• Journal of KIISE:Information Networking
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• v.31 no.3
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• pp.243-251
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• 2004

This paper proposes a digital image watermarking scheme, which is robust to geometrical attacks. The method improves image normalization-based watermarking (INW) technique that doesn't effectively deal with geometrical attacks with cropping. Image normalization is based on the moments of the image, however, in general, geometrical attacks bring the image boundary cropping and the moments are not preserved original ones. Thereafter the normalized images of before and after are not same form, i.e., the synchronization is lost. To solve the cropping problem of INW, Invariant Centroid (IC) is proposed in this paper. IC is a gravity center of a central area on a gray scale image that is invariant although an image is geometrically attacked and the only central area, which has less cropping possibility by geometrical attacks, is used for normalization. Experimental results show that the IC-based method is especially robust to geometrical attack with cropping.

• Korean Journal of Remote Sensing
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• v.29 no.5
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• pp.517-525
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• 2013

Time-series data of Normal Difference Vegetation Index (NDVI) obtained by the Moderate-resolution Imaging Spectroradiometer(MODIS) satellite imagery gives a waveform that reveals the characteristics of the phenology. The waveform can be decomposed into harmonics of various periods by the Fourier transformation. The resulting $n^{th}$ harmonics represent the amount of NDVI change in a period of a year divided by n. The values of each harmonics or their relative relation have been used to classify the vegetation species and to build a vegetation map. Here, we propose a method to estimate the annual amount of carbon absorbed on the forest from the $1^{st}$ harmonic NDVI value. The $1^{st}$ harmonic value represents the amount of growth of the leaves. By the allometric equation of trees, the growth of leaves can be considered to be proportional to the total amount of carbon absorption. We compared the $1^{st}$ harmonic NDVI values of the 6220 sample points with the reference data of the carbon absorption obtained by the field survey in the forest of South Korea. The $1^{st}$ harmonic values were roughly proportional to the amount of carbon absorption irrespective of the species and ages of the vegetation. The resulting proportionality constant between the carbon absorption and the $1^{st}$ harmonic value was 236 tCO2/5.29ha/year. The total amount of carbon dioxide absorption in the forest of South Korea over the last ten years has been estimated to be about 56 million ton, and this coincides with the previous reports obtained by other methods. Considering that the amount of the carbon absorption becomes a kind of currency like carbon credit, our method is very useful due to its generality.