Measurements of the relative intensity of ship exhaust gas as a function of distance to infrared sensors

Rheenen, Arthur D. van; Brendhagen, Erik; Heen, Lars Trygve; Madsen, Eirik Blix; Fonnum, Helge; Steenfeldt-Foss, Pål; Wikan, Kjell; Almklov, Bernt

doi:10.1117/12.737061

Cited by 1 publication

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“…separate plume pixels from background pixels in a box drawn around the plume. The method employed to accomplish the plume pixel identification is described in an earlier SPIE Europe Remote Sensing contribution [1]. Briefly, we estimate the intensity distribution of pixels that we assume do not contain any bits of plume, in an area of the frame that is spatially well separated from the plume, but not too far, so that azimuthal variations may be ignored.…”

Section: Analysis Techniquementioning

confidence: 99%

Comparison of distance dependence of ship signature and intensity of ship exhaust gas measured in both MWIR and LWIR transmission bands

2009

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A ship's exhaust gas contains both hot gas molecules, which emit infrared radiation at specific wavelengths (line emitters), and soot particles which emit broad-banded, like a black body. Our modeling shows that the observed radiance from these emissions falls at different rates with distance. The attenuation of intensity is caused by absorption and scattering of the emitted radiation in the atmosphere. The hottest part of the exhaust plume is spatially confined to a relative small volume. Usually, a ship's hull and its superstructure have a higher temperature than the sky or sea background. The temperature difference is generally not very large. However, the ship has a spatial extent that is much larger than the plume's. In this work we study how both the emitted radiation from the plume and the ship's total signature decrease with increasing distance. This study is based on experimental data that was collected during a measurement campaign at the southwest coast of Norway. Shore-based digital IR cameras, both LWIR and MWIR, recorded image sequences of ships as they sailed away from close to shore (~ 1 km) in a zigzag pattern out to about 10 km. We used a statistical method to identify the gas cloud pixels and used their integrated radiance as a measure for the plume intensity. The ship signature is defined here as the integrated radiance over all the ship's pixels in the imagery. From infrared spectroscopic data, collected using a Fourier Transform Infrared spectrometer aimed at the ship's plume when the ship is close to shore, a model is obtained for the composition of the exhaust gas. This model was used to perform FASCODE simulations to study numerically the attenuation with distance of the plume radiance. Our work shows that this approach may be well suited to explain the observed signal decay rate with distance.

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Section: Analysis Techniquementioning

confidence: 99%