We assess the impacts of multi-satellite altimetry on the representation of ocean circulations down to submesoscales of the order of 1 km. Sub-km horizontal grid spacing is increasingly used in regional forecasting models to resolve submesoscale flows. To assimilate satellite altimetry data into a model of sub-km grid spacing, we need to deal with a set of particular difficulties. Among those difficulties are the limited footprint size of altimetry measurement, dynamical imbalance, density compensation, spatial localization and temporal intermittency, and others. Leveraging a real-time multiscale three-dimensional variational data assimilation (MS-3DVAR) and forecasting system, which has successfully supported the Salinity Processes in the Upper Ocean Regional Study (SPURS) field campaign in the North Atlantic Ocean (SPURS-1), and the SPURS multi-scale observing network, we illustrate those difficulties, address methodologies and formulations to deal with those difficulties, and show positive impacts of multi-satellite altimetry on the representation of submesoscale flows. The results from the 2016 SPURS in the Eastern Tropical Pacific (SPURS-2) will also be presented.