Embedded wavelet-based coding of three-dimensional oceanographic images with land masses

We describe the Wavelets Around Land Masses (WAVAL) system for the embedded coding of 3D oceanographic images. These images differ from those arising in other applications in that valid data exists only at grid points corresponding to sea; grids points that cover land or lie beyond the bathymetry have no associated data. For these images, the WAVAL system employs a 3D lifting wavelet transform tailored specifically to the potentially sparse nature of the data by processing only the valid sea data points in between land masses. We introduce successiveapproximation runlength (SARL) coding, an embedded-coding procedure which adds successive-approximation properties to the well known stackrun (SR) algorithm. SARL is employed to code wavelet coefficients resulting from the 3D transform in the WAVAL system; however, it is a general technique applicable to other coding tasks in which embedded coding is desired but for which zerotree-techniques are impractical. Experimental results show that the WAVAL system achieves substantial improvement in rate-distortion performance over the technique currently used by the US Navy for compression of oceanographic imagery.