Quality assessment of Ikonos and Quickbird fused images for urban mapping
Creators: name: Meenakshisundaram, Valarmathy
Publisher: name: University of Calgary
Year: 2005

description: Bibliography: p. 95-98
description: Some pages are in colour.
description: New series of very high spatial resolution (VHR) satellites Ikonos and Quickbird have enabled mapping and updating of GIS databases of urban areas that is presently carried out using field surveys and aerial images. Satellites provide higher spatial resolution in panchromatic (PAN) mode compared to that in multispectral (MS) mode. High spatial and high spectral resolution are desirable for urban mapping as high spatial resolution provides better geometric quality while high spectral resolution provides better object identification. Image fusion techniques aim at increasing the spatial resolution of MS images using information from PAN image. However, fusion methods alter the spectral content of the original images. This is not desirable in applications requiring spectral information such as visual interpretation or classification procedures that depend on the spectral information of MS images. In this study, fused images obtained for Ikonos PAN and MS and Quickbird PAN and MS images by the standard methods namely IHS (Intensity-Hue-Saturation) and PCA (Principal Component Analysis), and simple wavelet methods namely, IHS with wavelet (IHS+W), PCA with wavelet (PCA+W), Wavelet Addition (WA) and Wavelet Substitution (WS) and complex ARSIS ("Amelioration de la Resolution Spatiale par Injection of Structures") methods are compared and analysed visually and statistically for urban mapping. Since PAN is less correlated with the Blue band, it results in high spectral error in the fused Blue band ofIHS, IHS+W, WA and WS methods. The ARSIS models aim at synthesizing the images at high resolution close to reality. However, it is found that the ARSIS models produce similar results to the WA and WS methods in some bands and introduce more error in the NIR band compared to other methods. The ARSIS M2 method provides similar results as the PCA method. Based on the subjective (visual) assessment, of all the methods ARSIS M2 and PCA method provides good spatial quality while best preserving the colour of objects. Thus, these fused MS images are better for visual interpretation and mapping. VHR images have inadequate spectral resolution for complete discrimination of urban classes: roads and buildings. The high within-class spectral variance in VHR images results in misclassifications. The problem is increased in the fused images where there are more spatial details compared to the original MS images. Also, the spectral variance in each class is further increased by fusion methods resulting in more misclassifications. However, because of the high redundancy in the MS bands, the classified fused images of different methods do not show much difference. Considering other pre and post­processing steps involved in automated urban feature extraction, classification is only a part of the whole process. Future Worldview satellite from Digital Globe will provide higher spatial resolution for PAN (0.5 m) and 8-MS bands (2 m). With such a very high resolution, the need for the fusion of PAN and MS images has to be further investigated especially for automatic feature extraction procedures.