A document describes a solution to missing flux values in time-domain optical and radio astronomical survey data that form “light curves.” The technique incorporates a priori astronomical knowledge into a missing value imputation technique. It is assumed that missing values in astronomical time series are either Missing At Random (MAR), or missing due to the flux of the source falling below the instrument’s sensitivity threshold, termed Threshold Removed Observations (TRO).

The imputation technique consists of two stages: (1) classification of a flagged missing observation as MAR or TRO, and (2) imputation of the missing values according to their classification. Having classified the unlabeled MAR+TRO set of observations as either MAR or TRO, standard linear interpolation is applied to infer the values of the MAR values, and cubic spline interpolation to infer the values of the TRO observations.

This work was done by Colorado J. Reed of University of Iowa, and Umaa D. Rebbapragada, Kiri L. Wagstaff, and David R. Thompson of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48544


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Missing Value Imputation in Astronomical Time-Series Data

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This article first appeared in the August, 2014 issue of NASA Tech Briefs Magazine.

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