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R. T. H. Collis

Increasing demand is outstripping world food production, despite increased yields due to technological progress. Combined with adverse weather and governmental policies, this has led to a major rundown of reserve grain stocks over the last few years. Without adequate reserves to provide equalization, weather must now be recognized as a critical factor in balancing the supply and demand of world food. Regardless of long term trends, such as the return of an Ice Age, unsettled weather conditions now appear more likely than those of the abnormally favorable period which ended in 1972. This possibility and its implications must be considered in planning and determining national and world food policies. There is an urgent need for better understanding and utilization of information on weather variability and climatic change in this context.

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R. T. H. Collis

Lidar, using pulsed lasers as energy sources, applies the radar principle at wavelengths in and near the visual spectrum to probe the atmosphere. It can detect particulate matter of much smaller dimensions and sparser concentration than is possible with meteorological radar. Lidar may be used to measure cloud base heights although difficulties arise with diffuse clouds, especially in foggy conditions. Inhomogeneities in turbidity that occur at the heights of temperature inversions in the relatively clear atmosphere are also revealed by lidar. Examples of work in progress that show promise of providing a measurement of visibility are presented.

It is concluded that lidar can already contribute usefully in routine meteorological service, but that its full potential in ceilometry and visibility measurement awaits further developments. For routine unattended use, high pulse-rate low peak-power lidars are advocated on grounds of safety.

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R. T. H. Collis and M. G. H. Ligda

Abstract

No abstract available.

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W. Viezee, E. E. Uthe, and R. T. H. Collis

Abstract

Lidar (laser radar) data obtained at Hamilton AFB, Calif., under conditions of low ceiling and visibility, are analyzed by hand and by electronic computer to explore the operational utility of lidar in determining cloud ceiling and visibility for aircraft landing operations. Hand analyses of the data show the ability of the lidar to describe the spatial configuration of the low-cloud structure in the direction of the landing-approach path. The problems inherent in evaluating lidar observations are discussed, and initial approaches to quantitative solutions by computer are presented. It is demonstrated that operationally useful information on the ceiling conditions contained in the hand analyses can be represented by digitizing the lidar data and subjecting these data to computer analysis.

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W. Viezee, R. T. H. Collis, and J. D. Lawrenee Jr.

Abstract

In March and April of 1969 and 1970, lidar (laser radar) observations of the atmospheric structure were made in the lee of the Sierra Nevada during the occurrence of mountain lee waves. Rawinsonde ascents and, on some occasions, research aircraft flights supported the lidar observations. The objective of the program was to explore the applicability of the lidar technique to atmospheric turbulence detection. The observations demonstrate that a ground-based lidar can delineate significant features of the atmospheric flow pattern by monitoring echoes from concentrations of particulate matter that characterize the airflow structure in the form of either visible or subvisible clouds and dust.

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R. T. H. Collis, F. G. Fernald, and J. E. Alder

Abstract

Early in 1967 a series of observations using pulsed ruby lidars were made near Independence, Calif.; the objective was to investigate the value of lidar for studying air motion in the Sierra wave, with special reference to indications of turbulence.

Although no intense wave activity occurred, appreciable wave motions were observed, both in what appeared to the eye to be clear air and in air where the particulate matter was sufficiently concentrated as to be visible as clouds. Interruptions in the smooth laminar flow in the clear air were observed, and measurements were made of the length, amplitude and height of waves shown by clouds.

With previously existing techniques, only limited observation of such phenomena have been possible. It is thus concluded that lidar observations are of considerable value in studying wave motion, even in the absence of visible clouds. There is also a possibility that lidar could indicate the presence of turbulence by revealing the breakdown of wave motion or the presence of rotors.

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V. R. Noonkester, D. R. Jensen, J. H. Richter, W. Viezee, and R. T. H. Collis

Abstract

Boundary layer probing by multiple remote sensors can greatly improve the understanding of processes in this complex region. For this purpose one needs to know the unique information each individual sensor can provide. Two promising boundary layer remote sensors, a microwave, frequency-modulated, continuous-wave (FM-CW) radar and a laser radar (lidar), were operated simultaneously to probe a common volume. As expected, the lidar sometimes separately detected aerosol layers, notably cloud bases, and the radar sometimes separately detected refractive layers and insects. Boundaries of aerosol structures were often found to be regions of radar returns such as in layers, convective activity, and breaking waves. In contrast, however, a refractive layer was observed within an apparently well-mixed aerosol layer. The data indicate that the radar may have a characteristic echo which is coincident with cloud and fog tops. This experiment shows that FM-CW radars and lidars can separately sense layering in the boundary region and that they provide complementary information on boundary layer mixing processes.

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D. A. Leone, R. M. Endlich, J. Petričeks, R. T. H. Collis, and J. R. Porter

A systematic and objective approach was used to optimize the siting of the individual radars forming the Next Generation Weather Radar (NEXRAD) network. Prime consideration was given to meteorological factors, in conjunction with the user agencies' needs and the population distribution. The latter was assessed by a novel technique using weather satellite photographs showing urban illumination at night. Priority coverage areas were identified for population centers based on the expected paths of storms and their travel speeds. Radar viewing of the priority coverage areas down to low altitudes is needed so that approaching storms can be detected and warnings issued as early as possible. Other siting criteria taken into account included consideration of terrain features and local obstructions, locations of airways and civilian and military airports, electromagnetic interference, and integration of NEXRAD data into the national weather system.

The methodology for selecting the network is described. Environmental impacts and costs of site acquisition and preparation were also involved in the study, but are not discussed in this paper.

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