snr

Includes an interactive SNR calculator.

Signal To Noise Ratio for the OpenHSI Camera

Tip

This module can be imported using from openhsi.snr import *

This module contains a 6SV1.1 Atmospheric Correction class that computes the pixel radiance given some parameters and a servable interactive SNR widget. 6SV is an open souce radiative transfer code that predicts the solar spectrum received by a sensor facing the Earth. Since it is written in Fortran, we use a Python wrapper called Py6S to expose the functionality and that means we are limited to using 6SV1.1 rather than the newer 6SV2.1.

Theory

The F number of an optical system is a measure of overall light throughput (the ability to produce contrast at a given resolution) and is given by
\[ F/\# = \frac{f}{ \varnothing _{\text{EA}}} \] where \(f\) is the focal length and \(\varnothing _{\text{EA}}\) is the effective aperture diameter.

Assuming the dominant source of noise is photon shot noise \(\sigma_s=\sqrt{S}\), the SNR is given by \[ \text{SNR} \approx S/\sigma_s = \sqrt{S}\] where the signal \[S= \eta_{QE} N\Delta t\] with \(\eta_{QE,\lambda}\) the quantum efficiency, \(N\) the photons per second and \(\Delta t\) the exposure time.

The number of photons per second is given by the formula \[ N_\lambda = L_\lambda \rho_\lambda \eta_{opt} \eta_G \eta_{QE} A_d \Delta\lambda \frac{\lambda}{hc} \frac{\pi}{4(F/\#)^2} \] where \(L_\lambda\) is the solar radiance at Earth’s surface given the geolocation and UTC time, \(\rho_\lambda\) is the surface reflectance, \(\eta_{opt}\) is the optical efficiency, \(\eta_G\) is the grating efficiency, \(\eta_{QE}\) is the quantum efficiency of the sensor, \(A_d\) is the detector area, \(\Delta \lambda\) is the FWHM or bandwidth, and \(\lambda\) is wavelength.

ref_model.show()

100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 100/100 [00:02<00:00, 38.09it/s]

CPU times: user 427 ms, sys: 358 ms, total: 785 ms
Wall time: 5.02 s

source

Widget_SNR

 Widget_SNR (ref_model:openhsi.atmos.Model6SV)

*OpenHSI SNR calculator [1;32mParameters of ‘Widget_SNR’ ========================== [0m [1;31mParameters changed from their default values are marked in red.[0m [1;36mSoft bound values are marked in cyan.[0m C/V= Constant/Variable, RO/RW = ReadOnly/ReadWrite, AN=Allow None

[1;34mName Value Type Bounds Mode [0m

aperture_mm 4 Number (1, 200) V RW focal_length_mm 16 Number V RW pixel_length_x_μm 65 Number (1, 80) V RW pixel_length_y_μm 6.9 Number (1, 60) V RW integration_time_ms 10 Number (5, 100) V RW bandwidth_nm 1.5 Number (0.1, 20) V RW surface_albedo 0.3 Number (0, 1.0) V RW optical_trans_efficiency 0.9 Number (0.1, 1) V RW QE_model ‘./nbs/assets/cmv2000qe.csv’ Selector V RW DE_model ’./nbs/assets/300lpmm_17.5_grating.cs… Selector V RW

[1;32mParameter docstrings: =====================[0m

[1;34maperture_mm: aperture (mm)[0m [1;31mfocal_length_mm: focal length (mm)[0m [1;34mpixel_length_x_μm: pixel length x (μm)[0m [1;31mpixel_length_y_μm: pixel length y (μm)[0m [1;34mintegration_time_ms: integration time (ms)[0m [1;31mbandwidth_nm: FWHM bandwidth (nm)[0m [1;34msurface_albedo: constant surface albedo reflectance[0m [1;31moptical_trans_efficiency: Optical transmission efficiency[0m [1;34mQE_model: Camera QE model[0m [1;31mDE_model: Grating efficiency model[0m*

	Type	Details
ref_model	Model6SV	the 6SV model from openhsi.atmos

widget = Widget_SNR(ref_model=ref_model,name="Interactive SNR Widget")
pn.Row(widget.param,widget.view)

FutureWarning: In a future version of pandas all arguments of DataFrame.drop except for the argument 'labels' will be keyword-only.
  self.QE.drop("type", 1,inplace=True)
<ipython-input-7-93891e1ae51d>:50: FutureWarning: In a future version of pandas all arguments of DataFrame.drop except for the argument 'labels' will be keyword-only.
  self.DE.drop("type", 1,inplace=True)