Cloud optical depth measured with ground-based, uncooled infrared imagers

Shaw, Joseph A.; Nugent, Paul W.; Pust, Nathan J.; Redman, Brian J.; Piazzolla, Sabino

doi:10.1117/12.981294

Cited by 6 publications

(15 citation statements)

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“…With a few modifications to extend the models to larger zenith angles, the reflective all-sky ICI used the same algorithms as previous infrared cloud imaging systems to detect clouds and estimate their optical depth [14,15,23]. Figure 3 shows sky images at three different points in the processing.…”

Section: Resultsmentioning

confidence: 99%

“…3(b). Finally, the corrected sky radiance images were used to derive the cloud optical depth according to the approach described in [14,15,23], as shown in Fig. 3(c).…”

Section: Resultsmentioning

confidence: 99%

“…The ICI3 is a lens-based cloud imager system with a diagonal FOV of 110° [23]. For this comparison, the two systems were operated together for a period of twenty-five days in May-June 2012 at Montana State University.…”

Section: Resultsmentioning

confidence: 99%

“…For these needs, autonomous imaging systems have been developed to make measurements of parameters such as the fraction of the sky that is cloudy [20], cloud height [21], cloud emissivity [22], and cloud optical depth [23,24]. Ground-based infrared imaging systems are particularly well suited to addressing these needs with day and night consistency and high temporal resolution.…”

Section: Introductionmentioning

confidence: 99%

“…Our Infrared Cloud Imager (ICI) systems are based on uncooled thermal imagers that combine microbolometer detectors with advanced radiometric calibration algorithms [14,15,[33][34][35] and radiometric image processing to compensate for the atmosphere and calculate cloud fraction and products such as cloud emissivity, optical depth, and attenuation [14,15,23,36,37]. This paper describes a reflective all-sky Infrared Cloud Imager (ICI) system that uses a metal sphere to reflect the full sky into a low-cost, weather-proof microbolometer camera positioned off axis to allow for an unobstructed view of the zenith sky.…”

Section: Introductionmentioning

confidence: 99%

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Reflective all-sky thermal infrared cloud imager

et al. 2018

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Abstract:A reflective all-sky imaging system has been built using a long-wave infrared microbolometer camera and a reflective metal sphere. This compact system was developed for measuring spatial and temporal patterns of clouds and their optical depth in support of applications including Earth-space optical communications. The camera is mounted to the side of the reflective sphere to leave the zenith sky unobstructed. The resulting geometric distortion is removed through an angular map derived from a combination of checkerboardtarget imaging, geometric ray tracing, and sun-location-based alignment. A tape of highemissivity material on the side of the reflector acts as a reference that is used to estimate and remove thermal emission from the metal sphere. Once a bias that is under continuing study was removed, sky radiance measurements from the all-sky imager in the 8-14 μm wavelength range agreed to within 0.91 W/(m 2 sr) of measurements from a previously calibrated, lensbased infrared cloud imager over its 110° field of view.

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Section: Resultsmentioning

confidence: 99%

“…3(b). Finally, the corrected sky radiance images were used to derive the cloud optical depth according to the approach described in [14,15,23], as shown in Fig. 3(c).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reflective all-sky thermal infrared cloud imager

et al. 2018

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Physics principles in radiometric infrared imaging of clouds in the atmosphere

Shaw

Nugent²

2013

Eur. J. Phys.

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Imaging the atmosphere with a thermal infrared camera can yield a rich variety of information, ranging from the water-vapour content to the spatial distribution of clouds. Such remote sensing measurements are being used to study climate and to characterize ground-station sites for Earth-space optical communications. The key to turning interesting but qualitative images into the highly accurate quantitative images required for this type of research is careful radiometric calibration. This is especially true when using uncooled microbolometer cameras, which are becoming widely available at relatively low cost. When such cameras are calibrated properly, their images illustrate a variety of important basic principles of optics and atmospheric physics related to thermal emission and absorption by atmospheric gases and clouds.

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Empirical model for longwave and midwave radiometric and spatial characteristics of clouds for target detection considerations

et al. 2023

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The presence of clouds affects the detection of small airborne targets for infrared imaging. Clouds increase the signal of the background and create nonuniformity behind a desired target. This results in low and varying contrast. Clear sky conditions provide a low noise, uniform background that gives a better chance of detection. Understanding key variables of the clouds nonuniform structure allows for better detection and for accurate infrared search and track (IRST) models. Atmospheric modeling software, such as moderate resolution atmospheric transmission (MODTRAN), provides background path radiance in the emissive midwave infrared and longwave infrared bands. These modeled skies have been matched with measured skies in various conditions with low error. MODTRAN clouds, however, assume total cloud cover of uniform thickness and no varying transmission. MODTRAN clouds do not consider the spatially and radiometrically varying structures that make clouds unique. Studied spatial and radiometric characteristics of clouds are used in an empirical approach to predict cloud radiometric temperatures and structures with four simple equations. These cloud properties are measured at night to avoid solar contributions and focus on their emissive characteristics. The empirically modeled clouds are projections from measured or MODTRAN modeled clear skies. This method of modeling clouds allows for easy implementation of a nonclear sky background into IRST models. The range in which a target is first detected from its background can now be compared between clear and cloudy skies.

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Cloud optical depth measured with ground-based, uncooled infrared imagers

Cited by 6 publications

References 0 publications

Reflective all-sky thermal infrared cloud imager

Reflective all-sky thermal infrared cloud imager

Physics principles in radiometric infrared imaging of clouds in the atmosphere

Empirical model for longwave and midwave radiometric and spatial characteristics of clouds for target detection considerations

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