Fringe projective 3D profile sensor can obtain dense coordinates map of object outline fast and quantitatively. Phase
unwrapping technique plays an important role in the performance of the sensor when phase-shifting fringe patterns are
used. The multi-period phase shift method can considerably increase the accuracy of measuring phase value. However,
due to error of intensity approximation arisen from digital grating and the spatial resolution limits on the projector and
cameras of the senor, the result of unwrapped phase value is still within noise only by means of temporal
phase-unwrapping. A new algorithm combining the spatial and temporal phase-unwrapping methods is presented. The
algorithm, which is a good compromise between the number of needed gratings and the unwrapping reliability, is
especially designed for using two groups of digital phase-shifting gratings with different period. Experiments have been
carried out by selecting about thirty pairs of periods to illustrate the efficiency of temporal and spatial criterions, and the
results offer the tolerance of phase calculation which is unwrapped correctly. The algorithm has been implemented on a
test system, and the ratio of unwrapping successfully reaches to 80% with the repeated error 0.05 rad.
Epitaxial layers and monolayer of Ga0.98 In0.02As0.24Sb0.76 quaternary alloys lattice matched to GaSb substrates were grown by our home-made low pressure metal organic chemical vapor deposition (LP-MOCVD). Lattice mis-match (Δa/a~2.5%) between Ga0.98In0.02As0.24Sb0.76 quaternary alloys and GaSb substrate was obtained. Mirrorlike surface
morphologies were investigated by SEM and AFM. Undoped Ga0.98In0.02As0.24Sb0.76 epitaxial layers grown on semi-insulated GaAs substrates indicates n-type with carrier density of 1.8×1017cm-3 and electron mobility of 2551 cm2v-1 s-1. Growth at this temperature yielded a root-mean-square (rms) surface roughness of 160 nm. The effects of growth parameters on epitaxial layers were discussed. It is shown that under proper growth conditions, containing growth temperature (570~620°C), V/III ratios (2~6) and flux of carrier gas, smooth and high quality Ga0.98In0.02As0.24Sb0.76 epitaxial layers can be achieved.
Traditional standard products are processed and supplied on an individual scene basis. It reduces the complexity of data product generation and is of benefit to product catalogues. In fact, a lot of product users need consecutive multi-scenes. Putting them together is necessary and brings errors. In this paper, a pass processing approach will be discussed. This approach is based on pass model, using a few Ground Control Points (GCPs) to improve the satellite ephemeris and attitude data. It has been proved that this method is more effective than individual one.
In the paper a interferometric sensor for measuring temperature by means of liquid-core fiber is described. The experimental results and theoretical calculations show that a temperature variation of 10-4 degrees C can be measured. We have developed a liquid-core multimode fiber. The liquid-core fiber are composed of hollow silica filled of chlorobenzene. High sensitivity is achieved by the interferometric measuring. It can profitably be employed in spectrum research and sensing.
Under the illumination of high resolution radar wave, a target can not be considered as a single dot target, it must be an extended target composed of many scatter dots. This paper mainly studies the model and the echo character of millimeter high resolution ground target. Because of the moving between target and system, Doppler frequency is important and useful information. An extend target is composed of many scatter dots. Each scatter dot, because of different position and angle, generates different Doppler frequency. Each kind of target has different geometry form. There are great distinction of the number and the position of scatter dots among targets. An extended target echo is a complicated Doppler modulation signal. The distinction of Doppler modulation echo of different target is very great. This property is very usable for target recognition. First, the echo spectral is computed by Fourier transform. Second, we choose the total spectral energy and four segment spectral energy as characters. Finally, target recognition adopted BP neural network to get high recognition ratio.
The unequally training set causes the low classification rate of a neural network recognizer. In order to equalize the training set, two methods are proposed in this paper. The first way controls the training parameters according to the property of training samples, i.e. adjusts the study rate with a fuzzy rule. The fuzzy rule is defined by the distribution of the training set and the important level of each kind of samples. The classification rate can be improved in this way and the fast convergence property can be achieved. The second means of equalizing the training set reduces the over- represented samples by fuzzy clustering and increases the deficient samples by interpolating. The BP neural network is used as recognizer here. From the results of the computer simulations, the two methods show to be effective when the training data are imbalance. The two ways improve the classification rate of neural network recognizer by equalizing the training set.
This paper studies the relationship between high range resolution and signal bandwidth. In order to generate big bandwidth, a novel spread spectrum radar waveform is present in this paper. This paper derives the ambiguous function of intrapulse and interpulse FM radar waveform. The result proves that this kind of waveform stimulus is of big time duration and big bandwidth. This waveform trades off the drawback of interpulse stepped frequency waveform in range resolution. There is not range ambiguous problem in time domain. According to the distinguishing feature of this kind of waveform, a novel two-stage pulse compression system using surface acoustic wave (SAW) device is put forward. It aims to generate a intrapulse rectangular spectrum by means of SAW device. Then, the system can obtain spread rectangular spectrum using interpulse frequency shifting. After matched pulse compression processing, this waveform holds high resolution in range domain and in velocity domain. The system total compression ratio can be controlled by the intrapulse compression ratio and interpulse compression ratio.
The radial basis function network (RBFN) is analyzed and the fuzzy radial basis function network (FRBFN) which is more suitable for the radar target recognition is proposed in this paper. Here both of the two networks are used as classifiers. This FRBFN utilize fuzzy clustering method to determine the structure of the net. The generalization property of the two networks are discussed. It is shown from the theoretical analysis and experiment that the FRBFN has better generalization property. The Doppler echoes of the targets gotten from a current surveillance radar are used in the experiment. The experimental results shows that the classification rate of the FRBFN is higher than that of the RBFN. The network proposed in this paper is promising in the application of radar target recognition.
Some conclusions have been drawn from the growth of KCl and AgCl optical fiber in the present paper. There is a temperature region with gradient near the solid-melt interface. The phase change latent heat is transmitted by the grown crystal. According to thermal transmission equation, the thermal conductivity (TC) in crystal, Ks, and that in melt, Km, near the solid-melt interface affect strongly on the temperature gradient along the grown axis in crystal and melt. Generally, thermal conductivity in crystal Ks is greater than that in the melt, Km. Similarly, K (metal) > K (nonmetal). TC of non-conducting crystal and metal will reduce with temperature increased TC in conducting liquid is 10 - 1000 times greater than that of non-conducting liquid. Halide ionic crystal with NaCl-type structure is nonconductor, whose TC Ks 1/T, in vicinity of melting point. However halid melt is conducting and its TC, Km, increases as greatly as to transcend the value of Kg. Therefore the temperature gradient in crystal is inevitably greater than that in melt near the solid-melt interface.