The brightness reversal of submarine sand waves in “HJ-1A/B” CCD sun glitter images

The brightness reversal of submarine sand waves appearing in the small satellite constellation for environ- ment and disaster monitoring and forecasting （＂HJ- 1A/B＂） CCD sun glitter images can affect the observation and depth inversion of sand wave topography. The simulations of the normalized sun glitter radiance on the submarine sand waves confirm that the reversal would happen at a specific sensor viewing angle, defined as the critical angle. The difference between the calculated critical angle position and the reversal position in the image is about 1＇, which is excellent in agreement. Both the simulation and actual image show that sand wave crests would be indistinct at the reversal position, which may cause problems when using these sun glitter images to analyze spatial characteristics and migration of sand waves. When using the sun glitter image to obtain the depth inversion, one should take the advantage of image properties of sand waves and choose the location in between the reversal position and the brightest position. It is also necessary to pay attention to the brightness reversal when using ＂HI-1A/B＂ CCD images to analyze other oceanic features, such as internal waves, oil slicks, eddies, and ship wakes.

Investigation on in-flight particle velocity in supersonic plasma spraying

In-flight particle velocity and flux distribution were measured using CCD thermal spray monitor system during supersonic plasma spray processing with nano-structured Al_2O_3-TiO_2 feed stocks. According to the results of particle flux measurement, the largest radian of the divergent particle stream is about 0.2. Within the measuring range, top speed of in-flight particles reached 800m/s. Particle acceleration was accomplished within 4cm down stream of the nozzle. Average particle velocity (about 450m/s) exceeded local sound speed (340m/s) even at a mean standoff distance of 17cm. With increasing mean standoff distance, average velocity of in-flight particle decreased according to a parabolic rule approximately. Image diagnosis showed that the result of in-flight particle velocity measurement is credible.

Study on the influence of the discharge voltage on the ignition process of Hall thrusters

A high-speed charge-coupled device camera was used to capture images of the plume and acceleration channel of a Hall effect thruster during ignition at different discharge voltages.To better understand the influence of changes in the discharge voltage on the plasma parameters during thruster ignition,a particle-in-cell numerical model was used to calculate the distribution characteristics of the ion density and electric potential at different ignition moments under different discharge voltages.The results show that when the discharge voltage is high,the ion densities in the plume and acceleration channel are significantly higher at the initial phase of thruster ignition;with the gradual strengthening of the ignition process,the propellant avalanche ionization during thruster ignition occurs earlier and the pulse current peak increases.The main reason for these phenomena is that the change in the discharge voltage results in different energy acquisitions of the emitted electrons entering the thruster channel.

An image compression method for space multispectral time delay and integration charge coupled device camera

Multispectral time delay and integration charge coupled device （TDICCD） image compression requires a low- complexity encoder because it is usually completed on board where the energy and memory are limited. The Consultative Committee for Space Data Systems （CCSDS） has proposed an image data compression （CCSDS-IDC） algorithm which is so far most widely implemented in hardware. However, it cannot reduce spectral redundancy in mukispectral images. In this paper, we propose a low-complexity improved CCSDS-IDC （ICCSDS-IDC）-based distributed source coding （DSC） scheme for multispectral TDICCD image consisting of a few bands. Our scheme is based on an ICCSDS-IDC approach that uses a bit plane extractor to parse the differences in the original image and its wavelet transformed coefficient. The output of bit plane extractor will be encoded by a first order entropy coder. Low-density parity-check-based Slepian-Wolf （SW） coder is adopted to implement the DSC strategy. Experimental results on space multispectral TDICCD images show that the proposed scheme significantly outperforms the CCSDS-IDC-based coder in each band.

An improved adaptive preprocessing method for TDI CCD images

In order to achieve high quality images with time-delayed integration(TDI) charge-coupled device(CCD) imaging system, an improved adaptive preprocessing method is proposed with functions of both denoising and edge enhancement. It is a weighted average filter integrating the average filter and the improved range filter. The weighted factors are deduced in terms of a cost function, which are adjustable to different images. To validate the proposed method, extensive tests are carried out on a developed TDI CCD imaging system. The experimental results confirm that this preprocessing method can fulfill the noise removal and edge sharpening simultaneously, which can play an important role in remote sensing field.

On-line full scan inspection of particle size and shape using digital image processing

An on-line full scan inspection system is developed for particle size analysis. A particle image is first obtained through optical line scan technology and is then analyzed using digital image processing. The system is composed of a particle separation module, an image acquisition module, an image processing module, and an electric control module. Experiments are carried out using non-uniform 0.1 mm particles. The main advantage of this system consists of a full analysis of particles without any overlap or miss, thus improving the Area Scan Charge Coupled Device （CCD） acquisition problems. Particle size distribution, roundness, and sphericity can be obtained using the system with a deviation of repeated precision of around ±1%. The developed system is shown to be also convenient and versatile for any particle size and shape for academic and industrial users.

Registration of Correspondent Points in the Stereo-Pairs of Chang'E-1 Lunar Mission Using SIFT Algorithm

In this article, an appropriate strategy for registration of correspondent points in the stereo-pairs of Chang’E-1 lunar mission has been introduced. It consists of area-based method and feature-based method as two steps. Firstly, one subimage was extracted from nadir image as reference image. Making use of area-based method, another subimage which is called target image can be obtained from backward or forward image overlapping the same region of lunar surface with reference image. Secondly, feature points of each subimage can be extracted by SIFT （scale invariant feature transform） algorithm. Lastly, for each feature point given in reference image, the position of correspondence in target image can be estimated according to the parameters of Chang’E-1 lunar orbiter. In contrast to standard SIFT matching algorithm, the method proposed in this article can narrow the search space and accelerate the speed of computation while achieving reduction of the percentage of false registration.