CoAuthors

Gregg Jacobs (Naval Research Laboratory, United States)

Altimetry is one of the most important data sources for assimilation into operational models. Operational models require the data in near-real time, when the environmental corrections and precision orbit are not available in their most accurate form on the geophysical data records. AltiKa represent the beginning of a new class of altimeters operating at Ka band frequency with a small footprint and high pulse rate. Prior to assimilation, the altimeter data passes through quality control (QC) developed at the Naval Research Laboratory. Early results from the QC showed AltiKa to perform at or better than previous Ku band altimeters, which lower sensor noise and fewer data dropouts. To check the impact of AltiKa on the operational models, a six month series of data denial experiments were performed using the operation Gulf of Mexico forecast model in a nowcast mode. Compared to the operational model, the AltiKa only nowcast has 1/2 the rms error in steric SSH and mixed layer depth of the Jason-2 only nowcast. From these experiments, it isn't possible to determine if the performance gain with AltiKa comes from the better performance of the altimeter or from the different track spacing of AltiKa. To test the performance versus sampling difference, the data denial experiments were performed using Envisat and Jason-2 in 2009. Envisat and AltiKa follow the same track, but have very different sensor performance. In these experiments, neither altimeter has a significantly small rms error compared to the operational model assimilating all data. Thus, closer track spacing of the Envisat/AltiKa altimeters is not sufficient to explain the improved model nowcasts with AltiKa and the better performance of AltiKa leads to a better nowcast.