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1

Digitale Medien

How to handle topography in practical geoid determination: three examples (2000)

Omang, O. C. D. ; Forsberg, R.

Springer

Journal of geodesy 74 (2000), S. 458-466

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ISSN: 1432-1394

Schlagwort(e): Key words: Terrain effects – Indirect effects – RTM – Helmert – Gravity – Geoid – GPS/levelling

Quelle: Springer Online Journal Archives 1860-2000

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Abstract. Three different methods of handling topography in geoid determination were investigated. The first two methods employ the residual terrain model (RTM) remove–restore technique, yielding the quasigeoid, whereas the third method uses the classical Helmert condensation method, yielding the geoid. All three methods were used with the geopotential model Earth Gravity Model (1996) (EGM96) as a reference, and the results were compared to precise global positioning system (GPS) levelling networks in Scandinavia. An investigation of the Helmert method, focusing on the different types of indirect effects and their effects on the geoid, was also carried out. The three different methods used produce almost identical results at the 5-cm level, when compared to the GPS levelling networks. However, small systematic differences existed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s001900000107

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2

Digitale Medien

A comparison of stable platform and strapdown airborne gravity (2000)

Glennie, C. L. ; Schwarz, K. P. ; Bruton, A. M. ; [weitere]

Springer

Journal of geodesy 74 (2000), S. 383-389

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ISSN: 1432-1394

Schlagwort(e): Key words: Airborne gravimetry ; Strapdown gravity system ; Analysis of flight tests ; DGPS/INS integration

Quelle: Springer Online Journal Archives 1860-2000

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Abstract. To date, operational airborne gravity results have been obtained using either a damped two-axis stable platform gravimeter system such as the LaCoste and Romberg (LCR) S-model marine gravimeter or a strapdown inertial navigation system (INS), showing comparable accuracies. In June 1998 three flight tests were undertaken which tested an LCR gravimeter and a strapdown INS gravity system side by side. To the authors' knowledge, this was the first time such a comparison flight was undertaken. The flights occurred in Disko Bay, off the west coast of Greenland. Several of the flight lines were partly flown along existing shipborne gravity profiles to allow for an independent source of comparison of the results. The results and analysis of these flight tests are presented. The measurement method and error models for both the stable platform and strapdown INS gravity systems are presented and contrasted. An intercomparison of gravity estimates from both systems is given, along with a comparison of the individual estimates with existing shipborne gravity profiles. The results of the flight tests show that the gravity estimates from the two systems agree at the 2–3 mGal level, after the removal of a linear bias. This is near the combined noise level of the two systems. It appears that a combination of both systems would provide an ideal airborne gravity survey system, combining the excellent bias stability of the LCR gravimeter with the higher dynamic range and increased spatial resolution of the strapdown INS.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s001900000082

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3

Digitale Medien

Geoid models around Sognefjord using depth data (1998)

Dahl, O. C. ; Forsberg, R.

Springer

Journal of geodesy 72 (1998), S. 547-556

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ISSN: 1432-1394

Schlagwort(e): Key words. Bathymetry ; Gravity ; Terrain effects ; Quasigeoid minus geoid ; Geoid ; GPS/levelling

Quelle: Springer Online Journal Archives 1860-2000

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Abstract. Bathymetry data from Sognefjord, Norway, have been included in a terrain model, and their influence on the geoid has been calculated. The test area, located in the western part of Norway, was chosen due to its deep fjords and high mountains. Inclusion of bathymetry data in the terrain model altered the computed gravimetric geoid by as much as a few decimeters. The effect was detectable to a distance of more than 100 km. All calculated geoids, both with and without bathymetry data in the terrain model, fit the geoidal heights determined by available Global Positioning System (GPS) and levelling heights at the sub-decimetre level. Contrary to expectations, the accuracy in geoid prediction was reduced when using bathymetric data. The geoid changes were largest over the fjord where no GPS points were located. Different methods on the same area [isostatic and Residual Terrain Model (RTM)-terrain reductions] showed differences of approximately 1 m. Rigorous distinction between quasigeoid and geoid was found to be essential in this kind of area.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s001900050193

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4

Digitale Medien

Harmonic continuation and gridding effects on geoid height prediction (1992)

Tscherning, C. C. ; Forsberg, R.

Springer

Journal of geodesy 66 (1992), S. 41-53

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ISSN: 1432-1394

Quelle: Springer Online Journal Archives 1860-2000

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Abstract Least-squares collocation and Stokes integral formula, as implemented using the Fast Fourier Technique, handle the harmonic downward continuation problem quite differently. FFT furthermore requires gridded data, amplifying the difference of methods. We have in this paper studied numerically the effects of downward continuation and gridding in a mountainous area in central Norway. Topographically smoothed data were used in order to reduce these effects. Despite the smoothing, it was found that the vertical gravity gradient had values up to -11 mgal/km. The corresponding differences between geoid heights and the height anomalies at altitude reached 12 cm. The differences between geoid heights obtained using collocation or FFT with gravity data at terrain level or sea level showed differences between the values of up to 10 cm r.m.s. A part of this difference was a consequence of different data areas used in the FFT and collocation solution, though. Major discrepancies between the solutions were found in areas where the topographic smoothing could not be applied (deep fjords with no depth information in the used DTM) or where there seemed to be gross errors in the data. We conclude that proper handling of harmonic continuation is important, even when we as here have used a 1 km resolution DTM for the calculation of topographic effects. The effect of data gridding, required for the FFT method, seems not to be as serious as the need to limit the data distribution area, required when least squares collocation is used with randomly distributed data.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00806809

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5

Digitale Medien

Airborne gravimetry used in precise geoid computations by ring integration (1998)

Kearsley, A. H. W. ; Forsberg, R. ; Olesen, A. ; [weitere]

Springer

Journal of geodesy 72 (1998), S. 600-605

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ISSN: 1432-1394

Schlagwort(e): Key words. Airborne gravimetry ; Gravity field extension ; Geoid computation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Architektur, Bauingenieurwesen, Vermessung

Notizen: Abstract. Two detailed geoids have been computed in the region of North Jutland. The first computation used marine data in the offshore areas. For the second computation the marine data set was replaced by the sparser airborne gravity data resulting from the AGMASCO campaign of September 1996. The results of comparisons of the geoid heights at on-shore geometric control showed that the geoid heights computed from the airborne gravity data matched in precision those computed using the marine data, supporting the view that airborne techniques have enormous potential for mapping those unsurveyed areas between the land-based data and the off-shore marine or altimetrically derived data.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s001900050198

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6

Digitale Medien

Endosperm Balance Number and the polar-nuclei activation hypotheses for endosperm development in interspecific crosses of Solanaceae and Gramineae, respectively (1995)

Katsiotis, A. ; Hanneman, R. E. ; Forsberg, R. A.

Springer

Theoretical and applied genetics 91 (1995), S. 848-855

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ISSN: 1432-2242

Schlagwort(e): Endosperm development ; Evolution ; Imprinting ; Incompatibility ; Reciprocal crosses

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract The Endosperm Balance Number (EBN) and the polar-nuclei activation (PNA) hypotheses have been developed to interpret, explain and predict interspecific and interploidy crossabilities in the Solanums and the Gramineae, respectively. Although these two hypotheses evolved independently, they share a number of common features. Assignment of EBNs and ‘activation/response values’ (AVs/RVs) depend on plumpness, size, and germinability of hybrid seeds. Also, both hypotheses emphasize the importance of a balanced parental genic contribution for the normal development of endosperm. However, in the EBN hypothesis a 2 maternal∶1 paternal EBN ratio is a prerequisite for successful interspecific crossability, while the PNA hypothesis is based on the stimulative strength of the male nuclei to initiate mitotic divisions in the primary endosperm nucleus and is idependent on a 2∶1 ratio between the RV of the polar nuclei and the AV of the male gamete. Differences and similarities betweeen the EBN and PNA hypotheses are summarized and contrasted. It is proposed that EBN and PNA be considered as the same concept.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00223891

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7

Digitale Medien

Discovery of 2n gametes in tetraploid oat Avena vaviloviana (1995)

Katsiotis, A. ; Forsberg, R. A.

Springer

Euphytica 81 (1995), S. 1-6

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ISSN: 1573-5060

Schlagwort(e): Avena ; 2n gametes ; binucleate cell ; evolution ; sexual polyploidization

Quelle: Springer Online Journal Archives 1860-2000

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Sexual polyploidization via the action of 2n gametes (gametes with the sporophytic chromosome number) has been identified as the most important evolutionary mode of polyploidization among plant genera. This study was conducted to determine whether 2n gametes are present in the tetraploid level of the genus Avena (2n=4×=28) Twenty tetraploid Avena lines, representing four species and one interspecific hybrid, were screened for pollen grain size in order to differentiate between n and 2n pollen. Avena vaviloviana (Malz.) Mordv. line PI 412767 was observed to contain large pollen grains at a 1.0% frequency. Cytogenetic analyses of pollen mother cells of PI 412767 revealed cells with double the normal chromosome number (i.e., 56 chromosomes at metaphase I and anaphase I). The mode of chromosome doubling was found to be failure of cell wall formation during the last mitotic division that preceded meiosis. The resulting binucleate cells underwent normal meiotic divisions and formed pollen grains with 28 chromosomes. Based on the formation and function of 2n gametes, three models involving diploid and tetraploid oat lines are proposed to describe possible evolutionary pathways for hexaploid oats. If stable synthetic hexaploid oat lines could be developed by utilizing 2n gametes from diploid and tetraploid oat species through bilateral sexual polyploidization, the resulting hexaploids could be used in breeding programs for transferring genes from diploids and tetraploids to cultivated hexaploids.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00022452

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8

Digitale Medien

Pollen grain size in four ploidy levels of genusAvena (1995)

Katsiotis, A. ; Forsberg, R. A.

Springer

Euphytica 83 (1995), S. 103-108

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ISSN: 1573-5060

Schlagwort(e): oat ; Avena sativa ; pollen grain size ; chromosome number

Quelle: Springer Online Journal Archives 1860-2000

Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft

Notizen: Summary Pollen grain size in many genera positively correlated with chromosome number. In this study, oat (Avena) pollen grain size was examined in diploids (2×=14, one species, for accessions), tetraploids (4×=28, five species, 20 accessions), hexaploids (6×=42, one species, eight cultivars), and in 10 octoploid (8×=56) accessions. Mature anthers ready to dehisce pollen were sampled from one to six plants per accession, and pollen grains were squeezed out of the anther with tweezers. Oat pollen grains are slightly elliptical, and the length of the major axis was found to be highly correlated with the minor axis width (r=0.94**). Pollen grain length, 39.3 μm for diploids, 41.3 μm for tetraploids, 47.0 μm for hexaploids, and 48.8 μm for octoploids, was positively correlated (r=0.86**) with ploidy level. No genomic or species effects appeared to influence this trait. Only tetraploidAvena vaviloviana accession PI 412767 produced two distinct class sizes of pollen grains, 99% normal (43.0 μm) and 1% large (52.7 μm).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01678036

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