In this paper, we present a visual sensitivity based low-bit-rate image compression algorithm. Using the idea that different image regions have different perceptual significance relative to quality, the input image is divided into edges, textures and smooth regions. For the edges, the standard JPEG algorithm with an appropriate quantitative step is applied so that the details can be preserved. For the textures, the JPEG algorithm is applied on the down-scale version. For the smooth regions, a skipping scheme is employed in the compression process so as to save bits. Experimental results show the superior performance of our method in terms of both compression efficiency and visual quality.
The principle and method of remote sensing precipitable water by Global Positioning System (GPS) are introduced. A series of tropospheric delay are obtained from the dual frequency receiver's data of global tracking stations in East Asia and precise satellite ephemeris of IGS from July 31 to August 20, 1997. During this period, typhoon and severe storm passed through the region several times. The continuous precipitable water (PW) with the interval of 30 minutes are estimated at Shanghai and Wuhan GPS sites. The results are compared with PW from conventional radiosonde during the same period, and the RMS is about 0.50 cm. They fit well in main tendency and agree with each other at most of the time, especially when severe storm affects the region. The continuous change of precipitable water reflects the weather process precisely.
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