Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 17
earth Science and applicatiOnS frOm Space  GRACE-II GRAVITY RECOVERY AND CLIMATE ExPERIMENT II LAUNCH: 2016–2020 MISSION SIZE: medium ORBIT: Leo, sso AGENCY: nasa ESTIMATED COST: $450 million AREAS OF INTEREST: Climate, Water INSTRUMENTS: microwave- or laser-based ranging system BENEFITS: improved measurement of changes in earth’s mass distribution due to dynamic processes Data on changes in volume of ice sheets due to climate change, leading to better climate models and estimates of sea-level rise improved understanding of groundwater dynamics on continental scales improved prediction of changes in sea level GRaCe, twin satellites launched in march 2002, is making detailed measurements of earth’s gravity field. analyses of data from GRaCe have led to important discoveries about gravity and earth’s natural systems, which in turn have far-reaching benefits to society and the world’s population. Data from GRaCe are providing scientists with a globally consistent measurement of the distribution of earth’s mass and its variability in time and space. this variability in mass is due primarily to water motion. thus, measurements from GRaCe provide an integral con- straint on many geophysical processes related to land, ocean, atmo- sphere, and glaciological subsystems. a record of time variations in earth’s gravity field reflects the redistribution and exchange of mass within and between these reservoirs. over one-quarter of the world’s population relies on groundwater as its principal source of drinking water. Yet global observations of this critical resource are highly variable in density, with most in situ observations located within heavily exploited groundwater basins in the developed world, and few elsewhere. GRaCe-ii would extend and improve on the first GRaCe mission. Resolution would be increased to around 100 kilometers. accuracy could be boosted by development of a laser-based satellite-to-satellite interferometer and a drag-free propulsion system, with boosters continually fired to minimize orbital degradation caused by atmospheric drag. the re- sulting data would foster major breakthroughs in a number of areas of earth science.