Inland Waters and Land
Rivers and Lakes
The need to globally understand fresh water resources has increased the use of radar altimetry data for measuring river and lake water levels. The advantages of altimetry measurements are the continuity, global coverage and accuracy of the measurements available.
The SENTINEL-3 improved along-track resolution (approximately 300 m) in SAR mode facilitates the measurement of narrow rivers and small lakes. The Level-2 SRAL/MWR products have a field (surface type) indicating whether the records are for enclosed seas or lakes.
New disseminated Level-1 products (Level-1A, Level-1B-s and Level1B) allow improved water level retrieval through improved and customised land contamination and retracking techniques over inland waters.
Figure 1: Tanganika river water height from January 2002 to January 2010 using ENVISAT, JASON-1 and JASON-2 satellite data. The measurement location is at -5.19 degrees latitude and 29.49 degrees longitude. The height reference is the mean sea level (MSL) surface (Credit: ESA/DMU).
For further information about applications related to river and lake monitoring see: Rivers and Lakes (ESA), Hydroweb (LEGOS), Global Reservoir and Lake Monitoring (US Dept. of Agriculture), CRUCIAL project and DAHITI project.
Digital Terrain Models
Detailed and accurate Digital Terrain Models (DTM) are widely used in earth sciences. DTM data derived from in situ and aircraft measurements have historically been available on a regional scale.
Satellite altimeter measurements can be used to derive DTM products and will be of use to Copernicus services. Satellite radar altimetry height estimation, over land targets, requires careful classification of each waveform according to shape, followed by the application of re-tracking algorithms to obtain the best range to surface measurement.
The first altimeter-informed Global Digital Terrain Model (GDTM), Altimeter Corrected Elevations (ACE), was created by fusing altimeter derived heights produced using a system of multiple altimeter re-trackers, with ground-truth from a range of publicly available datasets to create an enhanced GDTM. A new ACE2 dataset was created by synergistically merging the Shuttle Radar Topography Mission (SRTM) dataset together with satellite radar altimetry.
Figure 2: ACE2 Digital Terrain Model. (Credit: ESA/DMU)
For further information about applications related to land monitoring see: ACE2 project (ESA).
For further information about land applications and services available, see: Copernicus website.