KEYWORDS: Global Positioning System, Kinematics, Satellites, Algorithm development, Chemical elements, Receivers, Time metrology, Geodesy, Filtering (signal processing), Data processing
GPS precise positioning depends on the right determination of phase ambiguity vector. Generally there are three methods for integer ambiguity resolution, including direct rounding to integer method, searching method and ambiguity function method. Direct rounding to integer method is the fastest algorithm among the three methods, but it requires highly precise approximation of the ambiguities, which usually can be only obtained through long term of measurement. The efficiency (speed) of searching method has a very close relationship to the precision of real-valued ambiguity solution, and usually this method is very slow, especially for the data which comes from short time measuring. The efficiency of ambiguity function method is determined by the accuracy of approximation position and the volume of the cube centered at the initial position. The original ambiguities are transformed into another space by a modified ambiguity transformation algorithm purposed by this paper, which is the most effective one compared to the others. In the new ambiguity space, new ambiguities are far more precise than their original partners. Then we compute the successful probability of direct rounding to integer method both in original space and new space. If the success probability is larger than a given value, then direct rounding to integer method is used to obtain the true ambiguities, otherwise go to a subroutine for the searching method.
The errors in GPS measurement generally consist of systematic error (such as clock bias, iron-sphere, trop- sphere effect, etc.), random error (such as measuring error) and outlier. Systematic error can be canceled by differencing technique or adding parameters into the equation system. Outlier may be detected by adding parameters or by statistic method such as expectation shifting or variance inflating. Because wavelet analysis has many good natures both in the time domain and in the frequency domain, as can automatically zoom in or out with different scales (frequencies), the arbitrary details of a signal can be observed and analyzed by the aid of Wavelet analysis. Based on the above features, Wavelet analysis is reputed as a mathematical microscope.
The data obtained by a balloon borne camera taking photography of the earth can be database inputs of environment and disaster (e.g. landslide, mud-rock flow). It obviously overcomes the disadvantages of low resolving power of remote sensing satellite respect to the disaster area and high expenses of aerial photogrammetry. It is feasible and valuable for the investigation and assessment of environment and engineering disaster. This paper focuses on the real-time target monitoring and navigation with a GPS unit equipped on the balloon platform for remote sensing flying. It makes the balloon possible to follow a set course, including the adjustment of altitude according to the terrain. Some aspects of integrated development of GPS and Mapinfo are also presented. The implementation of this system provides a guarantee for the balloon's remote sensing flying.
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