Multisource and Multitemporal Data Fusion in Remote Sensing

The sharp and recent increase in the availability of data captured by different sensors combined with their considerably heterogeneous natures poses a serious challenge for the effective and efficient processing of remotely sensed data. Such an increase in remote sensing and ancillary datasets, however, opens up the possibility of utilizing multimodal datasets in a joint manner to further improve the performance of the processing approaches with respect to the application at hand. Multisource data fusion has, therefore, received enormous attention from researchers worldwide for a wide variety of applications. Moreover, thanks to the revisit capability of several spaceborne sensors, the integration of the temporal information with the spatial and/or spectral/backscattering information of the remotely sensed data is possible and helps to move from a representation of 2D/3D data to 4D data structures, where the time variable adds new information as well as challenges for the information extraction algorithms. There are a huge number of research works dedicated to multisource and multitemporal data fusion, but the methods for the fusion of different modalities have expanded in different paths according to each research community. This paper brings together the advances of multisource and multitemporal data fusion approaches with respect to different research communities and provides a thorough and discipline-specific starting point for researchers at different levels (i.e., students, researchers, and senior researchers) willing to conduct novel investigations on this challenging topic by supplying sufficient detail and references

Learning-based stereo matching for 3D reconstruction

Stereo matching has been widely adopted for 3D reconstruction of real world scenes and has enormous applications in the fields of Computer Graphics, Vision, and Robotics. Being an ill-posed problem, estimating accurate disparity maps is a challenging task. However, humans rely on binocular vision to perceive 3D environments and can estimate 3D information more rapidly and robustly than many active and passive sensors that have been developed. One of the reasons is that human brains can utilize prior knowledge to understand the scene and to infer the most reasonable depth hypothesis even when the visual cues are lacking. Recent advances in machine learning have shown that the brain's discrimination power can be mimicked using deep convolutional neural networks. Hence, it is worth investigating how learning-based techniques can be used to enhance stereo matching for 3D reconstruction. Toward this goal, a sequence of techniques were developed in this thesis: a novel disparity filtering approach that selects accurate disparity values through analyzing the corresponding cost volumes using 3D neural networks; a robust semi-dense stereo matching algorithm that utilizes two neural networks for computing matching cost and performing confidence-based filtering; a novel network structure that learns global smoothness constraints and directly performs multi-view stereo matching based on global information; and finally a point cloud consolidation method that uses a neural network to reproject noisy data generated by multi-view stereo matching under different viewpoints. Qualitative and quantitative comparisons with existing works demonstrate the respective merits of these presented techniques

A fully automated three-stage procedure for spatio-temporal leaf segmentation with regard to the B-spline-based phenotyping of cucumber plants

Plant phenotyping deals with the metrological acquisition of plants in order to investigate the impact of environmental factors and a plant’s genotype on its appearance. Phenotyping methods that are used as standard in crop science are often invasive or even destructive. Due to the increase of automation within geodetic measurement systems and with the development of quasi-continuous measurement techniques, geodetic techniques are perfectly suitable for performing automated and non-invasive phenotyping and, hence, are an alternative to standard phenotyping methods. In this contribution, sequentially acquired point clouds of cucumber plants are used to determine the plants’ phenotypes in terms of their leaf areas. The focus of this contribution is on the spatio-temporal segmentation of the acquired point clouds, which automatically groups and tracks those sub point clouds that describe the same leaf. The application on example data sets reveals a successful segmentation of 93% of the leafs. Afterwards, the segmented leaves are approximated by means of B-spline surfaces, which provide the basis for the subsequent determination of the leaf areas. In order to validate the results, the determined leaf areas are compared to results obtained by means of standard methods used in crop science. The investigations reveal consistency of the results with maximal deviations in the determined leaf areas of up to 5