design strategy for vector and tensor calibration

In Holmes et al 2012 (new version coming soon) we showed practical methods for designing an imaging survey for high-quality photometric calibration: You don't need a separate calibration program (separate from the main science program) if you design it our way. This is like a scalar calibration: We are asking What is the sensitivity at every location in the focal plane? We could have asked What is the astrometric distortion away from a tangent-plane at every location in the focal plane?, which is a vector calibration question, or we could have asked What is the point-spread function at every location in the focal plane?, which is a tensor calibration question. Of course the astrometry and PSF vary with time in ground-based surveys, but for space-based surveys these are relevant self-calibration questions. We learned in the above-cited paper that certain kinds of redundancy and non-redundancy make scalar calibration work, but the requirements will go up as the rank of the calibration goes up too. So repeat for these higher-order calibrations! Whatever you do might be highly relevant for Euclid or WFIRST, which both depend crucially on the ability to calibrate precisely. Even ground-based surveys, though dominated by atmospheric effects, might have fixed distortions in the WCS and PSF that a good survey strategy could uncover better than any separate calibration program.

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