ComputeExposureSummaryStatsTask

class lsst.pipe.tasks.computeExposureSummaryStats.ComputeExposureSummaryStatsTask(**kwargs)

Bases: Task

Task to compute exposure summary statistics.

This task computes various quantities suitable for DPDD and other downstream processing at the detector centers, including: - expTime - psfSigma - psfArea - psfIxx - psfIyy - psfIxy - ra - dec - pixelScale (arcsec/pixel) - zenithDistance - zeroPoint - skyBg - skyNoise - meanVar - raCorners - decCorners - astromOffsetMean - astromOffsetStd

These additional quantities are computed from the stars in the detector: - psfStarDeltaE1Median - psfStarDeltaE2Median - psfStarDeltaE1Scatter - psfStarDeltaE2Scatter - psfStarDeltaSizeMedian - psfStarDeltaSizeScatter - psfStarScaledDeltaSizeScatter

These quantities are computed based on the PSF model and image mask to assess the robustness of the PSF model across a given detector (against, e.g., extrapolation instability): - maxDistToNearestPsf - psfTraceRadiusDelta - psfApFluxDelta

This quantity is computed based on the aperture correction map, the psfSigma, and the image mask to assess the robustness of the aperture corrections across a given detector: - psfApCorrSigmaScaledDelta

These quantities are computed to assess depth: - effTime - effTimePsfSigmaScale - effTimeSkyBgScale - effTimeZeroPointScale - magLim

Methods Summary

run(exposure, sources, background)	Measure exposure statistics from the exposure, sources, and background.
update_background_stats(summary, background)	Compute summary-statistic fields that depend only on the background model.
update_effective_time_stats(summary, exposure)	Compute effective exposure time statistics to estimate depth.
update_magnitude_limit_stats(summary, exposure)	Compute a summary statistic for the point-source magnitude limit at a given signal-to-noise ratio using exposure-level metadata.
update_masked_image_stats(summary, masked_image)	Compute summary-statistic fields that depend on the masked image itself.
update_photo_calib_stats(summary, photo_calib)	Compute all summary-statistic fields that depend on the photometric calibration model.
update_psf_stats(summary, psf, bbox[, ...])	Compute all summary-statistic fields that depend on the PSF model.
update_wcs_stats(summary, wcs, bbox, visitInfo)	Compute all summary-statistic fields that depend on the WCS model.

Methods Documentation

run(exposure, sources, background)

Measure exposure statistics from the exposure, sources, and background.

Parameters

exposure : lsst.afw.image.ExposureF sources : lsst.afw.table.SourceCatalog background : lsst.afw.math.BackgroundList

Returns

summary : lsst.afw.image.ExposureSummary

update_background_stats(summary, background)

Compute summary-statistic fields that depend only on the background model.

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

backgroundlsst.afw.math.BackgroundList or None

Background model. If None, all fields that depend on the background will be reset (generally to NaN).

Notes

This does not include fields that depend on the background-subtracted masked image; when the background changes, it should generally be applied to the image and update_masked_image_stats should be called as well.

update_effective_time_stats(summary, exposure)

Compute effective exposure time statistics to estimate depth.

The effective exposure time is the equivalent shutter open time that would be needed under nominal conditions to give the same signal-to-noise for a point source as what is achieved by the observation of interest. This metric combines measurements of the point-spread function, the sky brightness, and the transparency. It assumes that the observation is sky-background dominated.

The effective exposure time and its subcomponents are defined in [1]_.

References

[1]

Neilsen, E.H., Bernstein, G., Gruendl, R., and Kent, S. (2016). Limiting Magnitude, au, teff, and Image Quality in DES Year 1 https://www.osti.gov/biblio/1250877/

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

exposurelsst.afw.image.ExposureF

Exposure to grab band and exposure time metadata

update_magnitude_limit_stats(summary, exposure)

Compute a summary statistic for the point-source magnitude limit at a given signal-to-noise ratio using exposure-level metadata.

The magnitude limit is calculated at a given SNR from the PSF, sky, zeropoint, and readnoise in accordance with SMTN-002 [1]_, LSE-40 [2], and DMTN-296 [3].

References

[1]

“Calculating LSST limiting magnitudes and SNR” (SMTN-002)

[2]

“Photon Rates and SNR Calculations” (LSE-40)

[3]

“Calculations of Image and Catalog Depth” (DMTN-296)

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

exposurelsst.afw.image.ExposureF

Exposure to grab band and exposure time metadata

update_masked_image_stats(summary, masked_image)

Compute summary-statistic fields that depend on the masked image itself.

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

masked_imagelsst.afw.image.MaskedImage or None

Masked image. If None, all fields that depend on the masked image will be reset (generally to NaN).

update_photo_calib_stats(summary, photo_calib)

Compute all summary-statistic fields that depend on the photometric calibration model.

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

photo_caliblsst.afw.image.PhotoCalib or None

Photometric calibration model. If None, all fields that depend on the photometric calibration will be reset (generally to NaN).

update_psf_stats(summary, psf, bbox, sources=None, image_mask=None, image_ap_corr_map=None, sources_is_astropy=False)

Compute all summary-statistic fields that depend on the PSF model.

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

psflsst.afw.detection.Psf or None

Point spread function model. If None, all fields that depend on the PSF will be reset (generally to NaN).

bboxlsst.geom.Box2I

Bounding box of the image for which summary stats are being computed.

sourceslsst.afw.table.SourceCatalog or astropy.table.Table

Catalog for quantities that are computed from source table columns. If None, these quantities will be reset (generally to NaN). The type of this table must correspond to the sources_is_astropy argument.

image_masklsst.afw.image.Mask, optional

Mask image that may be used to compute distance-to-nearest-star metrics.

sources_is_astropybool, optional

Whether sources is an astropy.table.Table instance instead of an lsst.afw.table.Catalog instance. Default is False (the latter).

update_wcs_stats(summary, wcs, bbox, visitInfo)

Compute all summary-statistic fields that depend on the WCS model.

Parameters

summarylsst.afw.image.ExposureSummaryStats

Summary object to update in-place.

wcslsst.afw.geom.SkyWcs or None

Astrometric calibration model. If None, all fields that depend on the WCS will be reset (generally to NaN).

bboxlsst.geom.Box2I

Bounding box of the image for which summary stats are being computed.

visitInfolsst.afw.image.VisitInfo

Observation information used in together with wcs to compute the zenith distance.