The sensitivity of Sentinel-1 SAR polarimetric parameters to rice paddy growth

Abstract

The rice growth condition is essential in precision agriculture to quantify cultivation inputs and manage agricultural practices, hence ensuring optimum production and promoting environmental conservation through the adequate use of fertilizers and irrigation of the rice paddy. The effectiveness of C-band Sentinel-1 Synthetic Aperture Radar (SAR) dual-polarimetric (VH and VV) data in monitoring the rice paddy growth was investigated in this study. We used multi-temporal Sentinel-1 Single Look Complex (SLC) images acquired in the Interferometric Wide Swath (IW) mode throughout the entire rice growth cycle. Field surveys were conducted at different rice phenological stages to collect in situ measurements of the rice paddy height. Data analysis involved temporal variation and correlation analysis between the rice paddy height and six Sentinel-1 SAR polarimetric parameters, including backscattering intensity in both VH and VV polarizations, the backscattering ratio, and three dual-polarimetric decomposition parameters: entropy, anisotropy, and alpha. It was found that the VH backscattering intensity is highly sensitive to rice growth in all growth stages, with the coefficient of determination (R2) greater than 0.70, and is therefore promising for rice paddy height retrieval. The temporal variation of polarimetric decomposition parameters showed possibilities in identifying rice phenological stages. However, their temporal profiles showed offsets that likely resulted from the different incidence angles of Sentinel-1 satellites and geometric inaccuracies of SAR data, such as speckle noise and georeferencing errors. Based on the fact that polarimetric decomposition parameters were found to be highly correlated with rice paddy height in one parcel, further research with a large number of sample parcels is recommended.

The rice growth condition is essential in precision agriculture to quantify cultivation inputs and manage agricultural practices, hence ensuring optimum production and promoting environmental conservation through the adequate use of fertilizers and irrigation of the rice paddy. The effectiveness of C-band Sentinel-1 Synthetic Aperture Radar (SAR) dual-polarimetric (VH and VV) data in monitoring the rice paddy growth was investigated in this study. We used multi-temporal Sentinel-1 Single Look Complex (SLC) images acquired in the Interferometric Wide Swath (IW) mode throughout the entire rice growth cycle. Field surveys were conducted at different rice phenological stages to collect in situ measurements of the rice paddy height. Data analysis involved temporal variation and correlation analysis between the rice paddy height and six Sentinel-1 SAR polarimetric parameters, including backscattering intensity in both VH and VV polarizations, the backscattering ratio, and three dual-polarimetric decomposition parameters: entropy, anisotropy, and alpha. It was found that the VH backscattering intensity is highly sensitive to rice growth in all growth stages, with the coefficient of determination (R2) greater than 0.70, and is therefore promising for rice paddy height retrieval. The temporal variation of polarimetric decomposition parameters showed possibilities in identifying rice phenological stages. However, their temporal profiles showed offsets that likely resulted from the different incidence angles of Sentinel-1 satellites and geometric inaccuracies of SAR data, such as speckle noise and georeferencing errors. Based on the fact that polarimetric decomposition parameters were found to be highly correlated with rice paddy height in one parcel, further research with a large number of sample parcels is recommended.

부 경 대 학 교 대 학 원 벼의 성장 조건은 재배 투입량을 정량화하고 농업 관행을 관리하기 위해 정밀 농업에서 필수적이며, 따라서 비료의 적절한 사용과 논의 관개를 통해 최적의 생산을 보장하고 환경 보전을 촉진해야 한다. 본 연구에서는 C 밴드 센티넬-1 합성개구안테나 이중편파 (VH and VV) 데이터를 이용하여 벼의 성장을 관측하였다. 벼 재배 전체 기간동안 Interferometric Wide Swath (IW) 모드에서 얻은 시계열 센티넬-1 Single Look Complex (SLC) 이미지를 사용하였다. 현장조사는 벼 높이 데이터를 수집하기 위해 벼 성장 시기에 걸쳐 월별로 수행하였다. 데이터 분석에는 논 높이와 VH 및 VV 후방 산란 강도, 후방 산란 비율, 세 가지 이중 편광 분해 매개 변수(엔트로피, 등방성, 알파)를 포함하여 6개의 센티넬-1 합성개구안테나 편광 매개 변수 사이의 시간적 변화와 상관 분석이 포함되었다. VH 후방 산란 강도는 결정 계수(R2)가 0.70보다 큰 모든 벼 성장 단계에서 매우 민감하였으므로 벼 높이 관측에 유망한 것으로 나타났다. 편광 분해 매개변수의 시간적 변화는 벼의 계절적 성장 단계를 식별하는 가능성을 보여주었다. 그러나 이들의 시간적 프로파일은 센티넬-1 위성의 다른 입사각과 스펙클 노이즈 및 지리 관측 오류와 같은 SAR 데이터의 기하학적 부정확성으로 인한 오프셋을 보여주었다. 따라서, 한 필지에서 편광분해 매개변수가 벼의 높이와 높은 상관관계가 있는 것으로 나타난 것에 기초하여 더욱 많은 수의 표본 필지를 대상으로 한 추가 연구가 진행되어야 할 것이다.