Accurate method of generating infrared imaging features by the angular disturbance of an airborne platform.

The imaging quality of an airborne infrared (IR) system is limited by the angular disturbance of the airborne platform. Based on the full-chain (IR scene-atmosphere-optical system-detector-airborne platform) signal transmission process, this study focused on the low-frequency sinusoidal angular disturbance features of the airborne platform and accurately calculated the point spread function caused by the angular disturbance and the IR imaging features when the IR system's different locations were dynamically simulated in a three-dimensional scene. First, the degradation mechanism of the IR imaging features resulting from the angular disturbance was analyzed from the viewpoint of scene radiation signal transmission and detector sampling. Then, the dynamic simulation in the three-dimensional scene resulting from the angular disturbance was realized by considering the geometric transformation of the spatial imaging, scale registration of the spatial sampling, radiation coupling, and angular disturbance caused by the airborne platform. Finally, the distances detected under different disturbance conditions were predicted using the established model. The obtained results provide data supporting the demonstration, verification, and optimization of the IR imaging system's design scheme.

Performance analysis of the infrared imaging system for aircraft plume detection from geostationary orbit.

In view of the optical detection requirements of wide-area and continuous surveillance of air targets, the detection ability of an infrared imaging system in geostationary orbit for aircraft plumes is studied. The point spread model of the subpixel imaging of the full chain, including the aircraft plume, the sea surface, the environmental atmosphere, the optical system, and the imaging detector is established. The detection ability of the typical imaging system in geostationary orbit is analyzed from the signal-to-noise ratio (SNR) and the detection range in combination with the effect of the point spread function (PSF) of the optical system. Meanwhile, the optimal coupling condition of the PSF to the spatial resolution is discussed. The imaging characteristics of the aircraft target on the focal plane of the infrared imaging system under different spatial sampling rates are simulated and verified. Research shows that the SNR of the system first increases, and then decreases gradually with an increase of the spatial sampling rate. The detectable range covered by the pixel footprint decreases as the detector size increases. When the detector size is 15, 20, and 30 µm, the target can be detected with a spatial resolution of 200-700, 300-700, and 400-600 m, respectively.

Accurate deduction of infrared imaging features of subpixel targets based on the conversion of radiation fields of measured area targets.

The accurate generation of infrared (IR) imaging features of subpixel targets plays a very important role in the demonstration, verification, and optimization of system design schemes as well as in research into detection algorithms for small targets in the development of remote IR early warning systems. Based on the generation mechanism of target full-link IR imaging features, this study theoretically considers target radiation characteristics, the working environment, and the spatial response and energy-conversion characteristics of IR sensors, and an accurate deduction model of IR imaging features of subpixel targets is proposed and established. First, the surface-radiation field distribution of the target and background are inverted based on the measured data and the model of radiation calibration; then, the accurate simulation of IR imaging features of subpixel targets is realized by considering the geometric transformation of the spatial imaging, the aperiodic transfer function, scale registration of spatial sampling, and radiation coupling. Finally, the accuracy of the proposed model is verified by using the outfield experiment data. The experimental results show that the IR imaging-diffusion features of subpixel targets with different duty cycles are in good agreement with the prediction results of the model. The results obtained provide data support for the demonstration, verification, and optimization of the system design scheme, as well as for research into detection algorithms of small targets in the development of remote IR early warning systems.

Bidirectional reflectance characteristics of the sea surface based on midinfrared measured data.

In order to establish a more realistic radiation model of the sea surface, the effects of solar radiation, sky radiation, and atmospheric thermal radiation on sea surface radiation are taken into consideration, on the basis of which the infrared radiative transfer equation of the sea surface is deduced in this paper. A method for calculating the bidirectional reflection characteristics of the sea surface based on measured data is proposed according to the projection imaging of beam propagation. Based on the measurements of sea surface temperature, incident sky radiation, incident solar radiation, and radiance of sea crests at different times, the radiative transfer equation is used to retrieve the bidirectional reflectance of a midwave infrared sea surface. Meanwhile, the results of the method mentioned above are compared with the calculated results of Cox-Munk, Mermelstein, Wu, and Beckmann bidirectional reflection characteristics models. Research shows that the bidirectional reflectance at the wave crest of a sea surface increases gradually, when the solar incident zenith angle changes from 56.39° to 76.02° as well as the direction of observation remaining constant (θr=80.0°; ϕr=73.0°). The reflection ability at the wave crest of the sea surface is strongest when the incident direction of the sun is close to the observation direction, which is in accordance with the law of reflection. The Cox-Munk model and Wu model are closer to our values when the solar incidence zenith angle is small (θi≤65.93°). On the other hand, the calculated values of the Mermelstein and Wu models are closer to the values in this paper when the solar incidence zenith angle is large (θi≤65.93°). In general, the error of the Beckmann model is a little greater than that of the other three models.