Comparison of columnar water-vapor measurements from solar transmittance methods.

In the fall of 1997 the Atmospheric Radiation Measurement program conducted a study of water-vapor-abundance-measurement at its southern Great Plains site. The large number of instruments included four solar radiometers to measure the columnar water vapor (CWV) by measuring solar transmittance in the 0.94-mum water-vapor absorption band. At first, no attempt was made to standardize our procedures to the same radiative transfer model and its underlying water-vapor spectroscopy. In the second round of comparison we used the same line-by-line code (which includes recently corrected H(2)O spectroscopy) to retrieve CWV from all four solar radiometers, thus decreasing the mean CWV by 8-13%. The remaining spread of 8% is an indication of the other-than-model uncertainties involved in the retrieval.

SAGE II aerosol validation: selected altitude measurements, including particle micromeasurements.

Correlative aerosol measurements taken at a limited number of altitudes during coordinated field experiments are used to test the validity of particulate extinction coefficients derived from limb path solar radiance measurements taken by the Stratospheric Aerosol and Gas Experiment (SAGE) II Sun photometer. In particular, results are presented from correlative measurement missions that were conducted during January 1985, August 1985, and July 1986. Correlative sensors included impactors, laser spectrometers, and filter samplers aboard an U-2-airplane, an upward pointing lidar aboard a P-3 airplane, and balloon-borne optical particle counters (dustsondes). The main body of this paper focuses on the July 29, 1986, validation experiment, which minimized the many difficulties (e.g., spatial and temporal inhomogeneities, imperfect coincidences) that can complicate the validation process. On this day, correlative aerosol measurements taken at an altitude of 20.5 km agreed with each other within their respective uncertainties, and particulate extinction values calculated at SAGE II wavelengths from these measurements validated corresponding SAGE II values. Additional validation efforts on days when measurement and logistical conditions were much less favorable for validation are discussed in an appendix.

SAGE II aerosol data validation based on retrieved aerosol model size distribution from SAGE II aerosol measurements.

This paper describes an investigation of the comprehensive aerosol correlative measurement experiments conducted between November 1984 and July 1986 for satellite measurement program of the Stratospheric Aerosol and Gas Experiment (SAGE II). The correlative sensors involved in the experiments consist of the NASA Ames Research Center impactor/laser probe, the University of Wyoming dustsonde, and the NASA Langley Research Center airborne 14-inch (36 cm) lidar system. The approach of the analysis is to compare the primary aerosol quantities measured by the ground-based instruments with the calculated ones based on the aerosol size distributions retrieved from the SAGE II aerosol extinction measurements. The analysis shows that the aerosol size distributions derived from the SAGE II observations agree qualitatively with the in situ measurements made by the impactor/laser probe. The SAGE II-derived vertical distributions of the ratio N0.15/N0.25 (where Nr is the cumulative aerosol concentration for particle radii greater than r, in micrometers) and the aerosol backscatter profiles at 0.532- and 0.6943-micrometer lidar wavelengths are shown to agree with the dustsonde and the 14-inch (36-cm) lidar observations, with the differences being within the respective uncertainties of the SAGE II and the other instruments.

Staphylococcal adherence to polyvinyl chloride and heparin-bonded polyurethane catheters is species dependent and enhanced by fibronectin.

Intravenous hyperalimentation has improved the survival of premature infants. However, long-term placement of intravenous catheters may result in the development of catheter-related sepsis. Fibronectin in plasma contains binding sites for staphylococcal species as well as marked affinity for inert plastics and therefore may provide a substrate for bacterial adherence to indwelling catheters. We determined the adherence of labeled [( 3H]leucine) coagulase-positive (CPS) and coagulase-negative (CNS) staphylococci to untreated and fibronectin-coated polyvinyl chloride (PVC) and heparin-bonded polyurethane (HBP) catheter segments and quantitated the binding of 14C-labeled, purified fibronectin to these catheters. PVC catheter segments bound significantly more CNS than CPS (P less than 0.05), while HBP catheters bound more CPS than CNS (P less than 0.05). Fibronectin significantly increased the adherence of CPS to PVC catheters (P less than 0.05) and CNS to HBP catheters (P less than 0.05). PVC catheters bound more fibronectin (P less than 0.0001) than did HBP catheters. Catheter composition may influence the spectrum of nosocomial pathogens to which infants are susceptible through different bacterial adherences and interactions with adhesive proteins.

Orbiting lidar simulations. 2: Density, temperature, aerosol, and cloud measurements by a wavelength-combining technique.

A technique is described for combining several wavelength backscatter measurements to yield profiles of molecular density and temperature plus aerosol and cloud backscatter with associated error-bar profiles. Error sources include signal, transmission, calibration, conventional density, lidar density normalization, temperature or pressure estimation at a reference height, and backscatter wavelength-dependence estimation. Strong particulate contamination limits the technique to the cloud-free upper troposphere and above. Error bars automatically returned as part of the measurement show when such contamination occurs. Relative density (temperature) profiles have rms errors of 0.5-2% (1.2-2.5 K) in the nonvolcanic stratosphere and upper troposphere. The density profiles significantly improve aerosol retrievals. The fine vertical resolution of the temperature profiles would permit defining the tropopause to approximately 0.5 km and higher wave structures to 1 or 2 km.

Orbiting lidar simulations. 1: Aerosol and cloud measurements by an independent-wavelength technique.

Aerosol and cloud measurements are simulated for a space shuttle lidar. Expected errors (in signal, transmission, density, and calibration) are calculated algebraically and checked by simulating measurements and retrievals using random number generators. Vertical resolution is 0.1-0.5 km in the troposphere, 0.5-2.0 km above, except 0.25-1.0 km in mesospheric cloud and aerosol layers. Horizontal resolution is 100-2000 km. By day vertical structure is retrieved for tenuous clouds, Saharan aerosols, and boundary layer aerosols (at 0.53 and 1.06 microm) as well as strong volcanic stratospheric aerosols (at 0.53 microm). Quantitative backscatter is retrieved provided that particulate optical depth does not exceed approximately 0.3. By night all these constituents are retrieved plus upper tropospheric and stratospheric aerosols (at 1.06 microm), mesospheric aerosols (at 0.53 microm), and noctilucent clouds (at 1.06 and 0.53 microm). Molecular density is a leading source of error in measuring nonvolcanic stratospheric and upper tropospheric aerosols.

High-Latitude Stratospheric Aerosols Measured by the SAM II Satellite System in 1978 and 1979.

Results of the first year of data collection by the SAM (Stratospheric Aerosol Measurement) II satellite system are presented. Almost 10,000 profiles of stratospheric aerosol extinction in the Arctic and Antarctic regions are used to construct plots of weekly averaged aerosol extinction versus altitude and time and stratospheric optical depth versus time. Corresponding temperature fields are presented. These data show striking similarities in the aerosol behavior for corresponding seasons. Wintertime polar stratospheric clouds that are strongly correlated with temperature are documented. They are much more prevalent in the Antarctic stratosphere during the cold austral winter and increase the stratospheric optical depths by as much as an order of magnitude for a period of about 2 months. These clouds might represent a sink for stratospheric water vapor and must be considered in the radiative budget for this region and time.

Methodology for error analysis and simulation of lidar aerosol measurements.

We present a methodology for objective and automated determination of the uncertainty in aerosol measurements made by lidar. The methodology is based on standard error-propagation procedures, a large data base on atmospheric behavior, and considerable experience in processing lidar data. It yields algebraic expressions for probable error as a function of the atmospheric, background lighting, and lidar parameters. This error includes contributions from (1) lidar signal; (2) molecular density; (3) atmospheric transmission; and (4) lidar calibration. The validity of the algebraic error expressions is tested by performing simulated measurements and analyses, in which random errors of appropriate size are injected at appropriate steps. As an example, the methodology is applied to a new airborne lidar system used for measurements of the stratospheric aerosol. It is shown that for stratospheric measurements below about 25 km, molecular density uncertainties are the dominant source of error for wavelengths shorter than about 1.1 microm during nonvolcanic conditions. Because the influence of molecular scattering (relative to particulate scattering) decreases with increasing wavelength, stratospheric measurements with a Nd:YAG lidar can thus be more accurate than those made with a ruby lidar, provided that a suitable detector is used.