Coronagraph Noise Modeling¶

The crux of coronagraph noise modeling is to determine the photon count rate incident upon the detector due to both the target planet and an assortment of different telescope, instrumental, and astrophysical noise sources. The following classes and functions serve as your interface to the photon count rate calculations. The core function for these calculations is count_rates(), but it may be accessed using the CoronagraphNoise object.

class coronagraph.count_rates.CoronagraphNoise(telescope=<coronagraph.teleplanstar.Telescope object>, planet=<coronagraph.teleplanstar.Planet object>, star=<coronagraph.teleplanstar.Star object>, texp=10.0, wantsnr=10.0, FIX_OWA=False, COMPUTE_LAM=False, SILENT=False, NIR=False, THERMAL=True, GROUND=False, vod=False, set_fpa=None, roll_maneuver=True)¶

The primary interface for coronagraph noise modeling. This object wraps around the functionality of count_rates(). Simply instantiate a CoronagraphNoise object by passing it telescope, planet, and star objects, and then call CoronagraphNoise.run_count_rates() to perform the photon count rate calculation.

Parameters:

telescope (Telescope) – Initialized object containing Telescope parameters
planet (Planet) – Initialized object containing Planet parameters
star (Star) – Initialized object containing Star parameters
texp (float) – Exposure time for which to generate synthetic data [hours]
wantsnr (float, optional) – Desired signal-to-noise ratio in each pixel
FIX_OWA (bool, optional) – Set to fix OWA at OWA*lammin/D, as would occur if lenslet array is limiting the OWA
COMPUTE_LAM (bool, optional) – Set to compute lo-res wavelength grid, otherwise the grid input as variable lam is used
SILENT (bool, optional) – Set to suppress print statements
NIR (bool, optional) – Re-adjusts pixel size in NIR, as would occur if a second instrument was designed to handle the NIR
THERMAL (bool, optional) – Set to compute thermal photon counts due to telescope temperature
GROUND (bool, optional) – Set to simulate ground-based observations through atmosphere
vod (bool, optional) – “Valley of Death” red QE parameterization from Robinson et al. (2016)
set_fpa (float, optional) – Specify the fraction of planetary signal in Airy pattern, default will calculate it from the photometric aperture size X
roll_maneuver (bool, optional) – This assumes an extra factor of 2 hit to the background noise due to a telescope roll maneuver needed to subtract out the background. See Brown (2005) for more details.

Note

The results of the coronagraph noise calculation will become available as attributes of the CoronagraphNoise object after CoronagraphNoise.run_count_rates() is called.

run_count_rates(Ahr, lamhr, solhr)¶

Calculate the photon count rates and signal to noise on a coronagraph observation given a wavelength-dependent planetary geometric albedo and stellar flux density.

Parameters:	Ahr (array) – High-res, wavelength-dependent planetary geometric albedo lamhr (array) – High-res wavelength grid [um] solhr (array) – High-res TOA solar spectrum [W/m**2/um]

Calling run_count_rates() creates the following attributes for the CoronagraphNoise instance:

Variables:

Ahr (array) – High-res, wavelength-dependent planetary geometric albedo
lamhr (array) – High-res wavelength grid [um]
solhr (array) – High-res TOA solar spectrum [W/m**2/um]
lam (array) – Observed wavelength grid [$mu$m]
dlam (array) – Observed wavelength grid widths [$mu$m]
A (array) – Planetary geometric albedo at observed resolution
Cratio (array) – Planet-to-star flux contrast ratio
cp (array) – Planetary photon count rate [photons/s]
csp (array) – Speckle count rate [photons/s]
cz (array) – Zodi photon count rate [photons/s]
cez (array) – Exo-zodi photon count rate [photons/s]
cth (array) – Thermal photon count rate [photons/s]
cD (array) – Dark current photon count rate [photons/s]
cR (array) – Read noise photon count rate [photons/s]
cc (array) – Clock induced charge photon count rate [photons/s]
cb (array) – Total background photon noise count rate [photons/s]
DtSNR (array) – Integration time to wantsnr [hours]
SNRt (array) – S/N in a texp hour exposure
Aobs (array) – Observed albedo with noise
Asig (array) – Observed uncertainties on albedo
Cobs (array) – Observed Fp/Fs with noise
Csig (array) – Observed uncertainties on Fp/Fs

make_fake_data(texp=None)¶

Make a fake/synthetic dataset by sampling from a Gaussian.

Parameters:	texp (float, optional) – Exposure time [hours]. If not provided, the `CoronagraphNoise.texp` will be used by default.

Calling make_fake_data() creates the following attributes for the CoronagraphNoise instance:

Variables:	SNRt (array) – S/N in a `texp` hour exposure Aobs (array) – Observed albedo with noise Asig (array) – Observed uncertainties on albedo Cobs (array) – Observed Fp/Fs with noise Csig (array) – Observed uncertainties on Fp/Fs

plot_spectrum(SNR_threshold=1.0, Nsig=6.0, ax0=None, err_kws={'alpha': 1, 'c': 'k', 'fmt': '.'}, plot_kws={'alpha': 0.5, 'c': 'C4', 'lw': 1.0}, draw_box=True)¶

Plot noised direct-imaging spectrum.

Parameters:

SNR_threshold (float) – Threshold SNR below which do not plot
Nsig (float) – Number of standard deviations about median observed points to set yaxis limits
ax0 (matplotlib.axes) – Optional axis to provide
err_kws (dic) – Keyword arguments for errorbar
plot_kws (dic) – Keyword arguments for plot
draw_box (bool) – Draw important quantities in a box?

Returns:

fig (matplotlib.figure.Figure) – Returns a figure if ax0 is None
ax (matplotlib.axes) – Returns an axis if ax0 is None

Note

Only returns fig and ax is ax0 is None

plot_SNR(ax0=None, plot_kws={'ls': 'steps-mid'})¶

Plot the S/N on the planet as a function of wavelength.

Parameters:

ax0 (matplotlib.axes) – Optional axis to provide
plot_kws (dic) – Keyword arguments for plot

Returns:

fig (matplotlib.figure.Figure) – Returns a figure if ax0 is None
ax (matplotlib.axes) – Returns an axis if ax0 is None

Note

Only returns fig and ax is ax0 is None

plot_time_to_wantsnr(ax0=None, plot_kws={'alpha': 1.0, 'ls': 'steps-mid'})¶

Plot the exposure time to get a SNR on the planet spectrum.

Parameters:

ax0 (matplotlib.axes) – Optional axis to provide
plot_kws (dic) – Keyword arguments for plot

Returns:

fig (matplotlib.figure.Figure) – Returns a figure if ax0 is None
ax (matplotlib.axes) – Returns an axis if ax0 is None

Note

Only returns fig and ax is ax0 is None

coronagraph.count_rates.count_rates(Ahr, lamhr, solhr, alpha, Phi, Rp, Teff, Rs, r, d, Nez, mode='IFS', filter_wheel=None, lammin=0.4, lammax=2.5, Res=70.0, diam=10.0, Tput=0.2, C=1e-10, IWA=3.0, OWA=20.0, Tsys=260.0, Tdet=50.0, emis=0.9, De=0.0001, DNHpix=3.0, Re=0.1, Rc=0.0, Dtmax=1.0, X=1.5, qe=0.9, MzV=23.0, MezV=22.0, A_collect=None, diam_circumscribed=None, diam_inscribed=None, lam=None, dlam=None, Tput_lam=None, qe_lam=None, lammin_lenslet=None, wantsnr=10.0, FIX_OWA=False, COMPUTE_LAM=False, SILENT=False, NIR=False, THERMAL=False, GROUND=False, vod=False, set_fpa=None, CIRC=True, roll_maneuver=True)¶

Runs coronagraph model (Robinson et al., 2016) to calculate planet and noise photon count rates for specified telescope and system parameters.

Parameters:

Ahr (array) – High-res, wavelength-dependent planetary geometric albedo
lamhr (array) – High-res wavelength grid [um]
solhr (array) – High-res TOA solar spectrum [W/m**2/um]
alpha (float) – Planet phase angle [deg]
Phi (float) – Planet phase function
Rp (float) – Planet radius [R_earth]
Teff (float) – Stellar effective temperature [K]
Rs (float) – Stellar radius [R_sun]
r (float) – Planet semi-major axis [AU]
d (float) – Distance to observed star-planet system [pc]
Nez (float) – Number of exozodis in exoplanetary disk
mode (str, optional) – Telescope observing mode: “IFS” or “Imaging”
filter_wheel (Wheel, optional) – Wheel object containing imaging filters
lammin (float, optional) – Minimum wavelength [um]
lammax (float, optional) – Maximum wavelength [um]
Res (float, optional) – Instrument spectral resolution (lam / dlam)
diam (float, optional) – Telescope diameter [m]
Tput (float, optional) – Telescope and instrument throughput
C (float, optional) – Coronagraph design contrast
IWA (float, optional) – Coronagraph Inner Working Angle (lam / diam)
OWA (float, optional) – Coronagraph Outer Working Angle (lam / diam)
Tsys (float, optional) – Telescope mirror temperature [K]
Tdet (float, optional) – Telescope detector temperature [K]
emis (float, optional) – Effective emissivity for the observing system (of order unity)
De (float, optional) – Dark current [counts/s]
DNHpix (float, optional) – Number of horizontal/spatial pixels for dispersed spectrum
Re (float, optional) – Read noise counts per pixel
Rc (float, optional) – Clock induced charge [counts/pixel/photon]
Dtmax (float, optional) – Detector maximum exposure time [hours]
X (float, optional) – Width of photometric aperture (lam / diam)
qe (float, optional) – Detector quantum efficiency
MzV (float, optional) – V-band zodiacal light surface brightness [mag/arcsec**2]
MezV (float, optional) – V-band exozodiacal light surface brightness [mag/arcsec**2]
A_collect (float, optional) – Mirror collecting area (m**2) (uses $\pi(D/2)^2$ by default)
diam_circumscribed (float, optional) – Circumscribed telescope diameter [m] used for IWA and OWA (uses diam if None provided)
diam_inscribed (float, optional) – Inscribed telescope diameter [m] used for lenslet calculations (uses diam if None provided)
lam (array-like, optional) – Wavelength grid for spectrograph [microns] (uses lammin, lammax, and resolution to determine if None provided)
dlam (array-like, optional) – Wavelength grid widths for spectrograph [microns] (uses lammin, lammax, and resolution to determine if None provided)
Tput_lam (tuple of arrays) – Wavelength-dependent throughput e.g. (wls, tputs)
qe_lam (tuple of arrays) – Wavelength-dependent throughput e.g. (wls, qe)
lammin_lenslet (float, optional) – Minimum wavelength to use for lenslet calculation (default is lammin)
wantsnr (float, optional) – Desired signal-to-noise ratio in each pixel
FIX_OWA (bool, optional) – Set to fix OWA at OWA*lammin/D, as would occur if lenslet array is limiting the OWA
COMPUTE_LAM (bool, optional) – Set to compute lo-res wavelength grid, otherwise the grid input as variable lam is used
SILENT (bool, optional) – Set to suppress print statements
NIR (bool, optional) – Re-adjusts pixel size in NIR, as would occur if a second instrument was designed to handle the NIR
THERMAL (bool, optional) – Set to compute thermal photon counts due to telescope temperature
GROUND (bool, optional) – Set to simulate ground-based observations through atmosphere
vod (bool, optional) – “Valley of Death” red QE parameterization from Robinson et al. (2016)
set_fpa (float, optional) – Specify the fraction of planetary signal in Airy pattern, default will calculate it from the photometric aperture size X
CIRC (bool, optional) – Set to use a circular aperture
roll_maneuver (bool, optional) – This assumes an extra factor of 2 hit to the background noise due to a telescope roll maneuver needed to subtract out the background. See Brown (2005) for more details.

Returns:

lam (ndarray) – Observational wavelength grid [um]
dlam (ndarray) – Observational spectral element width [um]
A (ndarray) – Planetary geometric albedo on lam grid
q (ndarray) – Quantum efficiency grid
Cratio (ndarray) – Planet-star contrast ratio
cp (ndarray) – Planetary photon count rate on detector [1/s]
csp (ndarray) – Speckle photon count rate on detector [1/s]
cz (ndarray) – Zodiacal photon count rate on detector [1/s]
cez (ndarray) – Exozodiacal photon count rate on detector [1/s]
cD (ndarray) – Dark current photon count rate on detector [1/s]
cR (ndarray) – Read noise photon count rate on detector [1/s]
cth (ndarray) – Instrument thermal photon count rate on detector [1/s]
cc (ndarray) – Clock induced charge photon count rate [1/s]
DtSNR (ndarray) – Exposure time required to get desired S/N (wantsnr) [hours]