Thriving on Our Changing Planet A Decadal Strategy for Earth Observation from Space (2018) / Chapter Skim
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10 Earth Surface and Interior: Dynamics and Hazards
10 Earth Surface and Interior: Dynamics and Hazards
Pages 499-560
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From page 499... ...
Climatic processes affect the dynamics of Earth's ice sheets and glaciers, and along with local tectonic processes, modulate changes in average sea level. Long-term climatic trends (e.g., toward increased drought, storminess, or climate extremes)
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the dynamics of Earth's core and its changing magnetic field, and the interaction between mantle convection and plate motions. Two objectives ranked Important (S-5b and S-5c)
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These critical measurements are also priorities of other panels, but over the past three decades, geodesists have been at the leading edge of developing the precise measurement tools, such as satellite altimetry, gravity (i.e., mass) change, InSAR, and the terrestrial reference frame.
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, GPS, and InSAR. These same tools are used to maintain the terrestrial reference frame to the 0.1 mm/yr accuracy needed to monitor global sea level.
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Temporal variations in gravity capture shrinkage and growth of key water resources -- glaciers, ice sheets, and subsurface water. Tracking mass changes in both the surface and subsurface using gravity with an increasingly higher spatial resolution, as with Gravity Recovery and Climate Experiment-Follow On (GRACE-FO)
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From page 504... ...
Fluid motions in the core generate the magnetic field, protecting us from space radiation. Mantle convection drives plate tectonics and deforms Earth's surface, creating volcanic eruptions, earthquakes, tsunamis, and landslides, and sometimes causing great destruction.
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From page 505... ...
SOURCE: Modified from NASA Earth Observatory, "Tohoku Earthquake and Tsunami: Looking Back from Space -- Closeup of Tsunami Damage, Rikuzentakata," March 14, 2011, https://earthobservatory.nasa.gov/Features/ Gallery/tsunami.php.
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From page 506... ...
Some of these insights were based on data from a single satellite, some from a synthesis of data from multiple satellites, and some from the integration of multiple satellite data with airborne observations. Importantly, the invaluable terrestrial reference frame that permits reliable integration of nearly all Earth observations from space was also significantly enhanced during the past decade.
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From page 507... ...
SOURCE: Geospatial Information Authority of Japan, "The 2015 Nepal Earthquake: Crustal Deformation Detected by ALOS-2 Data," last updated August 4, 2015, http://www.gsi.go.jp/cais/topic150429-index-e.html.
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Geostationary sensors deliver these data, but at the expense of spatial resolution, and so they can detect only the largest activity (e.g., Prata and Kerkmann, 2007)
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is a catalyst for numerous surface processes, including water and sediment routing, landslide initiation, coastal inundation, and ice-sheet dynamics. Topographic data, like those revealing fault displacements or changes caused by volcanic eruptions, illuminate active tectonic processes and serve as a base upon which many other geophysical measures depend (e.g., InSAR; Pritchard et al., 2004)
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. These data have also illuminated details of surface processes at submeter scales, documented controls on landscape thresholds (e.g., the triggers for gully formation or landslide initiation)
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Vertical Surface Deformation and Mass Change A new, global perspective on vertical land motion has emerged from the GRACE mission. For example, GRACE data have been used to estimate great earthquake (M>8)
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Constellations offer a promising strategy in the sensor-web FIGURE 10.7 A decade of gravimetric data from GRACE illustrates decadal trends in mass changes as a response to seismic deformation (years of large earthquakes are shown) , as well as to mass loss owing to loss of groundwater, surface water, or ice, and mass gains owing to postglacial crustal rebound, the end of a drought, and increased snow accumulation on parts of existing ice sheets.
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Novel insights can be gained from innovative analyses of existing data. For example, vertical positioning data from GPS/GNSS can be used to monitor water changes caused by snowpack, soil moisture, and groundwater variations, whereas reflected signals from GPS/GNSS can be used to estimate soil moisture, snow depth, snow-water equivalent, vegetation, firn density, permafrost changes, and sea level (Box 10.1)
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GPS is also a key component of the terrestrial reference frame, and on-orbit GPS occultation measurements provide valuable information about atmospheric temperature and humidity. Additionally, GPS positions can be used to infer changes in water loads (from ice sheets, glaciers, snow, lakes, and soil moisture)
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Maintaining the reference frame to a positional accuracy of 1 mm and a rate accuracy of 0.1 mm/yr requires NASA's continued participation and support of VLBI and SLR for defining the terrestrial reference frame and its changes with time, and for monitoring Earth rotation (Davis et al., 2016)
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Advances from the last decade of space-based measurements suggest that scientists are on the verge of a breakthrough in natural hazards research if a strategic set of observations are taken now. Objective S-1a: Measure the pre-, syn- and posteruption surface deformation and products of Earth's entire active land volcano inventory with a time scale of days to weeks.
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. ASTER detected persistently elevated temperatures as early as 11 months prior to the eruption owing to its thermal sensitivity and its higher spatial resolution (90 m/pixel)
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• ength and time scales over which responses should be quantified: Surface deformation associated L with the earthquake cycle occurs over spatial scales ranging from meters to thousands of kilometers and time scales ranging from seconds to thousands of years. The relevant deformation scales observ able from spaceborne radar interferometry range from 10 m to 1000 km.
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EARTH SURFACE AND INTERIOR: DYNAMICS AND HAZARDS 519 FIGURE 10.10 Upper panel: Cascadia subduction zone is accumulating seismic energy between the surface and about 40 km deep. The last rupture in 1700 caused 2 m of subsidence along the Washington shoreline and generated a large tsunami that impacted the entire Pacific Basin.
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in order to warn and evacuate local populations. • elevant quantities: The important quantities to be measured are high-resolution, bare-earth topog R raphy; land-surface deformation; precipitation; and permafrost melt, combined with hyperspectral imaging of vegetation and rock/soil composition to improve and augment existing high spatial resolution land-cover data.
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Linkages of S-1 Objectives to Other Panels and Integrating Themes Extreme events like volcanic eruptions, earthquakes, tsunamis, and large landslides can have spatially extensive consequences on hydrology, ecology, weather, climate, and human habitability. Such events commonly damage or destroy infrastructure, disrupt ecological patterns, rearrange drainage networks, and abruptly alter the biogeochemistry, nutrient fluxes, water budget, and energy balance in affected areas.
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Objective S-2b: Assess surface deformation (<10 mm) , extent of surface change (<100 m spatial resolution)
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EARTH SURFACE AND INTERIOR: DYNAMICS AND HAZARDS 523 A SEM activations per disaster macro-categories Hydrometeorological –604 Population (Flood, storm, snow, fire, density drought) (person/km2)
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and ASTER sensor webs and led to the acquisition of high spatial resolution image data for the next 6 months of the eruption. Heat flow measured in the SWIR and TIR during the development of one of the largest lava flow fields in the last 50 years, combined with digital elevation models, constrained models of future lava flows.
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Linkages of S-2 Objectives to Other Panels and Integrating Themes Responses to disruptive, extreme geological events like earthquakes or volcanic eruptions require both rapid quantification of event characteristics and timely dissemination of those data. Efficient and accurate observation and prompt communication are critical ingredients underpinning effective societal responses.
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, mass input from the cryosphere, ocean and atmo sphere dynamics, gravitational changes, and vertical land motion. The global ice sheets contain the greatest potential for rapid sea-level rise in the coming decades.
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since 1993. Precise sea-surface height measurements also require geodetic-quality GPS receivers for orbits, microwave radiometers to correct for water-vapor path delays, dual frequencies for ionospheric corrections, and a stable and well-defined terrestrial reference frame (GPS, SLR, VLBI)
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Observations of ice-sheet change needed for projections of sea-level rise include ice-surface topography measurements from satellite laser altimetry or lidar, ice velocity using both InSAR and GPS, mass estimates using both GRACE and GRACE-FO, and the basic geometry of the base of the ice sheet through airborne radar campaigns. An unresolved issue is that sea-level and ice-mass changes relative to a terrestrial reference frame are sensitive to geocenter motion, but satellite gravity measurements are not.
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Positive values indicate uplift; negative values indicate subsidence. The inset shows the expected relative sea-level rise for the Mississippi Delta using a projection of global mean sea level (bottom curve)
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. Objective S-4a: Quantify global, decadal landscape change produced by abrupt events and by continuous reshaping of Earth's surface from surface processes, tectonics, and societal activity.
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Capturing quan titatively impulsive and persistent temporal processes and both modes of topographic change -- in which elevation changes may or may not be accompanied by changes in slope or composition of surface materials -- is necessary to ultimately understand the processes that drive landscape change. • elevant quantities: Earth's landscape comprises the rock, soil, water, ice, snow, and biomass R extending from the base of the vadose zone to the top of the vegetative canopy (the critical zone)
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Abrupt vegetation disturbance by fire or deforestation or gradual vegetative migration in the face of climate change commonly modify landscape stability and susceptibility to erosion during storms, seismic shaking, or other impulsive events. Overall, understanding landscape change requires a high-resolution, baseline depiction of Earth's topographic, ecological, and compositional land scapes, as well as the ability to capture changes that occur over short time scales (days to months)
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EARTH SURFACE AND INTERIOR: DYNAMICS AND HAZARDS 533 FIGURE 10.17 Before and after images of Langtang village, Nepal, which was buried by a landslide during the 2015 Gorkha earthquake. The M7.8 earthquake triggered more than 4,000 landslides.
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The physical shape and composition of the land surface, its soils, and its ecology are critical controls on the ways in which water, carbon, nutrients, and energy cycle through the critical zone, making this interface a nexus for many integrating themes. Along with soil characteristics, surface water, snowmelt, and groundwater (Hydrology Objectives H-1c, H-3b, H-4a, H-4b, and H-4c; Ecology Objective E-1d; Climate Objective C-2e; and Weather Objectives W-1a, W-3a, and W-4a)
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, which prevents Earth's atmosphere from being depleted by the solar wind and shields society from harmful radiation. Core motions and waves are responsible for prominent changes in Earth's magnetic field, as seen in features such as the movement of the geomagnetic poles and the South Atlantic magnetic anomaly.
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Although plate tectonics explains the occurrence of earthquakes, volcanoes, mountain belts, and geologic features, fundamental questions remain. Specifically, what is the nature of plate boundary deformation; what fraction of the strain rate is elastic, to be released in future earthquakes; and what fraction
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• riority -- Very Important: Better characterization of deep Earth dynamics and its drivers is key to P understanding deep Earth phenomena such as geomagnetic field variations, mantle convection, and plate motions. Because Earth's deep interior cannot be probed directly, our understanding is largely based on indirect measurements and observations.
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establishing more accurate terrestrial reference frames for monitoring Earth rotation parameters, deformation, and mass transport. • elevant quantities: Accurate global monitoring of the magnetic field provides valuable insights R because the magnetic field of the core passes almost unobstructed through the mantle.
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Linkages of S-5 Objectives to Other Panels and Integrating Themes Earth's magnetic field plays a critical role in shielding the biosphere and society from harmful radiation and enabling global communication, and so an improved understanding of its character and temporal variability could prove invaluable. A significant increase (or decrease)
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• elevant quantities: The relevant measurements include vertical surface deformation from InSAR and R GPS, plus ground-based head data at multiple wells in the watershed. Such measurements require production records from some wells and drawdown tests at several.
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Linkages of S-6 Objectives to Other Panels and Integrating Themes Water is clearly an integral part of multiple Earth systems, and it is central to the hydrology, climate, weather, and ecosystems panels. Although surface water fluxes are moderately well characterized, deep water is one of the most difficult components of the water cycle to measure (Hydrology Objective H-3b)
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The surface expressions of the chemical compositions of many resources, including soils, are visible in the spectrum of reflected and emitted energy signatures. These signatures can be effectively monitored with high spatial resolution data collected from spaceborne instruments.
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The terrestrial reference frame includes motion of the geocenter relative to the frame. • easurement basis: In the United States terrestrial reference frame activities are organized by NASA M and strongly supported by international partners and the International Earth Rotation Service.
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. • ontinuity versus new: The accuracy of the terrestrial reference frame requires long time series at C globally distributed VLBI/SLR/GPS stations.
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are tied to the terrestrial reference frame, and so they can achieve better than 1 mm position and 1 mm/yr velocity accuracies, respectively. All of the measurement requirements listed in Table 10.3, except the spatial resolution, could be achieved with GNSS.
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GPS relies on a well-defined terrestrial reference frame. However, GPS/GNSS networks are supported by multiple U.S.
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• easurement basis: The topographic depiction needs sufficient spatial resolution to discriminate M landscape-forming elements from one another, such as hillslopes, river channels, floodplains, and landslides. Moreover, the baseline depiction needs sufficiently high resolution to allow changes in the distribution of these landscape elements and related surface processes to be measured.
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For these reasons, the value of the proposed topography degrades appreciably both at spatial resolutions exceeding several meters and with the inclusion of confounding elements such as vegetation. • ontinuity versus new: Technology development is needed to permit sustained, high-resolution (≤5 C m horizontal, ≤1m vertical)
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The Sentinel-2 multispectral spacecraft series with 13 spectral bands (4 VNIR bands at 10 meters, 6 SWIR bands at 20 meters, and 3 TIR bands at 60 meters spatial resolution) provides 5-day repeat coverage and thus fulfills several of the measurement requirements.
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Localized activity could then be associated with imaged landscape changes to determine the impact of human activity on landscapes across global-scale watersheds. • easurement maturity: High-resolution spaceborne optical and near-infrared imaging is demon M strated and mature.
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• ontinuity versus new: Future gravity missions are needed to maintain at least the continuity of the C GRACE/GRACE-FO gravity measurement, primarily for global mean sea-level change studies. How ever, investing in constellations of gravity missions in optimal complementary orbits or improved gradiometers would likely reduce errors and resolution, increase temporal resolution, and allow time-variable gravity measurements that would considerably improve our understanding of earth quakes and glacial isostatic adjustment as well as cryospheric and hydrologic change.
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Magnetic Field Vector (Low Earth Orbit) Measurements of the magnetic field at satellite altitude are sensitive to spatial and temporal variations in the core field (Objective S-5a)
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A constellation of vector magnetic satellites would also enable progress in the science objectives listed earlier. • ontinuity versus new: Geomagnetic field models require continuous time series of measurements C to track the secular variation of the geomagnetic field.
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• ontinuity versus new: The crustal magnetic field has to be surveyed only once. Repeat measure C ments offer limited benefit.
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• ontinuity versus new: NISAR should meet the low-latitude requirements when it is launched, but C future InSAR missions are necessary to ensure continued and higher latitude observations. Ice Topography and Change Although similar to the bare-earth topography measurement, knowledge of topography change over the Greenland and Antarctica ice sheets and other ice caps and glaciers is different in that a time series, not a single estimate, is required to estimate ice-sheet mass balance (Objective S-3a)
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The trend in ice topography is also sensitive to errors in glacial isostatic adjustment models. • ontinuity versus new: A mission beyond ICESat-2 is required to meet the goals of continuous C observations of ice topography change in order to study glacier-scale dynamics.
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• Global navigation and protection from excessive cosmic radiation depend on the shape, strength, and persistence of Earth's magnetic field. A constellation of satellites with vector magnetometers can measure spatial and temporal variations in the magnetic field needed to update global geomagnetic field models.
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2017. Evaluation of the global mean sea level budget between 1993 and 2014.
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2009. Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets.
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Journal of Geophysical Research: Solid Earth 104(B12)
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