The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
Christian Hirt - One of the best experts on this subject based on the ideXlab platform.
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ellipsoidal topographic potential new solutions for spectral forward gravity modeling of topography with respect to a Reference ellipsoid
Journal of Geophysical Research, 2013Co-Authors: Sten Claessens, Christian HirtAbstract:Forward gravity modeling in the spectral domain traditionally relies on spherical approximation. However, this level of approximation is insufficient for some present day high-accuracy applications. Here we present two solutions that avoid the traditional spherical approximation in spectral forward gravity modeling. The first solution (the extended integration method) applies integration over masses from a Reference Sphere to the topography and applies a correction for the masses between ellipsoid and Sphere. The second solution (the harmonic combination method) computes topographic potential coefficients from a combination of surface spherical harmonic coefficients of topographic heights above the ellipsoid, based on a relation among spherical harmonic functions introduced by Claessens (2005). Using a degree 2160 spherical harmonic model of the topographic masses, both methods are applied to derive the Earth's ellipsoidal topographic potential in spherical harmonics. The harmonic combination method converges fastest and—akin to the EGM2008 geopotential model—generates additional spherical harmonic coefficients in spectral band 2161 to 2190 which are found crucial for accurate evaluation of the ellipsoidal topographic potential at high degrees. Therefore, we recommend use of the harmonic combination method to model ellipticity in spectral-domain forward modeling. The method yields ellipsoidal topographic potential coefficients which are “compatible” with global Earth geopotential models constructed in ellipsoidal approximation, such as EGM2008. It shows that the spherical approximation significantly underestimates degree correlation coefficients among geopotential and topographic potential. The topographic potential model is, for example, of immediate value for the calculation of Bouguer gravity anomalies in fully ellipsoidal approximation.
Jiubin Tan - One of the best experts on this subject based on the ideXlab platform.
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transversal strapdown ins based on Reference ellipsoid for vehicle in the polar region
IEEE Transactions on Vehicular Technology, 2016Co-Authors: Yueyang Ben, Jiubin TanAbstract:The transversal coordinate system has been proposed to solve the problem of navigation in the Polar Region for a strapdown inertial navigation system (INS). However, it is assumed that the Earth is a perfect Sphere in the transversal coordinate system, which is not accurate for a high-precision INS. To solve this problem, we consider the Earth as a Reference ellipsoid and then deduct its radii of curvature in our transversal coordinate system. In addition, with the aid of the Bessel geodetic projection method, transformations of navigation quantities from a local-level coordinate system to our transversal coordinate system are derived based on the Reference ellipsoid. Numerical results indicate that our method based on the Reference ellipsoid performs better than the method based on a Reference Sphere.
Sanjay V. Patel - One of the best experts on this subject based on the ideXlab platform.
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relationship between corneal topographic indices and scleral lens base curve
Eye & Contact Lens-science and Clinical Practice, 2010Co-Authors: Muriel Schornack, Sanjay V. PatelAbstract:Objectives: To determine whether parameters of anterior corneal contour as identified by topographic analysis (steep and flat simulated keratometry, Reference Sphere) predict the base curve of Jupiter scleral lenses in patients with dry eye syndrome and keratoconus. Methods: We identified 33 eyes with dry eye syndrome and 21 eyes with keratoconus that were fit with Jupiter scleral lenses of standard design between June 2006 and July 2009. Steep and flat simulated keratometry powers and shape factor from axial topographic maps, Reference Sphere from elevation maps, and base curve of the scleral lens prescribed for each eye were recorded. Correlations between topographic indices and base curve were evaluated by using the Pearson correlation coefficient, and significances were completed by using generalized estimating equation models. Results: In dry eye syndrome, the base curve of the final scleral lens prescribed correlated with the steep keratometric power (r = 0.70, P = 0.05, n = 33), the flat keratometric power (r = 0.71, P Conclusions: In eyes with normal and abnormal ocular contour, base curve of scleral lenses correlates with Reference Sphere and steep and flat keratometric powers, but the predictive relationship is weak (r2 ∼0.50). Diagnostic fitting may be the most efficient method of fitting scleral lenses at present.
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relationship between corneal topographic indices and scleral lens base curve
Eye & Contact Lens-science and Clinical Practice, 2010Co-Authors: Muriel Schornack, Sanjay V. PatelAbstract:OBJECTIVES To determine whether parameters of anterior corneal contour as identified by topographic analysis (steep and flat simulated keratometry, Reference Sphere) predict the base curve of Jupiter scleral lenses in patients with dry eye syndrome and keratoconus. METHODS We identified 33 eyes with dry eye syndrome and 21 eyes with keratoconus that were fit with Jupiter scleral lenses of standard design between June 2006 and July 2009. Steep and flat simulated keratometry powers and shape factor from axial topographic maps, Reference Sphere from elevation maps, and base curve of the scleral lens prescribed for each eye were recorded. Correlations between topographic indices and base curve were evaluated by using the Pearson correlation coefficient, and significances were completed by using generalized estimating equation models. RESULTS In dry eye syndrome, the base curve of the final scleral lens prescribed correlated with the steep keratometric power (r = 0.70, P = 0.05, n = 33), the flat keratometric power (r = 0.71, P<0.001, n = 33), and the Reference Sphere (r = 0.73, P = 0.002, n = 33). In eyes with keratoconus, base curve also correlated with the steep keratometric power (r = 0.72, P<0.001, n = 19), the flat keratometric power (r = 0.70, P<0.001, n = 19), and the Reference Sphere (r = 0.68, P<0.001, n = 21). There were no correlations between base curve and shape factor. CONCLUSIONS In eyes with normal and abnormal ocular contour, base curve of scleral lenses correlates with Reference Sphere and steep and flat keratometric powers, but the predictive relationship is weak (r ∼0.50). Diagnostic fitting may be the most efficient method of fitting scleral lenses at present.
Sten Claessens - One of the best experts on this subject based on the ideXlab platform.
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ellipsoidal topographic potential new solutions for spectral forward gravity modeling of topography with respect to a Reference ellipsoid
Journal of Geophysical Research, 2013Co-Authors: Sten Claessens, Christian HirtAbstract:Forward gravity modeling in the spectral domain traditionally relies on spherical approximation. However, this level of approximation is insufficient for some present day high-accuracy applications. Here we present two solutions that avoid the traditional spherical approximation in spectral forward gravity modeling. The first solution (the extended integration method) applies integration over masses from a Reference Sphere to the topography and applies a correction for the masses between ellipsoid and Sphere. The second solution (the harmonic combination method) computes topographic potential coefficients from a combination of surface spherical harmonic coefficients of topographic heights above the ellipsoid, based on a relation among spherical harmonic functions introduced by Claessens (2005). Using a degree 2160 spherical harmonic model of the topographic masses, both methods are applied to derive the Earth's ellipsoidal topographic potential in spherical harmonics. The harmonic combination method converges fastest and—akin to the EGM2008 geopotential model—generates additional spherical harmonic coefficients in spectral band 2161 to 2190 which are found crucial for accurate evaluation of the ellipsoidal topographic potential at high degrees. Therefore, we recommend use of the harmonic combination method to model ellipticity in spectral-domain forward modeling. The method yields ellipsoidal topographic potential coefficients which are “compatible” with global Earth geopotential models constructed in ellipsoidal approximation, such as EGM2008. It shows that the spherical approximation significantly underestimates degree correlation coefficients among geopotential and topographic potential. The topographic potential model is, for example, of immediate value for the calculation of Bouguer gravity anomalies in fully ellipsoidal approximation.
Souichi Telada - One of the best experts on this subject based on the ideXlab platform.
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three spherical mirror test for radius of curvature measurement using a fabry perot cavity
Optics Express, 2019Co-Authors: Youichi Bitou, Osamu Sato, Souichi TeladaAbstract:A three-spherical-mirror test method that uses a Fabry-Perot (FP) cavity is proposed for a radius of curvature measurement system, especially for radii larger than 10 m. By using the three-spherical-mirror test with mode spacing measurement in an FP cavity, the local value of the radius of curvature of a mirror can be determined in situ and this mirror can then be used as the Reference spherical mirror in a radius of curvature measurement system. We demonstrated determinations of radii of curvature of around 10 m using the three-spherical-mirror test with uncertainties of around 1.5 × 10−4 and then measured the radius of curvature of around 20 m with uncertainties of around 3.1 × 10−4 by using the spherical mirror, of which the radius of curvature was determined by the three-spherical-mirror test, as the Reference Sphere. The proposed system has high practical applicability because measurements can be conducted under usual air conditions and the measurement results are directly traceable to the time standard because beat frequency measurement is used.