Michael M. Watkins

Michael M. Watkins
California Institute of Technology | CIT · Jet Propulsion Laboratory

PhD

About

164
Publications
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13,241
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Publications

Publications (164)
Article
The Advanced Pointing Imaging Camera (APIC) is designed to obtain high-resolution imaging data to measure a target’s geophysical and geodetic properties. The development of APIC originates from NASA’s Homesteader program of technology development for candidate New Frontiers missions. The unique science enabled by APIC derives from its ability to si...
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We examined the first‐ever laser ranging interferometer (LRI) measurements of inter‐satellite tracking acquired by Gravity Recovery and Climate Experiment (GRACE) Follow‐On satellites. Through direct along‐orbit analysis of instantaneous inter‐satellite measurements, we demonstrate the higher sensitivity of LRI (than K‐band microwave ranging [KBR])...
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Plain Language Summary Mass change is a fundamental climate system indicator and provides an integrated global view of how Earth's water cycle and energy balance are evolving. The Gravity Recovery and Climate Experiment (GRACE) mission monitored mass changes every month from 2002 through 2017. Since June 2018, GRACE Follow‐On (GRACE‐FO) continues t...
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Time-resolved satellite gravimetry has revolutionized understanding of mass transport in the Earth system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has enabled monitoring of the terrestrial water cycle, ice sheet and glacier mass balance, sea level change and ocean bottom pressure variations, as well as understanding response...
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Estimating the future evolution of the Antarctic Ice Sheet (AIS) is critical for improving future sea level rise (SLR) projections. Numerical ice sheet models are invaluable tools for bounding Antarctic vulnerability; yet, few continental-scale projections of century-scale AIS SLR contribution exist, and those that do vary by up to an order of magn...
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Drought struck California during 7 of the 9 years from 2007 through 2015, reducing the state's available water resources. Pumping of Central Valley groundwater has produced spectacular land subsidence. Uplift of the adjacent Sierra Nevada mountains has been proposed to be either tectonic uplift or solid Earth's elastic response to unloading of Cent...
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The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 ± 0.2) × 10[superscript 6] km[superscript 3] of crustal mate...
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Recent advances in processing data from the Gravity Recovery and Climate Experiment (GRACE) have led to a new generation of gravity solutions constrained within a Bayesian framework to remove correlated errors rather than relying on empirical filters. The JPL RL05M mascon solution is one such solution, solving for mass variations using spherical ca...
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The extended length of the GRACE data time series (now 13.5 years) provides the unique opportunity to estimate global mass variations due to ocean tides at large (∼300 km) spatial scales. State-of-the-art global tide models rely heavily on satellite altimetry data, which are sparse for latitudes higher than 66°. Thus, the performance of the models...
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Quantifying the Greenland Ice Sheet’s future contribution to sea level rise is a challenging task that requires accurate estimates of ice flow sensitivity to climate change. Forward models of ice flow dynamics are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is so challeng...
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Concerns about North Atlantic Meridional Overturning Circulation (NAMOC) changes imply the need for a continuous, large-scale observation capability to detect changes on interannual to decadal time scales. Here we present the first measurements of Lower North Atlantic Deep Water (LNADW) transport changes using only time-variable gravity observation...
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Due to its eccentric orbit about Jupiter, Europa experiences periodic tidal deformation, which causes changes in its gravitational field and induces both radial and transverse displacements of the surface. The amplitude and phase of these tidal changes are diagnostic of internal structure, and can be measured with sufficient radiometric and optical...
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A solution for a very-high-resolution GRAIL gravity field determines lunar Love number and tidal dissipation Q, but does not detect the inner core.
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We discuss several classes of improvements to gravity solutions from the Gravity Recovery and Climate Experiment (GRACE) mission. These include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution JPL RL05, and an alternate JPL RL05M mascon solution benefitting from...
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The Gravity Recovery and Interior Laboratory (GRAIL) mission has sampled lunar gravity with unprecedented accuracy and resolution. The lunar GM, the product of the gravitational constant G and the mass M, is very well determined. However, uncertainties in the mass and mean density, 3345.56 ± 0.40 kg/m3, are limited by the accuracy of G. Values of t...
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resolution and accuracy of the lunar spherical harmonic gravity field have been dramatically improved as a result of the Gravity Recovery and Interior Laboratory (GRAIL) mission. From the Primary Mission, previous harmonic gravity fields resulted in an average n = 420 surface resolution and a Bouguer spectrum to n = 330. The GRAIL Extended Mission...
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A GRAIL S21 value implies a misalignment of principal axes derived by Lunar Laser Ranging. A fluid outer core shaped by internal gravity can affect axes.
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A high-resolution view of the Orientale Basin and surroundings from the Gravity Recovery and Interior Laboratory (GRAIL).
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The gravity field of the Earth, caused by the distribution of masses inside and on the surface of the Earth, changes in time due to the redistribution of mass. Such mass fluxes can be due both to natural processes (such as the seasonal water cycle, ocean dynamics, or atmospheric variations), as well as due to human actions, such as the systematic w...
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Using satellite observations from the joint NASA/DLR Gravity Recovery And Climate Experiment (GRACE) mission to monitor, simulate, and understand ongoing changes in the Earth's hydrosphere and water cycle was the topic of a recent workshop sponsored by the NASA Jet Propulsion Laboratory's Center for Climate Sciences and GRACE team, with support fro...
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The Gravity Recovery and Interior Laboratory (GRAIL) is a spacecraft-to-spacecraft tracking mission that was developed to map the structure of the lunar interior by producing a detailed map of the gravity field. The resulting model of the interior will be used to address outstanding questions regarding the Moon’s thermal evolution, and will be appl...
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The lunar gravity field and topography provide a way to probe the interior structure of the Moon. Prior to the Gravity Recovery and Interior Laboratory (GRAIL) mission, knowledge of the lunar gravity was limited mostly to the nearside of the Moon, since the farside was not directly observable from missions such as Lunar Prospector. The farside grav...
Conference Paper
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The Gravity Recovery and Interior Laboratory (GRAIL) mission has completed its primary three-month tour that resulted in a gravitational field of 660 degree-and-order or equivalent surface resolution of 8 km. The primary measurement for the gravity field is the inter-spacecraft K-Band Range Rate (KBRR) measurement derived from dual spacecraft one-w...
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The twin satellites of the US/German Gravity Recovery And Climate Experiment (GRACE) mission have been in orbit for nearly 11 years. In this time, the GRACE measurements of time-variable and long-term mean gravity field have provided unprecedented insights into the geophysical processes that influence the changes in global mass distribution, at bot...
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GRACE Follow-On, a joint US/German satellite mission to extend the critical global mass flux data records from the GRACE mission, continues to mature and advance on both sides of the Atlantic. In early January 2012, GRACE-FO was advanced by NASA to Phase A following the successful Mission Concept Review in late October, 2011. The transition into Ph...
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The GRAIL extended mission has provided gravity models that are being used to map the upper crust of the Moon in unprecedented detail.
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Analyses of GRAIL data indicate a relatively thin lunar crust, leading to the conclusion that the Moon is not enriched in refractory elements compared to Earth.
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GRAIL gravity data show that the crust of the Moon has been highly fractured by billions of years of impact cratering.
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GRAIL analyses provide lunar gravity field, Love number, and moment of inertia with improved uncertainties.
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The Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon utilized an integrated scientific measurement system comprised of flight, ground, mission, and data system elements in order to meet the end-to-end performance required to achieve its scientific objectives. Modeling and simulation efforts were carried out early in the mission...
Conference Paper
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This paper discusses an initial gravity science results from the the Gravity Recovery And Interior Laboratory (GRAIL) mission. The inter-satellite and ground-based Doppler measurements during the three-month prime science phase were processed and a 420th degree and order spherical harmonics lunar gravity field, called GL0420A, was computed. The roo...
Conference Paper
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The Gravity Recovery And Interior Laboratory (GRAIL) mission has constructed a lunar gravity field with unprecedented uniform accuracy on the farside and nearside of the Moon. GRAIL lunar gravity field determination begins with preprocessing of the gravity science measurements by applying corrections for time tag error, general relativity, measurem...
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High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kg m(-3), substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of...
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Spacecraft-to-spacecraft tracking observations from the Gravity Recovery and Interior Laboratory (GRAIL) have been used to construct a gravitational field of the Moon to spherical harmonic degree and order 420. The GRAIL field reveals features not previously resolved, including tectonic structures, volcanic landforms, basin rings, crater central pe...
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The selection of Gale crater as the Mars Science Laboratory landing site took over five years, involved broad participation of the science community via five open workshops, and narrowed an initial >50 sites (25 by 20 km) to four finalists (Eberswalde, Gale, Holden and Mawrth) based on science and safety. Engineering constraints important to the se...
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Substantial advances in our geophysical understanding of the lunar crust are now possible due to recent and ongoing acquisition of high resolution topography and gravity data sets from the LOLA and GRAIL missions.
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We have developed a laser stabilization system capable of measuring nm-level distance variations between satellites separated on orbit by 250 km. We describe construction of the reference cavity, show performance results and environmental tests.
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The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) were launched on March 17, 2002 and have operated continuously for just over 10 years. The mission objectives are to sense the spatial and temporal variations of the Earth's mass distribution through its effects on the gravity field at the GRACE satellite altitude. The prima...
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This paper presents the results of simulations of a high-resolution and temporal lunar gravity field expected from the Gravity Recovery and Interior Laboratory mission. An overall mission capability is presented based on detailed error analysis of spacecraft dynamics and kinematics models, realistic ground-based and interspacecraft tracking measure...
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The Gravity Recovery And Interior Laboratory (GRAIL) mission is on track to initiate its science phase on March 8, 2012. GRAIL will determine the structure of the lunar interior, and advance understanding of lunar thermal evolution.
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The Gravity Recovery and Interior Laboratory (GRAIL) mission, a component of NASA's Discovery Program, launched successfully from Cape Canaveral Air Force Station on September 10, 2011. The dual spacecraft traversed independent, low-energy trajectories to the Moon via the EL-1 Lagrange point and inserted into elliptical, 11.5-hour polar orbits arou...
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Shortly after the Feb. 27, 2010 Maule, Chile subduction zone mega-thrust earthquake of energy scale magnitude 8.8, we began to use a data stacking method to examine the effects of the change in gravity field on the GRACE A-B intersatellite range accelerations. The initial discovery of the robust influence of the in co-seismic + afterslip deformatio...
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The Gravity Recovery and Climate Experiment (GRACE) has demonstrated that satellite gravimetry can be a valuable tool for regional to global water cycle observation. Studies of ice sheet and glacier mass losses, ocean bottom pressure and circulation, and variability of water stored on and in the land including groundwater all have benefited from GR...
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An overall Gravity Recovery And Interior Laboratory (GRAIL) mission capability is presented based on a sensitivity analysis considering detailed spacecraft dynamics and kinematics models with realistic measurement uncertainties. Also shown is the effect of various perturbing forces, measurement models, and data arc lengths on overall estimation per...
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The measurements of mass transport between the earth's atmosphere, oceans and solid earth is a critical component of global climate change processes and is an important component of the signals associated with global sea level and polar ice mass change, depletion and recharge of continental aquifers, and change in the deep ocean currents. This mass...
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Full-text available
The process of identifying the landing site for NASA’s 2011 Mars Science Laboratory (MSL) began in 2005 by defining science objectives, related to evaluating the potential habitability of a location on Mars, and engineering parameters, such as elevation, latitude, winds, and rock abundance, to determine acceptable surface and atmospheric characteri...
Conference Paper
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Preparatory to flight, the GRAIL Science team has conducted extensive modeling and simulation, exercising its intended process for recovery of both a high-resolution lunar gravity field and parameters describing the time-varying signature of the hypothesized solid inner core of the Moon. In this analysis, we have modeled all known perturbing non-gr...
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The Mars Science Laboratory will land at Mawrth Vallis, Holden, Gale, or Eberswalde Craters (locations important to the potential habitability of Mars) after 4 community workshops and the consideration of more than 50 candidates over the past 4 years.
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Knowledge of the interior and evolution of the Moon, and by extension, other terrestrial planetary bodies, will be greatly advanced by the Gravity Recovery And Interior Laboratory (GRAIL) mission, which is on track for launch in September 2011.
Conference Paper
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This paper presents the expected results of estimating a high-resolution lunar gravity field and time-varying tide and lunar core signatures using the measurements from the Gravity Recovery And Interior Laboratory (GRAIL) mission. An overall GRAIL mission capability is presented based on detailed error analysis of spacecraft dynamics and kinematics...
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Land glacier extent and volume at the northern and southern margins of the Drake Passage have been in a state of dramatic demise since the early 1990s. Here time-varying space gravity observations from the Gravity Recovery and Climate Experiment (GRACE) are combined with Global Positioning System (GPS) bedrock uplift data to simultaneously solve fo...
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Land glacier extent and volume in the northern Antarctic Peninsula (NAP) have been in a state of dramatic demise since the early 1990's. Using JPL global mascons, GRACE gravity trend observations are combined with Global Positioning System (GPS) bedrock uplift data in order to simultaneously solve for ice loss and for viscoelastic Earth glacial iso...
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NASA has included a GRACE Follow-On mission in its proposed budget for fiscal year 2011. As of the time of this abstract submission (September 2, 2010), although the FY11 NASA budget has not been approved by Congress, we continue to anticipate a new start for the mission in FY11. We also anticipate and welcome a continuation of the GRACE partnershi...
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We have used GPS carrier phase integer ambiguity resolution to investigate improvements in the orbit determination for the Jason-1 satellite altimeter mission. The technique has been implemented in the GIPSY orbit determination software developed by JPL. The radial accuracy of the Jason-1 orbits is already near 1 cm, and thus it is difficult to det...
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Accelerating ice mass losses are well-documented in the Southern Patagonian Icefield (SPI) as well as in the northern Antarctic Peninsula (NAP). New GRACE data that allow continuity with past mass change measurements therefore bear heavily on answering this question. GRACE is an especially potent method because these data do not require independent...
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Detailed scientific investigations of target materials and surface characteristics are focusing on four potential landing sites (Holden, Gale and Eberswalde craters and Mawrth Vallis) for the Mars Science Laboratory.
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At the time of this presentation, the joint NASA/DLR GRACE mission will have delivered new insights into mass flux in the Earth System for more than 8 years. The value of this extended dataset is particularly remarkable, given that the mission was designed for a 5-year lifetime. This presentation will summarize the current status of the GRACE missi...
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Full-text available
Because missions such as TOPEX/POSEIDON don't extend to high latitudes, Arctic ocean tidal solutions aren't constrained by altimetry data. The resulting errors in tidal models alias into monthly GRACE gravity field solutions at all latitudes. Fortunately, GRACE inter-satellite ranging data can be used to solve for these tides directly. Seven years...
Article
GRACE was launched in March 2002 and since then has produced an essentially continuous set of gravity data now approaching 8 years in length. This ever-lengthening data span has been key in allowing users of the data to begin to understand the important relationships between annual, interannual, and longer term variability in mass flux in the Earth...
Article
Using a new high-resolution global-mascon analysis of the accelerations recorded by K-band microwave interferometers between the satellite pair constituting the Gravity Recovery and Climate Experiment (GRACE) we determine a strong negative 6.25-yr trend in cryospheric mass as they pass over the Patagonia icefields (PIF) and Graham Land (GL) of the...
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This abstract describes the four landing sites under consideration and the selection process for the Mars Science Laboratory (MSL) after discussion of seven downselected sites at the third Landing Site Workshop and a subsequent project meeting.
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We continue to utilize our capability to perform comprehensive spherical harmonic and mascon solutions to compare and contrast the effects of the selected solution basis function and of the range of plausible analyst choices in terms of specific solution parameterization (spatial resolution, nuisance parameters, etc). We have been successful this y...
Article
The geophysical inverse problem using satellite observations, such as GRACE, to estimate gravity change and mass variations at the Earth's surface is a well-known ill-posed problem. Different methods using different basis function (representing the gravity field) for different purposes (global or regional inversion) have been employed to obtain a s...
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The GRACE RL04 gravity field data products from UTCSR, GFZ and JPL have been available to the user community for more than 18 months. In this time, we have reached a better understanding of the quality of these products, and its connection to the quality and attributes of the input data and background models used in earlier data processing. In this...
Article
The mass transport between the earth's atmosphere, oceans and solid earth is a critical component of global climate change processes and is an important component of the signals associated with global sea level and polar ice mass change, depletion and recharge of continental aquifers, and change in the deep ocean currents. This mass exchange has a...
Article
Arctic ocean tidal solutions are not constrained by altimetry data because missions such as TOPEX/POSEIDON do not extend to high latitudes. The resulting errors in tidal models alias into the monthly GRACE gravity field solutions at all latitudes. Fortunately, it is possible to use the GRACE inter-satellite ranging data to solve for these tides dir...
Article
Six landing sites remain under consideration for the Mars Science Laboratory after the Second Landing Site Workshop and a subsequent project meeting. The downselection process, definition of the sites, and subsequent activities are discussed.