Imaging lidar systems are used from the air to generate images of submerged objects for detection... more Imaging lidar systems are used from the air to generate images of submerged objects for detection and classification. In many cases, the dominant degradation of image quality is the distortion caused by optical refraction at the air-water interface. A simple, generalized algorithm is presented that produces significant image quality improvement when relatively sophisticated sensor hardware is available to collect the input images. The method requires sequential pairs of images made with a range-gated imaging lidar system. One image is made with the range gate set to match the depth of the object of interest. A second image with the range gate set to the sea surface above the target is made within a short time delay (< 1/30 second) before the sea surface changes shape noticeably. After removal of gross image motion (tracking error), all the local maxima and minima in the observed sea surface image are located. At these same selected locations (i.e., look directions), the pixel intensity values from the object image are saved in a new output image file. The process is repeated for each pair of images in the sequence, and an average intensity is computed when any given pixel is selected more than once. This averaging tends to reduce the effect of non-uniform illumination of the target due to wave focusing and defocusing. Intensity maxima in the surface image correspond to points near the high points in the sea surface (wave crests) and the minima correspond to low points (troughs). At look angles away from nadir the intensity extrema are displaced from the physical water height extrema but by a nearly constant angle. This observed behavior allows this "Min-Max Image Reconstruction Method" to be used successfully at angles up to at least 38 degrees from nadir. This paper demonstrates improvement in output image quality for multiple looks at a ~1 meter diameter submerged object.
The Phased Array Mirror, Extendible Large Aperture (PAMELA™) technology has been developed to ans... more The Phased Array Mirror, Extendible Large Aperture (PAMELA™) technology has been developed to answer the need for large aperture active and adaptive optical reflector systems1,2. The PAMELA system consists of a large reflector made up of smaller, hexagonal segments which utilize piston sensors on each of the segments. These are non-contacting, inductively-coupled edge-sensors which measure the relative piston displacement between adjacent segments. A wavefront sensor provides the tilt information for each segment.
Steward Observatory, Tucson, Arizona 85721 'The Multiple Mirror Telescope Observatory is a joint ... more Steward Observatory, Tucson, Arizona 85721 'The Multiple Mirror Telescope Observatory is a joint venture of the Smithsonian Institution and the University of Arizona.
The experiences in coaligning and phasing the Multi-Mirror Telescope (MMT), together with studies... more The experiences in coaligning and phasing the Multi-Mirror Telescope (MMT), together with studies in setting up radio telescopes, are presented. These experiences are discussed, and on the basis they furnish, schemes are suggested for coaligning and phasing four large future telescopes with complex primary mirror systems. These telescopes are MT2, a 15-m-equivalent MMT, the University of California Ten Meter Telescope,
The standard chopper-wheel method of calibrating millimeter-wavelength corrected antenna temperat... more The standard chopper-wheel method of calibrating millimeter-wavelength corrected antenna temperature data has several deficiencies which require significant corrections to produce repeatable measurements. Reducing the chopper-wheel brightness temperature below ambient temperature can result in a simplified calibration equation and a more accurate correction for atmospheric attenuation. An empirical calibration procedure is described to determine the effective temperature of a cooled chopper which is nearly at the mean atmospheric temperature. With this cooled chopper, the equivalent calibration temperature is simply related to the ambient temperature but is essentially independent of the precipitable water vapor. Measurements on the NRAO 11-m telescope near 3 mm wavelength confirm the accuracy of the atmospheric absorption correction using the cooled-chopper technique.
Imaging lidar systems are used from the air to generate images of submerged objects for detection... more Imaging lidar systems are used from the air to generate images of submerged objects for detection and classification. In many cases, the dominant degradation of image quality is the distortion caused by optical refraction at the air-water interface. A simple, generalized algorithm is presented that produces significant image quality improvement when relatively sophisticated sensor hardware is available to collect the input images. The method requires sequential pairs of images made with a range-gated imaging lidar system. One image is made with the range gate set to match the depth of the object of interest. A second image with the range gate set to the sea surface above the target is made within a short time delay (< 1/30 second) before the sea surface changes shape noticeably. After removal of gross image motion (tracking error), all the local maxima and minima in the observed sea surface image are located. At these same selected locations (i.e., look directions), the pixel intensity values from the object image are saved in a new output image file. The process is repeated for each pair of images in the sequence, and an average intensity is computed when any given pixel is selected more than once. This averaging tends to reduce the effect of non-uniform illumination of the target due to wave focusing and defocusing. Intensity maxima in the surface image correspond to points near the high points in the sea surface (wave crests) and the minima correspond to low points (troughs). At look angles away from nadir the intensity extrema are displaced from the physical water height extrema but by a nearly constant angle. This observed behavior allows this "Min-Max Image Reconstruction Method" to be used successfully at angles up to at least 38 degrees from nadir. This paper demonstrates improvement in output image quality for multiple looks at a ~1 meter diameter submerged object.
The Phased Array Mirror, Extendible Large Aperture (PAMELA™) technology has been developed to ans... more The Phased Array Mirror, Extendible Large Aperture (PAMELA™) technology has been developed to answer the need for large aperture active and adaptive optical reflector systems1,2. The PAMELA system consists of a large reflector made up of smaller, hexagonal segments which utilize piston sensors on each of the segments. These are non-contacting, inductively-coupled edge-sensors which measure the relative piston displacement between adjacent segments. A wavefront sensor provides the tilt information for each segment.
Steward Observatory, Tucson, Arizona 85721 'The Multiple Mirror Telescope Observatory is a joint ... more Steward Observatory, Tucson, Arizona 85721 'The Multiple Mirror Telescope Observatory is a joint venture of the Smithsonian Institution and the University of Arizona.
The experiences in coaligning and phasing the Multi-Mirror Telescope (MMT), together with studies... more The experiences in coaligning and phasing the Multi-Mirror Telescope (MMT), together with studies in setting up radio telescopes, are presented. These experiences are discussed, and on the basis they furnish, schemes are suggested for coaligning and phasing four large future telescopes with complex primary mirror systems. These telescopes are MT2, a 15-m-equivalent MMT, the University of California Ten Meter Telescope,
The standard chopper-wheel method of calibrating millimeter-wavelength corrected antenna temperat... more The standard chopper-wheel method of calibrating millimeter-wavelength corrected antenna temperature data has several deficiencies which require significant corrections to produce repeatable measurements. Reducing the chopper-wheel brightness temperature below ambient temperature can result in a simplified calibration equation and a more accurate correction for atmospheric attenuation. An empirical calibration procedure is described to determine the effective temperature of a cooled chopper which is nearly at the mean atmospheric temperature. With this cooled chopper, the equivalent calibration temperature is simply related to the ambient temperature but is essentially independent of the precipitable water vapor. Measurements on the NRAO 11-m telescope near 3 mm wavelength confirm the accuracy of the atmospheric absorption correction using the cooled-chopper technique.
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