Autocovariance Structures for Radial Averages in Small‐Angle X‐Ray Scattering Experiments

Small‐angle X‐ray scattering (SAXS) is a technique for obtaining low‐resolution structural information about biological macromolecules, by exposing a dilute solution to a high‐intensity X‐ray beam and capturing the resulting scattering pattern on a two‐dimensional detector. The two‐dimensional pattern is reduced to a one‐dimensional curve through radial averaging, that is, by averaging across annuli on the detector plane. Subsequent analysis of structure relies on these one‐dimensional data. This article reviews the technique of SAXS and investigates autocorrelation structure in the detector plane and in the radial averages. Across a range of experimental conditions and molecular types, spatial autocorrelation in the detector plane is present and is well‐described by a stationary kernel convolution model. The corresponding autocorrelation structure for the radial averages is non‐stationary. Implications of the autocorrelation structure for inference about macromolecular structure are discussed.