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the elevation data of the port background area, which is shown in Figure 6. By combining meteorological observation data of the port area to obtain average temperature information of land surface, and based on topographic factors such as slope and aspect, the modulating effect of topography on radiation flux and energy exchange is characterized. A port temperature model is constructed to achieve a re-fined characterization of the temperature field under the combined influence of meteorological conditions and topographic features.
Tx ð; y; t i Þ ¼ T 0 ðt i Þþb 1 Demðx; yÞþb 2 Slopeðx; yÞþb 3 Aspectðx; yÞ ð15Þ
where T( x, y, t i) is the predicted temperature at the i-th time instant, Dem( x, y) istheelevation, Slope( x, y) istheslope, Aspect( x, y) is the aspect, T 0( t i) is the baseline temperature obtained from meteorological data at the i-th time instant, β₁ is the regression coefficient of the elevation factor, the temperature of the land material decreases with the increase of elevation; β₂ is the regression coefficient of the slope factor, the slope is negatively correlated with temperature; β₃ is the regression coefficient of the aspect factor, the relationship between slope aspect and temperature is“ positive in the south and negative in the north”.
The temporal meteorological data is integrated with the spatial background model by pixel-by-pixel. Taking 8:30 in winter as an example, the temperature of the port background is modulated, and the result is shown in Figure 7.
3 Port infrared scene modeling
3.1 Calculation of target temperature distribution
Fluent is widely used in numerical calculation fields such as fluid flow, heat conduction and thermal radiation. It can deal with complex fluid flow and heat transfer process, especially suitable for the simulation of fluid dynamics and heat conduction. The three-dimensional ship target model was established in SpaceClaim. The ship is roughly divided into three components: the deck, hull, and superstructure. Geometric inspection and feature simplification are subsequently performed on the model. Unstructured meshing is then carried out in Workbench Meshing. The global element size is determined based on the overall dimensions of the model, followed by local mesh refinement on key surfaces with significant heat flux variations. The meshing results of the target model are shown in Figure 8.
The surface temperature of the ship target is solved using Fluent, with the energy equation enabled under steady-state conditions. Turbulence is modeled using the k – ω SST shear stress transfer model [ 29 ]. Radiative heat transfer is taken into account through the Discrete Ordinates( DO) model, with solar radiation effects incorporated based on the Solar Ray Tracing algorithm to describe the transmission and distribution of solar energy. The calculation of solar radiation is related to the latitude, and longitude, time zone, date and other factors of port image data. The temperature results in different seasons are shown in Figure 9.
Figure 7. The port background temperature after modulated.
Figure
8. Ship target grid division diagram.
The spatial resolution of the remote sensing background data is 30 m. The ship target calculated in Fluent is modeled at its true scale. In order to match the resolution of the remote sensing image and maintain data consistency, a bilinear interpolation method [ 30 ] is adopted to downscale and resample the high-resolution target grid. The coordinates of the known points are( x 1, y 1),( x 1, y 2),( x 2, y 1),( x 2, y 2). For a given y value, the linear interpolation in the x direction is first performed:
fðx; y 1 Þ ¼ x 2 � x
fðx 1; y x 2 � x 1 Þþ x � x 1 fðx 2; y
1 x 2 � x 1 Þ ð16Þ 1 fðx; y 2 Þ ¼ x 2 � x
fðx 1; y x 2 � x 2 Þþ x � x 1 fðx 2; y
1 x 2 � x 2 Þ ð17Þ 1
Then, interpolation is performed in the y-direction. Substituting the interpolated results obtained in the x-direction into the following equation, the final interpolated value at the target position is obtained:
fðx; yÞ ¼ y 2 � y
fðx; y y 2 � y 1 Þþ y 2 � y fðx; y
1 y 2 � y 2 Þ 1
In the actual imaging process, when the target completely covers a pixel, the radiation intensity of the pixel is directly