A large percentage of the world’s population resides near the coasts and derives its livelihood from the coastal environment, and much of the global economy relies on the ocean to do business. With so many lives depending on our coastal regions, it is important to understand the nature and magnitude of coastal processes through periodic mapping of shoreline changes, ocean currents, wind velocities, ship locations and oil spills.
NISAR will also be capable of measuring changes in groundwater reserves across the land. Climate change, coupled with growing populations, is causing increasing stress on groundwater resources globally. By measuring changes in Earth’s surface, we can understand processes occurring below the surface. Subsidence is often the first indication of changes in reservoirs or over-exploitation of aquifers. Subsidence that continues for too long can lead to irreversible collapse of the aquifer system. Informed decisions allow us to make the most of our resources sustainably and economically.
NISAR’s unique combination of radar, frequent orbit passes and polar orbit also mean that the satellite can be used to study floods, precisely measuring very small changes of water level in areas with standing vegetation.
Water: Sustaining Life
In many arid parts of the world, rainfall and surface water can't meet the needs of the people who live in those regions. Groundwater makes up the difference, acting as a reservoir that can be tapped through wells. Unfortunately, climate change coupled with growing populations is causing increasing stress on groundwater resources around the world.
Over-exploitation of groundwater leads to lowering of the water table and, in alluvial basins, compaction of the aquifer system. These processes cause sinking of the land surface (subsidence). Subsidence is often the first indication of over-exploitation and can also cause problems for infrastructure such as aqueducts, flood-control projects, highways, bridges and railways. If subsidence continues for too long, it can lead to irreversible collapse of the aquifer system, reducing its ability to recharge when water is available.
Subsidence as a Measure of Groundwater Depletion
To increase resilience and adapt to changes, water resource managers need to be able to detect new areas of subsidence and to monitor known areas of continuing subsidence. This will also give an indication of groundwater depletion over long periods. Currently this is measured by periodic leveling or GPS surveys and by monitoring water levels in a limited number of wells, but the resulting datasets are sparse in space and time.
NISAR will provide systematic measurement across entire aquifers. The ability to map surface deformation of a few millimeters monthly over large areas at resolutions of a few tens of meters has opened up new possibilities for remote monitoring of groundwater resources.
Managing Water Globally
NISAR offers the promise of extending these observations to regions of the world with no effective means to monitor the state of their groundwater. This would provide information to large segments of the global population dependent on groundwater to bridge gaps in surface and rain water supply. It may allow us for the first time to indirectly measure the volume of groundwater that is pumped and recharged around the world. This will become more important as Earth’s changing climate and the growing global population outpaces the world’s supply of freshwater in aquifers.
Another capability of NISAR is its ability to easily identify and map the extent of surface water in lakes and rivers. NISAR can be used to track floods, even under vegetation canopies. Floods are important not only for their impact on society, but as a significant means for redistribution of sediment on flood plains.