KEYWORDS: Modulation transfer functions, Imaging systems, Minimum resolvable temperature difference, Thermography, Spatial frequencies, Signal to noise ratio, Systems modeling, Thermal modeling, Absorption, Infrared imaging
There are much more need to characterize and evaluate performance of IRFPA in field. MRTD, MTF, NETD and
operating range R are some of the key parameters of IR devices and used to characterize their performance. Around
of these parameters there are two ways: analysis in theory and test. The research of these parameters in theory can be
used to predict the performance of IR devices and these parameters can be proved by experiments. Whereas these
parameters are hard to be tested in field, their test reports are based on experiment in laboratory. So it is very hard to
explain or predict the test results of IR devices in theory because of the influence of atmosphere. This paper presents
research of transfer function of atmosphere. A model of transfer function with the modified absorption and scatter
coefficient is introduced based on the theory of transfer function. The operating range can be modified by transfer
function of atmosphere. The experiment results show this model can be used together with operating range in some
circumstances. It could be used in the predicting the operating range of IR devices in theory.
Parameters of infrared cameras play an important role in the application of IR cameras. Most of these parameters' testing
principles are based on the measurement of radiation. In order to make measurement accurately, factors such as distant
from the test camera to the apparatus, optics index of reflection of measurement unit and atmospheric transmission must
be evaluated carefully. By means of the analysis of radiation energy, the concept of "working range" of a
double-blackbody parameters measurement unit and its mathematics model are proposed. The distribution of radiation is
simulated.
It had been proved that MTF plays a key role in evaluation the quality of imaging system even in infrared spectral bands. Two methods of MTF test procedures have been used widely in visible domain, i.e. the direct method which is based on measuring the response to sinusoidal; and the indirect method, which is based upon computing the Fourier transform of the measured line spread function. However it can also be used in infrared spectral bands even in the evaluation of the system with staring arrays. But there is still something different in infrared imaging system. The infrared flux will be influenced by many factors such as: optimum focus, not normalized to zero spatial frequency properly, signal out of linear region, blackbody or ambient temperature changes during the test, S/N ratio and the width of the slit on the sensor's surface. Concerning the applications of staring arrays system both MRTD and MTF are the main factors in the target acquisition characteristics in infrared wavebands. So the MTF test could be implemented on fixed special frequency, for example 20lp/mm, We will deal with the influence of illumination on sensor with SRF (slit response function) method under a special frequency.
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