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At least 55 records · Page 3

Using Federated Learning to Overcome Data Gravity in Space

Humans intend to take longer missions to outer space. Understanding the impact that space has on human health is paramount to the success of these missions. Controlled experiments with model organisms are run to infer the impact of space conditions on human health, but the data these experiments generate are too large to transfer to Earth for building models. The same is true for space-relevant data generated on Earth. Ideally, these datasets should be combined to improve statistical power and model accuracy without having to transfer data. Federated learning is such a method which trains an algorithm across decentralized computing systems, each of which has their own local copy of training and testing data. In this research, made possible by NASA@Work, the AI for Life in Space group at NASA demonstrates the use of federated learning to train an ensemble of causality inference models on a combination of data residing on the International Space Station (ISS) and in the cloud. Our work leverages CRISP, a causal inference platform developed during the 2020 Frontier Development Lab’s “Astronaut Health Challenge.” We also leverage the OpenFL federated learning library which was collaboratively developed at Intel and UPenn. We used publicly available data from the NASA Ames Life Sciences Data Archive to identify features in ionizing radiation experiments as causal of changes in cardiac blood velocity. This research demonstrates, for the first time, the possibility of running machine learning algorithms on datasets separated by astronomical distances. In this experiment, all the data were generated in terra, half of which were transferred to the ISS and analyzed on the Spaceborne Computer. In the future, our research will leverage federated learning on data generated in situ on the ISS with data generated terrestrially to predict the impact of spaceflight on mammalian female reproductive capacity.

James Casaletto↗

Structure of the Jovian envelope from Pioneer 10 gravity data

Measurement of Jupiter's zonal harmonics J2 and J4 by the celestial mechanics experiment on Pioneer 10 may be used to obtain a constraint on the structure of the outer envelope of Jupiter, using an inversion technique which is insensitive to the structure of the deep interior for a plausible class of planetary models. The derived structure is consistent with an adiabatic, solar-composition envelope with a starting temperature of 250 plus or minus 40 K at 1 bar pressure.

Anderson, J. D.↗

Interior structure of Saturn inferred from Pioneer 11 gravity data

The structure of Saturn is studied via a fourth-order theory for rotating planets and equations of state for the envelope which depend parametrically on the helium abundance, on the starting temperature for the adiabat, and on adopted forms of the pressure-density curve in the region of transition from molecular to metallic hydrogen. Models are constrained by the values of J2 and J4 obtained from the Pioneer-Saturn celestial mechanics experiment. Equations of state are tested by computing Jupiter models, which can now be subjected to a more stringent comparison with observed zonal harmonics. It is found that Saturn has a low-density hydrogen-helium envelope with no evidence for enhancement of H2O, CH4, or other abundant compounds. Such compounds are presumably located near the core. The helium mass abundance for Saturn's envelope appears to be in the range of approximately 0.12 to 0.19, but this result is very model-dependent. The helium abundance in the envelope of Jupiter is apparently very similar to that of Saturn.

Hubbard, W. B.↗

A comparison of satellite Doppler and gravimetric geoid undulations considering terrain-corrected gravity data

Geoid undulations derived from Doppler satellite positioning are compared with corresponding values derived from terrestrial and satellite information using three different procedures. Doppler undulations are compared with uncorrected gravimetric undulations, and systematic differences of 1.6 m and 0.4 m are found for western and eastern U.S. stations, respectively. The systematic difference of 1.6 m was reduced to 0.1 m when terrain-related corrections were applied. Undulations computed from a spherical harmonic expansion to degree 180 yielded standard deviations only slightly poorer than the combined data. A more systematic difference in the western than in the eastern stations remained.

Rapp, R. H.↗

Estimating Geophysical Parameters From Gravity Data

ORBSIM program developed for accurate extraction of parameters of geophysical models from Doppler-radio-tracking data acquired from orbiting planetary spacecraft. Model of proposed planetary structure used in numerical integration along simulated trajectories of spacecraft around primary body. Written in FORTRAN 77.

Sjogren, William L.↗

A study of the earth's free core nutation using international deployment of accelerometers gravity data

In this study we consider the influence of the earth's free core nutation (FCN) on diurnal tidal admittance estimates for 11 stations of the globally distributed International Deployment of Accelerometers network. The FCN causes a resonant enhancement of the diurnal admittances which can be used to estimate some properties of the FCN. Estimations of the parameters describing the FCN (period, Q, and resonance strength) are made using data from individual stations and many stations simultaneously. These yield a result for the period of 423-452 sidereal days, which is shorter than theory predicts but is in agreement with many previous studies and suggests that the dynamical ellipticity of the core may be greater than its hydrostatic value.

Cummins, Phil R.↗

Venus gravity anomalies and their correlations with topography

This report provides a summary of the high-resolution gravity data obtained from the Pioneer Venus Orbiter radio tracking data. Gravity maps, covering a 70 deg latitude band through 360 deg of longitude, are displayed as line-of-sight and vertical gravity. Topography converted to gravity and Bouguer gravity maps are also shown in both systems. Topography to gravity ratios are made over several regions of the planet. There are markedly different ratios for the Aphrodite area as compared to the Beta and Atla areas.

Sjogren, W. L.↗

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

Gravity waves in satellite data from CRISTA and MLS are studied in depth this quarter. Results this quarter are somewhat limited due to the PI'S heavy involvement throughout this reporting period in on-site forecasting of mountain wave-induced turbulence for the NASA's ER-2 research aircraft at Kiruna, Sweden during the SAGE Ill Ozone Loss and Validation Experiment (SOLVE). Results reported concentrate on further mesoscale modeling studies of mountain waves over the southern Andes, evident in CRISTA and MLS data. Two-dimensional mesoscale model simulations are extended through generalization of model equations to include both rotation and a first-order turbulence closure scheme. Results of three experiments are analyzed in depth and submitted for publication. We also commence simulations with a three-dimensional mesoscale model (MM5) and present preliminary results for the CRISTA 1 period near southern South America. Combination of ground-based temperature data at 87 km from two sites with global HRDl data was continued this quarter, showing stationary planetary wave structures. This work was also submitted for publication.

Eckermann, Stephen D.↗

Least squares collocation applied to local gravimetric solutions from satellite gravity gradiometry data

An autonomous spaceborne gravity gradiometer mission is being considered as a post Geopotential Research Mission project. The introduction of satellite diometry data to geodesy is expected to improve solid earth gravity models. The possibility of utilizing gradiometer data for the determination of pertinent gravimetric quantities on a local basis is explored. The analytical technique of least squares collocation is investigated for its usefulness in local solutions of this type. It is assumed, in the error analysis, that the vertical gravity gradient component of the gradient tensor is used as the raw data signal from which the corresponding reference gradients are removed to create the centered observations required in the collocation solution. The reference gradients are computed from a high degree and order geopotential model. The solution can be made in terms of mean or point gravity anomalies, height anomalies, or other useful gravimetric quantities depending on the choice of covariance types. Selected for this study were 30 x 30 foot mean gravity and height anomalies. Existing software and new software are utilized to implement the collocation technique. It was determined that satellite gradiometry data at an altitude of 200 km can be used successfully for the determination of 30 x 30 foot mean gravity anomalies to an accuracy of 9.2 mgal from this algorithm. It is shown that the resulting accuracy estimates are sensitive to gravity model coefficient uncertainties, data reduction assumptions and satellite mission parameters.

Robbins, J. W.↗

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

Non-NASA Center↗

Modelling and Estimation of Dynamic Ocean Topography Within Global Geopotential Solutions

In this poster, we will present a report on the ongoing investigation "Improved Gravitational and Dynamic Height Models Through the use of Oceanographic Data." we have used a two year mean (1993-1994) of the Dynamic ocean Topography (DOT) field implied by the Semtner and Chervin POCM_4B model, and developed normal equations in surface spherical harmonics to degree and order 30. These normal equations, were combined with normal equations derived from TOPEX and ERS-1 altimeter data over the same time period. Combination solutions (based on satellite tracking data, altimeter data, surface gravity data and OCM data) were were developed Test solutions were obtained estimating the DOT field to 2Ox2O and 3ox3O. These solutions were tested with independent DOT values computed over 38 WOCE hydrographic sections, which contained a total of 3072 stations and represented 216000 km of travelled lines. The weighted standard deviation of the differences between the DOT obtained from the hydrographic data and and the field estimated from the joint combination solutions was computed for each of the test models, the weighted standard deviation for the baseline combination solution excluding the POCM4_B data was 9.7 cm for a DOT solution to 30x30, where introducing the POCM4_B data into the combination model reduced the standard deviation to 9.2 cm, indicating the the introduction of oceanographic information benefits the solution for the dynamic ocean topography. We will discuss the weighting schemes applied and the method of solution. Another aspect of our investigation involves testing alternate parametric representations of the dynamic height field. We looked at the alternative representations in terms of the Proudman functions (PF), and compared these to the use of spherical harmonics (SH) to represent the dynamic ocean topography, using once again the 1993 and 1994 output of the POCM4_B OCM as the reference model. A significant advantage of PF's over SH's is that the former require no "fill-in" values over areas where the DOT is undefined. We show that the PF and SH results using equal number of parameters agree quite well in overall content. In addition, PFs appear better suited for representation of high frequency signals close to the signal boundary. The development of the PF solutions for the DOT will be described and the statistics of the comparisons will be presented.

Lemoine, Frank G.↗