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  • Author or Editor: J. A. Weinman x
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J. A. Weinman
and
P. J. Guetter

Abstract

The equation of radiative transfer is applied to the analysis of solar irradiances penetrating into a plant canopy covered by a turbid atmosphere. The method of discrete coordinates is applied to vertically inhomogeneous atmospheres and plant canopies. It is shown that four-point quadrature yields results with an accuracy which is consistent with irradiance measurements.

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J. A. Weinman
and
P. J. Guetter

Abstract

The polarization of 37 GHz microwave radiances emerging from rain clouds above land, rough and calm water surfaces was computed from the equation of radiative transfer. Scattering was assumed to be characterized by a Rayleigh phase matrix. The radiative transfer equation was solved by means of a Neumann solution. It was found that the brightness temperatures of the upward directed radiances emerging from rain clouds were relatively independent of polarization. The weak polarization of radiation emitted by rain clouds can be used to discriminate between cool brightness temperatures emerging from rain clouds and open water. The brightness temperatures of radiances emerging from rain clouds over water can be transformed into a single-valued function of the rainfall rate if polarization effects are considered. A sample of Nimbus 6 data is analyzed in accord with the results of the theoretical analysis.

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R. W. Kobussen
and
J. A. Weinman

Abstract

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J. A. Weinman
and
F. S. Marzano

Abstract

Global precipitation measurements from space-based radars and microwave radiometers have been the subject of numerous studies during the past decade. Rainfall retrievals over land from spaceborne microwave radiometers depend mainly on scattering from frozen hydrometeors. Unfortunately, the relationship between frozen hydrometeors and rainfall varies considerably. The large field of view and related beam filling of microwave radiometer footprints introduce additional difficulties. Some of these problems will be addressed by the improved sensors that will be placed on the Global Precipitation Measurement (GPM) core satellite. Two shuttle missions demonstrated that X-band synthetic aperture radar (X-SAR) could observe rainfall over land. Several X-band SARs that can provide such measurements will be launched in the coming decade. These include four Constellation of Small Satellites for Mediterranean Basin Observations (COSMO-SkyMed), two TerraSAR-X, and a fifth Korea Multipurpose Satellite (KOMPSAT-5) to be launched by the Italian, German, and Korean Space Agencies, respectively. Data from these satellites could augment the information available to the GPM science community. The present study presents computations of normalized radar cross sections (NRCS) that employed a simple, idealized two-layer cloud model that contained both rain and frozen hydrometeors. The modeled spatial distributions of these hydrometeors varied with height and horizontal distance. An exploratory algorithm was developed to retrieve the shape, width, and simple representations of the vertical profiles of frozen hydrometeors and rain from modeled NRCS scans. A discussion of uncertainties in the retrieval is presented.

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J. A. Weinman
,
R. Meneghini
, and
K. Nakamura

Abstract

This study compares precipitation rate profiles derived from a single frequency radar and radiometer with such profiles derived from a dual-frequency radar.

Measurements obtained during the 1985–86 CRL/NASA rain measuring experiment from airborne X- and Ka-band radars and an X-band passive microwave radiometer were used to derive rainfall rate profiles over the Atlantic Ocean. The rainfall retrieval employs the classical Hitschfeld-Bordan radar equation constrained by a measurement of the path integrated extinction derived from passive radiometry.

The path-integrated extinction obtained from the radiometric measurements was compared with that obtained from coincident dual-frequency radar reflection measurements from the ocean surface. The mean rainfall rate derived from the path-integrated extinction retrieved from the measured microwave radiances agreed within 25% with the mean rainfall rate obtained from the reflected radar signals.

An analysis of the errors in the retrieval algorithm showed that errors in the path-integrated extinction significantly affect the retrieved rainfall profiles near the surface. A least squares linear extrapolation of the profile in the lowest kilometer was used to revise the boundary condition in the retrieval. The profiles were solved iteratively until the rainfall rate at the surface was within the range of scatter about the linear profile at higher altitudes.

An optimization analysis was applied to the derivation of rainfall rate profiles retrieved from a dual-frequency radar data. The results of the retrieval were compared to those obtained from the radar-radiometer retrievers.

The availability of only an X-band radiometer limited the retrieval of rainfall rate profiles to maritime cases. It appears that it will be possible to measure rainfall under most conditions when radiometers operating at several higher frequencies become available on future airborne radar experiments.

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E. W. Eloranta
,
J. M. King
, and
J. A. Weinman

Abstract

Vertical profiles of the horizontal radial wind component in the lowest kilometer of the atmosphere have been measured remotely with lidar. Wind speed determinations were made by observing the motion of naturally occurring aerosol density inhomogeneities. Lidar wind measurements compare favorably with simultaneous pilot balloon observations of the wind.

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S. T. Shipley
,
E. W. Eloranta
, and
J. A. Weinman

Abstract

Monostatic lidar is explored as a means for determining the rainfall rate over an extended atmospheric path with a spatial resolution comparable to that of rain gages. An empirical relationship is established between the optical extinction coefficient of rain β r (km−1) and the rainfall rate R (mm hr−1). Correlation of lidar-derived rainfall extinction and gage rainfall rates at Madison gives
β r R0.74
.

The β r -R relations obtained from the work of other authors compare well with this relationship.

A lidar equation which accounts for the multiple scattering of light in rain is presented. A numerical procedure which derives estimates of β r as a function of range from lidar returns is developed. Examples of lidar-derived rainfall rate range profiles in spatially inhomogeneous thunderstorms are given.

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J. L. Schols
,
J. A. Weinman
,
G. D. Alexander
,
R. E. Stewart
,
L. J. Angus
, and
A. C. L. Lee

Abstract

Microwave brightness temperatures emanating from a North Atlantic cyclone were measured by the Special Sensor Microwave/Imager (SSM/I) on the Defense Meteorological Satellite Program satellite. As other investigators have found before, low 85.5-GHz brightness temperatures (215 ± 20 K) were observed from cumulonimbus clouds along the squall line; however, 85.5-GHz microwave brightness temperatures observed from the nimbostratus clouds north of the low center were significantly higher (255 ± 20 K). In situ measurements from aircraft during the Canadian Atlantic Storm Program II showed that heavy snowfall consisting of large tenuous aggregates existed in the nimbostratus clouds at the time of the SSM/I overpass.

Distributions of snow, rain, liquid cloud water, and cloud ice mass were computed from a modified version of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model. That model employed a mixed-phase ice microphysics (MPIM) scheme that only considered one type of frozen hydrometeor. The frozen hydrometeor size distributions, density, and mass flux were modified to match the in situ observations where they were available and to account for the SSM/I observations using radiative transfer theory. Those revised hydrometeor representations were constrained to preserve the vertical hydrometeor mass flux distributions obtained from the MPIM scheme throughout the analysis.

Frozen dense accreted particles were required near the squall line to account for the microwave scattering effect. Snow aggregates, with density that decreased with increasing size, were needed to reproduce the high brightness temperatures observed from the nimbostratus clouds.

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R. W. Spencer
,
W. S. Olson
,
Wu Rongzhang
,
D. W. Martin
,
J. A. Weinman
, and
D. A. Santek

Abstract

In an examination of microwave data from the Nimbus 7 satellite, brightness temperatures were found that were much lower than those expected for the radiation emanating from rain-producing clouds. Every case of very cold brightness temperature coincided with heavy thunderstorm rainfall. The cold temperatures can be attributed to scattering by a layer of ice hydrometeors in the upper parts of the storms. Thus it appears that brightness temperatures observed by satellite microwave radiometers can at times distinguish heavy rain over land.

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J. J. Deluisi
,
P. M. Furukawa
,
D. A. Gillette
,
B. G. Schuster
,
R. J. Charlson
,
W. M. Porch
,
R. W. Fegley
,
B. M. Herman
,
R. A. Rabinoff
,
J. T. Twitty
, and
J. A. Weinman

Abstract

An exploratory field experiment was undertaken to determine the practicality of a method specifically designed to obtain the optical properties of aerosols as they relate to the earth's radiation balance. The method requires a basic set of data consisting of the vertical distribution of aerosol concentrations, size distribution, optical depth, and net radiation fluxes. From these data radiation absorptions are determined, and effective aerosol refractive indices consistent with the actual absorption are deduced through the application of precision radiative transfer calculations. The results of 11 experiment episodes involving a combined aircraft and surface-based measurement system are described. The episodes took place in an arid desert region located near Blythe, California, and in a semiarid agricultural region located near Big Spring, Texas. Part I deals with the physical-numerical depiction of such aerosol properties as optical depth, size distribution, and vertical profiles of concentration. Part II will deal with the analysis of measurements of the radiation field leading to the deduction of the effective aerosol refractive index compatible with the absorption of solar radiation.

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