KEYWORDS: Target detection, Hyperspectral imaging, Detection and tracking algorithms, Sensors, Image processing, Data processing, Hyperspectral target detection, Signal to noise ratio, Signal processing, Receivers
The high dimensionality of hyperspectral imagery is a huge challenge for remote sensing data processing. Band selection utilizes the most distinctive and informative band subset to reduce data dimensions. Although band selection can significantly alleviate the computational burden, the process itself may be time consuming because it needs to take all pixels into consideration, especially when the image spatial size is larger. An improved band similarity-based band selection method is proposed for hyperspectral imagery target detection, which includes four steps: (1) bad bands are removed by data preprocessing; (2) several selected pixels are used for band selection instead of using all the pixels to reduce the computational complexity; (3) hyperspectral imagery is analyzed for target detection; and (4) the number of selected bands is determined by adjusting the threshold of similarity metric, to ensure target detection operators have the best performance with selected bands. In the example, the well-known adaptive coherence estimator detector was used to evaluate the effectiveness of the proposed band selection method. The receiver operating characteristics curves were plotted to prove the proposed algorithm quantitatively. The experimental results show that our method can yield a better result in target detection than other band selection methods.
Cooled infrared focal plane array (Cooled IRFPA) has been applied widely in military and civil fields. In the cooled
focal plane array detector infrared imaging systems, narcissus as a unique defect has a degenerate effect on the image
quality of cooled infrared imaging systems, such as blocky, annular or "corner heat" fixed pattern noise in infrared
images. Therefore, the correction of narcissus effect using image processing method is important to infrared imaging
systems. Through analyzing manifestation of narcissus effect by statistical approach, a cooled infrared imaging system
model considering narcissus effect is established, by which a self-adaptive narcissus correction algorithm based on scene
statistic and radial compute is presented. From the simulation and the experiment on an actual cooled IRFPA module,
this algorithm is proved very effective on correcting narcissus effect and improving image quality. Moreover, the peak
signal to noise ratio (PSNR) also increases obviously.
In order to know how we can design effective NLO materials, we have studied several series of aromatic hydrocarbons used as NLO materials and found criteria as follows: (1) When the conjugated system is small then the nitro-group is an effective acceptor, and some of this kind of compound has a very high SHG response while fairly big conjugated compounds whose acceptor is nitro-group often reveal weak or no nonlinearity. (2) The compounds whose acceptor (-NO<SUB>2</SUB>) and donor (-NH<SUB>2</SUB>, -NHR or -NR<SUB>2</SUB>) are para-substituted on both ends of the conjugated chains always have very weak or SHG (second harmonic generation). (3) The substituted groups such as -CH<SUB>3</SUB>, -OCH<SUB>3</SUB>, -X(-Cl, -Br, -1) and biphenyl (C<SUB>6</SUB>H<SUB>5</SUB>C<SUB>6</SUB>H<SUB>4</SUB>-) are the best donors which are beneficial to SHG response and transparency. (4) The relatively big conjugated compounds often reveal fairly good second-order nonlinearity when greater than C equals O acts as their acceptor. We studied these laws theoretically and experimentally so as to give some useful guides to the research of the SHG materials.
The values of the second-order polarizability of twenty- three derivatives from coumarin were calculated with quantum chemistry program (CNDO/S-CI). 7-hydroxyl-4-methylcumarin was artificially synthesized, and its powder appeared to be particularly effective in second harmonic generation. The single crystal of this compound was grown by solvent evaporation. It is suggested that 7-hydroxyl-4-methylcumarin be an organic high-quality material of double frequency.