• Journal of Astronomy and Space Sciences
• /
• v.28 no.1
• /
• pp.63-70
• /
• 2011

The needs for satellite formation flying are gradually increasing to perform the advanced space missions in remote sensing and observation of the space or Earth. Formation flying in low Earth orbit can perform the scientific missions that cannot be realized with a single spacecraft. One of the various techniques of satellite formation flying is the determination of the precise baselines between the satellites within the formation, which has to be in company with the precision validation. In this paper, the baseline of Gravity Recovery and Climate Experiment (GRACE) A and B was determined with the real global positioning system (GPS) measurements of GRACE satellites. And baseline precision was validated with the batch and sequential processing methods using K/Ka-band ranging system (KBR) biased range measurements. Because the proposed sequential method validate the baseline precision, removing the KBR bias with the epoch difference instead of its estimation, the validating data (KBR biased range) are independent of the data validated (GPS-baseline) and this method can be applied to the real-time precision validation. The result of sequential precision validation was 1.5~3.0 mm which is similar to the batch precision validation.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.14 no.2
• /
• pp.199-207
• /
• 1996

According to the different baseline lengths, we quantitatively analyzed how much precision of the baseline de-termination is improved for GPS survey when using the precise ephemeris instead of the broadcast ephemeris of GPS satellites. For this research, we selected seven baselines ranging from 15 km to 201 km and performed GPS measurements more than six times for each baseline. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurements for each baseline are compared between the results of using the broadcast ephemeris and the precise ephemeris. As the result, the precision, stability and reliability of the base-line determination using the precise ephemeris is better than those of using the broadcast ephemeris for all base-lines. When using precise ephemeris for the baselines longer than 65 km, the precision less than 0.1ppm is always obtained and the precision improvement rate by using the precise ephemeris is considerably greater than that for the shorter baselines. We expect that this result might be a quantative basis for the decision about what ephemeris is better for the baseline length and the demanded precision in GPS survey.

• Journal of Korean Society for Geospatial Information Science
• /
• v.10 no.2 s.20
• /
• pp.57-66
• /
• 2002

This paper establised GPS network consist of 75km average baseline lengths over Jeollanamdo and Jeollabukdo nine point station and fixed Gwangju point station. We quantitavely analyzed how much precision of the baseline determination is improved for GPS survey when using the precise eqhemeris instead of tile broadcast ephemeris of GPS satellites. The observed data for each baseline were processed two times with the same conditions alternately changing the broadcast and the precise ephemeris. The standard deviations from the repeated measurments for each baseline ara compared between the results of using the broadcast ephemeris and the precise ephemeris. As the results, the precision, stability and reliability of the baseline determination using the precise ephemeris is better than those of using the broadcast ephemeris for all baselines.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.27 no.2
• /
• pp.149-157
• /
• 2009

The orbit ephemeris of Global Positioning System(GPS) is one element to determine the surveying accuracy and there are broadcasting ephemeris and precise ephemeris, IGS rapid orbit and IGS ultra rapid orbit in the orbit ephemeris of GPS. In this study, test area was selected in Uljin, Kyungsanbukdo and GPS surveying was accomplished at 37 points in the test area. Then baseline solution was done on 74 baseline using broadcasting ephemeris and precise ephemeris and analysis by TGO and the results were compared. Comparison results were showed that there were nearly no difference between the two results but in case of relative precision of the baseline, it was slightly better the baseline results of precise ephemeris which showed 0.706ppm than the baseline results of broadcasting ephemeris which showed 0.708ppm.

• Journal of Institute of Control, Robotics and Systems
• /
• v.11 no.3
• /
• pp.222-227
• /
• 2005

Resolving the integer ambiguity of GPS carrier phase measurements is the most important routine in precise positioning. In this paper, success rate is analyzed when using baseline information in the process of determining attitude. The result is verified through the simulation. Determining the initial position for the ambiguity resolution is estimated by using code measurement and baseline constraint. Success rate is estimated using covariance of the formed initial position. UKF has been used to overcome the nonlinear baseline condition during the process so that the higher success rate has been obtained compared with the general attitude determination.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.16 no.1
• /
• pp.51-58
• /
• 1998

The goal of this study is to propose a precision improvement scheme for long baseline determination based on the use of IGS ephemeris and different cutoff angles. It is also to present the adjustment results of ’96 Korea GPS fiducial network. In order to obtain more accurate coordinates in precise geodetic surveying, the revision of specification is necessary for the field operation and procedure of baseline processing.

• Journal of Institute of Control, Robotics and Systems
• /
• v.11 no.7
• /
• pp.621-626
• /
• 2005

With precise GPS carrier positioning result, we can get attitude information if GPS antenna has adequate attaching position on the vehicle. In this case, baseline length information can be bandied as an additional measurement or constraint. In this paper, we have proposed a method to improve the attitude accuracy. To overcome nonlinearity of baseline observation model, we analyze attitude estimation result using existing estimation method like a least square method and Kalman filter, and apply a new nonlinear estimation method an unscented Kalman filter Finally we confirm the improvement of attitude estimation result in the case of appling the unscented Kalman filter.

• Journal of Astronomy and Space Sciences
• /
• v.32 no.3
• /
• pp.221-228
• /
• 2015

To protect and manage the Korean space assets including satellites, it is important to have precise positions and orbit information of each space objects. While Korea currently lacks optical observatories dedicated to satellite tracking, the Korea Astronomy and Space Science Institute (KASI) is planning to establish an optical observatory for the active generation of space information. However, due to geopolitical reasons, it is difficult to acquire an adequately sufficient number of optical satellite observatories in Korea. Against this backdrop, this study examined the possible locations for such observatories, and performed simulations to determine the differences in precision of optical orbit estimation results in relation to the relative baseline distance between observatories. To simulate more realistic conditions of optical observation, white noise was introduced to generate observation data, which was then used to investigate the effects of baseline distance between optical observatories and the simulated white noise. We generated the optical observations with white noise to simulate the actual observation, estimated the orbits with several combinations of observation data from the observatories of various baseline differences, and compared the estimated orbits to check the improvement of precision. As a result, the effect of the baseline distance in combined optical GEO satellite observation is obvious but small compared to the observation resolution limit of optical GEO observation.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.27 no.1
• /
• pp.693-700
• /
• 2009

For real-time precise GPS data processing such as a long baseline network RTK (Real-Time Kinematic) survey, PPP (Precise Point Positioning) and monitoring of ionospheric/tropospheric delays, it is necessary to guarantee accuracy comparable to IGS (International GNSS Service) precise orbit with no latency. As a preliminary study for determining near real-time satellite orbits, the general procedures of satellite orbit determination, especially the dynamic approach, were studied. In addition, the transformation between terrestrial and inertial reference frames was tested to integrate acceleration. The IAU 1976/1980 precession/nutation model showed a consistency of 0.05 mas with IAU 2000A model. Since the IAU 2000A model has a large number of nutation components, it took more time to compute the transformation matrix. The classical method with IAU 2000A model was two times faster than the NRO (non-rotating origin) approach, while there is no practical difference between two transformation matrices.

• Journal of Astronomy and Space Sciences
• /
• v.27 no.4
• /
• pp.337-343
• /
• 2010

Optical observation system provides angle-only measurement for orbit determination of space object. Range measurement can be directly acquired using laser ranging or tone ranging system. Initial orbit determination (IOD) by using angle- only data set shows discrepancy according to the measurement time interval. To solve this problem, range measurement data should be added for IOD. In this study, two-site optical observation was used to derive the range information. We have observed nine geostationary earth orbit satellites by using two-site optical observation system. The determination result of the range shows the accuracy over 99.5% compared to the results from the satellite tool kit simulation. And we confirmed that the orbit determination by the Herrick-Gibbs method with the range information obtained from the two-site observation is more accurate than the orbit determination by Gauss method with the one-site observation. For more accurate two-site optical observation, a baseline should satisfy an optimal condition of length and more precise observation system needed.