Paul W. Nugent

Polarization lidar measurements of honey bees in flight for locating land mines.

A scanning polarized lidar was used to detect flying honey bees trained to locate buried land mines through odor detection. A lidar map of bee density shows good correlation with maps of chemical plume strength and bee density determined by visual and video counts. The co-polarized lidar backscatter signal was found to be more effective than the crosspolarized signal for detecting honey bees in flight. Laboratory measurements show that the depolarization ratio of scattered light is near zero for bee wings and up to 30% for bee bodies.

Radiometric cloud imaging with an uncooled microbolometer thermal infrared camera

An uncooled microbolometer-array thermal infrared camera has been incorporated into a remote sensing system for radiometric sky imaging. The radiometric calibration is validated and improved through direct comparison with spectrally integrated data from the Atmospheric Emitted Radiance Interferometer (AERI). With the improved calibration, the Infrared Cloud Imager (ICI) system routinely obtains sky images with radiometric uncertainty less than 0.5 W/(m(2 )sr) for extended deployments in challenging field environments. We demonstrate the infrared cloud imaging technique with still and time-lapse imagery of clear and cloudy skies, including stratus, cirrus, and wave clouds.

Infrared cloud imaging in support of Earth-space optical communication

The increasing need for high data return from near-Earth and deep-space missions is driving a demand for the establishment of Earth-space optical communication links. These links will require a nearly obstruction-free path to the communication platform, so there is a need to measure spatial and temporal statistics of clouds at potential ground-station sites. A technique is described that uses a ground-based thermal infrared imager to provide continuous day-night cloud detection and classification according to the cloud optical depth and potential communication channel attenuation. The benefit of retrieving cloud optical depth and corresponding attenuation is illustrated through measurements that identify cloudy times when optical communication may still be possible through thin clouds.

Errata: Correcting for focal-plane-array temperature dependence in microbolometer infrared cameras lacking thermal stabilization

Advances in microbolometer detectors have led to the develop- ment of infrared cameras that operate without active temperature stabili- zation. The response of these cameras varies with the temperature of the cameras focal plane array (FPA). This paper describes a method for sta- bilizing the cameras response through software processing. This stabili- zation is based on the difference between the cameras response at a measured temperature and at a reference temperature. This paper presents the mathematical basis for such a correction and demonstrates the resulting accuracy when applied to a commercially available long- wave infrared camera. The stabilized camera was then radiometrically calibrated so that the digital response from the camera could be related to the radiance or temperature of objects in the scene. For FPA temper- ature deviations within � 7.2°C changing by 0.5°C∕min, this method pro- duced a camera calibration with spatial-temporal rms variability of 0.21°C, yielding a total calibration uncertainty of 0.38°C limited primarily by the 0.32°C uncertainty in the blackbody source emissivity and temperature.

Physics principles in radiometric infrared imaging of clouds in the atmosphere

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.

Long-wave infrared imaging for non-invasive beehive population assessment

Long-wave infrared imaging is used for non-invasive assessment of the internal population of honey bee colonies. The radiometrically calibrated camera signal is related to the number of frames that are populated by bees inside each hive. This enables rapid measurement of population without opening the hive, which disturbs the bees and can endanger the queen. The best results are obtained just before sunrise, when there is maximum thermal contrast between the hive and the background. This technique can be important for bee hive monitoring or for applications requiring frequent hive assessment, such as the use of bees for detecting chemicals or explosives.

Long-wave infrared imaging of vegetation for detecting leaking CO2 gas

Abstract. The commercial development of uncooled-microbolometer, long-wave infrared (LWIR) imagers, combined with advanced radiometric calibration methods developed at Montana State University, has led to new uses of thermal imagery in remote sensing applications. One specific novel use of these calibrated imagers is imaging of vegetation for CO 2 gas leak detection. During a four-week period in the summer of 2011, a CO 2 leak was simulated in a test field run by the Zero Emissions Research and Technology Center in Bozeman, Montana. An LWIR imager was deployed on a scaffold before and during the CO 2 release, viewing a vegetation test area that included regions of high and low CO 2 flux. Increased root-level CO 2 concentration caused plant stress that led to reduced thermal regulation of the vegetation, which was consistent with increased diurnal variation of IR emission observed in this study. In a linear regression, the IR data were found to have a strong relationship to the CO 2 emission and to be consistent with the location of leaking CO 2 gas. Reducing the continuous data set to one image per day weakened the regression fit, but maintained sufficient significance to indicate that this method could be implemented with once-daily airborne images.

Radiometric calibration of infrared imagers using an internal shutter as an equivalent external blackbody

Abstract. Advances in microbolometer long-wave infrared (LWIR) detectors have led to the common use of infrared cameras that operate without active temperature stabilization, but the response of these cameras varies with their own temperature. Therefore, obtaining quantitative data requires a calibration that compensates for these errors. This paper describes a method for stabilizing the camera’s response through software processing of consecutive images of the scene and images of the camera’s internal shutter. An image of the shutter is processed so that it appears as if it were viewed through the lens. The differences between the scene and the image of the shutter treated as an external blackbody are then related to the radiance or temperature of the objects in the scene. This method has been applied to two commercial LWIR cameras over a focal plane array temperature range of ±7.2°C, changing at a rate of up to ±0.5°C/min. During these tests, the rms variability of the camera output was reduced from ±4.0°C to ±0.26°C.

Measuring the modulation transfer function of an imaging spectrometer with rooflines of opportunity

Measuring the modulation transfer function (MTF) of digital imagers focused at or near infinity in laboratory or field settings presents difficulties because the optical path is longer than a typical laboratory. Also, digital imagers can be hindered by low-resolution detectors, result- ing in the resolution of the optics surpassing that of the detector. We measure the MTF for a short-wave infrared hyperspectral imager devel- oped by Resonon, Inc., of Bozeman, Montana, which exhibits both char- acteristics. These difficulties are overcome with a technique that uses images of building rooflines in an oversampled, tilted knife-edge-based MTF measurement. The dark rooftops backlit by a uniformly cloudy sky provide the high-contrast edges required to perform knife-edge MTF mea- surements. The MTF response is measured at five wavelengths across the imagers spectral band: 1085, 1178, 1292, 1548, and 1629 nm. The MTF also is observed at various distances from the roof to investigate performance change with distance. Optimum imaging is observed at a distance of 150 m, potentially a result of imperfect infinity focus and atmo- spheric turbulence. In a laboratory validation of the MTF algorithm using a monochrome visible imager, the roofline MTF results are similar to re- sults from point-source and sine-card MTF measurements. C 2010 Society

Multispectral imaging systems on tethered balloons for optical remote sensing education and research

Abstract. A set of low-cost, compact multispectral imaging systems have been developed for deployment on tethered balloons for education and outreach based on basic principles of optical remote sensing. They have proven to be sufficiently capable, and they are now being used in research as well. The imagers use tiny complementary metal-oxide semiconductor cameras with low-cost optical filters to obtain images in red and near-infrared bands, and a more recent version includes a blue band. The red and near-infrared bands are used primarily for identifying and monitoring vegetation through the normalized difference vegetation index (NDVI), while the blue band can be used for studying water turbidity and so forth. The imagers are designed to be carried by tethered balloons to altitudes currently up to approximately 50 m. These undergraduate-student-built imaging systems are being used by university and college students for a broad range of applications in multispectral imaging, remote sensing, and environmental science.