Surface Water Quantity Remote Sensing

Wednesday, April 20, 2022 8:51 AM

Text below is based on content made available under Database for Hydrological Time Series of Inland Waters by Technische Universität München

Water level derived from Satellite Altimetry

Satellite altimetry has the potential to measure water levels of lakes, reservoirs, rivers and wetlands from space. However, satellite altimetry is limited due to its measuring technique, since it can only measure in nadir direction which means that the inland water body has to be crossed.

  1. The accuracy of the water level time series vary between few centimeters for large lakes and few decimeters for small rivers. Example of Water Level Time Series from Satellite Altimetry.
  2. The temporal resolution of the water level time series depends on the used altimeter satellites (e.g. 10 days for Jason-3, 35 days for Envisat) and the number of tracks crossing the inland water body.
  3. The Surface Water and Ocean Topography (SWOT) mission (to be launched in November 2022) will provide global observations of changing water levels, slopes, and inundation extents in rivers, lakes, and floodplains at higher temporal and spatial resolutions than possible with currently available satellite missions.

Surface area derived from Optical Imagery

Optical imagery has been used to monitor surface changes of the Earth. The extraction and identification of water bodies is essential for applications such as monitoring flooded regions and wetlands, but also for the water storage quantification of lakes and reservoirs. Remote sensing is also capable of observing long-term geomorphological changes of rivers and their meandering.

  1. The temporal resolution of the surface area time series depends on the used optical imagery (e.g. 16 days for Landsat, 10 days for Sentinel-2) and cloud free conditions.
  2. The spatial resolution for freely available imagery is generally upwards of 10m. Much higher resolution optical imagery (~ 12 cm resolution) is available from commercial sources.

Processing

At least a few datasets and processing tools are available to derive time series from these sources. Such as: Datasets:

  1. Database for Hydrological Time Series of Inland Waters

Tools:

  1. Google Earth Engine
  2. Microsoft's Planetary Computer

The resolution (both spatial and temporal) as well as the number of algorithms and tools available in this space has steadily continued to climb over the past years. However, they still may not be suitable for small-scale watersheds or intervention projects at field-scale.