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GPS signal occultation by the atmosphere, and the resulting useful data is explained.

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This animation illustrates the movements of the two GRACE-FO satellites as they orbit Earth.
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This animation illustrates the movements of the two GRACE-FO satellites as they orbit Earth. As the satellites pass over topographic or mass anomaly features, the relative distance between the satellites changes. This distance change is precisely tracked with the two ranging interferometers: the Microwave Instrument (MWI), as well as the technology-demonstration Laser Ranging Instrument (LRI). Every 30 days, the polar-orbiting satellites gather enough data to derive a global map of the surface mass distribution. The differences in this mass distribution from one month to the next provide fundamental indicators of the large-scale dynamics of the planet as mass (mostly in the form of water) is constantly redistributed within and between Earth’s atmosphere, oceans, groundwater and ice sheets. Since 2018, GRACE Follow-On (GRACE-FO) continues the legacy of GRACE (2002-2017), tracking Earth’s water movement and surface mass changes across the planet. Monitoring changes in ice sheets and glaciers, near-surface and underground water storage, the amount of water in large lakes and rivers, as well as changes in sea level and ocean currents provides an integrated global view of how Earth’s water cycle and energy balance are evolving—measurements that have important applications for everyday life.
GRACE-FO: from range observations to global mass change
NASA’s Gravity Recovery and Climate Experiment (GRACE, 2002 - 2017) mission, and its successor GRACE Follow-On (launched in 2018), map month-to-month changes in Earth's gravity field resulting from...
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NASA’s Gravity Recovery and Climate Experiment (GRACE, 2002 - 2017) mission, and its successor GRACE Follow-On (launched in 2018), map month-to-month changes in Earth's gravity field resulting from the movement of mass, such as water, near the surface of the planet. This animation shows how the total amount of water (snow, surface water, soil moisture, and groundwater) varies in space and time, with the passage of dry seasons and wet seasons as well as with flooding, drought, and transport due to water management. Blue colors represent wetter than average conditions (relative to 2004-2010), while red colors represent drier than average conditions. The yellow line in the graph on the left shows the evolution of the long-term inter-annual variations for the area outlined in yellow on the map (note: the average seasonal cycle has been removed). The Sacramento and San Joaquin River basins are outlined in yellow, and rivers and tributaries are shown as blue lines. The basins include California's Central Valley, the most productive agricultural region in the U.S. Repeated drought conditions and increased water use in California have led to a long-term decline of terrestrial water, interspersed with above-average precipitation periods (e.g., 2015/2016; 2022/2023) that have allowed some recovery of the land water storage.
GRACE and GRACE-FO track California's land water changes
Earth's gravity from space
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Earth's gravity from space
Earth's gravity from space
For 15 years, the GRACE mission has unlocked mysteries of how water moves around our planet. It gave us the first view of underground aquifers from space, and shows how fast polar ice sheets and mo...
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For 15 years, the GRACE mission has unlocked mysteries of how water moves around our planet. It gave us the first view of underground aquifers from space, and shows how fast polar ice sheets and mountain glaciers are melting.
15 Years of GRACE Earth Observations
Global ocean conveyor belt of warm and cold water is explained.
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Global ocean conveyor belt explanation.
Conveyor.mov
Between 2002 and 2020, Antarctica shed approximately 150 gigatons of ice per year, causing global sea level to rise by 0.4 millimeters per year.
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Between 2002 and 2020, Antarctica shed approximately 150 gigatons of ice per year, causing global sea level to rise by 0.4 millimeters per year.
Antarctic Ice Loss 2002-2020
This visualization shows extremes of the water cycle — droughts and pluvials — over a twenty-year period (2002-2021) based on observations from the GRACE and GRACE-FO satellites. Dry events are sho...
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This visualization shows extremes of the water cycle — droughts and pluvials — over a twenty-year period (2002-2021) based on observations from the GRACE and GRACE-FO satellites. Dry events are shown as red spheres and wet events as blue spheres, with earlier years being shown as lighter shades and later years as darker shades. The volume of the sphere is proportional to the intensity of the event, a quantity measured in cubic kilometer months. A total of 1,056 extreme wet and dry events appear over the course of the visualization. The plots at the bottom of the figure show that the total intensity of extreme events increased as global temperatures increased. The most intense event was a 2019 pluvial (excessive, persistent rain) in central Africa. In a study of 20 years of data from the NASA/German GRACE and GRACE-FO satellites, two NASA scientists confirmed that major droughts and pluvials — periods of excessive precipitation and water storage on the landscape — have been occurring more often. They also found that the worldwide intensity of these extreme wet and dry events – a metric that combines extent, duration, and severity — is closely linked to global warming. Floods and droughts account for more than 20% of the economic losses caused by extreme weather events in the U.S. each year, ranked second after hurricanes among major disasters. The economic impacts are similar around the world, though the human toll tends to be most devastating in poor and developing nations. From 2015-2021 — seven of the warmest years in the modern record — the frequency of extreme wet and dry events was four per year, compared with three per year in the previous 13 years. This makes sense, say the authors, because warmer air causes more moisture to evaporate from Earth's surface during dry events; warm air can also hold more moisture to fuel severe snow- and rainfall events.
Water Cycle Extremes: Droughts and Pluvials
Zoom in to view GRACE flying over Greenland.
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GRACE Greenland flyover
Greenland flyover by GRACE
These images show the changes in gravity anomalies from GRACE over the Amazon Basin for each month of 2004. 
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Amazon Basin seasonal hydrology
Amazon Basin seasonal hydrology
The mass of the Polar ice sheets have changed over the last decades. Research based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellites (2002-2017) and GRACE Follow-...
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The mass of the Polar ice sheets have changed over the last decades. Research based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellites (2002-2017) and GRACE Follow-On (since 2018 - ) indicates that between 2002 and 2020, Antarctica shed approximately 150 gigatons of ice per year, causing global sea level to rise by 0.4 millimeters per year; and Greenland shed approximately 280 gigatons of ice per year, causing global sea level to rise by 0.03 inches (0.8 millimeters) per year. These images, created from GRACE and GRACE-FO data, show changes in polar land ice mass since 2002. Orange and red shades indicate areas that lost ice mass, while light blue shades indicate areas that gained ice mass. White indicates areas where there has been very little or no change in ice mass since 2002. The average flow lines (grey; created from satellite radar interferometry) of the icesheets converge into the locations of prominent outlet glaciers, and coincide with areas of highest mass loss. This supports other observations that warming ocean waters near polar icesheets play a key role in contemporary ice mass loss.
GRACE and GRACE-FO polar ice mass loss
Research based on GRACE observations indicates that between 2002 and 2021, Greenland shed approximately 280 gigatons of ice per year.
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Research based on GRACE & GRACE-FO observations indicates that between 2002 and 2021, Greenland shed approximately 280 gigatons of ice per year.
Greenland Ice Loss 2002-2021
This animation illustrates the highs and lows of the Earth's gravity field as water in the basins of the U.S. changes over time.
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GRACE data over the United States, 2003-2012
GRACE data over the United States, 2003-2012
NASA’s Gravity Recovery and Climate Experiment (GRACE) has measured significant groundwater depletion around the world in recent years. These animations show trends in total water storage from Jan....
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GRACE Sees Groundwater Losses Around the World
GRACE Sees Groundwater Losses Around the World
The GRACE Intermediate Field 48 (GIF48 from UT-CSR) field model is an improved mean gravity field that combines GRACE observations with terrestrial and ocean gravity information for the small-scale...
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The GRACE Intermediate Field 48 (GIF48 from UT-CSR) field model is an improved mean gravity field that combines GRACE observations and terrestrial gravity information The terrestrial gravity information was taken from the DTU10 global gravity field. Shown here are the so-called free air gravity deviations from an ideal ellipsoidal Earth model, in units of milli-gal. Areas colored yellow, orange, or red are areas where the actual gravity field is larger than the featureless-Earth model predicts, while the progressively darker shades of blue indicate places where the gravity field is less.
Static gravity field - anomalies (1)
GRACE contribution to atmospheric studies explained.
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GRACE contribution to atmospheric studies explained.
Atmos.mov
This visualization of a gravity model was created with data from NASA's Gravity Recovery and Climate Experiment (GRACE) and shows variations in Earth’s gravity field.
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GRACE global gravity animation
GRACE global gravity animation
The force of gravity not only keeps us from floating away, it also lets NASA study Earth’s water and ice from space. Using a pair of twin satellites named "GRACE," we can monitor our planet’s water.
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The force of gravity not only keeps us from floating away, it also lets NASA study Earth’s water and ice from space. Using a pair of twin satellites named "GRACE," we can monitor where our planet’s water is going, even when it is underground.
Scale in the Sky
This image shows the mean annual amplitude of total water storage on Earth in 2007 as measured by GRACE.
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Total water storage from GRACE, 2007
Total water storage from GRACE, 2007
The GRACE satellites during component integration in a German clean room.
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The GRACE satellites are shown without solar panels during component integration in a German clean room.
GRACE Component Integration

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