Encoding of still pictures by a wavelet transform and singular value decomposition
This paper proposes a new scheme for picture compression which decomposes a picture to (3/spl times/3+1) subband pictures using the 2-D discrete wavelet transform three times, and then decomposes a picture block matrix A(16/spl times/16 pixels) of the lowest frequency subband picture to singular values and eigenvectors of AA/sup T/ and A/sup T/A and encode them by PCM. For all other subband pictures, first we encode the 0-level wavelet coefficient run-length by a modified Huffman code and then encode the non-0-level coefficients by PCM with non-linear quantizer.
Encoding of pictures using the singular value decomposition (SVD) and 1-D discrete cosine transform (DCT)
We propose an efficient encoding algorithm which decomposes a picture matrix A to singular values and eigen vectors of AA/sup T/ and A/sup T/A, and then encodes the singular values and DCT coefficients of eigen vectors by PCM. We transform the eigen vectors of the first decomposed term, which are flat and do not have higher frequency components, to 1 dimensional DCT coefficients. The magnitude of the coefficients is small when the vector is flat, allowing us to encode the coefficients efficiently using this characteristic. For decomposed terms other than the first decomposed term, we are able to encode the singular values and eigen vectors by PCM with a small number of bits without increasing quantization noise, since the singular values are very small.
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.