PPOPS

Performance Prediction for Optical Particle Spectrometer

Documentation: https://rtd-ppops.readthedocs.io/

Overview

This repository simulates the performance of a simple Optical Particle Spectrometer (OPS) using a physics-based model. The default optical system is based on Gao et al., Aerosol Sci. Technol., 2016, which is also what the POPS instrument sold by Handix Scientific is based on. The PPOPS model is semi-validated in that PPOPS modeled signal was within 50% of the actual signal of a POPS unit from Handix Scientific (see validation section of PPOPS website for more information).

The PPOPS model calculates the amount and direction of scattered light by aerosols according to Mie theory. The scattered light is integrated over the solid-angle acceptance of the collection mirror to calculate a truncated scattering cross section (the effective scattering cross section). This truncated scattering cross section is then used to calculate the instrument signal and noise current.

To summarize, the PPOPS workflow includes,

1. Use miepython to calculate the scattering amplitudes (S₁, S₂) according to Mie theory.
   1. Compute Mie coefficients (a_n, b_n) for electric and magnetic scattering modes.
   2. Generate angular functions (π_n, τ_n) that describe angle-dependent intensity.
2. Integrating over the OPS collection mirror’s polar and azimuthal acceptance to compute the truncated scattering cross section.
3. Convert the truncated scattering cross section to signal and noise current based on detector specifications.
4. Optionally, convert signal current to digitizer bins for direct comparison with POPS data.

Assumptions

This package makes several assumptions:

1. Particles are perfectly spherical.
2. Scattering is elastic.
3. All scattered light incident on the collection mirror is detected.
4. The only noise sources are signal noise, dark noise, and preamp noise (i.e., we neglect stray scattering).
5. The detector is shot noise limited.

Installation

PPOPS is available via PyPI

pip install ppops

Usage

See PPOPS website for more information.

import ppops

ops = ppops.OpticalParticleSpectrometer()

ops.estimate_signal_noise(diameters = [0.1, 0.5, 1.0], ior = 1.5+0.001j)

References

Gao, R.S., Telg, H., McLaughlin, R.J., Ciciora, S.J., Watts, L.A., Richardson, M.S., Schwarz, J.P., Perring, A.E., Thornberry, T.D., Rollins, A.W., Markovic, M.Z., Bates, T.S., Johnson, J.E., Fahey, D.W., 2016. A light-weight, high-sensitivity particle spectrometer for PM2.5 aerosol measurements. Aerosol Science and Technology 50, 88–99. https://doi.org/10.1080/02786826.2015.1131809

miepython: 10.5281/zenodo.7949263

Author Notes

This repository is intended as a transparent, well-documented implementation of Mie scattering and optical geometry for POPS performance prediction and analysis.

License

PPOPS is released under the MIT license.