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In PanSTARRS nomenclature, a detection is a source found in a single exposure or a stacked image. Each detection has associated quantities. Detections are combined into "objects" by spatial matching across different exposures and filters. 

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The starting point for the PS1 data archive is at the Pan-STARRS1 data archive home page.

Definition - what is a "detection"?

In PanSTARRS nomenclature, a detection is a source found in a single exposure or a stacked image.  Detections are matched across exposures to define objects.

Detections are identified through a standard peak-finding algorithm.  The image is convolved with an approximation of the PSF and then divided by a smoothed version of the variance image to define the significance image.  Peaks are defined as locations where the significance image exceeds a target threshold, representing the square of the desired signal-to-noise ratio.  Peaks are then ordered in decreasing significance, and peaks are retained only if a significant valley separates them from brighter nearby peaks.

The process of identifying detections is complex and involves multiple steps:

  1. Smooth the image with PSF (or a PSF estimate in the first pass)
  2. Smooth the variance with PSF**2
    • To speed these up, a 1D Gaussian with FWHM matching the PSF is used.
    • That is much faster and is only marginally different.
    • If the difference matters, the image is of poor quality.
  3. Create a significance image by dividing image**2 / variance.
  4. Find all peaks above target S/N (squared).
  5. Perform a footprint analysis
    • Generate isophotal footprint outlines (N sigma above sky).
    • Assign peaks to their containing footprints.
    • Cull insignificant peaks:
      • Cull in descending order of brightness.
      • A valid peak must be separated from a brighter peak by a significant valley.
      • As a recent improvement: on the second pass, cull on the unsubtracted image


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