Advantages

• Day/night and all weather operation.
  

• Generally unhindered by vegetation or canopy cover.
  

• All determined surface heights are with respect to one common reference frame.
  

• Satellites are placed in repeat orbits (up to 1km either side of a nominal ground track) enabling systematic monitoring of rivers, lakes, wetlands, inland seas and floodplains.
  

• Has the potential to contribute height information for any target beneath the satellite overpass, thus contributing information where traditional gauge (stage) data may be absent.
  

• Satellite altimetric instruments have been in continuous operation since 1991 and new missions are scheduled for the next decade. There is therefore the ability to monitor seasonal to interannual variations during the lifetime of these satellites.
  

• Techniques have been validated and results published in peer-reviewed journals.
  

Limitations

• These instruments are primarily designed to operate over uniform surfaces such as oceans and ice-sheets. Highly undulating or complex topography may cause data loss or non-interpretation of data.
  

• Retrieved heights are an "average" of all topography within the instrument footprint. Such values are further averaged in the direction of the satellite motion, giving, for example, one final height value every 580m (TOPEX/POSEIDON) or 350m (ERS) along the ground track. Altimetric values therefore differ from traditional gauge measurements which offer "spot" heights at specific locations.
  

• The height accuracy is dominated by knowledge of the satellite orbit, the altimetric range (distance between antenna and target), the geophysical range corrections and the size and type of the target.
  

• Unlike imaging instruments, altimeters only retrieve heights along a narrow swath determined by the instrument's footprint size. The effective footprint diameter can vary depending on the nature of the target, and can potentially range from several hundred meters to many kilometers.
  

• Minimum target size is controlled by the instrument footprint size and the telemetry/data rates, and also on the surrounding topography and the target-tracking method used.
  

• The satellite orbit scenario and target size also determine the spatial and temporal coverage. Improved temporal coverage is gained at the expense of spatial coverage for a single satellite mission.
  

• Major wind events, heavy precipitation, tidal effects and the presence of ice will effect data quality and accuracy.