An innovative transfer radiative code, TITAN (Thermal Infrared radiance simulaTion with Aggregation modeliNg),
in the infrared domain (3-14μm) is presented. It takes into account the 3D structure of the landscape and, thus, is able
to model the different radiative terms existing in such medium at ground and at-sensor levels. These different terms
are solar radiance, atmospheric radiance, emitted radiance and radiance due to the environment. Thus, it allows an
accurate spectral analysis of radiative components and of their relative impact to the total signal. Phenomenological
analysis of a street is proposed by assessing each term on every points of the modelled surface. Illustrations of the
potential of TITAN are given over urban area. Moreover, the impact on the signal when the 3D structure is taken into
account by comparing with a "equivalent" flat ground is estimated by calculating the percentage of each terms
contribution to the total signal at ground level for different wavelengths. Also, directional effects for each component
of total signal are simulated over a 3D street by varying sensor positions. Thus, these simulations angular variations
allow us to quantify the radiative temperature anisotropy and to understand the contribution of each term to the
directional behaviour.
The disposal of couples of images of the same landscape acquired with two spatial resolutions gives the opportunity
to assess the in-flight Modulation Transfer Function (MTF) of the lower resolution sensor in the common spectral
bands. For each couple, the higher resolution image stands for the landscape so that the ratio of the spectra obtained
by FFT of the two images, gives the lower resolution sensor MTF. This paper begins with a brief recall of the method
including the aliasing correction. The next step presents the data to be processed, provided by the Instituto Nacional
de Tecnica Aeroespacial (INTA). The model of the AHS MTF is described. The presentation of the corresponding
AHS results naturally follows. Last part of the paper consists in a comparison with other measurements:
measurements obtained with the edge method and laboratory measurements.
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