ESBO-ETC/esbo_etc/classes/sensor/Heterodyne.py

380 lines
17 KiB
Python

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