As aerospace detection technology evolves, limb optical detection is increasingly becoming a focal point of research, attributed to its high spatial coverage and elevated vertical resolution. Based on the SCIATRAN limb atmospheric radiation model, simulation analyses of limb radiation transmission characteristics in the middle and upper atmosphere were conducted for both clear and cloudy conditions in the visible to near-infrared spectrum. The study results indicate that observational tangent height and solar zenith angle are important parameters affecting limb radiation brightness in the middle and upper atmosphere, with limb radiation brightness showing a decreasing trend as tangent height increases; in the visible light spectrum, it gradually weakens with increasing solar zenith angle, but in the near-infrared spectrum, it first decreases and then increases. The presence of aerosols and cirrus clouds significantly affects the mid-to-high altitude atmospheric limb radiation brightness. Under stratospheric aerosol conditions, radiation brightness can increase up to 2744.31% compared to background conditions, and under cirrus clouds with an optical thickness of 1, the increase in radiation brightness can be up to 13.78 times compared to clear sky conditions. The study delves into and analyzes the impact of particle optical properties on limb atmospheric background radiation, offering theoretical and data foundations for comprehending its spectral characteristics and designing limb detectors.
The total atmospheric transmittance of the South China Sea was measured using a Fourier Transform Infrared Spectroradiometer. After measuring the direct solar spectrum data in 1.1-2μm using the Spectroradiometer, the Langley method was employed to extract the atmospheric spectral transmittance of the South China Sea. The Langley method was utilized to extract atmospheric spectral transmittance at different altitudes and angles, and the variation in atmospheric transmittance over the South China Sea was analyzed extensively. The Combined Atmospheric Radiative Transfer (CART) model was used on the above data, to simulate the atmospheric transmittance under similar circumstances and draw a comparison with the previously obtained results. The data obtained from the Spectroradiometer indicates that the slant path atmospheric transmittance is in coherence with the model simulation results, with a negligible absolute error of less than 2.3%. Furthermore, as the solar zenith angle increases, there is a gradual decrease in the transmittance of the entire measurement band. The short-wave atmosphere attenuates rapidly; however, the long-wave attenuation is slow.
Aerosol optical depth (AOD) is one of the basic parameters used to analyze physical properties of regional aerosols, but the in-situ observation or remote sensing AOD dataset could be scarce especially in ocean area. The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis has the longest temporal span, and its accuracy in China sea area is to be evaluated. This study provides a validation of MERRA-2 AOD products’ applicability in the eastern and southern China sea based on Aerosol Robotic Network (AERONET). The results indicated that the MERRA-2 AOD with 1-hour temporal resolution agreed with the time averaged AERONET AOD well, for its correlation coefficient is 0.887, root mean square error (RMSE) is 0.096, and mean absolute error (MAE) is 0.056. Presented analysis also revealed a systematic underestimation of AOD that MERRA-2 made, and that deviation tended to increase in higher AOD which demonstrated a slope of -0.26 when utilized linear fitting technics, but the mean bias (MB) of test dataset was only -0.001 because the AOD concentrated on lower than 0.2. These results illustrated the suitability of using MERRA-2 AOD product in aerosol researches of the China sea area.
In this paper, we investigate that the effects of weather, turbulence and pointing errors on laser beams, and establish a joint channel statistical model, then derive the performance parameters of free space optical communication system based on OOK modulation, such as average bit error rate, average channel capacity and outage probability, and finally derive their new expressions by using Meijer’s G function and H function. For an atmospheric laser communication system with a wavelength of 1550 nm and a link length of 1 km, the performance parameters of the system are simulated and analyzed. The results show that when the standard deviation of jitter is small, the communication system is obviously affected by turbulence, and the performance of communication system with different turbulence can be significantly improved by the aperture average effect; aperture averaging can also significantly compensate for the deterioration of the communication system performance due to the decrease of atmospheric visibility; when the standard deviation of jitter is large, the system performance is limited by the average aperture effect.
With the proposal of ocean strategic planning, the measurement of optical parameters and the study of atmospheric models have become particularly important. In order to solve the problem that traditional sun-photometer cannot track the sun accurately on the moving platform at sea, a design scheme of shipboard sun-photometer is proposed for the limitation of water vapor and aerosol measurement. In this paper, the overall structure of shipboard sun-photometer and tracking technology route are described in detail,and the depth analysis is carried out in three aspects:the sloshing compensation of the hull,how to locate the azimuth of the sun at sea,the size and accuracy of the tracking field of view. Firstly, the fisheye imaging system is combined with the astronomical and celestial trajectory tracking to perform rough tracking of the sun in the large field of view, and then fine tracking by the CCD image processing technology of the small field of view. Double compensation for hull sway through the attitude sensing system and the gyrostabilization platform. The measurement of marine water vapor and atmospheric aerosols is accomplished by fully automated real-time precise tracking of the sun. Finally, the key indicators were calculated and analyzed, and the tracking accuracy and measurement field of view were determined.
The gradient of the refractive index of the atmosphere causes the route to bend when the light propagates in the atmosphere, thereby the propagation path will change. For the applications of optical atmospheric detection and star-light navigation positioning, in order to obtain the precise position of the target, the influence of atmospheric refraction needs to be considered. This paper introduces a widely-used refractive index calculation model. The relationships between the index of atmospheric refraction and wavelength, atmospheric pressure, temperature and water vapor content are analyzed. Based on the limb detection method, the effect of atmospheric refraction on the line of sight is calculated and analyzed. At the condition of the 1km tangent height, ignoring the atmospheric refraction will cause the limb line path length up to 148.3 km added. In the limb detection mode, the deflected angle caused by atmospheric refraction decreases rapidly as the pitch angle increases. The difference of the tangent height caused by atmospheric refraction increases rapidly with the decreasing observation point height. When the observing point height is 7 km, variation of the tangent height caused by atmospheric refraction is 0.282 km and the deflected angle is 0.195°. Which indicates that the atmospheric refraction has a great influence on the path of limb observation, especially for tangent height below 30 km.
At present, when the infrared sensor detects the targets remotely, the target appears as a spot in the image plane, the geometry information is difficult to obtain, and the surface brightness temperature becomes an effective feature for the target recognition. However, due to the long distance of the target, the weak signal and the complex transmission path, the temperature features are difficult to extract accurately, which brings great uncertainty to the target recognition. Based on the principle of multi-spectral infrared radiation temperature measurement, this paper establishes a BP network model to estimate the point target temperature. Experiments show that the accuracy of extracting the faint targets temperature characteristics can be effectively improved, which shows great support for target recognition.
Synthetic aperture laser radar (inverse) combines the technology of laser radar with synthetic aperture, which has high imaging resolution, strong anti-interference, and good concealment. Due to the short laser wavelength and fast imaging time, the tiny vibrations of the moving target may achieve the target inverse synthetic aperture (range -Doppler) imaging in a very short time, which increases identification characteristics compared to the traditional optical remote point target detection and recognition; it reduces the complexity of data processing compared to radar, and optical imaging is easier to understand. Therefore, synthetic aperture laser radar has the advantages of both optics and radar, and has attracted more and more attention in long-distance target detection and recognition. Since 1960's, MIT Lincoln Laboratory has conducted research on the long-range target tracking and identification using laser radar. In this paper, the micro-motion feature extraction and recognition method for inverse synthetic aperture laser radar after target imaging is studied. The target images of different micro-motion form are analyzed by range-Doppler imaging model, and the geometric features of the target are extracted by the optical target segmentation algorithm. The Hough transform theory is used to extract the characteristics of the micro-motion period, and the micro-motion angle is inversed through the change of the target geometric features. The simulation test in field shows that this method can effectively extract the micro-motion characteristics of the target and lay a foundation for the micro-motion target recognition of synthetic aperture laser radar.
High-resolution remote sounding instruments have thousands of channels usually, the similarity between channels will cause redundancy, and may lead to the non-convergence of retrieval algorithm. In this paper, the channel selection of temperature retrieval is discussed based on air-borne High-spectral resolution Interferometer Sounder. The results show that, for the total 1724 channels of HIS 600-1075cm-1 band, the selected 45 channels contain 70% of the total information content,97 channels contain 80% of the total information content, greatly reducing the number of channels involved in retrieval algorithm, then using selected channels simulated for the measurements of HIS is discussed, the average absolute deviation between the retrieved temperature profile and the truth is 0.74K/Km. The result demonstrates that stepwise iterative method is possible to select channels for the airborne high-spectral infrared data.
A fast atmospheric radiative transfer model called Combined Atmospheric Radiative Transfer model (CART) has been
developed to rapidly calculate atmospheric transmittance and background radiance in the wavenumber range from 1 to
25000 cm-1 with spectral resolution of 1 cm-1. The spectral radiative properties of cirrus clouds at various effective sizes,
optical thicknesses, and altitudes from visible to infrared wavelength region are simulated using the CART. The analyses
show that the properties of cirrus clouds might be retrieved from the satellite-base spectral characteristics of cirrus clouds
based on these simulations.
This paper designs a style of particle counter which may measure the aerodynamic size and the
scattering intensity of two scattering angles of the aerosol particles. The scattering intensity can also be
calculated from the size and the refractive index according to the Mie theory. When the aerodynamic size is
equal to the optics size approximatively, we can inverse the refractive index of individual aerosol particles by
combining the relative results of the measurements.
Infrared solar spectra were measured automatically by an infrared solar spectrometer (ISS) capable of 0.4 cm-1 resolution. Good signal-o-noise ratio (SNR) and relatively high resolution made it possible to select unsaturated, temperature insensitive intervals for a specific absorption gas with minimal overlap by other interfering gases. In the wavelength range of 3.410-3.438μm, the absorption is mainly due to atmospheric methane and water vapor. A line-by-line (LBL) computation method was used to calculate theoretical atmospheric absorption. By adjusting the total column density to obtain an exact agreement between the calculated and observed absorption, the total column density of atmospheric methane and water vapor were obtained. In the paper, some result observed by ISS for more than one year were reported. Since the April of 1997, we have been monitoring the column abundances of atmospheric CH4 and H2O continually on every clear cloudless day with the method indicated above. The results show that CH4 has little variation in one day, but has considerable seasonal variation. More than one high density peaks were found, two of which occurred in hot summer and cold winter, and the smallest value was found in spring. The reason is explained as emissions of local sources and atmospheric transport. The precipitation of column water vapor has a largely variation even in one day, the smallest precipitation appeared in winter, the biggest value was found in hot summer, seasonal variation could be as large as 40 times.
An IR solar spectrometer (ISS), which basically consists of three components: coelstat, spectrometer and data acquiring unit, was developed. With ISS we measured the solar spectra in the wavelength range of 2915 - 2920 cm-1 on the ground to derive the abundance of atmospheric CH4. In this spectrum range, CH4 is the main absorption gas and other gases' absorption can be omitted. The measurement results in the winter of 1991 show that the mixing ratio of CH4 is around 1.6 ppm, with the mean measurement error about 10%.
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