Query: Using satellite data rather than tide-gauge data that is normally used to measure sea levels allows for more precise estimates of global sea level, since it provides measurements of the open ocean.

Relevant passages:
Remote sensing <=SEP=> Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation . Remote sensing is used in numerous fields , including geography , land surveying and most Earth Science disciplines ( for example , hydrology , ecology  , oceanography , glaciology , geology ) ; it also has military , intelligence , commercial , economic , planning , and humanitarian applications .   In current usage , the term `` remote sensing '' generally refers to the use of satellite - or aircraft-based sensor technologies to detect and classify objects on Earth , including on the surface and in the atmosphere and oceans , based on propagated signals ( e.g. electromagnetic radiation ) . It may be split into `` active '' remote sensing ( i.e. , when a signal is emitted by a satellite or aircraft and its reflection by the object is detected by the sensor ) and `` passive '' remote sensing ( i.e. , when the reflection of sunlight is detected by the sensor ) .

OSTM/Jason-2 <=SEP=> OSTM/Jason-2, or Ocean Surface Topography Mission/Jason-2 satellite, was an international Earth observation satellite altimeter joint mission for sea surface height measurements between NASA and CNES. It was the third satellite in a series started in 1992 by the NASA/CNES TOPEX/Poseidon mission  and continued by the NASA/CNES Jason-1 mission launched in 2001.

Sea level rise <=SEP=> A sea level rise is an increase in the volume of water in the world 's oceans , resulting in an increase in global mean sea level . Sea level rise is usually attributed to global climate change by thermal expansion of the water in the oceans and by melting of Ice sheets and glaciers on land . Melting of floating ice shelves or icebergs at sea raises sea levels only slightly .   Sea level rise at specific locations may be more or less than the global average . Local factors might include tectonic effects , subsidence of the land , tides , currents , storms , etc. .  Sea level rise is expected to continue for centuries . Because of the slow inertia , long response time for parts of the climate system , it has been estimated that we are already committed to a sea-level rise of approximately 2.3 m for each degree Celsius of temperature rise within the next 2,000 years . IPCC Summary for Policymakers , AR5 , 2014 , indicated that the global mean sea level rise will continue during the 21st century , very likely at a faster rate than observed from 1971 to 2010 . Projected rates and amounts vary . A January 2017 NOAA report suggests a range of GMSL rise of 0.3 -- 2.5 m possible during the 21st century .   Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems .

Tide gauge <=SEP=> A tide gauge ( also known as mareograph or marigraph , as well as sea-level recorder ) is a device for measuring the change in sea level relative to a datum .   Sensors continuously record the height of the water level with respect to a height reference surface close to the geoid . Water enters the device by the bottom pipe ( far end of the tube , see picture ) , and electronic sensors measure its height and send the data to a tiny computer .   Historical data are available for about 1,450 stations worldwide , of which about 950 provided updates to the global data center since January 2010 . At some places records cover centuries , for example in Amsterdam where data dating back to 1700 is available . When it comes to estimating the greater ocean picture , new modern tide gauges can often be improved upon by using satellite data .   Tide gauges are used to measure tides and quantify the size of tsunamis .  The measurements make it possible to derive the mean sea level . Using this method , sea level slopes up to several 0.1 m/1000 km and more have been detected .   A tsunami can be detected when the sea level begins to rise , although warnings from seismic activity can be more useful .