• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.53-56
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• 2006

KOMPSAT (KOrea Multi-Purpose SATellite)-5 for the earth observation and scientific research is scheduled to launch in 2009. The second payload, AOPOD (Atmosphere Occultation and Precision Orbit Determination) system, consists of a space-borne dual frequency GPS receiver and a laser retro reflector. GPS radio occultations from AOPOD system can be used to generate profiles of refractivity, temperature, pressure and water vapor in the neutral atmosphere with a high vertical resolution. Also the radio occultation in the ionosphere provides an inexpensive tool of vertical electron density profile. Currently, many LEO missions with GPS radio occultation receivers are on orbit and more GPS occultation missions are planed to launch in the near future. In this paper, we simulated radio occultation measurements from KOMPSAT-5 and retrieved atmospheric profiles using the simulated data.

• 한국위성정보통신학회논문지
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• 제8권1호
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• pp.14-22
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• 2013

GPS 전파엄폐는 GPS 전파가 대기에 의해 굴절 및 지연되는 현상에 기초하여 대기의 물리적 특성을 관측하기 위한 원격탐사 기법이다. 2006년 미국과 대만이 공동 개발한 FORMOSAT-3/COSMIC 위성은 하루 2500여건의 전파엄폐 자료를 준실시간으로 제공하고 있으며, 우리나라의 다목적실용위성 5호의 AOPOD(Atmosphere Occultation and Precision Orbit Determination) 시스템은 이중주파수 GPS 수신기 및 전파엄폐 자료수신용 안테나를 장착함으로써 전파엄폐 자료의 획득이 가능하도록 설계되어 대류권과 전리층 연구에 활용될 것으로 기대되고 있다. 본 연구에서는 GPS 전파엄폐의 신호처리와 지오메트리 분석기법을 검토하고, 대류권 온습도와 전리층 전자밀도 및 신틸레이션(scintillation) 산출기법을 분석하며, 이러한 전자엄폐 탐측자료를 활용하기 위한 방안으로서 전리층 총전자수 변화를 통한 지진감시와 효율적인 자료서비스를 위한 오픈 API(application programming interface) 구축에 대해 검토하고자 한다.

• Journal of Astronomy and Space Sciences
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• 제27권4호
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• pp.345-352
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• 2010

Korea multi-purpose satellite-5 (KOMPSAT-5) is a low earth orbit (LEO) satellite scheduled to be launched in 2010. To satisfy the precision orbit determination (POD) requirement for a high resolution synthetic aperture radar image of KOMPSAT-5, KOMPSAT-5 has atmosphere occultation POD (AOPOD) system which consists of a space-borne dual frequency global positioning system (GPS) receiver and a laser retro reflector array. A space-borne dual frequency GPS receiver on a LEO satellite provides position data for the POD and radio occultation data for scientific applications. This paper describes an overview of AOPOD system and operation concepts of the radio occultation mission in KOMPSAT-5. We showed AOPOD system satisfies the requirements of KOMPSAT-5 in performance and stability.

• Journal of Astronomy and Space Sciences
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• 제24권4호
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• pp.297-308
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• 2007

2010년에 발사될 예정인 아리랑위성 5호의 부 탑재체인 AOPOD(Atmosphere Occultation and Precision Orbit Determination) 시스템은 GPS(Global Positioning System) 전파 엄폐(radio occultation) 자료를 제공한다. 이 논문에서는 아리랑위성 5호 궤도에서 발생하는 GPS 전파 엄폐의 발생 빈도 및 분포를 시뮬레이션하고, 현재 천문연구원에서 개발 중인 GPS 전파 엄폐 자료처리시스템인 KROPS(KASI Radio Occultation Processing System)를 사용한 전리층 전자밀도 산출결과를 제시하였다. 전자밀도를 산출하기 위해 2004년 6월 20일에 발생한 CHAMP(CHAllenging Minisatellite Payload) 위성의 GPS 전파 엄폐 관측값을 사용하였고 산출된 결과는 IRI(International Reference Ionosphere) - 2001 모델과 CHAMP 위성의 랑뮈어 탐침기(Planar Langmuir Probe) 및 이온존데 간과 비교하였다. 산출된 전자밀도를 이온존데 값과 비교했을 때, $F_2$층 최대전자밀도 고도인 $hmF_2$에서 약 5km, $F_2$층 최대전자밀도인 $NmF_2$에서 약 $3{\times}10^{10}el/m^3$의 차이를 보였으며, 랑뮈어 탐침기 값과 비교하여 고도 365.6km에서 두 값 모두 $1.6{\times}10^{11}el/m^3$로 일치하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.192-195
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• 2008

Radio occultation (RO) has been used in the planetary science since Microlab-1 was launched in 1995. With the RO technique, the profiles of atmosphere and the global atmospheric data can be obtained. In 2006, Taiwan launched six low Earth orbit (LEO) satellites as the RO constellation mission, known as FORMOSAT-3. In order to retrieve the RO data from original data, a retrieval algorithm, NCURO, is developed. The input of NCURO algorithm is mainly the excess phase of GPS signal, and the output is the dry pressure and dry temperature. Using temperature profiles retrieved by NCURO algorithm, temperature perturbation and potential energy of gravity wave have been evaluated. In this paper, the retrieval algorithm and the global distribution of energy of gravity waves are described and demonstrated.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.442-444
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• 2007

How to observe the atmosphere is a subject of atmospheric research. The meteorological satellites and the ground states are used to do observation. However, both ways do not satisfy the requirement of scientists, especially the profiles of atmosphere on the ocean and the data for global atmosphere. Radio occultation (RO) technique, which has been used in planet science, is a method to solve the problem. In RO technique, the low Earth orbit (LEO) satellite receives the two frequency signal of Global Positioning System (GPS) satellite. The excess phase of the signal is calculated to retrieve the profiles of atmosphere parameters. In moist troposphere, the fluctuations appear in the phase of the signal and open loop (OL) is used to resolve it. The quality of the GPS signal generally deteriorates as the altitude decreases. In the procedure, the SNR of the GPS signal is used as the criterion. However, the SNR decreases with fluctuation which makes it difficult to locate the data of poor quality. In this paper, the phase of the signal will be used as part of the criterion.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.312-315
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• 2006

Radio occultation technique has been used in planetary science to obtain reliable and accurate temperature profiles of the other planets' atmosphere for decades. It relies on the fact that radio waves are bent and delayed due to the gradient of atmospheric refractivity along-ray-path. With the advent of Global Positioning System (GPS), it becomes possible to retrieve the refractivity and temperature profiles of the Earth's atmosphere from the occultation data. We have developed a retrieval algorithm and compared the results of our algorithm with the data of CHAMP to verify the accuracy of our algorithm is good enough. In our algorithm, there are some smoothing steps when retrieving. We analysis the data of FORMOSAT-3 and compare the results with and without smoothing and the results of TACC to see is there any phenomenon deleted after smoothing.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.43-46
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• 2005

[1] There are systematical errors associated with ionospheric influence in retrieving key atmospheric parameters from radio occultation (RO) soundings. In order to obtain better-quality retrievals, we develop a new method, hereafter called National Central University Radio Occultation (NCURO) scheme, to reduce the ionospheric influence. The excess phase is divided into two parts, namely geometric excess length and path excess length (excess length along ray path due to refractivity effect). An excess phase equation is presented and implemented in the NCURO scheme Whose performance is evaluated through comparisons with model simulation and experimental data. The model simulation is based on the use of the ionospheric model 002001 and atmospheric model NRLMSISE-OO. Results show that the NCURO scheme significantly reduces the ionospheric influence at altitudes above 70 km as does the scheme presented in the literature, and provides better corrections for the atmospheric profile. INDEX TERMS: 2400 Ionosphere: Ionosphere; 6964 Radio Science: Radio wave propagation; 6969 Radio Science: Remote sensing.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.41.2-41.2
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• 2009

저궤도위성에서 수신한 지구대기에 의해 엄폐된(Occulted) GPS 신호를 이용한 연직 수증기량 산출에 관해 다루었다. 전파엄폐(Radio Occultation) 기법은 원래 행성대기에 의해 엄폐된(Occulted) 별빛을 이용하여 행성의 대기를 분석하는데 사용되던 기법을 일컫는 말로 최근엔 GPS를 이용한 지구대기 분석에 활용되고 있다. 1995년 GPS/MET 위성을 통해 처음으로 GPS 전파엄폐 기술을 통한 대기정보의 연직분포를 산출하였고, 현재는 COSMIC 위성군을 비롯해 많은 저궤도위성에서 GPS 전파엄폐기술을 통해 온도, 압력, 습도 등의 연직분포를 산출하고 있다. 이 중 연직 수증기량 분포는 기상예보를 위한 수치모델(Numerical Weather Model)에서 매우 중요한 초기 값이다. GPS 전파엄폐 기술을 통한 연직수증기량 산출은 라이오존데(Radiosonde)나 마이크로미터와 같은 연직수증기량 관측기기의 검증 및 상호 통합활용이라는 측면에서 활용가치가 매우 높다. 특히, GPS 전파엄폐 기법은 시공간적 제약이 상대적으로 전 지구적인 기후분석에는 적합한 기법으로 주목을 받고 있다. 이 연구에서는 COSMIC에서 제공하는 굴절각(Bending Angle)정보를 이용하여 연직 수증기량을 산출하는 알고리즘을 구현하였다. 또한 천문연이 보유하고 있는 마이크로미터에서 산출한 가강수량과의 비교.검증하기위한 방안을 도출하였다. 이 연구결과는 현재 진행 중인 다목적실용위성 5호의 전파엄폐용 수신기의 활용에 기여할 것으로 기대된다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.65-68
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• 2007

FORMOSAT-3 was launched in April of 2006. It consists of six low earth orbit (LEO) satellites that will be eventually deployed to an orbit at 800 km height. Its scientific goal is to utilize the radio occultation (RO) signals to measure the bending angles when the GPS signals transect the atmosphere. The bending angle is then used to infer atmospheric parameters, including refractivity, temperature, pressure, and relative humidity fields of global distributions through inversion schemes and auxiliary information. The expected number of RO events is around 2500 per day, of which 200 events or so fall into the polar region. Consequently, the FORMOSAT-3 observations are expected to play a key role to improve our knowledge in the weather forecasting and space physics research in the polar region. In this paper, we use temperature profiles retrieved from FORMOSAT-3 RO observations to study the climatology of gravity wave activity in the polar region. FORMOSAT-3 can provide about 200 RO observations a day in the polar region, much more than previous GPS RO missions, and, hence, more detailed climatology of gravity wave activity can be obtained.