vania-janet/multiturn-rag-retrieval-data huggingface dataset:
Taking a Measure of Sea Level Rise: Ice Height
Researchers combine ice height measurements with other observations to determine the thickness and volume of a piece of ice, which is then converted into mass.
In recent decades, Earth’s ice-covered regions have been losing more mass than they are gaining. Rising global temperatures are melting glaciers and ice sheets, reducing their thickness, length, and mass. The water from that melted ice flows into the ocean and adds to its volume: Scientists estimate that every 360 gigatons of added melt water raises global sea level by one millimeter. While melting ice is not the only contributor to sea level rise, satellite records since the 1990s show that it has been the largest contributor.
Scientists can use radar and laser altimeters to measure changes to ice elevation. These remote sensing instruments operate by sending radio or laser light pulses toward Earth’s surface and recording the reflections as they bounce back. By measuring the time between the outgoing and returning signal, and knowing the precise altitude of the satellite above ground, scientists can calculate the elevation of the ice surface. Then by comparing multiple altimeter passes over months and years, they can derive surface changes over time.

Although radar and laser altimeters use similar methodology, the two operate at different frequencies and return different information. Radar altimeters use microwave frequencies that illuminate large swaths on the ice sheets (for instance, a 1700-meter diameter). The instruments can “see” the surface in all atmospheric conditions, regardless of clouds, and the signals can penetrate snow to see ice layers. Lasers use shorter wavelengths that are focused into very narrow beams; they observe smaller patches of the surface. (ICESat-2, for instance, has a footprint with a 14-meter diameter.) Lasers cannot penetrate thick clouds, and their signals reflect off the top of the snow layer.
The two types of measurements are complementary. Radars can observe more ice area with greater frequency, but less precision. Laser altimeters can return more precise data about the ice surface, particularly over steeply sloping areas, but it observes the same swaths less often.
NASA’s Seasat was the first satellite to measure ice elevation from space, gathering data for three months in 1978 via radar altimeter.
Taking a Measure of Sea Level Rise: Ice Height
Since July 2020, ESA’s CryoSat-2 and NASA’s ICESat-2 have been flying in orbits that periodically overlap in the Arctic in order to enable simultaneous radar and laser observations. Those synchronized overpasses will allow scientists to make better measurements of sea ice thickness.
With Earth’s ice steadily shrinking, scientists are trying to understand the exact locations and pace of the changes. The map below shows changes in land ice thickness in Antarctica between 2003-2009 and 2018-2019, as measured by ICESat and ICESat-2. (Similar measurements have also been mapped for Greenland.)
In a study published in June 2020, scientists found that ice losses around the edges of Greenland and West Antarctica have contributed 14 millimeters (0.55 inches) to sea level rise since 2003. That is one third of the total amount of sea level rise observed over that period.

2003 - 2018

Mass losses in Greenland exceeded those in Antarctica during those 16 years. Researchers found that Greenland lost an average of 200 gigatons of ice per year, much of it from coastal glaciers. Analyzing various datasets, the scientists found that the main driver of loss in Greenland was surface melting due to ever-warmer summer temperatures. Warmer ocean water also eroded the glaciers at their fronts in some basins.
Antarctica’s ice sheet, which is about eight times larger than Greenland’s, has been losing around 118 gigatons of ice per year across the continent. Further analysis showed that warmer ocean temperatures caused most of the West Antarctic ice loss. Significant snow and ice accumulation in parts of East Antarctica offset some of those losses.
Ice scientists are currently working to build better ice mass balance models by combining observations from ICESat and ICESat-2 with those from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On satellites. Another effort called the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) combines data from 13 NASA and ESA missions to create mass change models. Scientists also use ice height in models of how ice sheets may change in the future, such as in the Ice Sheet Model Intercomparison Project (ISMIP6) that brings together ice sheet modeling groups around the world.
Find more stories about our changing oceans and coasts in Earth Observatory’s sea level rise collection.
October | 2014 | Terra
Coauthor Felix Landerer of JPL noted that during the same period warming in the top half of the ocean continued unabated, an unequivocal sign that our planet is heating up. Some recent studies reporting deep-ocean warming were, in fact, referring to the warming in the upper half of the ocean but below the topmost layer, which ends about 0.4 mile (700 meters) down.
Landerer also is a coauthor of another paper in the same journal issue on 1970-2005 ocean warming in the Southern Hemisphere. Before Argo floats were deployed, temperature measurements in the Southern Ocean were spotty, at best. Using satellite measurements and climate simulations of sea level changes around the world, the new study found the global ocean absorbed far more heat in those 35 years than previously thought — a whopping 24 to 58 percent more than early estimates.
Both papers result from the work of the newly formed NASA Sea Level Change Team, an interdisciplinary group tasked with using NASA satellite data to improve the accuracy and scale of current and future estimates of sea level change. The Southern Hemisphere paper was led by three scientists at Lawrence Livermore National Laboratory in Livermore, California.
NASA monitors Earth’s vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth’s interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
For more information about NASA’s Earth science activities in 2014, visit:
http://www.nasa.gov/earthrightnow
For more information on ocean surface topography from space, visit:
http://sealevel.jpl.nasa.gov
More information on NASA’s GRACE satellites is available at:
http://grace.jpl.nasa.gov
For more information on the Argo array, visit:
http://www.argo.ucsd.edu/index.html

Super Typhoon Phanfone

Posted on October 7, 2014 by Tassia Owen
As Jakarta Grows, So Do the Water Issues
Such developments come with risks because they sit at the front lines of Jakarta’s inevitable battle against sea level rise and storm surges, cautioned Sengupta.
Artificial islands are often among the fastest types of land to subside because their sand and soils settle and become compacted over time. Satellites and ground-based sensors have recorded parts of North Jakarta subsiding by dozens of millimeters per year. On new artificial islands, that rate has soared as high as 80 millimeters per year, Sengupta said.
Some of the new islands were built as part of Jakarta’s National Capital Integrated Coastal Development master plan—an effort to protect the city from flooding and to foster economic development. A key initiative was the construction of a giant seawall and 17 new artificial islands around Jakarta Bay. Though work on the project began in 2015, a range of environmental, economic, and technical concerns have slowed construction and reduced the scope.
The plan to construct a huge seawall is still in place, but it may not be enough to preserve the status quo in Jakarta. With environmental pressures mounting, Indonesian politicians hope to move the seat of government from Jakarta to a new location on the island of Borneo.
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Story by Adam Voiland.

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Sinking land, rising seas, and rainfall-driven floods pose big problems for Indonesia’s largest city.
Image of the Day for May 12, 2021

Instruments:
Landsat 5 — TM
Landsat 8 — OLI

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Sea Level Rise

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Land
Human Presence

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May 11, 2021

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References & Resources

Channel News Asia (2021, February 6) The fight against Jakarta’s devastating yearly floods. Accessed May 11, 2021.
Channel News Asia (2019, June 29) Staying in Jakarta: Will a great sea wall protect Indonesia's capital from coastal flooding? Accessed May 11, 2021.
KPPIP National Capital Integrated Coastal Development (NSICD) Phase A. Accessed May 11, 2021.
Taking a Measure of Sea Level Rise: Ice Height
Lasers cannot penetrate thick clouds, and their signals reflect off the top of the snow layer.
The two types of measurements are complementary. Radars can observe more ice area with greater frequency, but less precision. Laser altimeters can return more precise data about the ice surface, particularly over steeply sloping areas, but it observes the same swaths less often.
NASA’s Seasat was the first satellite to measure ice elevation from space, gathering data for three months in 1978 via radar altimeter. Since then, several more satellite radar altimeters have been flown by the U.S. Navy, the European Space Agency (ESA), and other international space agencies, including GEOSAT, ERS-1, ERS-2, Envisat, AltiKa, CryoSat-2, and the Copernicus Sentinel missions. Radar altimeters have provided continuous ice elevation data for Greenland and Antarctica since 1991.

In 2003, NASA launched the first Earth-observing laser altimeter aboard the Ice, Cloud and land Elevation Satellite (ICESat), which was also the first altimetry mission specifically designed to observe ice. ICESat operated until 2010, and NASA launched a more advanced ICESat-2 in 2018. While the first generation satellite carried three lasers that fired 40 pulses of infrared light per second and took measurements every 170 meters (560 feet), the successor carries two green lasers that fire 10,000 pulses per second and collect data every 70 centimeters (30 inches). ICESat-2 gathers enough data to estimate the annual height change of the Greenland and Antarctic Ice Sheets to within 4 millimeters (0.2 inches).
Since July 2020, ESA’s CryoSat-2 and NASA’s ICESat-2 have been flying in orbits that periodically overlap in the Arctic in order to enable simultaneous radar and laser observations. Those synchronized overpasses will allow scientists to make better measurements of sea ice thickness.
With Earth’s ice steadily shrinking, scientists are trying to understand the exact locations and pace of the changes. The map below shows changes in land ice thickness in Antarctica between 2003-2009 and 2018-2019, as measured by ICESat and ICESat-2. (Similar measurements have also been mapped for Greenland.)
Andaman Islands, Bay of Bengal
Satellite observations of the Andaman Islands collected before and after the disaster showed that the earthquake caused some islands to sink and others to rise. Satellite observations and field measurements helped researchers map the extent of the rupture caused by the earthquake.
On February 10, 2007, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image of the Andaman Islands. To the west of the main island group is North Sentinel Island, marked by a conspicuous coastline. The brightness of the coastline is no quirk in the satellite observations; the Sumatra-Andaman earthquake lifted this island, exposing the surrounding coral reef that had previously been submerged.
To assess the precise amount of uplift, researchers relied primarily on a different satellite sensor: NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). ASTER observes smaller areas of the globe each day than MODIS, but it sees those areas in more detail. Close examination of ASTER imagery—paired with field measurements—helped researches gauge the extent of uplift and subsidence (sinking) in the Andaman Islands and other island chains in the region. To learn more about how satellites helped scientists understand the Sumatra-Andaman earthquake, read the Earth Observatory Feature Rise and Fall.
NASA image by Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center.

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The Andaman Islands consist of more than 500 islands in the Bay of Bengal. The largest islands comprise Great Andaman, easily seen from space.
Image of the Day for February 15, 2007

Instrument:
Terra — MODIS

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ABCs from Space

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Land

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This approximately true-color image shows part of the Turks and Caicos Islands archipelago, observed September 18, 2001.

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FAQs • San Bruno, CA • CivicEngage
As a result, when performing coastal studies, FEMA and mapping partners rely more heavily on the modeling of wave and erosion processes and storm surge (water that is pushed toward the shore by the force of winds swirling around a storm) to predict coastal flood elevations. 

11.
How accurate are coastal flood study results?

FEMA works to create the most accurate FIRMs possible. Accuracy can be impacted by the quality of the underlying data, and the assumptions and approximations that must be made when conducting a coastal study. The accuracy of a coastal study depends directly on several parameters:The accuracy and resolution of data (i.e. topographic, bathymetric, wind, and water level data);The length of the historical water level and wave records;The incidence and severity of coastal flood events affecting the study area; andThe number and quality of coastal flood high water marks and hydrographs (used to calibrate computer models used in the study).In an effort to improve the accuracy and resolution of topographic and bathymetric data, FEMA and mapping partners (U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, and others) are using Light Detection and Ranging (LiDAR) technology to gather data for many coastal studies. This topographic collection approach represents a higher level of accuracy over traditional methods.Study accuracy also depends on:The resolution of the computer model grids and the ability of the grids to duplicate small-scale topographic, bathymetric, and land use features;The ability of the modeling schemes and algorithms to capture the physics of water flow, wave mechanics, and in some cases, erosion of dunes during the base flood; andThe ability of statistical procedures to estimate the 1-%-annual-chance flood conditions with a high degree of confidence.Because of the wide variety of factors that affect study results, no single benchmark exists for assessing study accuracy. 

12.
How can coastal flood studies be made more accurate?

FEMA readily shares methodology and data, and welcomes new information that will make the mapped flood hazard information even more accurate. It is important to note, however, that even when SFHAs are mapped with high precision for existing conditions, new residential and commercial development and natural changes in weather patterns may, over time, change conditions sufficiently to require a restudy to update the study to the new conditions. 

13.
October | 2014 | Terra
NASA Study Finds Earth’s Ocean Abyss Has Not Warmed

Posted on October 7, 2014 by Tassia Owen 
	Posted in News and Events 

While the upper part of the world’s oceans continue to absorb heat from global warming, ocean depths have not warmed measurably in the last decade. This image shows heat radiating from the Pacific Ocean as imaged by the NASA’s Clouds and the Earth’s Radiant Energy System instrument on the Terra satellite. (Blue regions indicate thick cloud cover.)
The cold waters of Earth’s deep ocean have not warmed measurably since 2005, according to a new NASA study, leaving unsolved the mystery of why global warming appears to have slowed in recent years.
Scientists at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, analyzed satellite and direct ocean temperature data from 2005 to 2013 and found the ocean abyss below 1.24 miles (1,995 meters) has not warmed measurably. Study coauthor Josh Willis of JPL said these findings do not throw suspicion on climate change itself.
“The sea level is still rising,” Willis noted. “We’re just trying to understand the nitty-gritty details.”
In the 21st century, greenhouse gases have continued to accumulate in the atmosphere, just as they did in the 20th century, but global average surface air temperatures have stopped rising in tandem with the gases. The temperature of the top half of the world’s oceans — above the 1.24-mile mark — is still climbing, but not fast enough to account for the stalled air temperatures.
Many processes on land, air and sea have been invoked to explain what is happening to the “missing” heat. One of the most prominent ideas is that the bottom half of the ocean is taking up the slack, but supporting evidence is slim. This latest study is the first to test the idea using satellite observations, as well as direct temperature measurements of the upper ocean. Scientists have been taking the temperature of the top half of the ocean directly since 2005, using a network of 3,000 floating temperature probes called the Argo array.
“The deep parts of the ocean are harder to measure,” said JPL’s William Llovel, lead author of the study published Sunday in the journal Nature Climate Change.
As Jakarta Grows, So Do the Water Issues
In recent decades, the flooding problems have grown even worse, driven partly by widespread pumping of groundwater that has caused the land to sink, or subside, at rapid rates. By some estimates, as much as 40 percent of the city now sits below sea level.
With mean global sea levels rising by 3.3 millimeters per year, and amid signs that rainstorms are getting more intense as the atmosphere heats up, damaging floods have become commonplace. Since 1990, major floods have happened every few years in Jakarta, with tens of thousands of people often displaced. The monsoon in 2007 brought especially damaging floods, with more than 70 percent of the city submerged.
Rapid urbanization, land use change, and population growth have exacerbated the problem. The Landsat images above show the evolution of the city over the past three decades. The widespread replacement of forests and other vegetation with impervious surfaces in inland areas along the Ciliwung and Cisadane rivers has reduced how much water the landscape can absorb, contributing to runoff and flash floods. With the population of the metropolitan area more than doubling between 1990 and 2020, more people have crowded into high-risk floodplains. Also, many river channels and canals have narrowed or become periodically clogged with sediment and trash, making them especially prone to overflowing.
Since the first image above was captured in 1990, artificial land and new development has spread into the shallow waters of Jakarta Bay. According to one analysis of Landsat data, people have built at least 1185 hectares (5 square miles) of new land along the coast. Much of the land has been used for high-end residential developments and a golf course, explained Dhritiraj Sengupta, a remote sensing scientist at East China Normal University. Such developments come with risks because they sit at the front lines of Jakarta’s inevitable battle against sea level rise and storm surges, cautioned Sengupta.
Artificial islands are often among the fastest types of land to subside because their sand and soils settle and become compacted over time. Satellites and ground-based sensors have recorded parts of North Jakarta subsiding by dozens of millimeters per year. On new artificial islands, that rate has soared as high as 80 millimeters per year, Sengupta said.
Water Cycle | Terra
Just like black asphalt absorbs radiation from the sun, resulting in a warmer surface temperature, the darkening of the ice sheet could warm the surface temperature around the snow, increasing snowmelt. This could result a shrinking Greenland ice sheet and have implications on sea level rise.
The combination of a well-understood sensor, high-quality analysis of the satellite data, and coordinated measurements at the surface led to the conclusion that a sensor artifact, a change to an image from defects or degradation of optics, was the culprit this time.
Satellites, like many scientific instruments, need to be calibrated to be able to maintain accuracy. If you’ve ever stepped on a scale and gotten a number that was far too high or too low to be accurate, you’ve been a witness to the degradation of an instrument. Scales can be fixed easily by taring, or resetting the instrument to zero when nothing is being weighed.
Fixing satellite sensor degradation, isn’t quite as easy, but is common practice. The complexity of an instrument like MODIS makes the calibration process much more difficult. Often, there are small instrument effects that are not obvious until many years of data from multiple applications indicate an issue. The dark ice example is one such case.
The vigilance of the MODIS scientists and those working with the instrument calibration led to five previous reprocessings with the sixth currently underway.. Each time the data is reprocessed, degradation of the instruments are taken into account and the data is calibrated based on data collected from other sensors on other satellites as well as from data collected on Earth. MODIS is on-board both Terra and Aqua, when data from these sensors don’t match up the data can be corrected based on data gathered on Earth.
While it may be easy to assume that an aging instrument may be less accurate, in reality the longer the data record that it collects, the more accurate the data can be through reprocessing. Just think, if Terra had only lasted it’s six year design life, instead of going on 16, this error in the data may never have been caught and accounted for in newer data collections.