simple-snr-calc

Signal-to-noise ratio calculator for remote sensing of satellites. Supports ground-based and space-based sensors across UV, optical, near-IR, and IR wavelengths.

Features

• Reflected solar + thermal emission: Lambertian sphere model with Tousey/Sussman phase angle factors, plus Planck blackbody thermal emission (optional)
• Ground- and space-based sensors: Atmosphere (extinction, sky background, seeing) can be enabled or disabled
• Full throughput chain: Optics coatings, spectral filters, and detector QE curves multiplied on a common wavelength grid
• Detector noise model: Shot noise, sky background, dark current, read noise, quantization noise with proper CCD/CMOS binning
• Search rate: Computes sky survey rate at a given SNR threshold
• Peak pixel fraction: Analytical ensquared energy and blur model for streaked targets
• YAML configuration: Single config file defines the entire observation scenario
• CLI and Python API: Run from the command line or import into your own code

Installation

# Clone the repo
git clone <repo-url>
cd simple-snr-calc

# Create a virtual environment and install
uv venv
uv pip install -e "."

Quick Start

CLI

# Run with an example config
simple-snr-calc configs/example_ground.yaml

# Debug logging
simple-snr-calc configs/example_ground.yaml --debug

Python API

from simple_snr_calc import load_config, SNRCalculator

# Load a YAML config
config = load_config("configs/example_ground.yaml")
calc = SNRCalculator(config)

# Single-point SNR
result = calc.compute_snr(mv=16.0, exposure_time=1.0)
print(f"SNR = {result.snr:.2f}")
print(f"Noise breakdown: {result.noise.variance_fractions()}")

# Full sweep (mV range x exposure time range)
results = calc.sweep()

Programmatic Config

from simple_snr_calc import SNRConfig, SNRCalculator
from simple_snr_calc.config import (
    TargetConfig, AtmosphereConfig, OpticsConfig,
    DetectorConfig, ObservationConfig,
)

config = SNRConfig(
    target=TargetConfig(albedo=0.2, range=2e9),
    atmosphere=AtmosphereConfig(enabled=False),  # space-based
    optics=OpticsConfig(
        aperture_diameter=0.3,
        focal_length=1.5,
        throughput_files=["optics/mirror-pwi-al.csv"],
    ),
    detector=DetectorConfig(qe_file="detectors/qe-imx455.csv"),
    observation=ObservationConfig(mv_range=[10.0, 18.0]),
)
calc = SNRCalculator(config)

Utilities

Individual functions are importable for use in other tools:

from simple_snr_calc import (
    load_solar_radiance,        # solar spectrum data
    planck_spectral_radiance,   # Planck blackbody B(lambda, T)
    load_curve,                 # load any CSV curve (QE, filter, etc.)
    phase_angle_factor,         # Lambertian sphere phase function
    radius_from_mv,             # apparent magnitude -> target radius
    build_throughput,           # optics x filter x QE chain
    compute_ensquared_energy,   # analytical Gaussian ensquared energy
    compute_search_rates,       # survey search rate
)

Configuration

All parameters are set in a single YAML file. See configs/example_ground.yaml and configs/example_space.yaml for annotated examples.

Key sections:

Section	Description
target	Albedo, range, phase angles, thermal emission settings
atmosphere	Enable/disable, transmission, sky background, Fried parameter
optics	Aperture, focal length, obscuration, jitter, throughput curves
filter	Filter name (looked up in data/filters/) or explicit file path
detector	Pixel size, dimensions, noise parameters, QE curve
observation	Exposure time, magnitude range, binning, coadding, SNR threshold

Set atmosphere.enabled: false for space-based sensors. Set target.thermal.enabled: true to include thermal emission.

Data Files

Spectral data lives in data/ with the following structure:

data/
  solar/       Solar radiance spectra
  optics/      Mirror and lens throughput curves
  filters/     Spectral filter transmission curves (Johnson-Cousins, Bayer, etc.)
  detectors/   Detector QE curves
  psf/         Blur efficiency lookup table

Curves are 2-column CSV files (wavelength in nm, fractional value) and can be added by placing new files in the appropriate directory.

License

See LICENSE.