• Journal of Korean Society for Geospatial Information Science
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• v.21 no.4
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• pp.95-100
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• 2013

Several observation equipments are being used for determination of the water vapor content and precipitable water vapor (PWV) because the water vapor is highly variable temporally and spatially. In this study, we used GNSS systems such as GPS and GLONASS in standalone and combined modes to compute PWV and validated their accuracy with respect to the results of other water-vapor monitoring systems. The other systems used were radiosonde and microwave radiometer, and the comparisons were convenient because all three systems were collocated at the test site. The differences of PWW were in the range of 0.6-3.4 mm in the mean sense, and their standard deviations were 1.0-3.8 mm. The relatively large difference of GNSS compared with the other two systems were believed to be caused by the fact that the GNSS antenna used in this study was the kind for which the international standard of phase center variations (PCV) calibration is not available. We expect better accuracy of PWV determination and improved availability of it through integrated data processing of GPS/GLONASS when an appropriate antenna with PCV correction model is used.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.299-309
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• 2013

A comprehensive SAR(Synthetic Aperture Radar) simulation is considered to be a complicated task since a full knowledge of the signal propagation characteristics, antenna pattern, system internal errors and interference noises should be taken into account. In high resolution target application modes, the time varying nature of target RCS(Radar Cross Section) strongly affects the generated SAR images. In this paper, in-depth SAR simulations are performed and analyzed incorporating the STK tools and MATLAB software. STK provides realistic orbit parameters while its radar module helps to extract accurate radiometric parameters of ground targets. SAR raw data corresponding to a given target is generated and processed using MATLAB simulator. The performance is measured by PSLR(Peak Sidelobe Ratio) and ISLR(Integrated Sidelobe Ratio) for a point target, which can be used as reference parameters for accurate radiometric calibration. Finally, high resolution target simulations are performed by adopting time varying target RCS characteristics.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.167-178
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• 2003

The design on the Telemetry Ground System for launch of KSLV(Korea Space Launch Vehicle) in the korean Space center has been conducted in this study. For the optimized system design, first of all, the system deployment plan reflecting the topographic and geographic environments of the space center and launch vehicle characteristics has been developed. The RF link budget analysis for the maximum tracking range, requirement for receiving subsystem including antenna subsystem, requirement for data processing subsystem are also analyzed based on the On-Board Telemetry characteristics and launch vehicle parameters. Based on those analysis, telemetry ground system containing tracking/receiving subsystem, recording subsystem and data processing subsystem, timing subsystem, calibration subsystem and monitoring and control subsystem are designed. Futhermore, the analysis for the maximum permissible data latency and communication protocol between each telemetry station and control center are conducted and the entire system is designed so that the major telemetry parameters selected to the best quality are provided in real time to the control center(RCC, RSC) for the launch mission operation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.3
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• pp.285-294
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• 2020

This study investigated the use of Ground Penetrating Radar (GPR) over a two-decade period on public roads, focusing on the electromagnetic characteristics of the pavement dielectrics and attenuation. From the results, a typical range of characteristic value, influencing factors, and a correction method were suggested. The typical dielectrics of asphalt pavements were 4-7, as measured by an air-coupled 1 GHz GPR antenna. The dielectrics of concrete pavements were very large in the early age, but were drastically reduced with ageing. Ten years on, collection was in the range of 6-12. The dielectrics were proportional to the relative humidity (R.H.) of the atmosphere. The effects were reduced to one eighth with an overlay. Attenuation generally increased with thickness of the road layer, and also increased where there was damage. The GPR results could also vary depending on the weather conditions as well as on the characteristics of the GPR equipment, even at the same frequency. Therefore, GPR surveys should be performed on road surfaces without debris on a single, fine day. The reliability of the GPR analysis could be improved by cores and equipment calibration with other non-destructive test surveys.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.358-365
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• 2007

In this paper, the effects of transmit beamforming on downlink performance in DS-CDMA communication systems are investigated. The uplink and downlink in FDD systems use different carrier frequencies. If the downlink uses the same weighting vectors as the uplink, the antenna beam for downlink is formed with certain DOA shift and it thus affects the beamforming gain. So, the impacts of different frequencies on the downlink beam patterns are studied. One possible algorithm to convert uplink beamforming weights to downlink, which is called frequency-calibrated processing, is also evaluated to reduce the degradation of downlink performance due to different frequencies. Under frequency selective channels, the downlink chooses a PUPW beamforming scheme when the uplink employs a PPPW vectors. To form a beam pattern for a PUPW after combining the downlink PPPWs converted from the uplink PPPWs, three approaches are studied. One method is to consider only one dominant path and thus obtain a single main-beam. In the others, multiple-beams weighted with the magnitudes of all paths and equally weighted with all paths are constructed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.7
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• pp.711-719
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• 2011

A study of miniaturization of an L-band orthomode transducer(OMT) for field experiments of radar backscatter is presented in this paper. The proposed OMT is not required the additional waveguide taper structures to connect with a standard adaptor by the newly designed junction structure which bases on a waveguide taper. Total length of the OMT for L-band is about 1.2 ${\lambda}_o$(310 mm) and it's a size of 60 % of the existing OMTs. And, to increase the matching and isolation performances of each polarization, two conducting posts are inserted. The bandwidth of 420 MHz and the isolation level of about 40 dB are measured in the operating frequency. The L-band scatterometer consisting of the manufactured OMT, a horn-antenna and network analyzer(Agilent 8753E) was used STCT and 2DTST to analysis the measurement accuracy of radar backscatter. The full-polarimetric RCSs of test-target, 55 cm trihedral corner reflector, measured by the calibrated scatterometer have errors of -0.2 dB and 0.25 dB for vv-/hh-polarization, respectively. The effective isolation level is about 35.8 dB in the operating frequency. Then, the horn-antenna used to measure has the length of 300 mm, the aperture size of $450{\times}450\;mm^2$, and HPBWs of $29.5^{\circ}$ and $36.5^{\circ}$ on the principle E-/H-planes.

• Korean Journal of Remote Sensing
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• v.23 no.2
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• pp.145-152
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• 2007

The polarimetric backscattering coefficients of a wet-land rice field which is an experimental plot belong to National Institute of Agricultural Science and Technology in Suwon are measured using ground-based polarimetric scatterometers at 1.8 and 5.3 GHz throughout a growth year from transplanting period to harvest period (May to October in 2006). The polarimetric scatterometers consist of a vector network analyzer with time-gating function and polarimetric antenna set, and are well calibrated to get VV-, HV-, VH-, HH-polarized backscattering coefficients from the measurements, based on single target calibration technique using a trihedral corner reflector. The polarimetric backscattering coefficients are measured at $30^{\circ},\;40^{\circ},\;50^{\circ}\;and\;60^{\circ}$ with 30 independent samples for each incidence angle at each frequency. In the measurement periods the ground truth data including fresh and dry biomass, plant height, stem density, leaf area, specific leaf area, and moisture contents are also collected for each measurement. The temporal variations of the measured backscattering coefficients as well as the measured plant height, LAI (leaf area index) and biomass are analyzed. Then, the measured polarimetric backscattering coefficients are compared with the rice growth parameters. The measured plant height increases monotonically while the measured LAI increases only till the ripening period and decreases after the ripening period. The measured backscattering coefficientsare fitted with polynomial expressions as functions of growth age, plant LAI and plant height for each polarization, frequency, and incidence angle. As the incidence angle is bigger, correlations of L band signature to the rice growth was higher than that of C band signatures. It is found that the HH-polarized backscattering coefficients are more sensitive than the VV-polarized backscattering coefficients to growth age and other input parameters. It is necessary to divide the data according to the growth period which shows the qualitative changes of growth such as panicale initiation, flowering or heading to derive functions to estimate rice growth.