Biomedical subjects
Publications and source records attributed to Joseph A Shaw.
This Polarization in Remote Sensing special issue of Applied Optics presents 11 papers that describe research in polarization measurements and applications. The subject matter covered ranges from a review of passive imaging polarimetry, the first paper, to a presentation of twilight atmospheric polarization measurements, the last.
Imaging polarimetry has emerged over the past three decades as a powerful tool to enhance the information available in a variety of remote sensing applications. We discuss the foundations of passive imaging polarimetry, the phenomenological reasons for designing a polarimetric sensor, and the primary architectures that have been exploited for developing imaging polarimeters. Considerations on imaging polarimeters such as calibration, optimization, and error performance are also discussed. We review many important sources and examples from the scientific literature.
An imaging Stokes-vector polarimeter using liquid crystal variable retarders (LCVRs) has been built and calibrated. Operating in five bands from 450 to 700 nm, the polarimeter can be changed quickly between narrow (12 degrees ) and wide (approximately 160 degrees) fields of view. The instrument is designed for studying the effects of differing sky polarization upon the measured polarization of ground-based objects. LCVRs exhibit variations in retardance with ray incidence angle and ray position in the aperture. Therefore LCVR-based Stokes polarimeters exhibit unique calibration challenges not found in other systems. Careful design and calibration of the instrument has achieved errors within +/-1.5%. Clear-sky measurements agree well with previously published data and cloudy data provide opportunities to explore spatial and spectral variations in sky polarization.
An instrument is demonstrated that can be used for optical detection of honeybees in a cluttered environment. The instrument uses a continuous-wave diode laser with a center wavelength of 808 nm and an output power of 28 mW as the laser transmitter source. Light scattered from moving honeybee wings will produce an intensity-modulated signal at a characteristic wing-beat frequency (170-270 Hz) that can be used to detect the honeybees against a cluttered background. The optical detection of honeybees has application in the biological detection of land mines and explosives, as was recently demonstrated.
We use Fraunhofer diffraction theory and meterological data to determine the nature of cloud-particle distributions and the mean particle sizes required for interpreting photographs of coronas and iridescence in mountain wave clouds. Traditional descriptions of coronas and iridescence usually explain these optical phenomena as diffraction by droplets of liquid water. Our analysis shows that the photographed displays have mean particle sizes from 7.6 to 24.3 microm, with over half the cases requiring diffraction by small (approximatley 20 microm) quasispherical ice particles rather than liquid water droplets. Previous documentation of coronas produced by ice particles are limited to observations in cirrus clouds that appear to be composed of small ice crystals, whereas our observations suggest that coronas and iridescence quite often can be created by tiny quasispherical ice particles that might be unique to mountain wave clouds. Furthermore, we see that the dominant colors in mountain wave-cloud coronas are red and blue, rather than the traditionally described red and green.