQty
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The calculated signal-to-noise ratio per wavelength.
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exp_time : SpectralQty
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The calculated exposure time per wavelength.
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sensitivity : SpectralQty
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The calculated sensitivity per wavelength.
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Returns
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-------
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"""
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# Concatenate the paths
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path = os.path.join(self.__common_conf.output.path, name)
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try:
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os.makedirs(path, exist_ok=True)
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except FileExistsError:
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logger.warning("Output directory '" + path + "' already exists.")
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res = QTable([t_signal.wl, t_signal.qty, t_background.qty, t_rms.qty],
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names=('Wavelength [' + t_signal.wl.unit.to_string() + ']',
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'Signal Temperature [' + t_signal.qty.unit.to_string() + ']',
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'Background Temperature [' + t_background.qty.unit.to_string() + ']',
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'RMS Noise Temperature [' + t_rms.qty.unit.to_string() + ']'),
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meta={'name': 'first table'})
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if snr is not None:
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res['SNR [-]'] = snr.qty
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if exp_time is not None:
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res['Exposure Time [' + exp_time.qty.unit.to_string() + ']'] = exp_time.qty
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if sensitivity is not None:
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res['Sensitivity [' + sensitivity.qty.unit.to_string() + ']'] = sensitivity.qty
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res.write(os.path.join(path, "result.csv"), format='ascii.csv', overwrite=True)
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def calcTemperatures(self, background: SpectralQty, signal: SpectralQty, obstruction: float):
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"""
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Calculate the noise temperatures of the signal and the background radiation.
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Parameters
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----------
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background : SpectralQty
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The received background radiation
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signal : SpectralQty
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The received signal radiation
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obstruction : float
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The obstruction factor of the aperture as ratio A_ob / A_ap
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Returns
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-------
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t_signal : SpectralQty
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The spectral signal temperature in Kelvins.
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t_background : SpectralQty
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The spectral signal temperature in Kelvins.
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"""
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logger.info("Calculating the system temperature.")
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# Add desired wavelength to wavelength bins
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wl_bins = np.sort(np.append(self.__common_conf.wl_bins(), self.__lambda_line)).view(u.Quantity)
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signal = signal.rebin(wl_bins)
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background = background.rebin(wl_bins)
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background = SpectralQty(background.wl, background.qty.to(u.W / (u.m ** 2 * u.Hz * u.sr),
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equivalencies=u.spectral_density(
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background.wl)))
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t_background = background * (
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self.__main_beam_efficiency * background.wl ** 2 / (2 * k_B) / self.__eta_fss * u.sr)
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t_background = SpectralQty(t_background.wl, t_background.qty.decompose())
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# Calculate the incoming photon current of the target
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logger.info("Calculating the signal temperature.")
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size = "extended" if signal.qty.unit.is_equivalent(u.W / (u.m ** 2 * u.nm * u.sr)) else "point"
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if size == "point":
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signal = SpectralQty(signal.wl, signal.qty.to(u.W / (u.m ** 2 * u.Hz),
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equivalencies=u.spectral_density(signal.wl)))
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t_signal = signal * (self.__aperture_efficiency * self.__common_conf.d_aperture() ** 2 *
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np.pi / 4 / (2 * k_B) / self.__eta_fss)
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t_signal = SpectralQty(t_signal.wl, t_signal.qty.decompose())
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else:
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signal = SpectralQty(signal.wl, signal.qty.to(u.W / (u.m ** 2 * u.Hz * u.sr),
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equivalencies=u.spectral_density(signal.wl)))
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t_signal = signal * (
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self.__main_beam_efficiency * signal.wl ** 2 / (2 * k_B) / self.__eta_fss * u.sr)
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t_signal = SpectralQty(t_signal.wl, t_signal.qty.decompose())
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if self.__lambda_local_oscillator is None:
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t_signal = t_signal * 2
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t_background = t_background * 2
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else:
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t_signal = SpectralQty(t_signal.wl, t_signal.qty + t_signal.rebin(
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2 * self.__lambda_local_oscillator - t_signal.wl).qty)
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t_background = SpectralQty(t_background.wl, t_background.qty + t_background.rebin(
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2 * self.__lambda_local_oscillator - t_background.wl).qty)
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logger.debug("Spectral signal temperature")
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logger.debug(t_signal)
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logger.debug("Target size: " + size)
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logger.debug("Obstruction: %.2f" % obstruction)
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logger.debug("Spectral background temperature")
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logger.debug(t_background)
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return t_signal, t_background
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@staticmethod
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def check_config(sensor: Entry, conf: Entry) -> Union[None, str]:
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"""
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Check the configuration for this class
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Parameters
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----------
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sensor : Entry
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The configuration entry to be checked.
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conf: Entry
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The complete configuration.
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Returns
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-------
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mes : Union[None, str]
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The error message of the check. This will be None if the check was successful.
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"""
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if not hasattr(sensor, "aperture_efficiency"):
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return "Missing container 'aperture_efficiency'."
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mes = sensor.aperture_efficiency.check_float("val")
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if mes is not None:
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return "aperture_efficiency: " + mes
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if not hasattr(sensor, "main_beam_efficiency"):
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return "Missing container 'main_beam_efficiency'."
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mes = sensor.main_beam_efficiency.check_float("val")
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if mes is not None:
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return "main_beam_efficiency: " + mes
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if not hasattr(sensor, "receiver_temp"):
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return "Missing container 'receiver_temp'."
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mes = sensor.receiver_temp.check_quantity("val", u.K)
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if mes is not None:
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return "receiver_temp: " + mes
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if not hasattr(sensor, "eta_fss"):
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return "Missing container 'eta_fss'."
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mes = sensor.eta_fss.check_float("val")
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if mes is not None:
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return "eta_fss: " + mes
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if not hasattr(sensor, "lambda_line"):
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return "Missing container 'lambda_line'."
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mes = sensor.lambda_line.check_quantity("val", u.nm)
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if mes is not None:
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return "lambda_line: " + mes
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if hasattr(sensor, "lambda_local_oscillator"):
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mes = sensor.lambda_local_oscillator.check_quantity("val", u.nm)
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if mes is not None:
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return "lambda_local_oscillator: " + mes
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if not hasattr(sensor, "kappa"):
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return "Missing container 'kappa'."
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mes = sensor.kappa.check_float("val")
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if mes is not None:
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return "kappa: " + mes
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if hasattr(sensor, "n_on") and isinstance(sensor.n_on, Entry):
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mes = sensor.n_on.check_float("val")
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if mes is not None:
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return "n_on: " + mes
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