1,720,990 research outputs found
Terrestriline laserskaneerimine ehituskonstruktsioonide m\uf5\uf5distamisel. Application of Terrestrial Laser Scanning Technology for Engineering Structure Surveys
No full textLaser Scanning of Built Environment and Landforms with Spatial Modelling Applications. Laserskaneerimine ehitiste ja looduslike pinnavormide m\uf5\uf5distamisel ning tulemuste modelleerimine
No full textQuantification of the Reaction of Estonian Beaches to Changing Wave Loads. Eesti rannikute reaktsioon muutuvatele lainekoormustele
No full textMeregeoidi mudelite iteratiivne t\ue4psustamine ja t\ue4psuse valideerimine. Iterative Refinement and Accuracy Validation of Marine Geoid Models
No full textRegional Geoid Modelling by the Least Squares Modified Hotine Formula Using Gridded Gravity Disturbances. Piirkondlik geoidi modelleerimine v\ue4himruutude meetodil modifitseeritud Hotine valemiga kasutades v\uf5rgustatud raskuskiirenduse h\ue4lbeid
No full textMerepinna realistliku d\ufcnaamilise topograafia saavutamine t\ue4ppisgeoidi ja meretaseme andmete kooskasutamisel. Developments Towards Deriving Realistic Dynamic Topography by Synergizing High-Resolution Geoid with Sea Level Data
No full textRõhuanduritel põhinev hüdrodünaamiline loodimine rakendatuna Eesti riikliku kõrgusvõrgu rekonstrueerimisel
No full textLevelling is a branch of surveying which is used to determine height differences with respect to benchmarks with known heights. Precise heights are important in many applications, e.g. in geodesy, engineering and oceanography. Nowadays, traditional spirit levelling on the land is used to achieve the highest precision (sub-cm, typically) in height determination. Frequently highly accurate across-water levelling is needed, e.g. to establish reliable connections between all parts of a levelling network, both on the mainland and on adjacent islands, or to calibrate satellite altimetry in polar areas. Therefore, various methods have been developed and practiced for across-water height determination, e.g. the global navigation satellite system- (GNSS) based levelling, hydrostatic, hydrodynamic, and trigonometric levelling. These methods differ from one another both by achievable precision and equipment required for conducting the measurements. Sea level observations have been used widely for determining height differences between coastal stations. Multi-annual sea level series from sea level gauges are mainly used for hydrodynamic levelling.
This doctoral thesis focuses on the usability and achievable accuracy of pressure gauges (PG) for hydrodynamic levelling. Automatic PGs are easy to use but they are known for time-dependent drift. Therefore, proper data filtering and processing algorithms need to be applied to acquired PG observations for geodetic purposes. Also, an optimal duration of the PG series needs to be determined. Note that it may not be possible to use long term (multi-annual) sea level series everywhere. Therefore, due to budget limitations and the required accuracy it is important to determine the most optimal duration of sea level observations. The study tested performance of PGs and the hydrodynamic levelling methodology on a practical case study in the West-Estonian Archipelago. Height differences between the mainland and two major islands (Saaremaa and Hiiumaa) were determined and evaluated by alternative levelling techniques. The height differences between Virtsu–Kuivastu, Triigi–Sõru and Heltermaa–Rohuküla with accuracy ±1.5 cm were achieved using hydrodynamic levelling. These results have practical application in the renovation of the Estonian National Levelling Network as well as for specifying land uplift velocities in West-Estonia where uplift velocities reach up to 2.5 mm/year. The knowledge related to optimal (one year) sea level observations and PG’s data sampling interval can be applied all over the world to transfer heights across water bodies with a small budget and labour costs but with accuracy at 1.5 cm levelLoodimine on mõõtmismeetod, mida kasutatakse reeperitevaheliste kõrguskasvude määramiseks. Täpseid kõrgusi on vaja geodeesias, ehituses, okeanograafias. Kõrguste määramiseks maismaal kasutatakse traditsiooniliselt kõrgtäpset loodimist, mis võimaldab määrata kõrgused mõne millimeetri täpsusega. Sageli tuleb kõrgusi kanda ka üle veekogude. Nimetatud vajadus võib tekkida, kui soovitakse ühendada mandril ja saartel olevad kõrgusvõrgu polügoonid või näiteks kalibreerida satelliitaltimeetria andmeid polaaraladel. Kõrguste üle vee kandmiseks on kasutatud erinevaid meetodeid: globaalsel satelliitnavigatsioonil (GNSS) põhinev loodimine, hüdrostaatiline, hüdrodünaamiline ja trigonomeetriline loodimine. Mainitud meetodid erinevad üksteisest nii täpsuse kui kasutatava mõõtevarustuse poolest. Rannikul asuvate punktide vaheliste kõrguskasvude määramiseks on kasutatud laialdaselt veevaatlusi. Hüdrodünaamilisel loodimisel tarvitatakse tavaliselt mitme aasta pikkusi veevaatlusseeriaid.
Doktoritöö keskendub hüdrodünaamilisel loodimisel rakendatavate rõhuandurite kasutatavusele ning täpsusele. Rõhuandureid on lihtne kasutada, kuid nad on tuntud oma ajalise triivi poolest. Seetõttu tuleb rõhuanduritega kogutud andmeid geodeesias kasutamiseks eelnevalt töödelda. Kõikjal pole võimalik kasutada pikaajalisi (mitu aastat) veevaatlusseeriaid. Sellest, limiteeritud eelarvest ning nõutavast täpsusest tulenevalt on oluline kindlaks teha optimaalne veevaatluste periood. Käesolev töö uurib rõhuandurite toimimist ja hüdrodünaamilise loodimise metoodikat ühe praktilise uuringu näitel Lääne-Eesti saarestikus. Hüdrodünaamilise loodimisega määrati kõrguskasvud mandri ning Saaremaa ja Hiiumaa vahel. Tulemusi kontrolliti alternatiivsete loodimismeetoditega. Hüdrodünaamilise loodimisega mõõdetud kõrguskasvude (Virtsu–Kuivastu, Triigi–Sõru ja Heltermaa–Rohuküla) täpsuseks saadi ±1.5 cm. Saadud tulemustel on praktiline väärtus Eesti riikliku kõrgusvõrgu rekonstrueerimisel ja Lääne-Eesti maapinna vertikaalliikumiste täpsustamisel (maakoor tõuseb selles piirkonnas kuni 2.5 mm/a). Teadmisi optimaalse (üks aasta) veevaatlusperioodi ja rõhuandurite andmete salvestamise intervalli kohta saab rakendada kõikjal maailmas, et väikeste kulutustega kanda kõrgusi üle veekogude 1.5 cm täpsusega.Publication of the thesis is supported by Estonian University of Life
Sciences and Doctoral School in the Field of Building and Environmental
Engineering
The geoid for the Baltic countries determined by the least squares modification of Stokes´formula
No full textPrecise knowledge of the geoid contributes to the studies ofthe Earth\u92s interior, the long-term geophysical processesand to oceanography. An accurate regional geoid model, inparticular, enables the user in many cases to replace thetraditional height determination techniques by faster and morecost-effective GPS-levelling. In regional gravimetric geoid determination, it has becomecustomary to utilize the modified Stokes formula, whichcombines local terrestrial data with a global geopotentialmodel. The Dissertation is devoted to the determination of ahighresolution geoid model for the three Baltic countries\u96Estonia, Latvia and Lithuania. Six differentdeterministic and stochastic modification methods are tested.These are: Wong and Gore (1969), Vincent and Marsh (1974),Vaníèek and Kleusberg (1987) and the biased, unbiasedand optimum least squares modifications by Sjöberg (1984b,1991, 2003d). Three former methods employ originally theresidual anomaly in Stokes\u92integral. For the sake ofcomparison these methods are expressed such that the fullgravity anomaly is utilised in all the six methods. The contribution of different error sources for geoidmodelling is studied by means of the expected global meansquare error (MSE). The least squares methods attempt tominimise all relevant error sources in geoid modelling byspecially determined modification parameters. Part of thepresent study contributes to some important computationalaspects of the least squares parameters sn. This study employs the new geopotential model GGM01s, whichis compiled from data of the GRACE twin-satellites. Three sets(one from each country) of GPSlevelling points were used for anindependent evaluation of computed geoid models. Generally, thepost-fit residuals from the least squares modifications areslightly smaller (up to 1 cm) than the respective values ofdeterministic methods. This could indicate that the efforts putinto minimization of the global MSE have been advantageous. The geoid model computed by the unbiased LS modificationprovides the\u93best\u94post-fit statistics and it isthus preferred as the final representation of the joint Balticgeoid. The modification parameters of this model are calculatedfrom the following initial conditions: (1) upper limit of theGGM01s and the modification degree of Stokes\u92function areboth set to 67, (2) terrestrial anomaly error variance andcorrelation length are set to 1 mGal2 and 0.1°,respectively, (3) integration cap size is 2°. Thisapproximate geoid model is supplemented by separately computedadditive corrections (the combined topographic and atmosphericeffects and ellipsoidal correction), which completes the geoidmodelling procedures. The new geoid model for the Balticcountries is named BALTgeoid-04. The RMS of the GPS-levellingpost-fit residuals are as follows: 5.3 cm for the joint Balticgeoid model and 2.8, 5.6 and 4.2 cm for Estonia, Latvia andLithuania, respectively. This fit indicates the suitability ofthe new geoid model for many practical applications. Key words: geoid:Stokes\u92formula, deterministicand stochastic modifications, least squares, additivecorrections, GRACE, Baltic
The geoid for the Baltic countries determined by the least squares modification of Stokes´formula [Elektronisk resurs]
No full textPrecise knowledge of the geoid contributes to the studies ofthe Earths interior, the long-term geophysical processesand to oceanography. An accurate regional geoid model, inparticular, enables the user in many cases to replace thetraditional height determination techniques by faster and morecost-effective GPS-levelling. In regional gravimetric geoid determination, it has becomecustomary to utilize the modified Stokes formula, whichcombines local terrestrial data with a global geopotentialmodel. The Dissertation is devoted to the determination of ahighresolution geoid model for the three Baltic countriesEstonia, Latvia and Lithuania. Six differentdeterministic and stochastic modification methods are tested.These are: Wong and Gore (1969), Vincent and Marsh (1974),Vaníèek and Kleusberg (1987) and the biased, unbiasedand optimum least squares modifications by Sjöberg (1984b,1991, 2003d). Three former methods employ originally theresidual anomaly in Stokesintegral. For the sake ofcomparison these methods are expressed such that the fullgravity anomaly is utilised in all the six methods. The contribution of different error sources for geoidmodelling is studied by means of the expected global meansquare error (MSE). The least squares methods attempt tominimise all relevant error sources in geoid modelling byspecially determined modification parameters. Part of thepresent study contributes to some important computationalaspects of the least squares parameters sn. This study employs the new geopotential model GGM01s, whichis compiled from data of the GRACE twin-satellites. Three sets(one from each country) of GPSlevelling points were used for anindependent evaluation of computed geoid models. Generally, thepost-fit residuals from the least squares modifications areslightly smaller (up to 1 cm) than the respective values ofdeterministic methods. This could indicate that the efforts putinto minimization of the global MSE have been advantageous. The geoid model computed by the unbiased LS modificationprovides thebestpost-fit statistics and it isthus preferred as the final representation of the joint Balticgeoid. The modification parameters of this model are calculatedfrom the following initial conditions: (1) upper limit of theGGM01s and the modification degree of Stokesfunction areboth set to 67, (2) terrestrial anomaly error variance andcorrelation length are set to 1 mGal2 and 0.1°,respectively, (3) integration cap size is 2°. Thisapproximate geoid model is supplemented by separately computedadditive corrections (the combined topographic and atmosphericeffects and ellipsoidal correction), which completes the geoidmodelling procedures. The new geoid model for the Balticcountries is named BALTgeoid-04. The RMS of the GPS-levellingpost-fit residuals are as follows: 5.3 cm for the joint Balticgeoid model and 2.8, 5.6 and 4.2 cm for Estonia, Latvia andLithuania, respectively. This fit indicates the suitability ofthe new geoid model for many practical applications. Key words: geoid:Stokesformula, deterministicand stochastic modifications, least squares, additivecorrections, GRACE, Baltic.</p
A numerical comparison of different ellipsoidal corrections to stokes' formula
No full textThis paper reviews the new method (recently derived by L.E. Sjoberg) of the ellipsoidal correction for Stokes' formula. Importantly, the correction can also be expressed in a series of spherical harmonics of the disturbing potential, which is a considerable computational advantage. In order to assess the applicability of this approach, it is numerically compared with two other methods. The results reveal that the new method practically coincides with one of the earlier methods, although their derivational approaches and resulting expressions are considerably different. The new method is adapted for the modified Stokes formula, which combines regional terrestrial gravity data with a global geopotential model. The magnitude of the ellipsoidal correction in the modified Stokes formula does not exceed cm level, globally.</p
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