Forced Measurement of Astronomical Sources at Low Signal-to-noise

We propose a modified moment matching algorithm to avoid catastrophic failures for sources with a low signal to noise ratio. The proposed modifications include a method to eliminate nonphysical negative pixel values and a forced single iteration with an initial guess derived from coadd measurements when iterative methods are unstable. We correct for all biases in measurements introduced by the method. We find that the proposed modifications allow the algorithm to avoid catastrophic failures in nearly 100% of the cases, especially at low SNR. Additionally, with a reasonable guess from coadd measurements, the algorithm measures the flux, centroid, size, shape, and ellipticity with a bias statistically consistent with zero. We show that the proposed method allows us to measure sources 7 times fainter than traditional methods when applied to images obtained from WIYN-ODI. We also present a scheme to find uncertainties in measurements when using the new method to measure astronomical sources.