Noise

Noise

This page describes ALMASim’s current noise model.

Location

Noise handling lives primarily in src/almasim/services/interferometry/noise.py.

Current Model

ALMASim uses a PWV-aware channel noise model that depends on:

  • precipitable water vapor

  • channel frequencies

  • channel width

  • integration time

  • elevation

  • antenna diameter

  • number of antennas

The noise profile is computed per channel and then calibrated against a reference noise level used by the simulation pipeline.

Inputs

The key inputs are:

  • pwv_mm

  • ground_temperature_k

  • per-channel observing frequencies

  • observing time

  • antenna count

  • array type through antenna diameter and array configuration

SNR Handling

ALMASim supports:

  • manual SNR override

  • automatic SNR derivation from metadata sensitivity fields

The current auto mode uses:

  • Cont_sens_mJybeam

  • Line_sens_10kms_mJybeam

This keeps the default behavior tied to available ALMA metadata rather than arbitrary hardcoded values.

What Noise Is Not

The background sky features described elsewhere are not part of the noise model.

ALMASim treats them separately:

  • noise is an observing/corruption term

  • background sky is an additive astrophysical sky component

Future Directions

Likely future improvements include:

  • more explicit atmospheric transmission coupling

  • richer correlator-dependent noise settings

  • better calibration of line and continuum sensitivity relationships across bands