From 8845e6065419d1d1a68a306ba65fd60c7b533c48 Mon Sep 17 00:00:00 2001 From: LukasK13 Date: Fri, 15 May 2020 14:34:55 +0200 Subject: [PATCH] Calculate exposure time, update docstring, documentation added --- esbo_etc/classes/sensor/Imager.py | 147 ++++++++++++++++++++++-------- 1 file changed, 107 insertions(+), 40 deletions(-) diff --git a/esbo_etc/classes/sensor/Imager.py b/esbo_etc/classes/sensor/Imager.py index c4553b6..ac9b8cf 100644 --- a/esbo_etc/classes/sensor/Imager.py +++ b/esbo_etc/classes/sensor/Imager.py @@ -3,7 +3,7 @@ from .ASensor import ASensor from ..IRadiant import IRadiant from ..Entry import Entry import numpy as np -from typing import Union +from typing import Union, Tuple from ..psf.Airy import Airy from ..psf.Zemax import Zemax from ..SpectralQty import SpectralQty @@ -92,7 +92,7 @@ class Imager(ASensor): common_conf.psf.osf, pixel_size) @u.quantity_input(exp_time="time") - def getSNR(self, exp_time: u.Quantity): + def getSNR(self, exp_time: u.Quantity) -> u.Quantity: """ Calculate the signal to background ratio (SNR) for the given exposure time using the CCD-equation. @@ -103,91 +103,158 @@ class Imager(ASensor): Returns ------- - snr : float - The calculated SNR + snr : Quantity + The calculated SNR as dimensionless quantity """ + # Calculate the electron currents + signal_current, background_current, read_noise, dark_current = self.__exposePixels() + # Calculate the number of collected electrons + signal = signal_current * exp_time + background = background_current * exp_time + dark = dark_current * exp_time + return self.__calcSNR(signal, background, read_noise, dark) - snr = self.__calcSNR(*self.__exposePixels(), exp_time) - return snr.value - - def getExpTime(self, snr: float) -> u.Quantity: + def getExpTime(self, snr: u.Quantity) -> u.Quantity: """ Calculate the necessary exposure time in order to achieve the given SNR. Parameters ---------- - snr : float - The SNR for which the necessary exposure time shall be calculated. + 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 number of exposed pixels which will be used for calculating the noise - # n_pix_exposed = self.__calcExposedPixels() - # # Calculate the electron current from the target and the background - # signal_current, background_current = self.__calcElectronCurrent(n_pix_exposed) - # # Fix the physical units of the SNR - # snr = snr * u.electron**0.5 - # - # # Calculate the ratio of the background- and dark-current to the signal current as auxiliary variable - # current_ratio = (background_current + n_pix_exposed * self.__dark_current) / signal_current - # # Calculate the necessary exposure time as inverse of the CCD-equation - # exp_time = snr ** 2 * (1 + current_ratio + np.sqrt( - # (1 + current_ratio) ** 2 + 4 * (self.__read_noise * n_pix_exposed) ** 2 / snr ** 2)) /\ - # (2 * signal_current) - # return exp_time + # Calculate the electron currents + signal_current, background_current, read_noise, dark_current = self.__exposePixels() + # Calculate the electron currents for all pixels + signal_current_tot = signal_current.sum() + background_current_tot = background_current.sum() + read_noise_tot = read_noise.sum() + dark_current_tot = dark_current.sum() + # Fix the physical units of the SNR + snr = snr * u.electron**0.5 - @u.quantity_input(signal_current=u.electron / u.s, background_current=u.electron / u.s, - read_noise=u.electron ** 0.5, dark_current=u.electron / u.s, exp_time="time") - def __calcSNR(self, signal_current: u.Quantity, background_current: u.Quantity, read_noise: u.Quantity, - dark_current: u.Quantity, exp_time: u.Quantity) -> u.dimensionless_unscaled: - # Calculate the SNR using the CCD-equation - signal = signal_current * exp_time - background = background_current * exp_time - dark = dark_current * exp_time + # Calculate the ratio of the background- and dark-current to the signal current as auxiliary variable + current_ratio = (background_current_tot + dark_current_tot) / signal_current_tot + # Calculate the necessary exposure time as inverse of the CCD-equation + exp_time = snr ** 2 * (1 + current_ratio + np.sqrt( + (1 + current_ratio) ** 2 + 4 * read_noise_tot ** 2 / snr ** 2)) /\ + (2 * signal_current_tot) + # Calculate the SNR in order to check for overexposed pixels + self.__calcSNR(signal_current * exp_time, background_current * exp_time, read_noise, dark_current * exp_time) + return exp_time + + @u.quantity_input(signal=u.electron, background=u.electron, read_noise=u.electron ** 0.5, dark=u.electron) + def __calcSNR(self, signal: u.Quantity, background: u.Quantity, read_noise: u.Quantity, + dark: u.Quantity) -> u.dimensionless_unscaled: + """ + Calculate the signal to noise ratio (SNR) of the given electron counts. + + Parameters + ---------- + signal : Quantity + The collected electrons from the target in electrons. + background : Quantity + The collected electrons from the background in electrons. + read_noise : Quantity + The read noise in electrons. + dark : Quantity + The electrons from the dark current in electrons. + + Returns + ------- + snr : Quantity + The signal to noise ration as dimensionless quantity + """ + # Calculate the total collected electrons per pixel total = signal + background + dark + # Check for overexposed pixels overexposed = total > self.__well_capacity if np.any(overexposed): + # Show a warning for the overexposed pixels warning(str(np.count_nonzero(overexposed)) + " pixels are overexposed.") info("Collected electrons from target: %1.2e electrons" % signal.sum().value) info("Collected electrons from background: %1.2e electrons" % background.sum().value) info("Electrons from dark current: %1.2e electrons" % dark.sum().value) info("Read noise: %1.2e electrons" % (read_noise ** 2).sum().value) info("Total collected electrons: %1.2e electrons" % total.sum().value) + # Calculate the SNR using the CCD-equation snr = signal.sum() / np.sqrt(total.sum() + (read_noise ** 2).sum()) # Return the value of the SNR, ignoring the physical units (electrons^0.5) return snr.value * u.dimensionless_unscaled - def __exposePixels(self) -> (u.electron / u.s, u.electron / u.s, u.electron, u.electron / u.s): - signal_current, size, obstruction, background_current = self.__calcPixelElectronCurrent() + def __exposePixels(self) -> Tuple[u.Quantity, u.Quantity, u.Quantity, u.Quantity]: + """ + Expose the pixels and calculate the signal and noise electron currents per pixel. + + Returns + ------- + signal_current : Quantity + The electron current from the target as PixelMask in electrons / s + background_current : Quantity + The electron current from the background as PixelMask in electrons / s + read_noise : Quantity + The read noise per pixel in electrons + dark_current : Quantity + The electron current from the dark noise as PixelMask in electrons / s + """ + # Calculate the total incoming electron current + signal_current, size, obstruction, background_current = self.__calcIncomingElectronCurrent() + # Initialize a new PixelMask mask = PixelMask(self.__pixel_geometry, self.__pixel_size, self.__center_offset) if size.lower() == "extended": + # Target is extended, a diameter of 0 pixels results in a mask with one pixel marked d_photometric_ap = 0 * u.pix + # Mask the pixels to be exposed mask.createPhotometricAperture("circle", d_photometric_ap / 2, np.array([0, 0]) << u.pix) else: + # Target is a point source if self.__contained_pixels is not None: + # Calculate the diameter of the photometric aperture as square root of the contained pixels d_photometric_ap = np.sqrt(self.__contained_pixels.value) * u.pix + # Mask the pixels to be exposed mask.createPhotometricAperture("square", d_photometric_ap / 2, np.array([0, 0]) << u.pix) else: + # Calculate the diameter of the photometric aperture from the given contained energy d_photometric_ap = self.__calcPhotometricAperture(obstruction) + # Mask the pixels to be exposed mask.createPhotometricAperture(self.__shape, d_photometric_ap / 2) - background = mask * background_current * u.pix + # Calculate the background current PixelMask + background_current = mask * background_current * u.pix + # Calculate the read noise PixelMask read_noise = mask * self.__read_noise * u.pix + # Calculate the dark current PixelMask dark_current = mask * self.__dark_current * u.pix info("The radius of the photometric aperture is %.2f pixels." % (d_photometric_ap.value / 2)) info("The photometric aperture contains " + str(np.count_nonzero(mask)) + " pixels.") if size.lower() != "extended": + # Map the PSF onto the pixel mask in order to get the relative irradiance of each pixel mask = self.__psf.mapToPixelMask(mask, getattr(getattr(self.__common_conf, "jitter_sigma", None), "val", None), obstruction) - signal = mask * signal_current - return signal, background, read_noise, dark_current + # Calculate the signal current PixelMask + signal_current = mask * signal_current + return signal_current, background_current, read_noise, dark_current def __calcPhotometricAperture(self, obstruction: float) -> u.Quantity: + """ + Calculate the diameter of the photometric aperture + + Parameters + ---------- + obstruction : float + The obstruction factor as A_ob / A_ap. + + Returns + ------- + d_photometric_ap : Quantity + The diameter of the photometric aperture in pixels. + """ # Calculate the reduced observation angle - # jitter_sigma = self.__common_conf.jitter_sigma() if hasattr(self.__common_conf, "jitter_sigma") else None jitter_sigma = getattr(getattr(self.__common_conf, "jitter_sigma", None), "val", None) reduced_observation_angle = self.__psf.calcReducedObservationAngle(self.__contained_energy, jitter_sigma, obstruction) @@ -202,7 +269,7 @@ class Imager(ASensor): d_photometric_ap = observation_angle / pixel_fov return d_photometric_ap * u.pix - def __calcPixelElectronCurrent(self) -> (u.electron / u.s, str, float, u.electron / (u.pix * u.s)): + def __calcIncomingElectronCurrent(self) -> Tuple[u.Quantity, str, float, u.Quantity]: """ Calculate the detected electron current of the signal and the background. @@ -213,7 +280,7 @@ class Imager(ASensor): size : str The size of the target. obstruction : float - The obstruction factor. + The obstruction factor as A_ob / A_ap. background_current : Quantity The electron current on the detector caused by the background in electrons / (s * pix). """