The DUACS system comprises of two components: Near Real Time (NRT) and Delayed-Time (DT also named REP or MY).

In NRT, the system’s primary objective is to provide operational applications with directly usable high-quality altimeter data from all missions available. Since November 29^th 2023, the DUACS system has been upgraded in order to process both L3 1Hz and 5Hz products:

In DT, the primary objective is to maintain a consistent and user-friendly altimeter database using the state-of-the-art recommendations from the altimetry community. The DT products/datasets are extended in time on a quarterly basis. Therefore, these datasets cover 1993 up to five-nine months before present. These datasets benefit from the highest quality altimeter measurements and geophysical corrections, and are produced with a unique system (no changes in time in the set up, extended in time using the same system) to minimize the risk of quality loss or spurious signals appearing over time.

Figure provides an overview of the system, where processing sequences can be divided into seven main steps:

1. Acquisition
2. Input data quality control
3. Multi-mission cross-calibration
4. Along-track SLA computation
5. Along-track product generation
6. Merged products generation
7. Final quality

Figure: Overview of the DUACS system processing.

Acquisition and data selection Processing flow management	L2P upstream data Description of measurements used as input of the DUACS system	Homogenization and cross-calibration Overview of homogeneization and standardization during the flow management	Along-track (L3) products generation description of generation steps
Merged gridded (L4) products generation description of generation steps	Derived products and quality control	System version changes DUACS NRT and MY system impacting version changes

To read more about the DUACS processing, you can also see Pujol et al, 2016