Analysis Of Phenological Characters On Rice Under Different Heavy Metal Stresses By Remote Sensing

With the rapid development of industry,paddy fields in some areas have been exposed to heavy metal pollution.The pollution of farmland by heavy metals will seriously affect the health of farmland ecosystem.The resulting food safety problems have also threatened human health.An effective method to monitor the degree of heavy metal stress in crops is crucial to ensure agricultural production and food safety.Vegetation phenology is a sensitive indicator of environmental changes.Soil contaminated by heavy metals will inevitably lead to the changes in the ground crops and surrounding environment,thus causing changes in phenology.The information of crop phenology is also essential for assessing crop productivity and conducting crop management.Remote sensing is an effective way to detect changes in vegetation phenology.Research on plant phenology based on remote sensing monitoring has become a hot topic in global climate change research.Therefore,using remote sensing to obtain phenological information of rice fields to monitor the degree of heavy metal stress in farmland is of great significance for food safety and environmental protection.In this paper,the rice fields around the Xiangjiang River in Zhuzhou City of Hunan Province are taken as the research area.Through the acquisition and collection of relevant remote sensing image data and measured data such as crop soil heavy metal concentration,with the purpose of exploring the evaluation potential of rice remote sensing phenology on heavy metal stress,we are going to analyze the differences of rice phenology under varied heavy metal stress levels and demonstrate that specific phenological characteristics are an effective indicator for monitoring heavy metal stress in rice.Extraction of phenological information by remote sensing is mainly based on the time series curve of vegetation index.This paper based on relevant research of the extraction of phenological information by remote sensing and selects EVI to invert the growth status on vegetation.We selected four paddy fields under mild and severe stress levels,sixteen HJ-1A/B CCD images were used to extract EVI values corresponding to the growth cycle of paddy field,and construct EVI time series.The EVI time series was denoised and smoothed by using asymmetric Gaussian model functions with high fidelity in the field of vegetation phenomenological detection to obtain a continuous time series curve.Then the first derivative curve was calculated based on the continuous time series curve by the first derivative analysis to determine the inclination rate of of the EVI time series curve.We obtained three key phenological periods of the rice crop:the tillering period(the fastest growing period),the heading period(the most prosperous growth period),the maturity period(the fastest declining period).Based on these three phenology periods,we constructed two metrics with phenological characteristics:date-intervals(L)and time-integrated EVI(TIEVI)to explore the rice phenological differences under mild and severe heavy metal stress levels.The results show that under severe stress the values of the metrics for presenting rice phenological differences of heavy metal stress are smaller than those under light stress,and prove that specific phenological characteristics can be used as an effective indicator for monitoring heavy metal stress on rice.This finding will help to monitor the heavy metal pollution on rice and measure the level of heavy metal pollution in the region from the perspective of phenology.