Terrestrial Datasets Research Articles

A contribution to data combination in ill-posed downward continuation problems

The spaceborne gravity field missions CHAMP, GRACE and GOCE, to be realized in the coming years, will improve our knowledge of the Earth's gravity field in the short, medium and long wavelength parts. Nevertheless, it is necessary to supplement this gravity field information with available terrestrial data. While the combination of data of different origin is comparably well-understood in well-posed problems there are some open questions in combining satellite derived and terrestrial data sets in the case of improperly posed problems. In this investigation, the future satellite missions are shortly characterized. The downward continuation process and its regularization based on Tikhonov's regularization method is reviewed. The test strategies to detect the contributions of satellite derived and terrestrial gravity field information applied in this investigation are summarized. A detailed simulation based on a GRACE-type SST mission scenario and additional terrestrial data with the task to derive parameters of a gravity field representation by local base functions is performed. The investigation tries to tackle a clarification of various questions related to the data combination by numerical tests.

A model of the secular change of the geomagnetic field for Antarctica

An improved model of geomagnetic secular change for the Antarctic was developed using observatory annual mean values measured in Antarctica during the last 40 years. Spherical cap harmonic analysis (SCHA) with a power series time dependence was used to model spatial and temporal variations of main field differences at spatial wavelengths from 3000 to 13,000 km. The model was designed to facilitate merging satellite, airborne, marine and terrestrial magnetic data sets recorded at very different epochs in the Antarctic where significant annual geomagnetic changes have occurred. It improves the fit to observatory data by up to about 50% relative to the International Geomagnetic Reference Field.

Applications of Geographic Information Systems (GIS) to habitat assessment and marine resource management

Marine scientists often assess habitats to understand the distribution and relative abundance of marine resources. Due to the spatial nature of habitats and associated temporal changes, however, assimilating data using traditional analytical methods is often difficult. Geographic Information Systems (GIS) are proving to be effective tools to help address problems inherent in the analysis of spatial data, GIS can be used to effectively collate, archive, display, analyze, and model spatial and temporal data. Additionally, by combining dissimilar data types, such as socio-political boundaries, bottom types, and fish distributions, for example, resource managers can use GIS to make informed management decisions. In this way, GIS provides resource managers with a means to integrate scientific data with prevailing cultural values and traditions. We have developed a working GIS for the Monterey Bay National Marine Sanctuary that allows interpretation of many terrestrial and marine data sets, including inter-tidal monitoring data, permit locations, seabird strandings, fisheries catch data, habitat types, marine political boundaries, as well as land cover classification from satellite imagery, watersheds, streams, roads, and political boundaries. We have linked terrestrial and marine data to create a broad spatial and temporal database that will be used in a variety of ways such as evaluating natural processes, permitting and monitoring coastal development and assessing environmental impacts (e.g. oil spills).

A Reevaluation of Impact Melt Production

The production of melt and vapor is an important process in impact cratering events. Because significant melting and vaporization do not occur in impacts at velocities currently achievable in the laboratory, a detailed study of the production of melt and vapor in planetary impact events is carried out with hydrocode simulations.Sandia's two-dimensional axisymmetric hydrocode CSQ was used to estimate the amount of melt and vapor produced for widely varying initial conditions: 10 to 80 km/sec for impact velocity, 0.2 to 10 km for the projectile radius. Runs with different materials demonstrate the material dependency of the final result. These results should apply to any size projectile (for given impact velocity and material), since the results can be dynamically scaled so long as gravity is unimportant in affecting the early-time flow.In contrast with the assumptions of previous analytical models, a clear difference in shape, impact-size dependence, and depth of burial has been found between the melt regions and the isobaric core. In particular, the depth of the isobaric core is not a good representation of the depth of the melt regions, which form deeper in the target. While near-surface effects cause the computed melt region shapes to look like “squashed spheres” the spherical shape is still a good analytical analog.One of the goals of melt production studies is to find proper scaling laws to infer melt production for any impact event of interest. We tested the point source limit scaling law for melt volumes (μ = 0.55–0.6) proposed by M. D. Bjorkman and K. A. Holsapple (1987,Int. J. Impact Eng.5, 155–163). Our results indicate that the point source limit concept does not apply to melt and vapor production. Rather, melt and vapor production follows an energy scaling law (μ = 0.67), in good agreement with previous results of T. J. Ahrens and J. D. O'Keefe [1977, inImpact and Explosion Cratering(D. J. Roddy, R. O. Pepin, and R. B. Merrill, Eds.), pp. 639–656, Pergamon Press, Elmsford, NY].Finally we tested the accuracy of our melt production calculation against a terrestrial dataset compiled by R. A. F. Grieve and M. J. Cintala (1992,Meteorities27, 526–538). The hydrocode melt volumes are in good agreement with the estimated volumes of that set of terrestrial craters on crystalline basements. At present there is no good model for melt production from impact craters on sedimentary targets.

NEOs and Impacts: The Galactic Connection

The orbit of the solar system within the Galaxy is subject both to adiabatic tidal forces and to irregular buffeting caused by encounters with molecular clouds and spiral arms, while the long-period comet flux varies with the differential of these forces. Quasi-periodic episodes of Earth bombardment by Oort cloud comets are expected, with the half-period of the solar vertical oscillations being prominent. Various terrestrial datasets are examined and show evidence of a periodicity ~27±1 Myr at a confidence level \(\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\thicksim}$}}\to { > } \)99.5%, consistently with the expectations. Bombardment episodes thus appear to exert a controlling influence on global terrestrial processes. Conversely, the long-term terrestrial record provides an empirical constraint on the source regions of NEOs as well as on the dark matter content of the Galactic disc. During such episodes, climatic effects due to stratospheric dusting by very large comets are likely to be a major factor in geological and biological change.

A gridded global data set of daily temperature and precipitation for terrestrial biospheric modeling

The first global terrestrial gridded data set of the daily average and range of temperature and daily precipitation has been developed, intended for use in terrestrial biospheric modeling. Data for the year 1987 are shown to illustrate our methodology. Daily station data, primarily from the World Meteorological Organization global synoptic surface network of stations, have been extensively quality checked and interpolated to a 1×1 degree grid by using a nearest neighbors interpolation scheme. Annual averages of the daily average temperatures have been compared with 1987 temperatures constructed from data supplied by P.D. Jones (personal communication, 1996). Agreement between these two data sets is good, except in some areas of the southern hemisphere where station coverage is poor. Monthly and annual totals of the daily precipitation data have been compared with the monthly 1987 data set produced by the Global Precipitation Climatology Centre. Agreement between the two data sets is good over much of the northern hemisphere and South America; however, large discrepancies are seen in east‐central and south‐central Africa and in most of Australia, primarily due to the poor station coverage there. Comparison of the time series from individual stations with those from the gridded data set indicate that the day‐to‐day variation of temperature and the fraction of wet days are preserved, except in the tropics where wet days are overestimated. Station densities have been tabulated in terms of total annual net primary productivity to identify countries where increases in station data will be most effective for terrestrial biospheric modeling.

Space flight data from the Isothermal Dendritic Growth Experiment

The Isothermal Dendritic Growth Experiment (IDGE) is a NASA space flight experiment which flew as part of the United States Microgravity Payload (USMP-2), in early 1994. The IDGE measured dendritic growth rates, tip radii, and crystal morphologies of ultra-pure succinonitrile [CN-(CH 2) 2-CN] at supercoolings in the range from 0.05–2.0 K. Data taken in the form of slow-scan binary digitized images telemetered to the ground from orbit in near-real time, combined with the IDGE terrestrial data set, provide the first quantitative assessment of various theories on dendritic solidification and the effects of convection on dendritic growth.

Neogene Siwalik mammalian lineages: species longevities, rates of change, and modes of speciation

The Siwalik sequence, particularly the interval from 18 to 7 Ma, provides one of the few terrestrial data sets that allows direct measurement of temporal durations of mammalian species. Its data are drawn from a single biogeographic subprovince and superposed collections likely represent successive samples of single lineages. Observed temporal ranges underestimate total species longevities if (1) species existed in other biogeographic provinces before or after the temporal ranges recorded in the Siwaliks, or (2) the fossil record inadequately samples species durations in the Siwalik subprovince. Some data, notably from Afghanistan, China, and Thailand, bear on the first variable. The second can be controlled by considering data quality, in this case the temporal distribution of good data sets, to assess the scale of accuracy available for defining range endpoints. In general, range endpoints can be estimated to the nearest 0.1 million years.The diverse Rodentia give a mean species longevity of 2.2 million years for the Miocene Siwaliks. This includes single records, but of course ignores unretrieved rare or short-lived taxa. The diverse Artiodactyla yield 3.1 million years. The difference may reflect greater body size and longer generation time; large Perissodactyla and Proboscidea have longer temporal ranges. Carnivorous mammals also show about 3 million year durations. Given these data, the average longevity for Sivapithecus species (1.6 million years) is modest. The deposits of the Clarks Fork Basin, Wyoming, offer a Paleogene data set comparable to that of the Neogene Siwaliks. Paleocene-Eocene mammals of North America yield shorter longevities (most less than one million years).Extinction is the dominant mode of species termination for Siwalik mammals. Most taxa originated by immigration (as at about 13.5 Ma) or abrupt speciation. There are some cases for insitu transformation of lineages, for example in the genera Punjabemys, Antemus, Percrocuta, Dorcatherium, Giraffokeryx, and Selenoportax. The rodent Kanisamys shows a rate of increase in tooth size of 0.5 darwins. This overall rate is moderate by Paleogene standards, but includes an interval of more rapid change between 9.0 and 8.5 Ma.

The lobes of lava flows on Earth and Olympus Mons, Mars

The lobate distal margins of lava flows provide a useful source of morphological information on the rheology of the lava if the lobes are assumed to represent the arrest of free-flowing isothermal Bingham fluids on a slope. The widths of lobes are a more useful practical index than lobe thicknesses because they are about an order of magnitude larger and can be more accurately measured from aerial photographs and other remote images. Lobes do not suffer from the changes in morphology that channels undergo during the course of eruptions. A terrestrial data set of flow lobe and ancillary measurements from lavas throughout the range alkali olivine basalt to rhyolite shows some features that are predicted by the isothermal Bingham fluid model. These are correlation of width and thickness over more than two orders of magnitude and essentially no correlation of aspect ratio with slope. There is a positive correlation of lobe width with silica content of the lava. From a data set of measurements on lava flow lobes from the Martian volcano Olympus Mons the mean value of aspect ratio (0.07) was found to be significantly less than that for the terrestrial data set (0.19). Higher general levels of effusion rate on Olympus Mons are probably the factor responsible. After normalisation, lobe widths on Olympus Mons are found to be largely equivalent to those expected for terrestrial flows with andesitic/basaltic silica contents.