L4 Derived product generation
The L4 derived products consist of the Absolute Dynamic Topography (ADT) (maps and along-track) and maps of geostrophic currents (absolute and anomalies).
The ADT products are obtained by adding a Mean Dynamic Topography (MDT) to the SLA field. The MDT used in the DT2014 reprocessing is described in QUID document.
The geostrophic current products disseminated to users are computed using a 9-point stencil width methodology (Arbic et al, 2012) for latitudes outside the ±5°N band. In the equatorial band, the Lagerloef methodology (Lagerloef et al, 1999) introducing the β plane approximation is used.
L3 and L4 Quality control
The production of homogeneous products with a high quality data and within a short delay is the key feature of the DUACS processing system. But some events (failure on payload or on instruments, delay, maintenance on servers), can impact the quality of measurements or the data flows. A strict quality control on each processing step is indispensable to appreciate the overall quality of the system and to provide the best user services.
The Quality Control is the final process used by DUACS before product delivery. In addition to daily automated controls and warnings to the operators, each production delivers a large QC Report composed of detailed logs, figures and statistics of each processing step. Altimetry experts analyze these reports twice a week (only for internal validation, those reports are not disseminated).