Document Type : Research Paper
Authors
1 Department of Photogrammetry & Remote Sensing, Faculty of Geomatics Engineering, K. N. Toosi University of Technology, Tehran, Iran
2 Department of Geodesy and Surveying Engineering, Tafresh University, Tafresh, , Iran
Abstract
Keywords
Main Subjects
Anomalies detection and cause analysis of autumn crops in individual croplands using time series of Sentinel-2 satellite data (Case Study: Golestan province)
EXTENDED ABSTRACT
Agriculture plays a crucial role in sustaining human livelihood by supplying essential resources such as food, fuel, and raw materials. Given the challenges posed by population growth and limited resources, effective agricultural management becomes imperative in order to fulfill fundamental human requirements. Satellite imagery and remote sensing technology serve as valuable tools for enhancing agricultural product management. These images encompass optical and radar data, which are extensively employed to examine vegetation conditions and, notably, to monitor crop progression. In the realm of agricultural product production, the effective management of factors such as soil, pests, climatic conditions, and unforeseen risks holds significant importance in ensuring sustainable agricultural productivity. In the context of remote sensing images, anomaly detection methods employ unsupervised learning techniques to autonomously identify and uncover uncommon attributes within spectral images. These methods operate in the absence of any prior knowledge about the target scene or spectrum. They rely on the assumption that certain patterns in the input space are more frequently observed, while others occur less frequently. The primary objective of these methods is to uncover and examine these patterns. Anomaly detection techniques can be applied to reflectance, radiance, and other measurement units. Essentially, these methods aim to create a model of the image background and identify pixels that deviate from the background model as anomalies.
In this study, the time series data from Sentinel-2 satellite images pertaining to agricultural fields were utilized. The high temporal resolution offered by the dual multispectral sensors present in the Sentinel-2 satellite platforms (2A and 2B) enabled the generation of a 5-day time series. This research methodology revolves around identifying anomalies in multispectral satellite images and simultaneously gathering field information from farmers through the completion of questionnaires for the selected agricultural lands. This research focuses on two distinct approaches for detecting anomalies. Firstly, individual analysis of images captured at each-time point during the cultivation periods is conducted to identify abnormalities. In the second part, the series of images captured at different stages of the crop year are examined to understand the anomaly formation process. The objective is to assess the effectiveness and sustainability of these two methodologies.
Based on the field investigations, agricultural lands experiencing anomalies exhibited poor performance during the corresponding year's harvest. The irregular occurrence of anomalies and the absence of temporal continuity in their detection pose challenges when relying solely on individual time-based images. Based on the cumulative series, anomalies have exhibited continuous presence from the initial detection date throughout the entire observation period, persisting until the end of the agricultural year. Numerous factors have been identified as contributing to the occurrence of farm anomalies. These factors can be categorized into five distinct groups: 1) Anomalies attributed to soil texture and land slope, 2) Anomalies resulting from drought conditions, 3) Anomalies caused by pests and fungi, 4) Anomalies associated with weed infestations, and 5) Multivariate anomalies. Each of these factors exerts its effects, leading to anomalies and their consequences, either persistently or intermittently. Based on the reported findings, anomaly detection methods relying on individual time-based images yielded unfavorable outcomes in both RX and MedSAM detection methods. This challenge arises from the unpredictable occurrence of anomalies throughout a crop year in agricultural fields. However, the utilization of time series-based methods has significantly mitigated this issue. Moreover, the MedSAM method has demonstrated greater success in producing results compared to the RX method.
Utilizing remote sensing technology is a viable and efficient approach to agricultural resource management. anomalies are a common phenomenon observed in agricultural fields, resulting from diverse factors. This article employs the time series data of Sentinel-2 satellite images to investigate the anomalies in autumn crop cultivation at the field level. The results revealed that the utilization of cumulative time series proves to be more effective in detecting and assessing the stability of anomalies compared to methods that analyze individual time points. Examining the temporal pattern of the anomaly detector's response can serve as a potential indicator for assessing the effectiveness of remedial measures in response to anomaly occurrences. The fields chosen for this research predominantly pertain to autumn and dry farming, and the authors of this article have set their research sights on investigating the applicability of this approach to spring crops (which have a more condensed growth period) and water-intensive crops like rice.
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