KASI Combination Center Report

This report presents the activities of the Korea Astronomy and Space Science Institute (KASI) as an IVS Combination Center during 2012, and it sketches the intended tasks for 2013

On the Analysis of VLBI Observations to GNSS Satellites

Space geodetic techniques such as Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) are used for the determination of celestial and terrestrial reference frames and Earth orientation parameters. It is of utmost importance to combine the observations from the different techniques to fully exploit the strengths and unique characteristics of the techniques, however, inaccurate local ties are problematic for a rigorous combination. To improve the link between the techniques, tests are under way to observe GNSS signals with VLBI radio telescopes directly, and to observe GNSS signals in GNSS antennas with subsequent processing in the VLBI system (“GNSS-VLBI Hybrid System”) including VLBI correlation. In both cases, the GNSS data type is the difference between the ranges from two stations to a satellite. However, it is still difficult to acquire those observations and thus we apply post-processed range measurements from a precise point positioning (PPP) solution with the C5++ software to build those single differences which are then used in the Vienna VLBI Software (VieVS). We use the CONT11 data set with identical clocks at seven sites to validate the models in VieVS and to assess the impact of the combined solution on the geodetic products

The First Experiment with VLBI-GPS Hybrid System

In this paper, we introduce our GPS-VLBI hybrid system and show the results of the first experiment which is now under way. In this hybrid system, GPS signals are captured by a normal GPS antenna, down-converted to IF signals, and then sampled by the VLBI sampler VSSP32 developed by NICT. The sampled GPS data are recorded and correlated in the same way as VLBI observation data. The correlator outputs are the group delay and the delay rate. Since the whole system uses the same frequency standard, many sources of systematic errors are common between the VLBI system and the GPS system. In this hybrid system, the GPS antenna can be regarded as an additional VLBI antenna having multiple beams towards GPS satellites. Therefore, we expect that this approach will provide enough data to improve zenith delay estimates and geodetic results

A standardized pathology report for gastric cancer: 2nd edition

The first edition of ‘A Standardized Pathology Report for Gastric Cancer’ was initiated by the Gastrointestinal Pathology Study Group of the Korean Society of Pathologists and published 17 years ago. Since then, significant advances have been made in the pathologic diagnosis, molecular genetics, and management of gastric cancer (GC). To reflect those changes, a committee for publishing a second edition of the report was formed within the Gastrointestinal Pathology Study Group of the Korean Society of Pathologists. This second edition consists of two parts: standard data elements and conditional data elements. The standard data elements contain the basic pathologic findings and items necessary to predict the prognosis of GC patients, and they are adequate for routine surgical pathology service. Other diagnostic and prognostic factors relevant to adjuvant therapy, including molecular biomarkers, are classified as conditional data elements to allow each pathologist to selectively choose items appropriate to the environment in their institution. We trust that the standardized pathology report will be helpful for GC diagnosis and facilitate large-scale multidisciplinary collaborative studies

VLBI TRF Combination Using GNSS Software

Space geodetic techniques can be used to obtain precise shape and rotation information of the Earth. To achieve this, the representative combination solution of each space geodetic technique has to be produced, and then those solutions need to be combined. In this study, the representative combination solution of very long baseline interferometry (VLBI), which is one of the space geodetic techniques, was produced, and the variations in the position coordinate of each station during 7 years were analyzed. Products from five analysis centers of the International VLBI Service for Geodesy and Astrometry (IVS) were used as the input data, and Bernese 5.0, which is the global navigation satellite system (GNSS) data processing software, was used. The analysis of the coordinate time series for the 43 VLBI stations indicated that the latitude component error was about 15.6 mm, the longitude component error was about 37.7 mm, and the height component error was about 30.9 mm, with respect to the reference frame, International Terrestrial Reference Frame 2008 (ITRF2008). The velocity vector of the 42 stations excluding the YEBES station showed a magnitude difference of 7.3 mm/yr (30.2%) and a direction difference of 13.8° (3.8%), with respect to ITRF2008. Among these, the 10 stations in Europe showed a magnitude difference of 7.8 mm/yr (30.3%) and a direction difference of 3.7° (1.0%), while the 14 stations in North America showed a magnitude difference of 2.7 mm/yr (15.8%) and a direction difference of 10.3° (2.9%)

Preliminary Study on the Plate Motion in Korean Peninsula with New Korean VLBL Array

Korean Peninsula has been postulated to be on the Eurasian plate(EU). On the other hand, recent seismological works and GPS researches suggest that it is on a separate plate called the Amurian plate (AM). However, the GPS results are inconsistent with each other beyond the estimated statistical errors. Moreover, the estimated plate motion parameter, which we obtained from the velocity data of six Korean GPS stations, was not well agreeing with any existing results. Therefore, independent measurements are required to distinguish those results. In near future, we will have 4 VLBI stations in Korea. This compact Korean VLBI array is capable of achieving good determination of the plate motion parameters if it is located on stable sites. We estimated the precision of the AM motion parameters with the Korean VLBI array. The results showed that the Korean VLBI array would verify the existence of the AM, as far as the observation precision of 0.2 - 0.5 mm/yr for station velocities is achieved. Therefore, new Korean geodetic VLBI array can contribute to crustal deformation studies in East Asia

On the Analysis of VLBI Observations to GNSS Satellites

Space geodetic techniques such as Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) are used for the determination of celestial and terrestrial reference frames and Earth orientation parameters. It is of utmost importance to combine the observations from the different techniques to fully exploit the strengths and unique characteristics of the techniques, however, inaccurate local ties are problematic for a rigorous combination. To improve the link between the techniques, tests are under way to observe GNSS signals with VLBI radio telescopes directly, and to observe GNSS signals in GNSS antennas with subsequent processing in the VLBI system (“GNSS-VLBI Hybrid System”) including VLBI correlation.In both cases, the GNSS data type is the difference between the ranges from two stations to a satellite. However, it is still difficult to acquire those observations and thus we apply post-processed range measurements from a precise point positioning (PPP) solution with the C5++ software to build those single differences which are then used in the Vienna VLBI Software (VieVS). We use the CONT11 data set with identical clocks at seven sites to validate the models in VieVS and to assess the impact of the combined solution on the geodetic products

Assessing the Impact of Global GNSS-VLBI Hybrid Observations

GNSS-VLBI hybrid observations refer to an approach where GNSS signals are received by GNSS antennas and correlated with VLBI correlators. The VLBI-like GNSS single differences (two stations to one satellite) are then analyzed together with standard VLBI observations. In this work, we use GNSS observations during CONT11, a continuous VLBI campaign over 15 days in September 2011. During CONT11, GNSS and VLBI are connected to the identical clocks at seven sites, which mean clock parameters can be regarded as site common parameters. We construct GNSS single differences between the ranges from two stations to a satellite, using post-processed range measurements from a precise point positioning (PPP) GPS solution with the C5++ software. Combining VLBI and VLBI-like GNSS delays during CONT11, we estimate station coordinates, Earth orientation parameters, and site common parameters, i.e. zenith wet delays and clock parameters with the Vienna VLBI Software (VieVS). We compare combined solutions with single technique solutions and assess the impact of GNSS-VLBI hybrid observations with respect to those parameters

Assessing the Impact of Global GNSS-VLBI Hybrid Observations

GNSS-VLBI hybrid observations refer to an approach where GNSS signals are received by GNSS antennas and correlated with VLBI correlators. The VLBI-like GNSS single differences (two stations to one satellite) are then analyzed together with standard VLBI observations. In this work, we use GNSS observations during CONT11, a continuous VLBI campaign over 15 days in September 2011. During CONT11, GNSS and VLBI are connected to the identical clocks at seven sites, which mean clock parameters can be regarded as site common parameters. We construct GNSS single differences between the ranges from two stations to a satellite, using post-processed range measurements from a precise point positioning (PPP) GPS solution with the C5++ software. Combining VLBI and VLBI-like GNSS delays during CONT11, we estimate station coordinates, Earth orientation parameters, and site common parameters, i.e. zenith wet delays and clock parameters with the Vienna VLBI Software (VieVS). We compare combined solutions with single technique solutions and assess the impact of GNSS-VLBI hybrid observations with respect to those parameters

GNSS zenith delays and gradients in the analysis of VLBI Intensive sessions

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique which is capable of estimating Universal Time (UT1 = UTC + ΔUT1). So-called VLBI Intensive sessions of the International VLBI Service for Geodesy and Astrometry (IVS) are dedicated to the rapid production of ΔUT1. However, the accuracy achieved with those sessions is still below what could be expected from formal uncertainties of the estimates and one of the reasons is the inappropriate modeling of azimuthal asymmetries of the troposphere delays, because usually no gradients are modeled or estimated. To overcome that deficiency, we introduced troposphere zenith delays and horizontal total gradients estimated from the observations of Global Navigation Satellite Systems (GNSS) i.e. the solution of the Center for Orbit Determination in Europe (CODE) in the analysis of VLBI Intensive sessions carried out from the beginning of 2008 till the end of 2014. We compared our results with the GNSS-derived length-of-day (LOD) estimates of CODE and the International GNSS Service (IGS) and find slight improvements of agreement by up to 1 μs for both INT1 and INT2 sessions with gradients from CODE. We do not see any additional significant improvement of LOD agreement when GNSS zenith delays are introduced