Jihye Won

Comparison of the Characteristics of Precipitable Water Vapor Measured by Global Positioning System and Microwave Radiometer

Korea Astronomy and Space Science Institute, Daejeon 305-348, KoreaIn this study, global positioning system (GPS)-derived precipitable water vapor (PWV) and microwave radiometer (MWR)-measured integrated water vapor (IWV) were compared and their characteristics were analyzed. Comparing those two quantities for two years from August 2009, we found that GPS PWV estimates were larger than MWR IWV. The average difference over the entire test period was 1.1 mm and the standard deviation was 1.2 mm. When the discrepan-cies between GPS PWV and MWR IWV were analyzed depending on season, the average difference was 0.7 mm and 1.9 mm in the winter and summer months, respectively. Thus, the average difference was about 2.5 times larger in summer than that in winter. However, MWR IWV measurements in the winter months were over-estimated than those in the sum -mer months as the water vapor content got larger. The results of the diurnal analysis showed that MWR IWV was under-estimated in the daytime, showing a difference of 0.8 mm. In the early morning hours, MWR IWV has a tendency to be over-estimated, with a difference of 1.3 mm with respect to GPS PWV.

Effects of Tropospheric Mapping Functions on GPS Data Processing

In processing space geodetic data, mapping functions are used to convert the tropospheric signal delay along the zenith direction to the line of sight direction. In this study, we compared three mapping functions by evaluating their effects on the tropospheric signal delay and position estimates in GPS data processing. The three mapping functions tested are Niell Mapping Function (NMF), Vienna Mapping Function 1 (VMF1), and Global Mapping Function (GMF). The tropospheric delay and height estimates from VMF1 and GMF are compared with the ones obtained with NMF. The differences among mapping functions show annual signals with the maximum occurring in February or August. To quantitatively estimate the discrepancies among mapping functions, we calculated the maximum difference and the amplitude using a curve fitting technique. Both the maximum difference and amplitude have high correlations with the latitude of the site. Also, the smallest difference was found around and the amplitudes increase toward higher latitudes. In the height estimates, the choice of mapping function did not significantly affect the vertical velocity estimate, and the precision of height estimates was improved at most of the sites when VMF1 or GMF was used instead of NMF.

Generation of Grid Maps of GPS Signal Delays in the Troposphere and Analysis of Relative Point Positioning Accuracy Enhancement

†,*,** Graduate school of Inha University, Incheon 402-751, Korea*** Department of Geoinformatic Engineering, Inha University, Incheon 402-751, Korea요 약 :대류권의 건조가스 및 수증기에 의한 GPS 신호의 지연은 GPS 측위 정확도를 저하시키는 주요 원인으로 정밀 측위를 위해서 반드시 소거해야할 대상이다. 이 논문에서는 실시간으로 대류권 지연정보를 생성하여 GPS 측위에 적용하기 앞서, 대류권 지연정보 생성 알고리즘의 가용성을 파악하기 위해 후처리 기반으로 전국의 GPS 상시관측망을 이용하여 한반도 상공의 대류권 지연량 격자 지도를 생성하는 과정을 구현하였다. GPS 자료처리 소프트웨어는 GIPSY 5.0을 사용하였고, 건조지연량과 습윤지연량을 구분하여 산출하기 위해 전국의 AWS 관측망의 관측자료를 이용하였다. 대류권 지연정보에 대한 격자 지도를 생성한 후 격자 지도의 정확도를 검증한 결과, 격자 지도와 GPS 관측소 위치에서 산출된 대류권 지연량의 RMSE는 ZHD 0.7mm, ZWD 7.5mm, ZTD 8.7mm로 나타났다. 산출된 대류권 지연정보를 단일주파수 기반 상대 측위 알고리즘에 적용하여 대류권 지연정보 보정시 측위정확도 향상 정도를 분석하였다. 결과로 측위정확도는 기선거리가 약 297km인 수원(SUWN)과 목포(MKPO)의 상대처리 결과에서 최대 36%가 향상됨을 확인할 수 있었다.핵심용어 : GPS, 대류권지연, 건조지연, 습윤지연, 격자지도Abstract : GPS signal delay that caused by dry gases and water vapor in troposphere is a main error source of GPS point positioning and it must be eliminated for precise point positioning. In this paper, we implemented to generate tropospheric delay grid map over the Korean Peninsula based on post-processing method by using the GPS permanent station network in order to determine the availability of tropospheric delay generation algorithm. GIPSY 5.0 was used for GPS data process and nationwide AWS observation network was used to calculate the amount of dry delay and wet delay separately. As the result of grid maps accuracy analysis, the RMSE between grid map data and GPS site data was 0.7mm in ZHD, 7.6mm in ZWD and 8.5mm in ZTD. After grid map accuracy analysis, we applied the calculated tropospheric delay grid map to single frequency relative positioning algorithm and analyzed the positioning accuracy enhancement. As the result, positioning accuracy was improved up to 36% in case of relative positioning of Suwon(SUWN) and Mokpo(MKPO), that the baseline distance is about 297km.Key words :GPS, ZTD, ZHD, ZWD, Grid Map †교신저자:연회원, dskim@inha.edu 032)873-4310 * 연회원, jhwon1021@inha.edu 032)873-4310 ** 연회원, h79s86@gmail.com 032)873-4310*** 연회원, kdpark@inha.ac.kr 032)860-7604

Observation of Atmospheric Water Vapors Using AIRS

The Atmospheric Infrared Sounder (AIRS) aboard the Aqua satellite, which is one of the Earth Observing System satellites managed by National Aeronautics and Space Administration, provides global measurements of the water vapor in the atmosphere using infrared (IR) channels. In this paper, we restored precipitable water vapor (PWV) over a permanent GPS station in Incheon using the IR measurements of AIRS and compared the result with GPS-based PWV estimates. As a result, AIRS PWV had similar trends with GPS PWV; the bias of AIRS PWV against GPS PWV is 0.3 cm and root mean square error (RMSE) 0.7 cm. In addition, the correlation coecient between AIRS PWV and GPS PWV was 0.89. Thus we conclude that the AIRS PWV reflects local characteristics of the water vapor content.

Analysis of Temporal and Spatial Variation of Precipitable Water Vapor According to Path of Typhoon EWINIAR using GPS Permanent Stations

ABSTRACT In this study, the temporal and spatial variation in precipitable water vapor (PWV) was analyzed for typhoon Ewiniar which had made landfall in the Korean peninsula in 2006. To make a contour map of PWV, zenith total delay (ZTD) was calculated using about 60 GPS permanent stations in Korea, and the pressure and temperature data of nearby AWS stations were interpolated and applied to the equation for calculating the PWV. While Typhoon Ewiniar was migrating north from the southern coast to the eastern coast of Korea, the PWV migrated showing a spatial distribution similar to that of rainfall. Also, the fluctuating pattern of the normalized PWV was analyzed, and the moving speed of the PWV was estimated using the delay time of the increase/decrease pattern in the eight-test stations. The result indicated that the moving speed of the PWV was about 35 km/h, which was similar to the average moving speed of the typhoon (38.9 km/h). Keywords: EWINIAR, GPS, precipitable water vapor, rainfall, normalized PWV

Validation of the Atmospheric Infrared Sounder Water Vapor Retrievals Using Global Positioning System: Case Study in South Korea

The atmospheric infrared sounder (AIRS) sensor loaded on the Aqua satellite observes the global vertical structure of atmosphere and enables verification of the water vapor distribution over the entire area of South Korea. In this study, we performed a comparative analysis of the accuracy of the total precipitable water (TPW) provided as the AIRS level 2 standard retrieval product by Jet Propulsion Laboratory (JPL) over the South Korean area using the global positioning system (GPS) TPW data. The analysis TPW for the period of one year in 2008 showed that the accuracy of the data produced by the combination of the Advanced Microwave Sounding Unit sensor with the AIRS sensor to correct the effect of clouds (AIRS-X) was higher than that of the AIRS IR-only data (AIRS-I). The annual means of the root mean square error with reference to the GPS data were 5.2 kg/m 2 and 4.3 kg/m 2 for AIRS-I and AIRS-X, respectively. The accuracy of AIRS-X was higher in summer than in winter while measurement values of AIRS-I and AIRS-X were lower than those of GPS TPW to some extent.