psf interpolation

Vakili and I spoke about his probabilistic interpolation of the point-spread function in imaging using Gaussian Processes and a basis derived from principal components. The LSST atmospheric PSF looks very stable, according to Vakili's image simulations (which use the LSST code), so I asked for shorter exposures to see more variability. We talked about the point that there might be PSF variations that are fast in time but slow in focal-plane position (from the atmosphere) and others that might be slow in time but fast in focal-plane position (from the optics) and maybe hybrid situations (if, say, the optics have some low-dimensional but fast variability). All these things could be captured by a sophisticated model.