H. Bâki Iz

Integrating Heterogeneous Data Sets with Partial Inconsistencies

In this study, we formulate two different approaches that will enable us to detect and control inconsistencies when integrating heterogeneous data sets. Through two numerical examples with simulated and real data, we compared both model solutions with a combination solution in which no attempt has been made to rectify the partial inconsistencies.

BLIMPBE and its Geodetic Applications

Adjustment of geodetic data using coordinate-based formulations leads to rank-deficient Gauss-Markov models depending on the observation type. Among alternatives, minimum norm least squares solution (equivalently BLUMBE) is used to overcome this deficiency. In this study we examine further extensions of the minimum norm solution in the least-squares solution space, such as partial MINOLESS, which make use of a selection matrix. We derive Best Linear Minimum Partial Bias Estimation (BLIMPBE) via bias minimization from which partial MINOLESS can be obtained as a special case. We show, through an example, that BLIMPBE can be used effectively to control the contribution of the various parameters to the overall solution in the presence of model or observation biases.

Use of Bloom's taxonomic complexity in online multiple choice tests in Geomatics education

Abstract Tests are the most common method to evaluate teaching effectiveness throughout the period of instruction (formative) and assess student learning outcomes at the end of the instruction period (summative). Teaching geomatics is not an exception to this rule. The recent proliferation of computer hardware and software technologies now makes Multiple Choice (MC) type assessment methods more attractive. MC tests provide more objective measures on assessing student learning with efficiency over the Internet. In this study we show, using in-house software, that multiple choice tests when combined with technology, especially multimedia, can be flexible and easy to use. The interface has two unique features: 1) it accommodates questions of various multimedia formats, diagrams, tables, images, or equations that can be conveniently incorporated into the examination; 2) it tracks the students time spent on each question during the examination. We found that 79 percent of the variation in the average time students spent on each question can be explained by Blooms taxonomy (with a correlation coefficient on 0.89. Hence by grouping exam questions at Blooms taxonomic levels we can detect student learning difficulties effectively within each level.

Deformation analysis of the unified lunar control networks

Abstract This study compares the latest Unified Lunar Control Network, ULCN 2005, solution with the earlier ULCN 1994 solution at global and local scales. At the global scale, the relative rotation, translation, and deformation (normal strains and shears) parameters between the two networks are estimated as a whole using their colocated station Cartesian coordinate differences. At the local scale, the network station coordinate differences are examined in local topocentric coordinate systems whose origins are located at the geometric center of quadrangles and tetrahedrons. This study identified that the omission of the topography in the old ULCN solutions shifted the geometric center of the lunar figure up to 5 km in the lunar equatorial plane and induced a few hundred-meter level global rotations of the ULCN 1994 reference frame with respect to ULCN 2005. The displacements between the old and new control networks are less than ± 2 km on the average at the local scale, which behave like translations, caused by the omission of lunar topography in the earlier solution. The contribution of local rigid body rotations and dilatational and compressional components to the local displacements are approximately ± 100 m for a quadrangle/tetrahedron of an average side length of 10 km.

New parameters of geometrically best fitting lunar figures

Abstract The parameters of various lunar figures are of interest to the scientific community working on lunar exploration. In this study, the size of the geometrically best fitting triaxial and rotational ellipsoids, and spheres, are estimated using the method of condition equations with common unknown parameters from the coordinates of 271,610 control points of the newly available lunar control, ULCN 2005. In the first set of solutions, the origin of the figures is calculated with respect to the center of the mass of the Moon. Their origins are set to coincide with the lunar center of mass in the second set of solutions. The new estimates are the most up-to-date values for the triaxial and rotational ellipsoidal and spherical parameters of the lunar figures and are significantly different up to half a km as compared to the most recent solutions.

Differencing Reveals Hidden Changes in Baseline Length Time-series

In order to make successful earthquake predictions, detection and monitoring of baseline changes are important for investigating their origins, including precursory crustal deformations in tectonically active areas. In this study, differencing two baselines that run approximately parallel to each other and normal to the expected crustal deformations, and that share a station is proposed for analysis. Differencing reduces common systematic baseline errors, thereby enabling detection of subtle transient systematic changes in the baseline time-series that are otherwise buried in the measurement noise. Mean shift analysis, a well-known statistical technique to determine hether the mean of a stochastic process has shifted using cumulative sum charts, can then be used to locate the change points in the time-series. The application of this method to the differences of concurrently observed very long baseline interferometry (VLBI) and global positioning system (GPS) baselines in the Japanese Keystone project, where periodic and persistent baseline changes are removed, revealed transient variations in the baseline lengths several months prior to the seismic activity in the Izu Islands that started on June 26, 2000. Reproduction of the results using GPS and VLBI, two alternative baseline measurement techniques, validated the accuracy of the proposed approach for detecting previously hidden transient changes in the baseline lengths.

Modeling regional sea level rise using local tide gauge data

Abstract Currently regional mean sea level trends and variations are inferred from the analysis of several individual local tide gauge data that spanonly a long period of time at a given region. In this study, we propose using a model to merge various tide gauge data, regardless of theirtime span, in a single solution, to estimate parameters representative of regional mean sea level trends. The proposed model can accountfor the geographical correlations among the local tide gauge stations as well as serial correlations, if needed, for individual stations’ data.Such a vigorous regional solution enables statistically optimal uncertainties for estimated and projected trends. The proposed formulationalso unifies all the local reference levels by modeling their offsets from a predefined station’s reference level. To test its effectiveness, theproposed model was used to investigate the regional mean sea level variations for the coastal areas of the Florida Panhandle using 26 localtide gauge stations that span approximately 830 years of monthly averages from the Permanent Service for Mean Sea Level repository. Thenew estimate for the regional trend is 2.14 mm/yr with a ±0.03 mm/yr standard error, which is an order of magnitude improvement overthe most recent mean sea level trend estimates and projections for the Florida region obtained from simple averages of local solutions.

Assessing consistency of Chang’E-1 and SELENE reference frames using nearly-colocated laser altimetry footprint positions

The consistency of the Chang’E-1 and SELENE reference frames as realized by the footprint positions of laser altimetry measurements of the lunar surface during both missions was analyzed using a global 12-parameter model for small (with respect to unity) deformations and rigid body motions. The rigid body motion and deformation parameters between the two reference frames estimated from nearly-colocated without tie measurements are found to be consistent, i.e., nearly zero for the estimates of the translations, rotations and shear parameters. However, the estimated three strain parameters, which are similar in magnitude and sign, reveal a prominent scale difference, between the Chang’E-1 and SELENE reference frames, of about 0.9 × 10−5. The scale difference can be attributed to calibration of the data sets using the known coordinates of the lunar laser ranging stations all located on the near side of the Moon.

More confounders at global and decadal scales in detecting recent sea level accelerations

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. J. Geod. Sci. 2015; 5:192–198 Research Article Open Access H. Bâki Iz* More confounders at global and decadal scales in detecting recent sea level accelerations DOI 10.1515/jogs-2015-0020 Received September 11, 2015; accepted December 31, 2015 Abstract: The residuals of 27 globally distributed long tide gauge recordswere scrutinized after removing the globally compounding effect of the periodic lunar node tides and almost periodic solar radiation’s sub and superharmonics from the tide gauge data. The spectral analysis of the residuals revealed additional unmodeled periodicities at decadal scales, 19 of which are within the close range of 12–14 years, at 27 tide gauge stations. The amplitudes of the periodicitieswere subsequently estimated for the spectrally detected periods and they were found to be statistically significant (p «0.05) for 18 out of 27 globally distributed tide gauge stations. It was shown that the estimated amplitudes at different localities may have biased the outcomeof all the previous studies based on tide gauge or satellite altimetry data that did not account for these periodicities, within the range −0.5 – 0.5 mm/yr., acting as another confounder in detecting 21 st century sea level rise.

Thermosteric contribution of warming oceans to the global sea level variations

Abstract Thermosteric contribution of warming oceans to the global sea level variations during the last century was evaluated at globally distributed 27 tide gauge stations with records over 80 years. The assessment was made using a recently proposed lagged model inclusive of a sea level trend, long and decadal periodicities, and lagged sea surface temperature measurements. The new model solutions revealed that almost all the long period periodic sea level changes experienced at these stations can be attributed to the lagged thermosteric effects of the warming oceans during the 20th century. Meanwhile, statistically significant (p<0.05) anomalous thermosteric contributions to the secular trends, some of them as large as 1.0±0.2 mm/yr, were detected at six tide gauge stations close to the equator and open seas. The findings of this study revealed a more complex impact of the warming oceans at the globally distributed tide gauge stations other than a secular contribution to the sea level trends of the previous studies.