Principal component analysis of up-the-ramp sampled infrared array data

Abstract

We describe the results of principal component analysis (PCA) of up-the-ramp sampled IR array data from the HST WFC3 IR, JWST NIRSpec, and prototype WFIRST WFI detectors. These systems use respectively Teledyne H1R, H2RG, and H4RG-10 near-IR detector arrays with a variety of IR array controllers. The PCA shows that the Legendre polynomials approximate the principal components of these systems (i.e. they roughly diagonalize the covariance matrix). In contrast to the monomial basis that is widely used for polynomial fitting and linearization today, the Legendre polynomials are an orthonormal basis. They provide a quantifiable, compact, and (nearly) linearly uncorrelated representation of the information content of the data. By fitting a few Legendre polynomials, nearly all of the meaningful information in representative WFC3 astronomical datacubes can be condensed from 15 upthe-ramp samples down to 6 compressible Legendre coefficients per pixel. The higher order coefficients contain time domain information that is lost when one projects up-the-ramp sampled datacubes onto 2-dimensional images by fitting a straight line, even if the data are linearized before fitting the line. Going forward, we believe that this time domain information is potentially important for disentangling the various non-linearities that can affect IR array observations, i.e. inherent pixel non-linearity, persistence, burn in, brighter-fatter effect, (potentially) non-linear interpixel capacitance (IPC), and perhaps others.

Brighter-fatter effect in near-infrared detectors -- III. Fourier-domain treatment of flat field correlations and application to WFIRST

“…Across all configuration settings, SCA 20828 has the lowest (or is tied for having the lowest) values of inter-pixel capacitance α H and α D , though there is spatial variation for all SCAs and the ranges of α have some region of overlap. When we performed the classical non-linearity fits with a cubic instead of a quartic polynomial, the coefficients β 2 g and β 3 g 2 changed significantly, which is expected given that the standard polynomial basis is not orthogonal (in future work, we may follow Rauscher et al 2019 and use the Legendre polynomial basis for this reason). This disadvantage of the standard basis is further demonstrated in Fig.…”

Assessing the suitability of H4RG near-infrared detectors for precise Doppler radial velocity measurements

“…40,41 However, recently published research by Rauscher demonstrates a new technique to preserve time domain information from HxRG datacubes which could be used to mitigate a number of usual and unusual detector effects including pixel nonlinearity, persistence, and the brighter-fatter effect. 36 While simulations of H4RGs is work that is still on-going, the most practical next step in characterizing performance would involve laboratory experiments to validate the errors in Table 1.…”

“…23 Applying this correction estimate to the test case shown in Figure 4.2 at iLocater's nominal integration time of 30 minutes gives an RV error of 0.8 cms −1 . Additionally, a new principal component analysis of H4RG detectors has been shown to provide valuable time-domain information that can be useful for further mitigation of intrinsic nonlinear pixel response 36. The impact of nonlinear pixel response on RV precision.…”

JWST’s PEARLS: Dust Attenuation and Gravitational Lensing in the Backlit-galaxy System VV 191

“…This set of calibration data improves flat-fielding and the uniformity of photometric zero-points (especially between NIRCam detectors) compared to our initial look with pmap-0913, while the newer pipeline routines are much better at rejecting "snowball" decay events, which previously left circular artifacts. We paid particular attention to cross-checks of the flux scale (important only for the serendipitous lensing targets discussed below) and treatment of the "1/f" readout noise, which manifests as gradual baseline drifts for each row along the x-direction (Rauscher et al 2012). All detectors at each wavelength were drizzlecombined into single mosaic images, although our analysis here uses only the single short-wavelength detector encompassing the galaxies in VV 191 and matching cropped regions on the long-wavelength detectors.…”