Korean Journal of Soil Science and Fertilizer (한국토양비료학회지)

Korean Society of Soil Science and Fertilizer (한국토양비료학회)
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Estimation of Soybean Growth Using Polarimetric Discrimination Ratio by Radar Scatterometer

레이더 산란계 편파 차이율을 이용한 콩 생육 추정

  • Kim, Yi-Hyun (Department of Agricultural Envrionment, National Academy of Agricultural Science, Rural Development Administration) ;
  • Hong, Suk-Young (Department of Agricultural Envrionment, National Academy of Agricultural Science, Rural Development Administration)
  • 김이현 (농촌진흥청 국립농업과학원 농업환경부) ;
  • 홍석영 (농촌진흥청 국립농업과학원 농업환경부)
  • Received : 2011.08.29
  • Accepted : 2011.09.30
  • Published : 2011.10.31
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Abstract

The soybean is one of the oldest cultivated crops in the world. Microwave remote sensing is an important tool because it can penetrate into cloud independent of weather and it can acquire day or night time data. Especially a ground-based polarimetric scatterometer has advantages of monitoring crop conditions continuously with full polarization and different frequencies. In this study, soybean growth parameters and soil moisture were estimated using polarimetric discrimination ratio (PDR) by radar scatterometer. A ground-based polarimetric scatterometer operating at multiple frequencies was used to continuously monitor the soybean growth condition and soil moisture change. It was set up to obtain data automatically every 10 minutes. The temporal trend of the PDR for all bands agreed with the soybean growth data such as fresh weight, Leaf Area Index, Vegetation Water Content, plant height; i.e., increased until about DOY 271 and decreased afterward. Soil moisture lowly related with PDR in all bands during whole growth stage. In contrast, PDR is relative correlated with soil moisture during below LAI 2. We also analyzed the relationship between the PDR of each band and growth data. It was found that L-band PDR is the most correlated with fresh weight (r=0.96), LAI (r=0.91), vegetation water content (r=0.94) and soil moisture (r=0.86). In addition, the relationship between C-, X-band PDR and growth data were moderately correlated ($r{\geq}0.83$) with the exception of the soil moisture. Based on the analysis of the relation between the PDR at L, C, X-band and soybean growth parameters, we predicted the growth parameters and soil moisture using L-band PDR. Overall good agreement has been observed between retrieved growth data and observed growth data. Results from this study show that PDR appear effective to estimate soybean growth parameters and soil moisture.

본 연구에서는 레이더파 편파 차이비율에서 얻어진 밴드별 Polarimetric Discrimination Ratio (PDR)와 콩 생육인자 및 토양수분과의 관계를 분석하고 PDR를 이용하여 콩 생육 및 토양수분을 추정하고자 하였다. 기후 등의 영향을 받지 않고 10분 단위로 레이더 산란 측정을 할 수 있는 L, C, X-밴드 레이더 산란계 자동측정시스템을 이용하여 PDR와 콩 생육인자 변화를 모니터링 하였다. 콩 생육시기에 따른 밴드별 PDR과 콩 생육인자 변화를 관측한 결과 L-밴드 PDR이 C-, X-밴드 PDR보다 높게 나타났고, 밴드별 PDR이 가장 높게 보인 시기는 L-밴드PDR (DOY 271), C-, X-밴드 PDR (DOY 273)로 거의 일치하였고, 엽면적지수, 식생수분함량, 생체중, 초장 등 콩생육인자들도 동일한 경향을 보였는데 콩 파종 이후 증가하다가 9월 27일 (DOY 270)에 최대값을 보인 후 감소하였다. 하지만 토양수분은 콩 생육인자들과 다른 경향을 보였다. 생육기간동안 토양수분의 변이가 컸고 PDR과 상관성 도 높지 않았다. 하지만 엽면적지수가 2이하 일 때 콩PDR이 증가함에 따라 토양수분도 증가하는 경향을 보였다. 밴드별 PDR과 콩 생육인자와의 상관관계를 분석하였다. L-밴드 PDR에서 생체중 (r=$0.96^{***}$), 엽면적지수 (r=$0.91^{***}$),식생수분함량 (r=$0.94^{***}$), 토양수분 (r=$0.86^{**}$)등 모든 콩생육인자들과 상관계수가 가장 높게 나타났다. C-, X-밴드 PDR에서도 토양수분을 제외한 다른 인자들과 대체로 상관성이 높았다 ($r{\geq}0.83$). 전체 생육기간에서 PDR과 토양수분과의 상관성은 낮았지만 엽면적지수 2 이하 일 때(DOY 220) 모든 밴드에서 PDR과 토양수분과의 상관계수가 전체 생육단계에서 조사한 것 보다 높게 나타났다. 콩 생육인자들과의 상관분석에서 상관계수가 가장 높은 L-밴드 PDR를 이용하여 콩 생육인자 추정을 위한 회귀식을 작성하고 생육인자 실측값과 추정값을 비교하였다. L-밴드 PDR과 생육인자들과의 관계를 비교해 본 결과 생체중 ($L^2$=0.95), 엽면적지수 ($L^2$=0.89), 식생수분함량 ($L^2$=0.93)에서 결정계수가 높게 나타났고 생육인자 실측값과 추정값을 1:1 선상에서 비교해 본 결과 작은 오차를 보여 추정모형의 유효성이 높다는 것이 증명되었다. 본 연구를 통해 PDR를 이용하여 콩 생육 및 토양수분을 추정할 수 있는 가능성을 확인하였다.

Keywords

References

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