Active and thermal imaging performance under bad weather conditions

Thermal imaging cameras are widely used in military contexts for their night vision capabilities and their observation range; there are based on passive infrared sensors (e.g. MWIR or LWIR range). Under bad weather conditions or when the target is partially hidden (e.g. foliage, military camouflage) they are more and more complemented by active imaging systems, a key technology to perform target identification at long range. The 2D flash imaging technique is based on a high powered pulsed laser source that illuminates the entire scene and a fast gated camera as the imaging system. Both technologies are well experienced under clear meteorological conditions; models including atmospheric effects such as turbulence are able to predict accurately their performances. However, under bad weather conditions such as rain, haze or snow, these models are not relevant. This paper introduces new models to predict performances under bad weather conditions for both active and infrared imaging systems. We first establish an enumeration of these “bad” atmospheric conditions, depending on their occurrence rate. Then we develop physical models to describe their intrinsic characteristics and their impact on the imaging system performances. Finally, we approximate these models to have a “first order” model easy to deploy for industrial applications. This theoretical work will be validated on real active and infrared data

Experiments and Models of Active and Thermal Imaging Under Bad Weather Conditions

Thermal imaging cameras are widely used in military contexts for their night vision capabilities and their observation range; there are based on passive infrared sensors (e.g. MWIR or LWIR range). Under bad weather conditions or when the target is partially hidden (e.g. foliage, military camouflage) they are more and more complemented by active imaging systems, a key technology to perform target identification at long range. The 2D flash imaging technique is based on a high powered pulsed laser source that illuminates the entire scene and a fast gated camera as the imaging system. Both technologies are well experienced under clear meteorological conditions; models including atmospheric effects such as turbulence are able to predict accurately their performances. However, under bad weather conditions such as rain, haze or snow, these models are not relevant. This paper introduces new models to predict performances under bad weather conditions for both active and infrared imaging systems. We point out their effects on controlled physical parameters (extinction, transmission, spatial resolution, thermal background, speckle, turbulence). Then we develop physical models to describe their intrinsic characteristics and their impact on the imaging system performances. Finally, we approximate these models to have a “first order” model easy to deploy for industrial applications. This theoretical work will be validated on real active and infrared data

Development of a transfer standard for laser thermometry

The measurement of gas temperatures is important in many combustion, chemical manufacturing and materials processing applications. Different laser spectroscopic methods are applied to measure the temperature of gases. Nevertheless, up to now none of these methods have been calibrated against the international temperature scale of 1990 (ITS-90). A transfer standard for laser thermometry (TSL) has been developed to calibrate laser thermometry techniques. The standard provides optical access to a sample volume of a gas maintained at a stable temperature within the range of 300 K to 1850 K. The gas temperature is measured using built-in, calibrated thermometers including thermocouples, Accufiber optical-fibre probes and an optical pyrometer for traceability to the ITS-90. Broadband Coherent Anti-Stokes Raman Scattering (CARS) and scanning CARS experiments have been performed inside the furnace. The measuring uncertainty of broadband CARS amounts to less than 4 per cent between room tempera ture and 800 K. At temperatures between 800 K and 1850 K an uncertainty of less than 2 per cent has been achieved. For scanning CARS the uncertainty and the precision amounts to 2 per cent between 295 K and 1850 K