Restoration of Atmospheric Turbulence Degraded Video using Kurtosis Minimization and Motion Compensation

In this thesis work, the background of atmospheric turbulence degradation in imaging was reviewed and two aspects are highlighted: blurring and geometric distortion. The turbulence burring parameter is determined by the atmospheric turbulence condition that is often unknown; therefore, a blur identification technique was developed that is based on a higher order statistics (HOS). It was observed that the kurtosis generally increases as an image becomes blurred (smoothed). Such an observation was interpreted in the frequency domain in terms of phase correlation. Kurtosis minimization based blur identification is built upon this observation. It was shown that kurtosis minimization is effective in identifying the blurring parameter directly from the degraded image. Kurtosis minimization is a general method for blur identification. It has been tested on a variety of blurs such as Gaussian blur, out of focus blur as well as motion blur. To compensate for the geometric distortion, earlier work on the turbulent motion compensation was extended to deal with situations in which there is camera/object motion. Trajectory smoothing is used to suppress the turbulent motion while preserving the real motion. Though the scintillation effect of atmospheric turbulence is not considered separately, it can be handled the same way as multiple frame denoising while motion trajectories are built.Ph.D.Committee Chair: Mersereau, Russell; Committee Co-Chair: Smith, Mark; Committee Member: Lanterman, Aaron; Committee Member: Wang, May; Committee Member: Tannenbaum, Allen; Committee Member: Williams, Dougla

Mitigating the effects of atmospheric distortion using DT-CWT fusion

This paper describes a new method for mitigating the effects of atmospheric distortion on observed images, particularly airborne turbulence which degrades a region of interest (ROI). In order to provide accurate detail from objects behind the dis-torting layer, a simple and efficient frame selection method is proposed to pick informative ROIs from only good-quality frames. We solve the space-variant distortion problem using region-based fusion based on the Dual Tree Complex Wavelet Transform (DT-CWT). We also propose an object alignment method for pre-processing the ROI since this can exhibit sig-nificant offsets and distortions between frames. Simple haze removal is used as the final step. The proposed method per-forms very well with atmospherically distorted videos and outperforms other existing methods. Index Terms — Image restoration, fusion, DT-CWT 1

Turbulence and Mixing in the Environment: Multi-Device Study in a Sub-tropical Estuary

In an estuary, mixing and dispersion result from a combination of large-scale advection and smallscale\ud turbulence, which are complex to estimate. The predictions of scalar transport and mixing are\ud often inferred and rarely accurate, due to inadequate understanding of the contributions of these\ud difference scales to estuarine recirculation. A multi-device field study was conducted in a small\ud sub-tropical estuary under neap tide conditions with near-zero fresh water discharge for about 48\ud hours. During the study, acoustic Doppler velocimeters (ADV) were sampled at high frequency (50\ud Hz), while an acoustic Doppler current profiler (ADCP) and global positioning system (GPS)\ud tracked drifters were used to obtain some lower frequency spatial distribution of the flow\ud parameters within the estuary. The velocity measurements were complemented with some\ud continuous measurement of water depth, conductivity, temperature and some other physiochemical\ud parameters. Thorough quality control was carried out by implementation of relevant error removal\ud filters on the individual data set to intercept spurious data. A triple decomposition (TD) technique\ud was introduced to access the contributions of tides, resonance and ‘true’ turbulence in the flow\ud field. The time series of mean flow measurements for both the ADCP and drifter were consistent\ud with those of the mean ADV data when sampled within a similar spatial domain. The tidal scale\ud fluctuation of velocity and water level were used to examine the response of the estuary to tidal\ud inertial current. The channel exhibited a mixed type wave with a typical phase-lag between 0.035π–\ud 0.116π. A striking feature of the ADV velocity data was the slow fluctuations, which exhibited\ud large amplitudes of up to 50% of the tidal amplitude, particularly in slack waters. Such slow\ud fluctuations were simultaneously observed in a number of physiochemical properties of the channel.\ud The ensuing turbulence field showed some degree of anisotropy. For all ADV units, the horizontal\ud turbulence ratio ranged between 0.4 and 0.9, and decreased towards the bed, while the vertical\ud turbulence ratio was on average unity at z = 0.32 m and approximately 0.5 for the upper ADV (z =\ud 0.55 m). The result of the statistical analysis suggested that the ebb phase turbulence field was\ud dominated by eddies that evolved from ejection type process, while that of the flood phase\ud contained mixed eddies with significant amount related to sweep type process. Over 65% of the\ud skewness values fell within the range expected of a finite Gaussian distribution and the bulk of the\ud excess kurtosis values (over 70%) fell within the range of -0.5 and +2. The TD technique described\ud herein allowed the characterisation of a broader temporal scale of fluctuations of the high frequency\ud data sampled within the durations of a few tidal cycles. The study provides characterisation of the\ud ranges of fluctuation required for an accurate modelling of shallow water dispersion and mixing in a\ud sub-tropical estuary

The development of convective instability, wind shear, and vertical motion in relation to convection activity and synoptic systems in AVE 4

Data from the Fourth Atmospheric Variability Experiment were used to investigate conditions/factors responsible for the development (local time rate-of-change) of convective instability, wind shear, and vertical motion in areas with varying degrees of convective activity. AVE IV sounding data were taken at 3 or 6 h intervals during a 36 h period on 24-25 April 1975 over approximately the eastern half of the United States. An error analysis was performed for each variable studied

Differential Zernike filter for phasing of segmented mirror and image processing

The major objective of this thesis is to study the differential Zernike filter and its applications in phasing segmented mirror and image processing. In terms of phasing, we provide both theoretical analysis and simulation for a differential Zernike filter based phasing technique, and find that the differential Zernike filter perform consistently better than its counterpart, traditional Zernike filter. We also combine the differential Zernike filter with a feedback loop, to represent a gradient-flow optimization dynamic system. This system is shown to be capable of separating (static) misalignment errors of segmented mirrors from (dynamical) atmospheric turbulence, and therefore compress the effects of atmospheric turbulence. Except for segmented mirror phasing, we also apply the Zernike feedback system in image processing. For the same system dynamics as well as in segment phasing, the Zernike filter feedback system is capable of compress the static noisy background, and makes the single particle tracking algorithm even working in case of very low signal-to-noise ratio. Finally, we apply an efficient multiple-particle tracking algorithm on a living cell image sequence. This algorithm is shown to be able to deal with higher particle density, while the single particle tracking methods are not working under this condition

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Aeronautical engineering: A continuing bibliography with indexes (supplement 258)

This bibliography lists 536 reports, articles, and other documents introduced into the NASA scientific and technical information system in October 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Bluff-body aerodynamics and transfer functions for non-catching precipitation measurement instruments.

Starting from the old and trivial technique of using a graduated cylinder to collect and manually measure precipitation, numerous advances were made for in-situ precipitation gauges. After decades of scarce innovation, a new family of in-situ precipitation gauges was developed. They are called Non-Catching Gauges (NCG) since they can measure precipitation and its microphysical and dynamic characteristics without the need to collect hydrometeors. The attention that NCGs are gathering today is quite notable, even if they represent only a small fraction of the total precipitation gauges deployed. Their use in the field is bound to continuously grow in time, due to several advantages, discussed in this work, that such instruments present over more traditional ones. However, their major disadvantage is their increased complexity, the effects of which are highlighted by the literature through evidence of calibration and correction issues. Various field intercomparison experiments showed the evidence of significant biases in NCGs measurements. The goal of this work is to investigate two main sources of bias, producing the largest impact on precipitation measurements. The first source of bias evaluated in this work is due to instrument calibration. Several attempts at developing a calibration procedure are presented both in the scientific literature and from the manufacturers. Nevertheless, those methods are hardly traceable to international standards and, in most cases, lack a suitable reference measure to compare against the instrumental output. In this work, a fully traceable calibration procedure is proposed, in analogy with the one already existing for catching type gauges. This requires drops of know diameter and fall velocity to be released over the instrument sensing area. For this reason, the Calibrated Rainfall Generator (CRG) is developed, able to release single drops on demand and measure them independently just before they reach the instrument sensing area. Detachment of drops is obtained by using an electrostatic system, while the measure of their diameter and fall velocity is performed by means of a photogrammetric approach. The Thies Laser Precipitation Monitor (LPM) was tested using the CRG considering two different output telegrams. The first one provides the raw measure of each drop sensed by the instrument while the second one provides the Particle Size and fall Velocity Distribution (PSVD) matrix. Both telegrams show a tendency to underestimate the drop diameter that increases with decreasing the drop size, while errors in the fall velocity measurements have a less definite trend. Furthermore, tests also show a large standard deviation of the measurements, significantly higher than the one of the reference measurements. The underestimation of drop size and fall velocity is also reflected into the RI measurements provided by the instrument, with a resulting underestimation that decreases with increasing the precipitation intensity. The difference between the two telegrams considered is large and may only be explained by differences in the instrument internal processing for the two telegrams. The second instrument tested using the CRG is the Biral VPF-750, a light scatter gauge. Results show a tendency to underestimate both the drop diameter and fall velocity. In the first case, the error decreases with increasing the drops size, similarly to the Thies LPM. However, the error in the fall velocity is considerably higher and instead increases with increasing the drop sizes. In terms of Rainfall Intensity (RI), the instrument shows a strong underestimation that, due to the opposite trend observed for drop diameter and fall velocity, is almost constant with the precipitation intensity. Both instruments show significant biases, corroborated by field intercomparison results from the literature, that is often larger than 10% for the investigated variables. This means that both gauges cannot be classified according to the guidelines proposed in this work for the development of a standard calibration procedure, derived from those already existing for CGs. The second source of bias is wind, a well-established source of environmental error for traditional Catching-type Gauges (CG) but also affecting NCGs. The wind-induced bias is investigated using a numerical approach, combining Computational Fluid Dynamics (CFD) and Lagrangian Particle Tracking (LPT) models. Two different CFD models were tested, the first providing a time-independent steady state solution, while the other is fully time-dependent. Both were compared against wind tunnel results, showing a good agreement with the experimental data, and proving their ability to capture the complex aerodynamic response of instruments when impacted by the wind. The Thies Laser Precipitation Monitor (LPM) is first chosen as a test instrument, being representative of the typical NCGs that are currently deployed in the field. CFD simulations show that wind direction is the primary factor determining the aerodynamic disturbance close to the instrument sensing area. Similar results were found for the OTT Parsivel2, that is another widely diffused NCG. For wind flow parallel to the laser beam, strong disturbance close to the gauge sensing area is observed. Meanwhile, wind coming perpendicular to the laser beam produces minimal flow disturbance. The wind-induced bias is also investigated for the Vaisala WXT-520, an impact disdrometer. This gauge is smaller ad has a more regular shape if compared to the optical disdrometers, but its measuring principle is based on the detection of the drop kinetic energy, while the size and fall velocity are indirectly obtained. CFD simulations show limited disturbance close to the sensing area of the instrument and a negligeable dependency on the wind direction (due to a more radially symmetric geometry). The instrument body further provide minimal shielding of the sensing area. Strong updraft however occurs upstream of the instrument for all wind directions, significantly affecting the fall velocity of the smaller and lighter drops. Using these results, three different LPT models are also tested. The first is an uncoupled model based on the time-independent CFD results and is used to evaluate the instrument performance for all wind speeds and directions considered. The other two models, due to their high computational requirements, are applied only to a selected number of combinations of wind speed and direction for the Thies LPM. Results show a good agreement and allow concluding that the significant increase in computational burden of the latter two models does not significantly improve the accuracy of the results. However, the one-way coupled model highlights the role of turbulence, that may have a significant impact on the instrumental performance when strong recirculation is present near its sensing area. In the case of the two other gauges, only the uncoupled LPT model in combination with the time-independent CFD model is used, this being the best compromise between numerical accuracy and computational cost. Results of the LPT model are presented in terms of variation in the retrieval of precipitation microphysical properties, Catch Ratios (CR), Collection Efficiency (CE) and Radar Retrieval Efficiency (RRE). For the three gauges considered, it is shown that smaller hydrometeors fall velocity close to the instrument sensing area is strongly affected by wind and is – in general – reduced. A significant wind-induced bias is also evident in the Drop Size Distribution (DSD) measured by the gauges. Optical gauges may report a significant lower number of small hydrometeors even at moderate wind speed. Due to the gauge body partially shielding the sensing area. Impact gauge DSD is also strongly influenced by wind, since hydrometeors with high kinetic energy are sensed as having a large diameter. The DSD is therefore shifted towards larger diameters and the instrument tends to overestimate the number of hydrometeors of all sizes. This suggests that the different shapes of the DSD function reported in the field by different instruments may be due, at least partially, to wind-induced biases. In terms of integral precipitation characteristics, the wind direction is the primary factor in determining the performance of optical gauges in windy conditions. For wind parallel to the laser beam, the instrument senses less and less precipitation with increasing the wind speed, with no hydrometeors even reaching the sensing area in some configurations . On the other hand, when the wind is perpendicular to the laser beam, the instrument performs similarly for all wind speeds, with CR and CE values close to one and only a moderate amount of overcatch being observed at high wind speed. Only for the OTT Parsivel2 a non negligeable overcatch is also evident for wind coming at a 45° angle with respect to the beam direction. For the Vaisala WXT-520 the Kinetic Catch Ratio (KCR) and Kinetic Collection Efficiency (KCE) are defined as substitutes for the CR and CE. At low wind speed, the KCR is below unity, due to the reduction in fall velocity produced by the updraft. However, with increasing wind speed, the kinetic energy of hydrometeors carried by wind increases considerably, overcoming the reduction caused by the updraft close to the gauge. For this reason, KCR values becomes much higher than unity, especially for small size hydrometeors. The increase in kinetic energy is reflected into increased KCE values, that are close to unity at low wind speed, but rapidly grow with increasing the wind speed. Wind direction has instead very limited influence on the measurements. In terms of RRE, optical gauges present limited bias for all combinations of wind speed and direction, except for the highest wind speed and flow parallel to the laser beam. This is because a large portion of the radar reflectivity factor (dBZ) is due to medium and large size hydrometeors, that are less influenced by wind. In the case of the impact disdrometer instead, RRE behaves very similarly to the CE, with values that increases with increasing wind speed. This is due to the shift toward larger diameters noted in the DSD that occurs when hydrometeors kinetic energy is increased by wind

Index to 1986 NASA Tech Briefs, volume 11, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1986 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences