Wonkyu Park

Extraction of digital elevation models from satellite stereo images through stereo matching based on epipolarity and scene geometry

Abstract This paper addresses the problem of generating digital elevation models from satellite images taken by linear pushbroom cameras. Since there exist unique geometric properties for linear pushbroom images, we argue that the conventional DEM generation schemes developed for perspective images are not suitable for satellite images. Using the geometric properties of linear pushbroom images, we design a new matching strategy optimized for linear pushbroom image in three aspects: conjugate search method, correlation patch design and match sequence determination. We will discuss in what aspect conventional approaches and our new approach differ and show how performance has improved by hiring proper techniques. A series of experiments using SPOT panchromatic stereo pairs showed that our approach outperformed conventional approaches in terms of accuracy and processing time.

MTF Assessment of High Resolution Satellite Images using ISO 12233 Slanted-Edge Method

The MTF (modulation transfer function) has been used to evaluate the performance of optical systems. More accurate access to on-orbit MTF opens the way to enhance images so that we can deduce more information from the images of IKONOS, OrbView, or SPOT. Generally, the MTF was assessed using various methods such as the point source method and the knife-edge method etc. In this paper, the value of the slanted-edge method is investigated as a tool to assess the on-orbit MTF. The slanted-edge method is the ISO 12233 standard for the MTF measurement of electronic still-picture cameras. The method is adapted to estimate the MTF values of line-scanning telescopes. We applied the method to measure the MTF of high resolution satellite images and also, we compared the MTF measurement with that of the knife-edge method applied to EOS-C test images to increase the confidence on MTF measurement on EOS-C. EOS-C is a 2.5m resolution satellite sensor for SI-200 satellite which is under the development by Satrec Initiative. The MTF measured from this method is used for the MTF compensation of satellite images by generating the MTF convolution kernel based on the PSF (point spread function).

Towards knowledge-based extraction of roads from 1 m-resolution satellite images

As the IKONOS satellite with 1 m-resolution camera was launched in 1999, mapping using spaceborne images will be an important issue in the computer vision area as well as photogrammetry, mainly because most major man-made objects of interest can be identifiable. One of the automatically identifiable objects of importance may be roads. Detecting roads using edge detection approaches may be very difficult because a number of edge elements from such as buildings, etc., can be generated from edge detector. In this paper, we propose a method for the extraction of approximated road regions based on region segmentation that utilizes region information. Our method consists of the following three steps. First, an image is segmented using the modified hierarchical multi-scale gradient watershed transformation. Then, the road candidates are identified using information about road gray level, elongatedness and connectedness. The identified road candidates are expanded by connecting the close-by roads knowing that roads are connected objects. Our method was tested on the simulated spaceborne images and the result shows that the automation of road extraction is quite promising.

MTF Assessment and Image Restoration Technique for Post-Launch Calibration of DubaiSat-1

MTF(modulation transfer function)는 광학 시스템의 성능을 평가하기 위하여 사용되는 중요한 파라미터 중 하나이다. 또한 열악한 우주 환경(방사능, 극한 열조건 및 전자기장 등), 대기 영향 및 시스템 성능의 저하 등으로 저하된 영상품질을 복원시켜주기 위한 파라미터로 사용될 수도 있다. 본 논문에서는 소형 지구관측위성인 DubaiSat-1이 발사된 후, 위성영상의 품질을 평가하기 위하여 MTF를 측정하였다. 일반적으로 MTF는 point source 혹은 knife-edge 방법 등과 같은 다양한 방법을 이용하여 측정되어왔다. 그러나 본 논문에서는 ISO에서 line source에 의한 MTF 측정을 표준화한 slanted-edge 방법을 이용하여 MTF를 측정하였다. Slanted-edge 방법은 전자 스틸 카메라(electronic still-picture camera)의 MTF를 측정하기 위한 ISO 12233 표준으로써, 라인스캐닝 망원경(line-scanning telescope)의 MTF를 추정하기 위하여 사용된 방법이다. 또한 PSF(point spread function) 기반으로 제작된 MTF 회선 커널(MTF convolution kernel)에 의한 MTF 보상(MTF compensation)과 영상의 노이즈 제거(image denoising)를 수행하여 영상의 품질 저하(degradation)를 완화시켰다.