Anisotropic Psf Sampling
Screen measured PSF FWHM sampling independently along both pixel axes using a supplied minimum; the two-pixel heuristic is not an exact Gaussian bandlimit.
Description
PSF sampling can differ along detector axes with unequal angular pixel scales.
PSF sampling can differ along detector axes with unequal angular pixel scales. Each axis needs its own pixels-per-FWHM calculation before applying a supplied minimum.1
Screen measured PSF FWHM sampling independently along both pixel axes using a supplied minimum; the two-pixel heuristic is not an exact Gaussian bandlimit.
When to use Anisotropic Psf Sampling
Use this tool to screen measured PSF FWHM sampling independently along both pixel axes using a supplied minimum; the two-pixel heuristic is not an exact Gaussian bandlimit.
Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
How to use Anisotropic Psf Sampling and understand its results
- Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
- Enter seeingFwhmArcseconds, xPixelScaleArcseconds, yPixelScaleArcseconds, minimumPixelsPerFwhm using the field table and calculation rules, then run the tool.
- Read xFwhmPixels, yFwhmPixels, adequatelySampledBothAxes. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| seeingFwhmArcseconds | Seeing fwhm arcseconds | number | Required |
| xPixelScaleArcseconds | X pixel scale arcseconds | number | Required |
| yPixelScaleArcseconds | Y pixel scale arcseconds | number | Required |
| minimumPixelsPerFwhm | Minimum pixels per fwhm | number | Required |
Enter positive seeing FWHM arcseconds, positive x/y scales in arcseconds per pixel and positive minimum pixels/FWHM. Return both axis samplings and a flag true when their smaller value meets the minimum inclusively.
xSampling=FWHM/xPixelScale; ySampling=FWHM/yPixelScale Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| xFwhmPixels | X fwhm pixels | number |
| yFwhmPixels | Y fwhm pixels | number |
| adequatelySampledBothAxes | Adequately sampled both axes | boolean |
{
"input": {
"seeingFwhmArcseconds": 1,
"xPixelScaleArcseconds": 0.4,
"yPixelScaleArcseconds": 0.6,
"minimumPixelsPerFwhm": 2
},
"output": {
"xFwhmPixels": 2.5,
"yFwhmPixels": 1.6666666666666667,
"adequatelySampledBothAxes": false
}
}Limitations and assumptions
A two-pixel heuristic is not an exact Gaussian bandlimit criterion. PSF shape, anisotropic seeing, detector response and reconstruction method are not modeled; one scalar FWHM is assumed.
Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors. A successfully returned false flag is an evaluated outcome; its meaning is explained above.
Alternative or Complementary methods
Use Detector Angular Field Of View: Compute centered rectilinear detector field of view using exact pinhole angles, rather than a small-angle plate-scale product. For a complementary task, use Parametric Trailing Loss: Evaluate an explicitly supplied quadratic trailing-loss model coefficient; this is a matched-filter SNR approximation, not an aperture-flux correction.
References
-
Anisotropic Psf Sampling — tool.io
Similar or alternative tools
- Detector Angular Field Of View
Compute centered rectilinear detector field of view using exact pinhole angles, rather than a small-angle plate-scale product.
- Parametric Trailing Loss
Evaluate an explicitly supplied quadratic trailing-loss model coefficient; this is a matched-filter SNR approximation, not an aperture-flux correction.