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Electronic Resource

The Iceland 1986 GPS geodetic survey: tectonic goals and data processing results (1993)

Foulger, G. R. ; Beutler, G. ; Bilham, Roger ; [et al.]

Springer

Journal of geodesy 67 (1993), S. 148-172

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ISSN: 1432-1394

Source: Springer Online Journal Archives 1860-2000

Topics: Architecture, Civil Engineering, Surveying

Notes: Summary The 1986 GPS survey of Iceland aimed to: (1) establish geodetic control in the South Iceland Seismic Zone (SISZ), to study destructive earthquakes there, (2) measure a country-wide network to form the basis of a new first order national network. 51 points were surveyed, with 20–30 km spacings within the SISZ and 100 km spacings elsewhere. The data were processed using the Bernese GPS software Version 3. Analysis was difficult due to poor satellite geometry and short-period ionospheric variations. However, an ambiguity-fixed, ionosphere-free solution gave accuracies of 1–2 cm in the horizontal and 2–3 cm in the vertical for the SISZ network and an ambiguity-free, ionosphere-free solution yielded accuracies of about 5 cm for the country-wide network. An ionosphere-free solution for the total survey with ambiguities fixed for the SISZ network only gave marginal additional improvements over the two separate solutions. GPS surveying has continued annually in Iceland with measurements in South Iceland in 1989 and 1992 (Hackman 1991; Sigmundsson 1992) and in North Iceland in 1987, 1990 and 1992 (Jahn et al. 1992; Foulger et al. 1992).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00806254

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Combining consecutive short arcs into long arcs for precise and efficient GPS Orbit Determination (1996)

Beutler, G. ; Brockmann, E. ; Hugentobler, U. ; [et al.]

Springer

Journal of geodesy 70 (1996), S. 287-299

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ISSN: 1432-1394

Source: Springer Online Journal Archives 1860-2000

Topics: Architecture, Civil Engineering, Surveying

Notes: Abstract. The final products of the CODE Analysis Center (Center for Orbit Determination in Europe) of the International GPS Service for Geodynamics (IGS) stem from overlapping 3-days-arcs. Until 31 December, 1994 these long arcs were computed from scratch, i.e. by processing three days of observations of about 40 stations (by mid 1995 about 60 stations were used) of the IGS Global Network in our parameter estimation program GPSEST. Because one-day-arcs have to be produced first (for the purpose of error detection etc.) the actual procedure was rather time-consuming. In the present article we develop the mathematical tools necessary to form arcs based on the normal equation systems of consecutive short arcs (one-day-solutions in the case of CODE). The procedure in its simplest version is as follows: • Each short arc is described by six initial conditions and a number of dynamical orbit parameters (e.g. radiation pressure parameters). The resulting long arc in turn shall be based on n consecutive short arcs and described by six initial conditions and again the same number of dynamical parameters as in the short arcs. • By asking position and velocity to be continuous at the boundaries of the short arcs we obtain a long arc which is actually defined by one set of initial conditions and n sets of dynamical parameters (if n short arcs are combined). • By asking the dynamical parameters to be identical in consecutive short arcs, the resulting long arc is characterized by exactly the same number of orbit parameters as each of the short arcs. • This procedure is not yet optimized because formally all n sets of orbit parameters have to be set up and solved for in the long arc solution (although they are not independent). In order to allow for an optimized solution we derive all necessary relations to eliminate the unnecessary parameters in the combination. Each long arc is characterized by the actual number of independent orbit parameters. The resulting procedure is very efficient. From the point of view of the result the new procedure is completely equivalent to an actual re-evaluation of all observations pertaining to the long arc. It is much more efficient and flexible, however because it allows us to construct 2-day-arcs, 3-day-arcs, etc. based on the previously stored daily normal equation systems without requiring much additional CPU time. The theory is developed in the first four sections. Technical aspects are dealt with in appendices A and B. The actual implementation into the Bernese GPS Software system and test results are given in section 5.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00867349

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Electronic Resource

Combining consecutive short arcs into long arcs for precise and efficient GPS Orbit Determination (1996)

Beutler, G. ; Brockmann, E. ; Hugentobler, U. ; [et al.]

Springer

Journal of geodesy 70 (1996), S. 287-299

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ISSN: 1432-1394

Source: Springer Online Journal Archives 1860-2000

Topics: Architecture, Civil Engineering, Surveying

Notes: Abstract The final products of theCODE Analysis Center (Center for Orbit Determination in Europe) of theInternational GPS Service for Geodynamics (IGS) stem fromoverlapping 3-day-arcs. Until 31 December, 1994 these long arcs were computedfrom scratch, i.e. by processing three days of observations of about 40 stations (by mid 1995 about 60 stations were used) of the IGS Global Network in our parameter estimation program GPSEST. Becauseone-day-arcs have to be produced first (for the purpose of error detection etc.) the actual procedure was rather time-consuming. In the present article we develop the mathematical tools necessary to form long arcs based on the normal equation systems of consecutive short arcs (one-day-solutions in the case of CODE). The procedure in its simplest version is as follows: Each short arc is described bysix initial conditions and a number of dynamical orbit parameters (e.g. radiation pressure parameters). The resulting long arc in turn shall be based onn consecutive short arcs and described bysix initial conditions and again the same number of dynamical parameters as in the short arcs.. By asking position and velocity to be continuous at the boundaries of the short arcs we obtain a long arc which is actually defined by one set of initial conditions andn sets of dynamical parameters (ifn short arcs are combined).. By asking the dynamical parameters to be identical in consecutive short arcs, the resulting long arc is characterized by exactly the same number of orbit parameters as each of the short arcs. This procedure isnot yet optimized becauseformally all n sets of orbit parameters have to be set up and solved for in the long arc solution (although they are not independent). In order to allow for an optimized solution we derive all necessary relations to eliminate the unnecessary parameters in the combination. Each long arc is characterized by the actual number of independent orbit parameters. The resulting procedure isvery efficient. From the point of view of the result the new procedure iscompletely equivalent to an actual re-evaluation of all observations pertaining to the long arc. It is much more efficient and flexible, however because it allows us to construct 2-day-arcs, 3-day-arcs, etc. based on the previously stored daily normal equation systems without requiring much additional CPU time. The theory is developed in the first four sections. Technical aspects are dealt with in appendices A and B. The actual implementation into the Bernese GPS Software system and test results are given in section 5.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00867349

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Effects of plant nutrition on the balance of insect relevant cardenolides and glucosinolates in Erysimum cheiranthoides (1995)

Hugentobler, U. ; Renwick, J. A. A.

Springer

Oecologia 102 (1995), S. 95-101

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ISSN: 1432-1939

Keywords: C/N balance ; Nutrient stress ; Oviposition ; Stimulant ; Deterrent

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The possible effects of environmental stress on plant chemistry that are important to herbivorous insects were examined by growing a wild crucifer, Erysimum cheiranthoides, under different nutrient regimes. Oviposition by the cabbage butterfly, Pieris rapae, is thought to be affected by the balance of glucosinolates (stimulants) and cardenolides (deterrents) at the surface of leaves. E. cheiranthoides seedlings were provided with three levels of nitrogen and two levels of sulfur for a period of 15 days before analysis of semiochemicals in whole leaf tissue and at the surface of the foliage. The ratio of cardenolides to glucosinolates in the plants at elevated C/N ratios followed the carbon/nutrient balance hypothesis. However, a high nitrogen supply enhanced biomass production to the extent that concentrations of secondary compounds were unchanged or reduced. The concentration of glucosinolates (glucoiberin and glucocheirolin) at the surface was positively related to whole tissue levels. However, cardenolide (erysimoside and erychroside) concentrations, which were highest in leaf tissue of nitrogen-deficient plants, had the lowest surface levels on foliage of these plants. Possible reasons for differential expression of cardenolides and glucosinolates in a plant as a result of nutrient deficiency are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00333315

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Energy flow in an apple plant-aphid (Aphis pomi De Geer) (Homoptera: Aphididae) ecosystem, with respect to nitrogen fertilization (1990)

Rutz, C. H. ; Hugentobler, U. ; Chi, H. ; [et al.]

Springer

Plant and soil 124 (1990), S. 273-279

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ISSN: 1573-5036

Keywords: aphid population ; aphids ; apple ; nitrogen fertilization

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The effect of nitrogen fertilization on the life table parameters of green apple aphids, feeding on apple saplings of different nutritional quality, was investigated. The experiments were carried out with cloned apple plants (cv. Golden Delicious), all originating from one seed, growing in a climate chamber under constant conditions. The apple saplings were irrigated with nutrient solutions containing different nitrogen levels (0.2, 0.5, 1, and 3 N), and infested with Aphis pomi De Geer. The 1 N treatment corresponded to a 15 mM nitrogen concentration, containing NO3 - and NH4 + in a 14:1 ratio. The levels of nitrogen fertilization studied here influenced the life table parameters of A. pomi in the following way: the mean generation time of A. pomi, growing on the 0.5 N treatment, was lower than the corresponding values found on the 0.2 and 1 N treatments. The highest net reproduction rate was produced on low (0.2 N) nitrogen nutrition. The intrinsic rate of natural increase was highest on the 0.5 N treatment.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00009272

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How rigid is a rigid plate? Geodetic constraint from the TrigNet CGPS network, South Africa (2013)

Malservisi, R., Hugentobler, U., Wonnacott, R., Hackl, M.

Oxford University Press

In: Geophysical Journal International

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Publication Date: 2013-02-15

Description: Rigidity and continuity of the Nubia plate is a fundamental assumption for the kinematic description, the dynamic implications of its interaction with surrounding plates and ultimately an important constraint to the geodynamics processes involved in continental lithospheric rupture. Geophysical, neotectonic and geodynamics considerations suggest the possibility that the Nubia plate is not completely rigid but could be undergoing internal deformation due to the southward propagation of the East African Rift. Here, we utilize the South African TrigNet geodetic network to evaluate the amount of internal deformation within the South African region and the possibility of motion between South Africa and the rest of the African continent. Our results show that the South African region behaves rigidly, with deformation of the order of 1 nanostrain yr –1 or less. The analysis shows some higher strain rates in the eastern region, and the presence of spatially correlated residuals in the Cape Town region and the region east of Johannesburg. Although not statistically significant, the spatial coherence of those residuals could indicate tectonic activity. A comparison of the Euler vector for the South African region with previously published Euler poles for the Nubia plate as well as the analysis of the residuals of Nubia sites with respect to a ‘rigid’ TrigNet are compatible with clockwise rotation of the South African block with respect to the African continent, consistent with a propagation of the East Africa Rift along the Okavango region.

Print ISSN: 0956-540X

Electronic ISSN: 1365-246X

Topics: Geosciences