Added Error Field

To create realistic observations, errors have been added to the model SST field considering 3 terms:

· The uncorrelated errors arise from the individual uncertainties in the retrieval process.

· Errors are correlated at the synoptic-scale arising both from changes in atmospheric conditions that affect radiative transfer through the atmosphere and from the orbital stability of the instrument. Correcting the retrieved SST to a depth SST also introduces errors due to the local ocean and meteorological conditions. For IR instruments, we use a the correlation lengthscale of 100km and for CIMR we use a correlation lengthscale of 1000km.

· Large-scale errors reflect orbit-to-orbit variations in instrument performance and retrieval stability.

For the IR instruments, the size of the errors for all 3 terms are based on the uncertainties contained in the original L3U files. For CIMR, SST uncertainty modelling (by C. Prigent) has been used to estimate the size of the uncorrelated and synoptic-scale uncertainties. The size of the adjustment uncertainty (but not the error) is assumed constant.

For both IR and CIMR observations, it is also assumed that the retrieval method has negligible bias (assumes effective application of bias correct measures against fiducial reference measurements will be standard in the future system).

The example error field shown assumes that the correlated errors occur with a lengthscale of 100km, and this is evident in the coherent patches of positive and negative errors.