Regular elevation data for mass balance estimations in Patagonian glaciers

Los Glaciares National Park is located southwest Argentina. It covers more than 700000 ha. and has many large glaciers which are responsible for feeding two huge lakes (Viedma and Argentino lake) with melting water. This meltwater crosses arid Patagonia and provides drinking water to the entire basin.
There is poor information about how much ice and snow melts every year. Elevation data for mass balance calculations is provided by remote sensing technologies, however free access is scarce. Changes in elevation can only be measured between four free digital elevation models (DEM) of mid-resolution, and each one corresponds to a specific year. That means only three mass balance calculations can be done.
The area is remote and vast, therefore we rely on remote sensing information.