in an imaging experiment.

Discussion {#sec:discussion}
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The results presented on damage noise have implications for the feasibility of determining assembling the 3D diffraction volume from the ensemble of noisy 2D measurements. The data-assembly algorithms use information common to different diffraction measurements to resolve unknown information about molecular orientation. Predicting the level of damage noise in individual 2D diffraction measurements is a first step toward understanding how damage affects these algorithms. The prediction that $SNR_D$ is greater than one even for longer pulse durations ($>$20 fs) is a preliminary indication that damage noise will not prevent data assembly under conditions currently available in experiment. This is because the contribution to the diffraction from the average molecular structure is greater than the shot-to-shot fluctuations of the diffraction, and it is the contribution from the averaged structure that is used to resolve the problem of unknown molecular orientations. That $SNR_{D+N}(q)$ is lower than $SNR_{D}(q)$ by more than an an order of magnitude (see Fig. \[fig:pulselength\_SNR\]) shows that shot noise dominates damage noise. This can be viewed positively because data-assembly algorithms can already cope with very low shot noise levels when assisted by a priori knowledge about the shot noise statistics[@LohEMC2009; @Fung2009]. However, 