Radiance Characters Of Aurora And Image Compression Encoding

In this paper, we take advantage of the three-band all-sky aurora graph data generated by the all-sky CCD observation device located in the Arctic Yellow River Station, and then we calculate the radiation intensity range of three-band all-sky aurora by extracting the auroral intensity data from the processed raw images. The intensity unit of the raw data is the Rayleigh, which is commonly used for the measurement of airglow and aurora in atmospheric physics. To introduce the characteristics of aurora radiation into the study of Space Target and Environmental Optics, Raleigh, the intensity unit of aurora is converted to the unit of radiation brightness which is commonly used in the field of optics.According to the mechanism of aurora, we verified the positive correlation among geomagnetic activity, solar variation and the aurora intensity. Solar variation effect the magnetic activity. By comparing the sunspot numbers to the geomagnetic activity indices, a conclusion can be drawn that the geomagnetic activity has a positive correlation with the solar variation. As is well known, the high-energy charged particles emitted by the sun are the fundamental reason of the occurrence of aurora. In addition, the solar activity influences the geomagnetic activity. In this paper, we will compare the obtained aurora intensity and the geomagnetic indices. The experiment results show that aurora intensity has a positive correlation with geomagnetic activity.Based on the theory of atmospheric transmission, various intensities of radiation background of sky and earth in the polar region is generated by MODTRAN Simulation under different conditions. Different zenith angles lead to different radiation intensity, and the experiment results show that: 1) approximate 45 degrees zenith angle can be used to simulate the sky background radiation; 2) approximate 135 degrees zenith angle can be used to simulate the earth background radiation. In addition, through the MODTRAN simulation, atmospheric transmittance from different directions of zenith angles can also be calculated, which gives us the approximate polar atmospheric transmittance matrix under the polar condition. Then the aurora intensity without atmospheric attenuation can be computed based on the matrix of polar atmospheric transmittance and the aurora intensity values we got previously. This result is alsoknown as the aurora background radiation intensity of high altitude target above the aurora. The latest raw image data of aurora obtained from the polar station needs to be immediately transmitted to the laboratory of inland. However, the size of the raw data is too large, such that the compression of the raw data is of great necessity to fit the narrow bandwidth of polar region. In this paper, we firstly elaborate the wavelet transform of image compression. In addition, we introduce three classical image compression methods which exploit the wavelet transform into the aurora images compression: EZW, SPIHT and JPEG2000. According to the characteristics of aurora image and the required compression conditions, an optimized aurora image compression method based on the EZW is proposed in this paper. Experiment results demonstrate that the proposed method achieves higher image quality compared with other methods at the same compression ratio.