Estimates of forward model and instrument error statistics in the troposphere
Presenter:
Sean Healy
ECMWF
RUAG, Sweden
Poster
A key requirement for assessing future observing systems in either an OSSE or EDA framework is a realistic estimate of the total observation uncertainty. The total uncertainty is composed of a term related to the instrument performance, and a term related forward model error statistics. In this work we have performed wave optics simulations to estimate the relative contribution of the instrument and forward model uncertainty in the troposphere. High-quality (HQ) and medium-quality (MQ) instrument performance has been simulated using 55 one-dimensional (1D) refractivity profiles, for both rising and setting occultations. The instrument error statistics have been estimated by comparing the retrieved bending angles with values computed with the Abel integral of the 1D refractivity profile. These results have been compared with forward model error statistics produced by horizontal gradients, by wave optics modelling through 55 two-dimensional (2D) refractivity slices. The forward model error statistics have been estimated for both a 1D and 2D bedning angle observation operator. The instrument simulation results emphasise the importance of an "advanced tracking" approach, using multiple correlators. We also show that the assumption that forward model error is much greater than instrument error in the troposphere is not correct in all cases, particularly when a 2D observation operator is used.
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