Functions vectorized
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@ -108,11 +108,15 @@ class Imager(ASensor):
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"""
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# Calculate the electron currents
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signal_current, background_current, read_noise, dark_current = self.__exposePixels()
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# Calculate the number of collected electrons
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signal = signal_current * exp_time
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background = background_current * exp_time
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dark = dark_current * exp_time
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return self.__calcSNR(signal, background, read_noise, dark)
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# Calculate the SNR using the CCD-equation
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snr = signal_current.sum() * exp_time / np.sqrt(
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(signal_current + background_current + dark_current).sum() * exp_time + (read_noise ** 2).sum())
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for exp_time_ in exp_time:
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# Print information
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self.__printDetails(signal_current * exp_time_, background_current * exp_time_, read_noise,
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dark_current * exp_time_, "t_exp=%.2f s: " % exp_time_.value)
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# Return the value of the SNR, ignoring the physical units (electrons^0.5)
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return snr.value * u.dimensionless_unscaled
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@u.quantity_input(snr=u.dimensionless_unscaled)
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def getExpTime(self, snr: u.Quantity) -> u.s:
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@ -137,16 +141,18 @@ class Imager(ASensor):
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read_noise_tot = read_noise.sum()
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dark_current_tot = dark_current.sum()
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# Fix the physical units of the SNR
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snr = snr * u.electron**0.5
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snr = snr * u.electron ** 0.5
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# Calculate the ratio of the background- and dark-current to the signal current as auxiliary variable
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current_ratio = (background_current_tot + dark_current_tot) / signal_current_tot
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# Calculate the necessary exposure time as inverse of the CCD-equation
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exp_time = snr ** 2 * (
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1 + current_ratio + np.sqrt((1 + current_ratio) ** 2 + 4 * read_noise_tot ** 2 / snr ** 2)) / (
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2 * signal_current_tot)
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# Calculate the SNR in order to check for overexposed pixels
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self.__calcSNR(signal_current * exp_time, background_current * exp_time, read_noise, dark_current * exp_time)
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1 + current_ratio + np.sqrt((1 + current_ratio) ** 2 + 4 * read_noise_tot ** 2 / snr ** 2)) / (
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2 * signal_current_tot)
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for snr_, exp_time_ in zip(snr, exp_time):
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# Print information
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self.__printDetails(signal_current * exp_time_, background_current * exp_time_, read_noise,
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dark_current * exp_time_, "SNR=%.2f: " % snr_.value)
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return exp_time
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@u.quantity_input(exp_time="time", snr=u.dimensionless_unscaled, target_brightness=u.mag)
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@ -173,15 +179,18 @@ class Imager(ASensor):
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# Fix the physical units of the SNR
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snr = snr * u.electron ** 0.5
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signal_current_lim = snr * (snr + np.sqrt(
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snr ** 2 + 4 * (exp_time * (background_current.sum() + dark_current.sum()) + (read_noise ** 2).sum()))) / (
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2 * exp_time)
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self.__calcSNR(signal_current_lim * exp_time, background_current * exp_time, read_noise,
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dark_current * exp_time)
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snr ** 2 + 4 * (exp_time * (background_current.sum() + dark_current.sum()) +
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(read_noise ** 2).sum()))) / (2 * exp_time)
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for snr_, exp_time_, signal_current_lim_ in zip(snr, exp_time, signal_current_lim):
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# Print information
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self.__printDetails(signal_current_lim_ * exp_time_, background_current * exp_time_, read_noise,
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dark_current * exp_time_,
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"SNR=%.2f t_exp=%.2f s: " % (snr_.value, exp_time_.value))
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return target_brightness - 2.5 * np.log10(signal_current_lim / signal_current.sum()) * u.mag
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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 __calcSNR(self, signal: u.Quantity, background: u.Quantity, read_noise: u.Quantity,
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dark: u.Quantity) -> u.dimensionless_unscaled:
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def __printDetails(self, signal: u.Quantity, background: u.Quantity, read_noise: u.Quantity,
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dark: u.Quantity, prefix: str = ""):
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"""
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Calculate the signal to noise ratio (SNR) of the given electron counts.
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@ -198,8 +207,6 @@ class Imager(ASensor):
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Returns
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-------
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snr : Quantity
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The signal to noise ration as dimensionless quantity
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"""
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# Calculate the total collected electrons per pixel
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total = signal + background + dark
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@ -207,16 +214,12 @@ class Imager(ASensor):
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overexposed = total > self.__well_capacity
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if np.any(overexposed):
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# Show a warning for the overexposed pixels
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warning(str(np.count_nonzero(overexposed)) + " pixels are overexposed.")
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info("Collected electrons from target: %1.2e electrons" % signal.sum().value)
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info("Collected electrons from background: %1.2e electrons" % background.sum().value)
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info("Electrons from dark current: %1.2e electrons" % dark.sum().value)
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info("Read noise: %1.2e electrons" % (read_noise ** 2).sum().value)
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info("Total collected electrons: %1.2e electrons" % total.sum().value)
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# Calculate the SNR using the CCD-equation
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snr = signal.sum() / np.sqrt(total.sum() + (read_noise ** 2).sum())
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# Return the value of the SNR, ignoring the physical units (electrons^0.5)
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return snr.value * u.dimensionless_unscaled
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warning(prefix + str(np.count_nonzero(overexposed)) + " pixels are overexposed.")
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info(prefix + "Collected electrons from target: %1.2e electrons" % signal.sum().value)
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info(prefix + "Collected electrons from background: %1.2e electrons" % background.sum().value)
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info(prefix + "Electrons from dark current: %1.2e electrons" % dark.sum().value)
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info(prefix + "Read noise: %1.2e electrons" % (read_noise ** 2).sum().value)
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info(prefix + "Total collected electrons: %1.2e electrons" % total.sum().value)
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def __exposePixels(self) -> Tuple[u.Quantity, u.Quantity, u.Quantity, u.Quantity]:
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"""
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@ -2,6 +2,7 @@ import esbo_etc as eetc
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import argparse
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import logging
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import sys
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import numpy as np
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if __name__ == "__main__":
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parser = argparse.ArgumentParser(prog="esbo_etc/esbo-etc.py", description='Exposure time calculator for ESBO-DS')
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@ -26,10 +27,10 @@ if __name__ == "__main__":
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if hasattr(conf.common, "exposure_time") and hasattr(conf.common, "snr"):
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sensitivity = imager.getSensitivity(conf.common.exposure_time(), conf.common.snr(), conf.astroscene.target.mag)
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print("The limiting apparent magnitude is: %.2f mag." % sensitivity.value)
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print("The limiting apparent magnitude is: " + str(np.array2string(sensitivity.value, precision=2)) + " mag.")
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elif hasattr(conf.common, "exposure_time"):
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snr = imager.getSNR(conf.common.exposure_time())
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print("The SNR is: %.2f." % snr.value)
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print("The SNR is: " + str(np.array2string(snr.value, precision=2)) + ".")
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elif hasattr(conf.common, "snr"):
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exp_time = imager.getExpTime(conf.common.snr())
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print("The necessary exposure time is: %.2f s." % exp_time.value)
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print("The necessary exposure time is: " + str(np.array2string(exp_time.value, precision=2)) + " s.")
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