Örsan Aytekin

Texture-Based Airport Runway Detection

The automatic detection of airports is essential due to the strategic importance of these targets. In this letter, a runway detection method based on textural properties is proposed since they are the most descriptive element of an airport. Since the best discriminative features for airport runways cannot be trivially predicted, the Adaboost algorithm is employed as a feature selector over a large set of features. Moreover, the selected features with corresponding weights can provide information on the hidden characteristics of runways. Thus, the Adaboost-based selected feature subset can be used for both detecting runways and identifying their textural characteristics. Thus, a coarse representation of possible runway locations is obtained. The performance of the proposed approach was validated by experiments carried on a data set of large images consisting of heavily negative samples.

Unsupervised building detection in complex urban environments from multispectral satellite imagery

A generic algorithm is presented for automatic extraction of buildings and roads from complex urban environments in high-resolution satellite images where the extraction of both object types at the same time enhances the performance. The proposed approach exploits spectral properties in conjunction with spatial properties, both of which actually provide complementary information to each other. First, a high-resolution pansharpened colour image is obtained by merging the high-resolution panchromatic (PAN) and the low-resolution multispectral images yielding a colour image at the resolution of the PAN band. Natural and man-made regions are classified and segmented by the Normalized Difference Vegetation Index (NDVI). Shadow regions are detected by the chromaticity to intensity ratio in the YIQ colour space. After the classification of the vegetation and the shadow areas, the rest of the image consists of man-made areas only. The man-made areas are partitioned by mean shift segmentation where some resulting segments are irrelevant to buildings in terms of shape. These artefacts are eliminated in two steps: First, each segment is thinned using morphological operations and its length is compared to a threshold which is determined according to the empirical length of the buildings. As a result, long segments which most probably represent roads are masked out. Second, the erroneous thin artefacts which are classified by principal component analysis (PCA) are removed. In parallel to PCA, small artefacts are wiped out based on morphological processes as well. The resultant man-made mask image is overlaid on the ground-truth image, where the buildings are previously labelled, for the accuracy assessment of the methodology. The method is applied to Quickbird images (2.4 m multispectral R, G, B, near-infrared (NIR) bands and 0.6 m PAN band) of eight different urban regions, each of which includes different properties of surface objects. The images are extending from simple to complex urban area. The simple image type includes a regular urban area with low density and regular building pattern. The complex image type involves almost all kinds of challenges such as small and large buildings, regions with bare soil, vegetation areas, shadows and so on. Although the performance of the algorithm slightly changes for various urban complexity levels, it performs well for all types of urban areas.

Automatic and unsupervised building extraction in complex urban environments from multi spectral satellite imagery

This paper presents an approach for building extraction in remotely sensed images composed of low-resolution multi-spectral and high resolution panchromatic bands. The proposed approach exploits spectral properties in conjunction with spatial properties, both of which actually provide complementary information to each other. First, high resolution pan-sharpened color image is obtained via the process of merging high resolution panchromatic and low resolution multispectral imagery yielding a color image at the resolution of panchromatic band. Natural and man-made regions are classified by using Normalized Difference Vegetation Index (NDVI). Then shadow is detected by using chromaticity to intensity ratio in YIQ color space. After the classification of the vegetation and the shadow areas, the rest of the image consists of man-made areas only. Then, the manmade areas are partitioned by mean shift segmentation. However, some resulting segments are irrelevant to buildings in shape. These artifacts are eliminated in two steps: First, each segment is thinned using morphological operations and the length of it is compared to a threshold which is specified according to the empirical length of buildings. As a result, long segments which most probably represent roads are masked out. Second, the erroneous thin artifacts are removed via principle component analysis (PCA). In parallel to PCA, small artifacts are wiped out based on morphological processes also. The resultant manmade mask image is overlaid on the ground truth image, where the buildings are manually labeled, for the assessment of the methodology. The proposed methodology is applied to various Quickbird images. The experiments show that the methodology performs well to extract buildings in complex environments.

Automatic segmentation of VHR images using type information of local structures acquired by mathematical morphology

The morphological profile (MP) and differential morphological profile (DMP) have been used extensively to acquire spatial information to be used in the segmentation of very high resolution (VHR) remotely sensed images. In most of the previous approaches, the maxima of the MP and DMP were investigated to estimate the best representative scale in the spatial domain for the pixel under consideration. Then, the object type (i.e. dark, bright or flat) was estimated based on the location of the maximum. Finally, the image segmentation was performed using the scale and type information as features. This approach usually causes over-segmentation. In this study, we also investigate the relevance of the DMP and the meaningful object types underlying the pixel of interest, however, instead of the maxima of the DMP, the type information is estimated using the whole DMP which is weighted by a weight function. Thus, the scale is not estimated directly but used indirectly in the estimation of the characteristic type for the object to which the pixel belongs. Then, the pixels are clustered based on their types only. The method has been applied to panchromatic high resolution QuickBird satellite images of the city of Ankara, Turkey. The results of the method were compared with previous studies and the proposed method seems to segment the images more precisely and semantically than the previous approaches.

Building detection in high resolution remotely sensed images based on morphological operators

Information retrieval from high resolution remotely sensed images is a challenging issue due to the inherent complexity and the curse of dimensionality of data under study. This paper presents an approach for building detection in high resolution remotely sensed images incorporating structural information of spatial data into spectral information. The proposed approach moves along eliminating irrelevant areas in a hierarchical manner. As a first step, pan-sharpened image is obtained from multi-spectral and panchromatic bands of Quickbird image. Vegetation and shadow regions are masked out by using Normalized Difference Vegetation Index (NDVI) and ratio of hue to intensity in YIQ model, respectively. Then, panchromatic band is filtered by mean shift filtering for smoothing structures while preserving the discontinuities near boundaries. Next, differential morphological profile (DMP) is calculated for each pixel and a relative measure of structure size is recorded as the first maximum value of DMP which generates a labeled image representing connected components according to sizes of structures. However, there appear some connected components which are irrelevant to buildings in shape. To eliminate those connected components, their skeletons are obtained via thinning to get a relative length measure along with measuring areas of connected components. These measures are compared to a threshold individually, which provides a cue for a candidate building structure.

Performance evaluation of building detection and digital surface model extraction algorithms: Outcomes of the PRRS 2008 Algorithm Performance Contest

This paper presents the initial results of the algorithm performance contest that was organized as part of the 5th IAPR Workshop on Pattern Recognition in Remote Sensing (PRRS 2008). The focus of the 2008 contest was automatic building detection and digital surface model (DSM) extraction. A QuickBird data set with manual ground truth was used for building detection evaluation, and a stereo Ikonos data set with a highly accurate reference DSM was used for DSM extraction evaluation. Nine submissions were received for the building detection task, and three submissions were received for the DSM extraction task. We provide an overview of the data sets, the summaries of the methods used for the submissions, the details of the evaluation criteria, and the results of the initial evaluation.

Airport runway detection in satellite images by Adaboost learning

Advances in hardware and pattern recognition techniques, along with the widespread utilization of remote sensing satellites, have urged the development of automatic target detection systems in satellite images. Automatic detection of airports is particularly essential, due to the strategic importance of these targets. In this paper, a runway detection method using a segmentation process based on textural properties is proposed for the detection of airport runways, which is the most distinguishing element of an airport. Several local textural features are extracted including not only low level features such as mean, standard deviation of image intensity and gradient, but also Zernike Moments, Circular-Mellin Features, Haralick Features, as well as features involving Gabor Filters, Wavelets and Fourier Power Spectrum Analysis. Since the subset of the mentioned features, which have a role in the discrimination of airport runways from other structures and landforms, cannot be predicted trivially, Adaboost learning algorithm is employed for both classification and determining the feature subset, due to its feature selector nature. By means of the features chosen in this way, a coarse representation of possible runway locations is obtained. Promising experimental results are achieved and given.

Building detection in satellite images by textural features and Adaboost

A method based on textural features and Adaboost for detecting buildings in satellite images is proposed. Several local textural features including mean and standard deviation of image intensity and gradient, Zernike moments, Circular-Mellin features, Haralick features, Fourier Power Spectrum, Wavelets, Gabor Filters, and a set features extracted from HSV color space are extracted. Adaboost learning algorithm is employed for both classification and determining the beneficial feature subset, due to its feature selector nature. Some operation including morphological operators are applied for post processing. The approach was tested on a set of satellite images having different types of buildings and promising experimental results are achieved.

Classification of hyperspectral images based on weighted DMPS

This paper presents a classification method for hyperspectral images utilizing Differential Morphological Profiles (DMPs) which permit to include in the analysis spatial information since they can provide an estimate of the size and contrast characteristics of the structures in an image. Due to the wide variety of objects present in a scene, the pixels belonging to the same semantic structure may not have homogeneous spatial and spectral features. In addition, instead of a single peak (which can be related to a measure of the scale), multiple local maxima and multiple responses are usually observed in the DMP. In order to handle such intra-class variability, class-specific weighting functions are employed in order to differently modulate the DMP values according to the different characteristics of the land cover types. In such way, it is possible to differentiate the behaviors of the DMP for each pixel in the image according to its semantic, providing an increase of the separability of the classes. At first, a DMP computed with opening by reconstruction (DMPO) and one with closing by reconstruction (DMPC) are derived on each of the first principle components extracted from the hyperspectral image. Then, both profiles are weighted by each class-specific weighting function and concatenated in a single data structure. The constructed feature vectors are considered by a random forest classifier.

Segmentation of High Resolution Satellite Imagery Based on Mean Shift Algorithm and Morphological Operations

Data-driven unsupervised segmentation of high resolution remotely sensed images is a primary step in understanding remotely sensed images. A new fully automatic method to delineate the segments corresponding to objects in high resolution remotely sensed images is introduced. There are extensive methods proposed in the literature which are mainly concentrated on pixel level information. The proposed method combines the structural information extracted by morphological processing with feature space analysis based on mean shift algorithm. The spectral and spatial bandwidth parameters of mean shift are adaptively determined by exploiting differential morphological profile (DMP). Spectral bandwidth is determined in relation to the first maximum value of DMP at each pixel and spatial bandwidth is determined by the corresponding index in DMP. In this method there is also no need to specify initially the maximum size of the structuring element for the morphological processes. By the use of mean shift filtering, the feature space points are grouped together which are close to each other both in the range of spatial and spectral bandwidths. The proposed method is applied on panchromatic high resolution QuickBird satellite images taken from urban areas. The results we obtained appear to be effective in terms of segmentation and combining the spectral and spatial information to extract more precise and more meaningful objects compared to fixed bandwidth mean shift segmentation.