Soil Moisture Measurement of Bare and Vegetated Surfaces by X-band Radars

Yisok Oh,Soon-Gu Kwon,Ji-Hwan Hwang 한국전자파학회JEES 2010 Journal of Electromagnetic Engineering and Science Vol.10 No.4

The radar backscatter from various earth surfaces is sensitive to the frequency of the incident wave. This study examined the radar sensitivities for surface parameters such as soil moisture content and surface roughness of both bare and vegetated surfaces at X-band. Because L-band frequencies are often used for sensing the surface parameters, the sensitivities of X-band are also compared with those of the L-band. The sensitivities of the X-band radar backscatter were examined with respect to soil moisture content and surface roughness of rough bare soil surfaces. These sensitivities were also examined using the same parameters for vegetated surfaces for various vegetation densities and incidence angles. Use of the X-band radar for soil moisture detection was as effective as L-band radar for bare soil surfaces. For vegetated surfaces, the soil moisture could be detected using an X-band radar at lower incidence angles, where the upper limit of the incidence angles was dependent on vegetation density.

A Simple Microwave Backscattering Model for Vegetation Canopies

Yisok Oh,Jin-Young Hong,Sung-Hwa Lee 한국전자파학회JEES 2005 Journal of Electromagnetic Engineering and Science Vol.5 No.4

A simple microwave backscattering model for vegetation canopies on earth surfaces is developed in this study. A natural earth surface is modeled as a two-layer structure comprising a vegetation layer and a ground layer. This scattering model includes various scattering mechanisms up to the first-order multiple scattering(double-bounce scattering). Radar backscatter from ground surface has been modeled by the polarimetric semi-empirical model (PSEM), while the backscatter from the vegetation layer modeled by the vector radiative transfer model. The vegetation layer is modeled by random distribution of mixed scattering particles, such as leaves, branches and trunks. The number of input parameters has been minimized to simplify the scattering model. The computation results are compared with the experimental measurements, which were obtained by ground-based scatterometers and NASA/JPL air-borne synthetic aperture radar(SAR) system. It was found that the scattering model agrees well with the experimental data, even though the model used only ten input parameters.

An Improved Radiative Transfer Model for Polarimetric Backscattering from Agricultural Fields at C- and X-Bands

Yisok Oh,Jisung Geba Chang,Maxim Shoshany 한국전자파학회JEES 2021 Journal of Electromagnetic Engineering and Science Vol.21 No.2

The first-order vector radiative transfer model (FVRTM) is modified mainly by examining the effects of leaf curvature of vegetation canopies, the higher-order multiple scattering among vegetation scattering particles, and the underlying-surface roughness for forward reflection on radar backscattering from farming fields at C- and X-bands. At first, we collected the backscattering coefficients measured by scatterometers and space-borne synthetic aperture radar (SAR), field-measured ground-truth data sets, and theoretical scattering models for radar backscattering from vegetation fields at microwaves. Then, these effects on the RTM were examined using the database at the C- and X-bands. Finally, an improved RTM was obtained by adjusting its parameters, mainly related with the leaf curvature, the higher-order multiple scattering, and the underlying-surface small-roughness characteristics, and its accuracy was verified by comparisons between the improved RTM and measurement data sets.

레이다를 이용한 토양 수분함유량 측정에서 초목 층의 영향 분석

박신명(Sinmyong Park),오이석(Yisok Oh) 한국전자파학회 2016 한국전자파학회논문지 Vol.27 No.7

본 논문에서는 초목 층 산란모델과 지표면 산란 모델을 이용하여 초목 층에서 수분함유량 측정에 초목 층과 레이다 파라미터가 갖는 영향에 대하여 분석하였다. 1<SUP>st</SUP>-order RTM(Radiative Transfer Model)을 이용하여 여러 상태의 초목 층밀도와 입사각, 주파수, 편파를 갖는 데이터베이스를 생성하고, WCM(Water Cloud Model)과 Oh 모델을 이용하여 후방산란계수로부터 지표면 수분함유량을 추출하였다. 수분함유량 추출 에러를 예측하기 위해 추출한 수분함유량과 RTM의 입력 변수인 수분함유량을 비교하였다. 수분함유량 추출 에러로부터 초목 층에서의 수분함유량 측정에서 초목 층 밀도와 입사각, 주파수, 편파에 따른 초목 층과 레이다 파라미터의 영향을 분석하였다. This paper presents the effect of vegetation layer and radar parameters on soil moisture measurement using the vegetation layer scattering model and surface scattering model. The database of backscattering coefficients for various vegetation layer densities, incidence angles, frequencies, and polarizations is generated using 1<SUP>st</SUP>-order RTM(Radiative Transfer Model). Then, surface soil moisture contents were estimated from the backscattering coefficients in the database using the WCM(Water Cloud Model) and Oh model. The retrieved soil moisture contents were compared with the soil moisture contents in the input parameters of the RTM to estimate the retrieval errors. The effects of vegetation layer and radar parameters on soil moisture measurement are analyzed using the retrieval errors.

A Simple Empirical Model for the Radar Backscatters of Skewed Sea Surfaces at X- and Ku-Bands

Taekyeong Jin,Yisok Oh 한국전자파학회JEES 2019 Journal of Electromagnetic Engineering and Science Vol.19 No.3

This paper presents a new simple empirical model for the backscattering coefficients of skewed sea surfaces. Instead of using a complicated bispectrum function for the backscattering coefficient of a skewed sea surface, a simple modifying term is multiplied to the auto-correlation length of the surface. The unknown constants of the modifying term are obtained by com-paring the simple empirical model with an extensive database for various wind speeds, incidence angles, polarizations, and frequencies. The accuracy of the new model is verified using measurement datasets.

An Improved Semi-Empirical Model for Radar Backscattering from Rough Sea Surfaces at X-Band

Taekyeong Jin,Yisok Oh 한국전자파학회JEES 2018 Journal of Electromagnetic Engineering and Science Vol.18 No.2

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the smallroughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

FDTD 방법을 이용한 Parasitic-Tuned 마이크로스트립 안테나 해석에 관한 연구

손영규(Youngkyu Sohn),오이석(Yisok Oh),구연건(Yeon-Geon Goo) 대한전자공학회 1995 대한전자공학회 학술대회 Vol.1995 No.12

편파화 정도와 동일 편파 위상 차를 이용한 SAR 영상 분류

장지성(Geba Chang),오이석(Yisok Oh) 한국전자파학회 2007 한국전자파학회논문지 Vol.18 No.12

본 논문에서는 편파화 정도(Degree of Polarization: DoP)와 동일 편파 위상차(Co-polarized Phase-Difference: CPD)를 이용한 SAR 영상 분류법을 제안한다. 우선, 측정된 stokes 산란 operator로부터 DoP와 CPD를 얻는 계산식을 유도하고, SAR 영상 분류 과정을 설명한다. 다음에는 측정에서 얻은 완전 편파 L밴드 SAR 영상 데이터에 분류법을 적용하여 그 정확성을 검증하고, 예외 경우를 검토한다. 마지막으로 제안된 분류법으로 SAR 영상을 크게 4가지 그룹인 맨땅, 낮은 식물, 높은 식물, 주거 지역(마을)으로 분류한 결과를 보인다. This paper proposes a polarimetric SAR image classification technique based on the degree of poarization(DoP) and co-polarized phase-difference(CPD) statistics. At first, the formulation for the DoP and CPD is derived. Then, the classification technique is verified with the SAR full polarimetric L-band data with consideration of exceptional cases. The technique has capability of classifying SAR data into four major classes, such as bare surface, short-vegetation canopy, tall-vegetation canopy, and village.

Effects of Size and Permittivity of Rat Brain on SAR Values at 900 ㎒ and 1,800 ㎒

Jong-Chul Hyun,Yisok Oh 한국전자파학회JEES 2006 Journal of Electromagnetic Engineering and Science Vol.6 No.1

The objective of this study is to evaluate the effects of size and permittivity on the specific absorption rate(SAR) values of rat brains during microwave exposure at mobile phone frequency bands. A finite difference time domain (FDTD) technique with perfect matching layer(PML) absorbing boundaries is used for this evaluation process. A color coded digital image of the Sprague Dawley(SD) rat based on magnetic resonance imaging(MRI) is used in FDTD calculation with appropriate permittivity values corresponding to different tissues for 3, 4, 7, and 10 week old rats. This study is comprised of three major parts. First, the rat model structure is scaled uniformly, i.e., the rat size is increased without change in permittivity. The simulated SAR values are compared with other experimental and numerical results. Second, the effect of permittivity on SAR values is examined by simulating the microwave exposure on rat brains with various permittivity values for a fixed rat size. Finally, the SAR distributions in depth, and the brain-averaged SAR and brain 1 voxel peak SAR values are computed during the microwave exposure on a rat model structure when both size and permittivity have varied corresponding to different ages ranging from 3 to 10 weeks. At 900 ㎒, the simulation results show that the brain-averaged SAR values decreased by about 54 % for size variation from the 3 week to the 10 week-old rat model, while the SAR values decreased only by about 16 % for permittivity variation. It is found that the brain averaged SAR values decreased by about 63 % when the variations in size and permittivity are taken together. At 1,800 ㎒, the brain-averaged SAR value is decreased by 200 % for size variation, 9.7 % for permittivity variation, and 207 % for both size and permittivity variations.

K- 밴드 도파관 슬롯 배열 안테나 설계

황지환(Jihwan Hwang),오이석(Yisok Oh) 한국통신학회 2002 한국통신학회 학술대회논문집 Vol.2002 No.7