Jung-Ho Cho

Seasonal variability of GPS-derived zenith tropospheric delay (1994-2006) and climate implications

[1] The total zenith tropospheric delay (ZTD) is an important parameter of the atmosphere and directly or indirectly reflects the weather and climate processes and variations. In this paper the ZTD time series with a 2-hour resolution are derived from globally distributed 150 International GPS Service (IGS) stations ( 1994 - 2006), which are used to investigate the secular trend and seasonal variation of ZTD as well as its implications in climate. The mean secular ZTD variation trend is about 1.5 +/- 0.001 mm/yr at all IGS stations. The secular variations are systematically increasing in most parts of the Northern Hemisphere and decreasing in most parts of the Southern Hemisphere. Furthermore, the ZTD trends are almost symmetrically decreasing with increasing altitude, while the summation of upward and downward trends at globally distributed GPS sites is almost zero, possibly reflecting that the secular ZTD variation is in balance at a global scale. Significant annual variations of ZTD are found over all GPS stations with the amplitude from 25 to 75 mm. The annual variation amplitudes of ZTD near oceanic coasts are generally larger than in the continental inland. Larger amplitudes of annual ZTD variation are mostly found at middle latitudes (near 20 degrees S and 40 degrees N) and smaller amplitudes of annual ZTD variation are located at higher latitudes ( e. g., Antarctic) and the equator areas. The phase of annual ZTD variation is about 60 degrees in the Southern Hemisphere ( about February, summer) and about 240 degrees in the Northern Hemisphere ( about August, summer). The mean amplitude of semiannual ZTD variations is about 10 mm, much smaller than annual variations. The semiannual amplitudes are larger in the Northern Hemisphere than in the Southern Hemisphere, indicating that the semiannual variation amplitudes of ZTD in the Southern Hemisphere are not significant. In addition, the higher-frequency variability (RMS of ZTD residuals) ranges from 15 to 65 mm of delay, depending on altitude of the station. Inland stations tend to have lower variability and sites at ocean and coasts have higher variability. These seasonal ZTD cycles are due mainly to the wet component variations (ZWD).

Quality Assessment of Tropospheric Delay Estimated by Precise Point Positioning in the Korean Peninsula

Over the last decade, the Global Navigation Satellite System (GNSS) has been increasingly utilized as a meteorological research tool. The Korea Astronomy and Space Science Institute (KASI) has also been developing a near real-time GNSS precipitable water vapor (PWV) information management system that can produce a precise PWV for the Korean Peninsula region using GNSS data processing and meteorological measurements. The goal of this paper is to evaluate whether the precise point positioning (PPP) strategy will be used as the new data processing strategy of the GNSS-PWV information management system. For this purpose, quality assessment has been performed by means of a comparative analysis of the troposphere zenith total delay (ZTD) estimates from KASI PPP solutions (KPS), KASI network solutions (KNS), and International GNSS Service (IGS) final troposphere products (IFTP) for ten permanent GNSS stations in the Korean Peninsula. The assessment consists largely of two steps: First, the troposphere ZTD of the KNS are compared to those of the IFTP for only DAEJ and SUWN, in which the IFTP are used as the reference. Second, the KPS are compared to the KNS for all ten GNSS stations. In this step, the KNS are used as a new reference rather than the IFTP, because it was proved in the previous step that the KNS can be a suitable reference. As a result, it was found that the ZTD values from both the KPS and the KNS followed the same overall pattern, with an RMS of 5.36 mm. When the average RMS was converted into an error of GNSS-PWV by considering the typical ratio of zenith wet delay and PWV, the GNSS-PWV error met the requirement for PWV accuracy in this application. Therefore, the PPP strategy can be used as a new data processing strategy in the near real-time GNSS-PWV information management system.

RETRIEVAL OF ELECTRON DENSITY PROFILE FOR KOMPSAT-5 GPS RADIO OCCULTATION DATA PROCESSING SYSTEM

The AOPOD (Atmosphere Occultation and Precision Orbit Determination) system, the secondary payload of KOMPSAT (KOrea Multi-Purpose SATellite)-5 scheduled to be launched in 2010, shall provide GPS radio occultation data. In this paper, we simulated the GPS radio occultation characteristic of KOMPSAT-5 and retrieved electron density profiles using KROPS (KASI Radio Occultation Processing Software). The electron density retrieved from CHAMP (CHAllenging Minisatellite Payload) GPS radio occultation data on June 20, 2004 was compared with IRI (International Reference Ionosphere) - 2001, PLP (Planar Langmuir Probe), and ionosonde measurements. When the result was compared with ionosonde measurements, the discrepancies were 5 km on the peak height () and on the electron density of the peak height (). By comparing with the Laugmuir Probe measurements of CHAMP satellite (PLP), both agrees with at the height of 365.6 km.

Characteristics of Perturbations in Recent Length of Day and Polar Motion

Various features of the existing perturbations in the Earth’s spin rotation are investigated for the recent and most reliable data by spectral analysis, filtering, and comparison with idealized model. First, theory of Earth’s spin rotational perturbation is briefly re-derived in the Earth-fixed coordinate frame. By spectral windowings, different periodic components of the length of day perturbation are separated, and their characters and excitations are discussed. Different periodic components of polar motion are acquired similarly and described with further discussion of their excitations. Causes of the long time trends of both the length of day and polar motion are discussed. Three possible causes are considered for the newly discovered 490-day period component in the polar motion.

Modelling Systematic Residuals in Absolute ZTD Estimation from GPS

Abstract —Tropsheric delay is one of important error sources in GPS positioning and InSAR applications. Accurate measurements of ZTD (Zenith Tropospheric Delay) can be used for correcting the atmospheric delay on GPS and InSAR as well as atmospheric science research and applications (e.g. numeric weather prediction). Traditionally, the GPS ZTD estimations were obtained based on the least squares (LS) principle, where the functional and stochastic models of GPS measurements need to be defined precisely. The functional models for GPS measurements have been investigated in considerable detail in the past two decades. However, most scientific GPS processing software packages, e.g. GAMIT, BERNESE or GIPSY, the stochastic models of GPS observation data are simplified, assuming that all the GPS measurements have the same variance, and that they are statistically independent in time and space. Such assumptions are unrealistic and will result in unreliable ZTD estimations as GPS observations from different satellites cannot have the same accuracy due to varying noise levels. In addition, it is impossible to model all systematic errors in the functional model, and therefore, modeling some systematic errors into the stochastic model is a current challenging topic to further realize the full potential of increasingly more accurate GPS positioning applications. This paper aims to improve the GPS ZTD estimations by modeling GPS systematic residuals into the stochastic model

Ionospheric Behaviors Over Korea Peninsula During the Super Geomagnetic Storm Using GPS Measurements

The super-geomagnetic storms called 2003 Halloween event globally occurred during the period of 29 through 31 which are the following days when the solar flares of X18 class exploded on 28 October 2003. The S4 index from GPS signal strength and the peak electron density (NmF2) from GPS tomography method are analyzed according to the date. The occurrences of the cycle slip and scintillation in the GPS signals are

RF ENVIRONMENT TEST ON A PROPOSED SITE FOR THE SENSOR STATION OF THE NEXT GENERATION SATELLITE NAVIGATION SYSTEM, GALILEO: I. THE RESULT OF THE TEST ON THE VICINITY OF KVN TAMLA SITE IN THE YEAR OF 2006 BY KASI

As the next generation of global satellite navigation system, the Galileo project is about to witness an initial orbit validation stage as the successful test of navigation message transmission from Giove-A in 2007. The Space Geodesy division ana the Radio Astronomy division of the Korea Astronomy & Space Science Institute had collaborated on the field survey for the Galileo Sensor Station (GSS) RF environment of the proposed site near Jeju Tamla University from August 3rd to August 5th, 2006. The power spectrums were measured in full-band and in-band (E5, E6 and L1 band) in frequency domain for 24 hours respectively. Finally, we performed a time domain analysis to characterize strong in-band interference source based on the result of the previous step.

ANALYSIS ON GPS PWV EFFECTS AS AN INITIAL INPUT DATA OF NWP MODEL

The Precipitable Water Vapor (PWV) from GPS with high resolution in terms of time and space might reduce the limitations of the numerical weather prediction (NWP) model for easily variable phenomena, such as precipitation and cloud. We have converted to PWV from Global Positioning System (GPS) data of Korea Astronomy and Space Science Institute (KASI) and Ministry of Maritime Affairs & Fisheries (MOMAF). First of all, we have selected the heavy rainfall case of having a predictability limitation in time and space due to small-scale motion. In order to evaluate the effect for GPS PWV, we have executed the sensitivity experiment with PWV from GPS data over Korean peninsula in the Weather Research & Forecasting 3-Dimensional Variational (WRF-3DVAR). We have also suggested the direction of further research for an improvement of the predictability of NWP model on the basis of this case.

AN ANALYSIS OF THE EFFECT ON THE DATA PROCESSING OF KOREA GPS NETWORK BY THE ABSOLUTE PHASE CENTER VARIATIONS OF GPS ANTENNA

The International GNSS Service (IGS) has prepared for a transition from the relative phase conte. variation (PCV) to the absolute PCV, because the terrestrial scale problem of the absolute PCV was resolved by estimating the PCV of the GPS satellites. Thus, the GPS data will be processed by using the absolute PCV which will be an IGS standard model in the near future. It is necessary to compare and analyze the results between the relative PCV and the absolute PCV for the establishment of the reliable processing strategy. This research analyzes the effect caused by the absolute PCV via the GPS network data processing. First, the four IGS stations, Daejeon, Suwon, Beijing and Wuhan, are selected to make longer baselines than 1000km, and processed by using the relative PCV and the absolute PCV to examine the effect of the antenna raydome. Beijing and Wuhan stations of which the length of baselines are longer than 1000km show the average difference of 1.33cm in the vertical component, and 2.97cm when the antenna raydomes are considered. Second, the 7 permanent GPS stations among the total 9 stations, operated by Korea Astronomy and Space Science Institute, are processed by applying the relative PCV and the absolute PCV, and their results are compared and analyzed. An insignificant effect of the absolute PCV is shown in Korea regional network with the average difference of 0.12cm in the vertical component.

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 (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 (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 (2.9%).