Gravitational Lensing effects on various Cosmological Observations and the determination of Cosmological Parameters

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We have proposed a new method to measure the cosmological constant using strong gravitational lens systems. The method if applied for HST14176+5226 observed by Subaru telescope in May, 2001 and the observation strongly suggests the existence of non-zero cosmological constant. We hove also shown that the method is also useful to determine the time variability of the vacuum energy.We apply for the first time the Minkowski functional to the cosmic shear field and show that the method determines the mean density of the universe more accurately than previous methods. We have also investigated detailed behavior of light propagation in realistic inhomogeneous universe and obtained basic date which is used to determine the model of the universe from the cosmological observation.We have proposed a method to confirm the existence of the dark cluster which we have discovered using the date of Hubble space telescope using gravitational scattering of the cosmic microwave background. We have examined lensing effects by large scale structure of the universe on the cosmic microwave background. In particular we have pointed out that the effect on the two-point correlation function of hot spots will be measurable in the future observations and the information of the amplitude of the density fluctuation is obtained independently with the density parameter.