Engineering topics

Snider, J. B.

Publications and source records attributed to Snider, J. B..

10 records

NASA NTRS1994

Observations of water vapor by ground-based microwave radiometers and Raman lidar

In November to December 1991, a substantial number of remote sensors and in situ instruments were operated together in Coffeyville, Kansas, during the climate experiment First ISCCP Regional Experiment Phase 2 (FIRE 2). Includede in the suite of instruments were (1) the NOAA Environmental Technology Laboratory (ETL) three-channel microwave radiometer, (2) the NASA GSFC Raman lidar, (3) ETL radio acoustic sounding system (RASS), and (4) frequent, research-quality radiosondes. The Raman lidar operated only at night and the focus of this portion of the experiment concentrated on clear conditions. The lidar data, together with frequent radiosondes and measurements of temperature profiles (every 15 min) by RASS allowed profiles of temperature and absolute humidity to be estimated every minute. We compared 20 min measurements of brightness temperature (T(sub b) with calculations of T(sub b) that were based on the Liebe and Layton (1987) and Liebe et al. (1993) microwave propagation models, as well as the Waters (1976) model. The comparisons showed the best agreement at 20.6 GHz with the Waters model, with the Liebe et al. (1993) model being best at 31.65 GHz. The results at 90 GHz gave about equal success with the Liebe and Layton (1987) and Liebe et al. (1993) models. Comparisons of precipitable water vapor derived independently from the two instruments also showed excellent agreement, even for averages as short as 2 min. The rms difference between Raman and radiometric determinations of precipitable water vapor was 0.03 cm which is roughly 2%. The experiments clearly demonstrate the potential of simultaneous operation of radiometers and Raman lidars for fundamental physical studies of water vapor.

Han, Yong↗

NASA NTRS1993

Radiometric observations of atmospheric attenuation at 20.6 and 31.65 GHz: The Wave Propagation Laboratory data base

The National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL) presently operates five dual-channel microwave radiometers, one triple-channel microwave radiometer, and one six-channel microwave radiometer. The dual-channel radiometers operate at frequencies of 20.6 or 23.87 GHz and 31.4 or 31.65 GHz. The triple-channel radiometer operates at 20.6, 31.65, and 90.0 GHz. The six-channel radiometer operates at frequencies of 20.6, 31.65, 52.85, 53.85, 55.45, and 58.8 GHz. Recent brightness temperature measurements and attenuation values from some of the above radiometers are presented. These radiometric measurements, taken in different locations throughout the world, have given WPL a diverse set of measurements under a variety of atmospheric conditions. We propose to do a more complete attenuation analysis on these measurements in the future. In addition, a new spinning reflector was installed recently for the dual-channel radiometer at the Platteville, Colorado site. This reflector will extend our measurement capabilities during precipating conditions. Locating the three-channel and portable dual-channel radiometers at or near Greeley, Colorado to support the Advanced Communications Technology Satellite (ACTS) program is discussed.

Jacobson, Mark D.↗

NASA NTRS1992

Stratocumulus cloud properties derived from simultaneous satellite and island-based instrumentation during FIRE

Cloud parameters derived from visible and infrared window data from the Geostationary Operational Environmental Satellite (GOES) are compared to corresponding properties determined from instrumentation on San Nicolas Island off the coast of California during the First ISCCP Regional Experiment marine stratocumulus intensive field observations period in July 1987. Examination of the satellite imagery revealed that the apparent bias can be explained by the persistence of the clouds over the northwest part of the island during periods of clearing around the island. Diurnal variations in the cloud cover were very significant; minimum cloudiness occurred during the late afternoon and maximum cloudiness early in the morning. Relationships were established between the satellite-derived cloud optical depth and two surface-observed quantities: cloud liquid water path and cloud thickness. Simultaneous observations of liquid water path and satellite-derived cloud optical depth were used to infer effective cloud-droplet radius, resulting in good agreement with correlative data. The diurnal variations in cloud amount are accompanied by changes in cloud thickness, cloud-top height, cloud liquid water path, and effective droplet size. These observations provide the most complete picture, to date, of the diurnal cycle of marine stratocumulus clouds, confirming previous satellite-based inferences of the diurnal behavior of marine stratocumulus at larger scales.

Minnis, Patrick↗

NASA NTRS1991

Comparison of OLYMPUS beacon and radiometric attenuation measurements at Blacksburg, Virginia

Measurements of attenuation of the 20 and 30 GHz beacons onboard the OLYMPUS satellite are compared to simultaneous observations of atmospheric attenuation by a multichannel microwave radiometer along the same path. Departures from high correlation between the two measurements are believed to be related to differences in antenna beamwidths. Mean equivalent zenith attenuations derived from the slant path data are compared to zenith observations made at previous locations.

Snider, J. B.↗

NASA NTRS1991

Diurnal variation of marine stratocumulus over San Nicolas Island during July 1987

A study is presented of surface measurements made at San Nicolas Island during the intensive field observation marine stratocumulus phase of the First International Satellite Cloud Climatology Program Regional Experiment, July 1987, to retrieve the average diurnal variation of marine stratocumulus and associated surface variables. The diurnal behavior of the cloud base appears to be consistent with model-predicted uncoupling of the cloud layer and the subcloud layer as the turbulent flux of moisture is limited by solar heating close to the cloud base. Also, variation in surface air temperature is consistent with the limitation of the turbulent flux of heat between the two layers, screening the surface from the effect of longwave cooling from the cloud top.

Blaskovic, Miriam↗

NASA NTRS1990

An eight-month sample of marine stratocumulus cloud fraction, albedo, and integrated liquid water

Surface-meteorology and shortwave/longwave irradiance measurements taken on the northwest tip of San Nicolas Island off the coast of Southern California from March through October 1987 are analyzed. Experimental details are summarized, and shortwave cloud-radiation parameterization is outlined with emphasis on a shortwave algorithm. Frequency distributions indicate the stratocumulus clouds at the island have a cloud base on the order of 400 m, an integrated liquid water content of 75 g/sq m, and an albedo of 0.55 with substantial diurnal variations. The longwave parameterization for cloud fraction is also considered, and it is noted that using these models for downward longwave and shortwave irradiances, cloud fraction, integrated liquid water content, and albedo are deduced from the data.

Fairall, C. W.↗

NASA NTRS1990

Attenuation statistics derived from emission measurements by a network of ground-based microwave radiometers

Two seasons of thermal emission measurements, running from December 1987 through February 1988 and from June through August 1988 of thermal emission measurements, taken by a multi-channel, ground-based microwave radiometer, are used to derive single-station zenith attenuation statistics at 20.6 and 31.65 GHz. For the summer period, statistics are also derived for 52.85 GHz. In addition, data from two dual-channel radiometers, separated from Denver by baseline distances of 49 and 168 km, are used to derive two-station attenuation diversity statistics at 20.6 and 31.65 GHz. The multi-channel radiometer is operated at Denver, Colorado; the dual-channel devices are operated at Platteville and Flagler, Colorado. The diversity statistics are presented by cumulative distributions of maximum and minimum attenuation.

Westwater, E. R.↗

NASA NTRS1989

Applications of ground-based radiometric observations of millimeter wave radiation

A three-channel transportable radiometer that operates at 20.6, 31.65, and 90.0 GHz has been developed. The design of the radiometer is described and the results of various experimental applications of the radiometer are presented. The experiments include a comparison of brightness temperature measurements at various frequencies with the water vapor absorption models of Waters (1976) and Lieve (1989). Measurements of absorption ratios for cloud attenuation are given and the radiometer measurements are compared with oxygen absorption calculated using the Rasenkranz (1988) model.

Westwater, E. R.↗

NASA NTRS1989

Observations of attenuation at 20.6, 31.65 and 90.0 GHz: Preliminary results from Wallops Island, VA

Ground based radiometric observations of atmospheric attenuation at 20.6, 31.65, and 90.0 GHz were made at Wallops Island, Virginia during April and May 1989. Early results from the analysis of the data set are compared with previous observations from California and Colorado. The relative attenuation ratios observed at each frequency during clear, cloudy, and rainy conditions are shown. Plans for complete analysis of the data are described.

Snider, J. B.↗

NASA NTRS1989

Observed reflectivities and liquid water content for marine stratocumulus

Simultaneous observations of cloud liquid water content and cloud reflectivity are used to verify their parametric relationship in a manner consistent with simple parameterizations often used in general-circulation climate models. The column amount of cloud liquid water was measured with a microwave radiometer on San Nicolas Island as described by Hogg et al., (1983). Cloud reflectivity was obtained through spatial coherence analysis of AVHRR imagery data as per Coakley and Baldwin (1984) and Coakley and Beckner (1988). The dependence of the observed reflectivity on the observed liquid water is discussed, and this empirical relationship is compared with the parameterization proposed by Stephens (1978).

Coakley, J. A., Jr.↗