Interactive comment on “Inter-Calibration of nine UV sensing instruments over Antarctica and Greenland since 1980” by Clark Weaver et al

here. Then, the definition of Delta_I. It is in relation to a certain 4-term polynomial (is that 3rd order? If not, which polynomial orders?). Is it a constraint that the polynomial becomes zero at SAZ=90? In P5,L11 that is suggested, but is it enforced? I would expect a deviation with respect to the assumed ’truth’ (see Figure 1) , so (I_obs zeta(SZA))/zeta(SZA). That said, what is the reasoning behind the fractional/relative deviation (as opposed to absolute deviation)? Now measurements near zero reflection are weighted more heavily, and the expression may blow up (especially when having I_obs in the denominator, instead of zeta). Are low reflectance measurements more important? Note that the curve zeta itself, (P4L12) seems to be fitted by minimizing the absolute deviations (is that the case?) as standard for LS fitting.