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NASA NTRS2002

Visions 2025 and Linkage to NEXT

This talk will describe the progress to date on creating a science-driven vision for the NASA Earth Science Enterprise (ESE) in the post-2010 period. This effort began in the Fall of 2001 by organizing five science workgroups with representatives from NASA, academia and other agencies: Long-Term Climate, Medium-Term Climate, Extreme Weather, Biosphere & Ecosystems, and Solid Earth, Ice Sheets, & Sea Level. Each workgroup was directed to scope out one Big Question, including not just the science but the observational and modeling requirements, the information system requirements, and the applications and benefits to society. This first set of five Big Questions is now in hand and has been presented to the ESE Director. It includes: water resources, intraseasonal predictability, tropical cyclogenesis, invasive species, and sea level. Each of these topics will be discussed briefly. How this effort fits into the NEXT vision exercise and into Administrator O'Keefe's new vision for NASA will also be discussed.

Wiscombe, W.↗
NASA NTRS1993

Effect of the earth's ellipticity on the lunar tidal potential

The earth's orbital acceleration about the moon is influenced by its ellipticity. In this paper it shown that the ellipticity affects tidal gravity by contributing directly to the lunar tide-generating potential (in addition to effecting the elastic-gravitational response of the solid earth and oceans to this potential).

Dahlen, F. A.↗
NASA NTRS1998

El Nino, La Nina and VLBI Measured LOD

VLBI is one of the most important techniques for measuring Earth orientation parameters (EOP), and is unique in its ability to make high accuracy measurements of UT1, and its time derivative, which is related to changes in the length of day, conventionally called LOD. These measurements of EOP give constraints on geophysical models of the solid-Earth, atmosphere and oceans. Changes in EOP are due either to external torques from gravitational forces, or to the exchange of angular momentum between the Earth, atmosphere and oceans. The effect of the external torques is strictly harmonic and nature, and is therefore easy to remove. We analyze an LOD time series derived from VLBI measurements with the goal of comparing this to predictions from AAM, and various ENSO indices. Previous work by ourselves and other investigators demonstrated a high degree of coherence between atmospheric angular momentum (AAM) and EOP. We continue to see this. As the angular momentum of the atmosphere increases, the rate of rotation of the Earth decreases, and vice versa. The signature of the ENSO is particularly strong. At the peak of the 1982-83 El Nino increased LOD by almost 1 ms. This was subsequently followed by a reduction in LOD of 0.75 ms. At its peak, in February of 1998, the 1997-98 El Nino increased LOD by 0.8 msec. As predicted at the 1998 Spring AGU, this has been followed by an abrupt decrease in LOD which is currently -0.4 ms. At this time (August, 1998) the current ENSO continues to develop in new and unexpected ways. We plan to update our analysis with all data available prior to the Fall AGU.

Clark, Thomas A.↗
NASA NTRS1993

The oceanic contribution to the Earth's seasonal angular momentum budget

Seasonal variations in the speed of the Earth's rotation manifest themselves as fluctuations in the length of the day (LOD) with an amplitude of about 1000 microseconds. We know from previous work that at least 95% of these variations can be accounted for in terms of angular momentum exchanged between the atmosphere and the solid Earth. Here we examine the respective contributions of the Antarctic Circumpolar Current (ACC) and the global oceans to the Earth's seasonal angular momentum budget, using in situ data from the Drake Passage and results from both the oceanic regional model (Fine Resolution Antarctic Model -- FRAM) of Webb et al. (1991) and the global ocanic model of Maier-Reimer et al. (1993) as analyzed by Brosche et al. (1990). The estimated annual contribution of the ACC (2-4 microsec) is much smaller than the total variation in the oceanic models or the existing LOD-AAM residual (both approximately 15-20 microsec). The estimated semi-annual ACC contribution (3-8 microsec) is offset by counter-current further north in both oceanic models, which exhibit larger semi-annual variations in planetary angular momentum. Further refinements in the Earth's seasonal angular momentum budget, therefore, will require the full (planetary plus relative) contribution of the global oceans in addition to that of the ACC.

Dickey, J. O.↗
NASA NTRS1982

Determination of intercontinental baselines and Earth orientation using VLBI

A series of experiments was conducted during the last decade to explore the capability of very long baseline interferometry (VLBI) to measure the crustal and rotational motions of the Earth with accuracies at the centimeter level. The observing stations are those of NASA's Deep Space Network in California, Spain and Australia. A multiparameter fit to the observed values of delay and delay rate yields radio source positions, polar motion, universal time, the precession constant, baseline vectors, and solid Earth tides. Source positions are obtained with formal errors of the order of 0''.01. UT1-UTC and polar motion are determined at 49 epochs, with formal error estimates for the more recent data of 0.5 msec for UT1-UTC and 2 to 6 mas for polar motion. Intercontinental baseline lengths are determined with formal errors of 5 to 10 cm. The Love numbers and Earth tide phase lag agree with the commonly accepted values.

Sovers, O. J.↗
NASA NTRS1974

Polar motion and earth tides from Beacon Explorer C

Seventeen months of range data from a Goddard Space Flight Center laser tracking station are analyzed to determine the tidal perturbations in the orbit of the Beacon Explorer-C satellite and the variation in the tracking station latitude. The tidal perturbations are found to have a value 15% smaller than that derived from seismic studies, and the discrepancy is attributed to the combined effects of the solid earth and the oceans. The latitudinal variation is calculated with a standard deviation of 1.38 m to the smoothed BIH values and is shown to be due to the Chandler and annual motions of the pole.

Kolenkiewicz, R.↗
NASA NTRS1988

Earth rotation and core topography

The NASA Geodynamics program has as one of its missions highly accurate monitoring of polar motion, including changes in length of day (LOD). These observations place fundamental constraints on processes occurring in the atmosphere, in the mantle, and in the core of the planet. Short-timescale (t less than or approx 1 yr) variations in LOD are mainly the result of interaction between the atmosphere and the solid earth, while variations in LOD on decade timescales result from the exchange of angular momentum between the mantle and the fluid core. One mechanism for this exchange of angular momentum is through topographic coupling between pressure variations associated with flow in the core interacting with topography at the core-mantel boundary (CMB). Work done under another NASA grant addressing the origin of long-wavelength geoid anomalies as well as evidence from seismology, resulted in several models of CMB topography. The purpose of work supported by NAG5-819 was to study further the problem of CMB topography, using geodesy, fluid mechanics, geomagnetics, and seismology. This is a final report.

Hager, Bradford H.↗
NASA NTRS1999

Understanding our Changing Planet: NASA's Earth Science Enterprise

NASA has been studying the Earth and its changing environment by observing the atmosphere, oceans, land, ice, and snow and their influence on climate and weather since the agency's creation. This study has lead to a new approach to understanding the interaction of the Earth's systems, Earth System Science. The Earth Science Enterprise, NASA's comprehensive program for Earth System Science, uses satellites and other tools to intensively study the Earth. The Earth Science Enterprise has three main components: (1) a series of Earth-observing satellites, (2) an advanced data system and (3) teams of scientist who study the data. Key areas of study include: (1) clouds, (2) water and energy cycles, (3) oceans, (4) chemistry of the atmosphere, (5) land surface, water and ecosystems processes; (6) glaciers and polar ice sheets, and (7) the solid earth.

Forehand, Lon↗
NASA NTRS1999

Refinement of Models for VLBI Analysis

Continual refinement of models and estimation methods is an integral part of improving VLBI measurements of Earth orientation and position along with advances in instrumentation and observing strategy. The modeling of the troposphere continues to be challenging with recent improvements in treating the mean gradient and gradient variations affecting the terrestrial reference frame scale and celestial declinations near the current limits of accuracy. Revised models of nutation and solid Earth tides are implemented in CALC 9.0 to conform to the latest IERS Conventions along with other changes to facilitate use by VLBI correlators. Using data since 1995 the celestial reference frame has been extended and improved consistent with the definition and 0.25 mas accuracy limit of the ICRF. The current definition of the VLBI terrestrial reference frame places a floor on the accuracy of station velocities at the 0.4 mm/yr level. The establishment of the IVS (International VLBI Service for Geodesy and Astrometry) in the past year will provide a forum for further improvements of VLBI data analysis.

Ma, C.↗
NASA NTRS1993

Effects of polar ice on the earth's rotation and gravitational potential

The contributions of the Antarctic and the Greenland ice sheets to the earth's gravity, displacement, and rotation are estimated using gridded values of the net surface accumulation rates in the ice sheets of these two regions. It is found that the contributions to the low-order zonal harmonic coefficients of the earth's gravitational potential from Antarctica are between 2 and 10 times larger than the uncertainties of the zonal harmonics derived from satellite solutions; for Greenland, the coefficients are within an order of magnitude of the uncertainties of the satellite solutions. Polar contributions to the displacement of the center of mass of the solid earth, as seen in the frame of reference of satellites tracked from the earth surface, range from less than 1 mm to 1.5 cm over a 60-yr period.

Trupin, Andrew S.↗
NASA NTRS1973

The space shuttle payload planning working groups. Volume 8: Earth and ocean physics

The findings and recommendations of the Earth and Ocean Physics working group of the space shuttle payload planning activity are presented. The requirements for the space shuttle mission are defined as: (1) precision measurement for earth and ocean physics experiments, (2) development and demonstration of new and improved sensors and analytical techniques, (3) acquisition of surface truth data for evaluation of new measurement techniques, (4) conduct of critical experiments to validate geophysical phenomena and instrumental results, and (5) development and validation of analytical/experimental models for global ocean dynamics and solid earth dynamics/earthquake prediction. Tables of data are presented to show the flight schedule estimated costs, and the mission model.

Source record↗
NASA NTRS1994

Scientific analysis of satellite ranging data

A network of satellite laser ranging (SLR) tracking systems with continuously improving accuracies is challenging the modelling capabilities of analysts worldwide. Various data analysis techniques have yielded many advances in the development of orbit, instrument and Earth models. The direct measurement of the distance to the satellite provided by the laser ranges has given us a simple metric which links the results obtained by diverse approaches. Different groups have used SLR data, often in combination with observations from other space geodetic techniques, to improve models of the static geopotential, the solid Earth, ocean tides, and atmospheric drag models for low Earth satellites. Radiation pressure models and other non-conservative forces for satellite orbits above the atmosphere have been developed to exploit the full accuracy of the latest SLR instruments. SLR is the baseline tracking system for the altimeter missions TOPEX/Poseidon, and ERS-1 and will play an important role in providing the reference frame for locating the geocentric position of the ocean surface, in providing an unchanging range standard for altimeter calibration, and for improving the geoid models to separate gravitational from ocean circulation signals seen in the sea surface. However, even with the many improvements in the models used to support the orbital analysis of laser observations, there remain systematic effects which limit the full exploitation of SLR accuracy today.

Smith, David E.↗
NASA NTRS2016

NASA's Earth Science Flight Program Meets the Challenges of Today and Tomorrow

NASA's Earth science flight program is a dynamic undertaking that consists of a large fleet of operating satellites, an array of satellite and instrument projects in various stages of development, a robust airborne science program, and a massive data archiving and distribution system. Each element of the flight program is complex and present unique challenges. NASA builds upon its successes and learns from its setbacks to manage this evolving portfolio to meet NASA's Earth science objectives. NASA fleet of 16 operating missions provide a wide range of scientific measurements made from dedicated Earth science satellites and from instruments mounted to the International Space Station. For operational missions, the program must address issues such as an aging satellites operating well beyond their prime mission, constellation flying, and collision avoidance with other spacecraft and orbital debris. Projects in development are divided into two broad categories: systematic missions and pathfinders. The Earth Systematic Missions (ESM) include a broad range of multi-disciplinary Earth-observing research satellite missions aimed at understanding the Earth system and its response to natural and human-induced forces and changes. Understanding these forces will help determine how to predict future changes, and how to mitigate or adapt to these changes. The Earth System Science Pathfinder (ESSP) program provides frequent, regular, competitively selected Earth science research opportunities that accommodate new and emerging scientific priorities and measurement capabilities. This results in a series of relatively low-cost, small-sized investigations and missions. Principal investigators whose scientific objectives support a variety of studies lead these missions, including studies of the atmosphere, oceans, land surface, polar ice regions, or solid Earth. This portfolio of missions and investigations provides opportunity for investment in innovative Earth science that enhances NASA's capability for better understanding the current state of the Earth system. ESM and ESSP projects often involve partnerships with other US agencies and/or international organizations. This adds to the complexity of mission development, but allows for a greater scientific return on NASA's investments. The Earth Science Airborne Science Program provides manned and unmanned aircraft systems that further science and advance the use of satellite data. NASA uses these assets worldwide in campaigns to investigate extreme weather events, observe Earth system processes, obtain data for Earth science modeling activities, and calibrate instruments flying aboard Earth science spacecraft. The Airborne Science Program has six dedicated aircraft and access to many other platforms. The Earth Science Multi-Mission Operations program acquires, preserves, and distributes observational data from operating spacecraft to support Earth Science research focus areas. The Earth Observing System Data and Information System (EOSDIS), which has been in operations since 1994, primarily accomplishes this. EOSDIS acquires, processes, archives, and distributes Earth Science data and information products. The archiving of NASA Earth Science information happens at eight Distributed Active Archive Centers (DAACs) and four disciplinary data centers located across the United States. The DAACs specialize by topic area, and make their data available to researchers around the world. The DAACs currently house over 9 petabytes of data, growing at a rate of 6.4 terabytes per day. NASA's current Earth Science portfolio is responsive to the National Research Council (NRC) 2007 Earth Science Decadal Survey and well as the 2010 NASA Response to President Obama's Climate Plan. As the program evolves into the future it will leverage the lessons learned from the current missions in operations and development, and plan for adjustments to future objectives in response to the anticipated 2017 NRC Decadal Survey.

Flight Program↗
NASA NTRS2002

The Torque of the Planet: NASA Researcher Uses NCCS Computers to Probe Atmosphere-Land-Ocean Coupling

The study of Earth science is like a giant puzzle, says Braulio Sanchez. "The more you know about the individual pieces, the easier it is to fit them together." A researcher with Goddard's Space Geodesy Branch, Sanchez has been using NCCS supercomputer and mass storage resources to show how the angular momenta of the atmosphere, the oceans, and the solid Earth are dynamically coupled. Sanchez has calculated the magnitude of atmospheric torque on the planet and has determined some of the possible effects that torque has on Earth's rotation.

Source record↗
NASA NTRS1990

Evaluation of orbit determination using dual-TDRS tracking

This paper describes the results of a study to evaluate the orbit determinatioin of Tracking and Data Relay Satellite System (TDRSS) user spacecraft within the dual-Tracking and Data Relay Satellite (TDRS) environment. Dense TDRSS tracking of the Earth Radiation Budget Satellite (ERBS) was acquired for the period August 16 through 22, 1989. This tracking information was processed to evaluate the orbit determination consistency achieved using the Goddard Trajectory Determination System batch least-squares estimator. The effects of the use of the second operational relay spacecraft, of refinements in orbit determination models (geopotentials, polar motion, solid earth tidal gravitational perturbations, ionospheric refraction corrections), and of methods for providing relay spacecraft spacecraft position information were also studied.

Oza, D. H.↗
NASA NTRS2001

Atmospheric Excitation of Planetary Normal Modes

The objectives of this study were to: (1) understand the phenomenon of continuous free oscillations of the Earth and (2) examine the idea of using this phenomenon for planetary seismology. We first describe the results on (1) and present our evaluations of the idea (2) in the final section. In 1997, after almost forty years since the initial attempt by Benioff et al, continuous free oscillations of the Earth were discovered. Spheroidal fundamental modes between 2 and 7 millihertz are excited continuously with acceleration amplitudes of about 0.3-0.5 nanogals. The signal is now commonly found in virtually all data recorded by STS-1 type broadband seismometers at quiet sites. Seasonal variation in amplitude and the existence of two coupled modes between the atmosphere and the solid Earth support that these oscillations are excited by the atmosphere. Stochastic excitation due to atmospheric turbulence is a favored mechanism, providing a good match between theory and data. The atmosphere has ample energy to support this theory because excitation of these modes require only 500-10000 W whereas the atmosphere contains about 117 W of kinetic energy. An application of this phenomenon includes planetary seismology, because other planets may be oscillating due to atmospheric excitation. The interior structure of planets could be learned by determining the eigenfrequencies in the continuous free oscillations. It is especially attractive to pursue this idea for tectonically quiet planets, since quakes may be too infrequent to be recorded by seismic instruments.

Tanimoto, Toshiro↗
NASA NTRS2012

The Algorithm Theoretical Basis Document for Tidal Corrections

This Algorithm Theoretical Basis Document deals with the tidal corrections that need to be applied to range measurements made by the Geoscience Laser Altimeter System (GLAS). These corrections result from the action of ocean tides and Earth tides which lead to deviations from an equilibrium surface. Since the effect of tides is dependent of the time of measurement, it is necessary to remove the instantaneous tide components when processing altimeter data, so that all measurements are made to the equilibrium surface. The three main tide components to consider are the ocean tide, the solid-earth tide and the ocean loading tide. There are also long period ocean tides and the pole tide. The approximate magnitudes of these components are illustrated in Table 1, together with estimates of their uncertainties (i.e. the residual error after correction). All of these components are important for GLAS measurements over the ice sheets since centimeter-level accuracy for surface elevation change detection is required. The effect of each tidal component is to be removed by approximating their magnitude using tidal prediction models. Conversely, assimilation of GLAS measurements into tidal models will help to improve them, especially at high latitudes.

Fricker, Helen A.↗
NASA NTRS1995

Universities Earth System Scientists Program

This document constitutes the final technical report for the National Aeronautics and Space Administration (NASA) Grant NAGW-3172. This grant was instituted to provide for the conduct of research under the Universities Space Research Association's (USRA's) Universities Earth System Scientist Program (UESSP) for the Office of Mission to Planet Earth (OMTPE) at NASA Headquarters. USRA was tasked with the following requirements in support of the Universities Earth System Scientists Programs: (1) Bring to OMTPE fundamental scientific and technical expertise not currently resident at NASA Headquarters covering the broad spectrum of Earth science disciplines; (2) Conduct basic research in order to help establish the state of the science and technological readiness, related to NASA issues and requirements, for the following, near-term, scientific uncertainties, and data/information needs in the areas of global climate change, clouds and radiative balance, sources and sinks of greenhouse gases and the processes that control them, solid earth, oceans, polar ice sheets, land-surface hydrology, ecological dynamics, biological diversity, and sustainable development; (3) Evaluate the scientific state-of-the-field in key selected areas and to assist in the definition of new research thrusts for missions, including those that would incorporate the long-term strategy of the U.S. Global Change Research Program (USGCRP). This will, in part, be accomplished by study and evaluation of the basic science needs of the community as they are used to drive the development and maintenance of a global-scale observing system, the focused research studies, and the implementation of an integrated program of modeling, prediction, and assessment; and (4) Produce specific recommendations and alternative strategies for OMTPE that can serve as a basis for interagency and national and international policy on issues related to Earth sciences.

Estes, John E.↗