An Improved EZW Hyperspectral Image Compression

The paper describes an efficient lossy and lossless three dimensional (3D) image compression of hyperspectral images. The method adopts the 3D spatial-spectral hybrid transform and the proposed transform-based coder. The hybrid transforms are that Karhunen-Loève Transform (KLT) which decorrelates spectral data of a hyperspectral image, and the integer Discrete Wavelet Transform (DWT) which is applied to the spatial data and produces decorrelated wavelet coefficients. Our simpler transform-based coder is inspired by Shapiro’s EZW algorithm, but encodes residual values and only implements dominant pass incorporating six symbols. The proposed method will be examined on AVIRIS images and evaluated using compression ratio for both lossless and lossy compression, and signal to noise ratio (SNR) for lossy compression. Experimental results show that the proposed image compression not only is more efficient but also has better compression ratio.

横向各向同性介质拟声波一阶速度—应力方程

基于弹性波的基本理论,首先推导了VTI介质拟声波一阶速度—应力方程,通过坐标变换,还得到了TTI介质拟声波一阶速度—应力方程,并从能量守恒的角度证明了上述方程比基于频散关系推导出的拟声波方程更加稳定。针对各向异性参数ε<δ的模型,对新推导的方程引入横波项,消除了残留的横波产生的数值模拟不稳定现象。通过对均匀二维模型和逆冲模型的正演模拟表明:新推导的方程不仅能很好地维持qP波的运动学特征,而且能够很好地适应任意旋转角度的TTI模型,并且在旋转角变化的TTI介质中数值稳定性要好于基于频散关系推导出的拟声波方程。