Support Vector Machine Classification of Object-Based Data for Crop Mapping, Using Multi-Temporal Landsat Imagery

Abstract

ABSTRACT:Crop mapping and time series analysis of agronomic cycles are critical for monitoring land use and land management practices, and analysing the issues of agro-environmental impacts and climate change. Multi-temporal Landsat data can be used to analyse decadal changes in cropping patterns at field level, owing to its medium spatial resolution and historical availability. This study attempts to develop robust remote sensing techniques, applicable across a large geographic extent, for state-wide mapping of cropping history in Queensland, Australia. In this context, traditional pixel-based classification was analysed in comparison with image object-based classification using advanced supervised machine-learning algorithms such as Support Vector Machine (SVM). For the Darling Downs region of southern Queensland we gathered a set of Landsat TM images from the 2010-2011 cropping season. Landsat data, along with the vegetation index images, were subjected to multiresolution segmentation to obtain polygon objects. Object-based methods enabled the analysis of aggregated sets of pixels, and exploited shape-related and textural variation, as well as spectral characteristics. SVM models were chosen after examining three shape-based parameters, twenty-three textural parameters and ten spectral parameters of the objects. We found that the object-based methods were superior to the pixel-based methods for classifying 4 major landuse/land cover classes, considering the complexities of within field spectral heterogeneity and spectral mixing. Comparative analysis clearly revealed that higher overall classification accuracy (95%) was observed in the object-based SVM compared with that of traditional pixel-based classification (89%) using maximum likelihood classifier (MLC). Object-based classification also resulted speckle-free images. Further, object-based SVM models were used to classify different broadacre crop types for summer and winter seasons. The influence of different shape, textural and spectral variables, and their weights on crop-mapping accuracy, was also examined. Temporal change in the spectral characteristics, specifically through vegetation indices derived from multi-temporal Landsat data, was found to be the most critical information that affects the accuracy of classification. However, use of these variables was constrained by the data availability and cloud cover.

Object-Based Flood Mapping and Affected Rice Field Estimation with Landsat 8 OLI and MODIS Data

“…The OBIA approach is conducted through a two-step process: (1) image segmentation by aggregating a number of individual pixels or image sub-objects to form larger objects (primitive objects) based on the homogeneity, intensity, and texture of each investigated image; and (2) image classification and feature extraction. The result of the OBIA approach was successfully proved to be more accurate than that of the pixel-based approaches for land cover classification in recent studies, such as discrimination of different species of mangroves with Worldview-2 imagery [23], flood area delineation in the trans-boundary areas using the ENVISAT/ASAR and Landsat TM data [4], and crop mapping using the multi-temporal Landsat imagery [22]. Other applications of the object-based method for flood water and wetland mapping were introduced in [24][25][26].…”

“…Traditional pixel-based image analysis algorithms for flood mapping and land use classification suffer from low accuracy, sub-pixel problems, and the speckle noise effect in the resulting images [20][21][22]. On the other hand, the object-based image analysis (OBIA) approach has been thoroughly developed in the last two decades to overcome the limitations and disadvantages of the traditional pixel-based approaches by generating and analyzing meaningful image objects instead of individual pixels and reducing the speckle noise effect.…”

Self-Guided Segmentation and Classification of Multi-Temporal Landsat 8 Images for Crop Type Mapping in Southeastern Brazil

“…The listed features are not readily available within pixel-based approaches. Consequently, object-based approaches have been widely used for crop classification in Landsat-like images [9,33,[36][37][38][39][40][41][42].…”

A Framework for Large-Area Mapping of Past and Present Cropping Activity Using Seasonal Landsat Images and Time Series Metrics

“…In the spatial aggregation step, spatial median values have been calculated, making the approach more robust against spatial outliers such as pixels affected by imperfect cloud or cloud-shadow masking. One of the benefits of the GEOBIA is that there is no removal of "salt and pepper" effects required [33,37].…”