John E. M. Goldsmith

The ARM program's water vapor intensive observation periods - Overview, initial accomplishments, and future challenges

A series of water vapor intensive observation periods (WVIOPs) were conducted at the Atmospheric Radiation Measurement (ARM) site in Oklahoma between 1996 and 2000. The goals of these WVIOPs are to characterize the accuracy of the operational water vapor observations and to develop techniques to improve the accuracy of these measurements. The initial focus of these experiments was on the lower atmosphere, for which the goal is an absolute accuracy of better than 2% in total column water vapor, corresponding to ~1 W m−2 of infrared radiation at the surface. To complement the operational water vapor instruments during the WVIOPs, additional instrumentation including a scanning Raman lidar, microwave radiometers, chilled-mirror hygrometers, a differential absorption lidar, and ground-based solar radiometers were deployed at the ARM site. The unique datasets from the 1996, 1997, and 1999 experiments have led to many results, including the discovery and characterization of a large (> 25%) sonde-to-sonde variab...

Twenty-Four-Hour Raman Lidar Water Vapor Measurements during the Atmospheric Radiation Measurement Program's 1996 and 1997 Water Vapor Intensive Observation Periods

Abstract Prior to the Atmospheric Radiation Measurement program’s first water vapor intensive observation period (WVIOP) at the Cloud and Radiation Testbed site near Lamont, Oklahoma, an automated 24-h Raman lidar was delivered to the site. This instrument, which makes high-resolution measurements of water vapor both spatially and temporally, is capable of making these measurements with no operator interaction (other than initial start-up) for days at a time. Water vapor measurements collected during the 1996 and 1997 WVIOPs are discussed here, illustrating both the nighttime and daytime capabilities of this system. System characteristics, calibration issues, and techniques are presented. Finally, detailed intercomparisons of the lidar’s data with those from a microwave radiometer, radiosondes, an instrumented tower, a chilled mirror flown on both a tethersonde and kite, and measurements from aircraft are shown and discussed, highlighting the accuracy and stability of this system for both nighttime and da...

Evaluation of daytime measurements of aerosols and water vapor made by an operational Raman lidar over the Southern Great Plains

Raman lidar water vapor and aerosol extinction profiles acquired during the daytime over the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in northern Oklahoma (36.606 N, 97.50 W, 315 m) are evaluated using profiles measured by in situ and remote sensing instruments deployed during the May 2003 Aerosol Intensive Operations Period (IOP). The automated algorithms used to derive these profiles from the Raman lidar data were first modified to reduce the adverse effects associated with a general loss of sensitivity of the Raman lidar since early 2002. The Raman lidar water vapor measurements, which are calibrated to match precipitable water vapor (PWV) derived from coincident microwave radiometer (MWR) measurements were, on average, 5-10% (0.3-0.6 g/m 3 ) higher than the other measurements. Some of this difference is due to out-of-date line parameters that were subsequently updated in the MWR PWV retrievals. The Raman lidar aerosol extinction measurements were, on average, about 0.03 km -1 higher than aerosol measurements derived from airborne Sun photometer measurements of aerosol optical thickness and in situ measurements of aerosol scattering and absorption. This bias, which was about 50% of the mean aerosol extinction measured during this IOP, decreased to about 10% when aerosol extinction comparisons were restricted to aerosol extinction values larger than 0.15 km -1 . The lidar measurements of the aerosol extinction/backscatter ratio and airborne Sun photometer measurements of the aerosol optical thickness were used along with in situ measurements of the aerosol size distribution to retrieve estimates of the aerosol single scattering albedo (ω o ) and the effective complex refractive index. Retrieved values of ω o ranged from (0.91-0.98) and were in generally good agreement with ω o derived from airborne in situ measurements of scattering and absorption. Elevated aerosol layers located between about 2.6 and 3.6 km were observed by the Raman lidar on 25 and 27 May. The airborne measurements and lidar retrievals indicated that these layers, which were likely smoke produced by Siberian forest fires, were primarily composed of relatively large particles (r eff ∼ 0.23 μm) and that the layers were relatively nonabsorbing (ω o ∼ 0.96-0.98). Preliminary results show that major modifications that were made to the Raman lidar system during 2004 have dramatically improved the sensitivity in the aerosol and water vapor channels and reduced random errors in the aerosol scattering ratio and water vapor retrievals by an order of magnitude.

Photochemical effects in two-photon-excited fluorescence detection of atomic oxygen in flames

This paper describes photochemical effects observed using 226-nm two-photon-excited fluorescence detection to measure the atomic oxygen concentration in hydrogen-oxygen flames. In a study of a lean atmospheric-pressure flame, we observed artificially high atomic-oxygen concentration levels in the postflame gases using all but the most gentle excitation conditions (intensities greater than ~0.1 GW/cm(2)). A similar study of a lean low-pressure (72-Torr) flame showed little evidence of photochemical production of atomic oxygen. Using a second laser system in a pump-probe configuration, with the probe laser monitoring the atomic oxygen concentration in a very lean flame while the pump laser was scanned across molecular-oxygen Schumann-Runge bands at 221 nm, we demonstrated that excess atomic oxygen concentrations can be produced by single-photon excitation of these bands in vibrationally excited oxygen molecules present in the flame. This production mechanism explains at least part of the artificially high concentration levels observed in the atmospheric-pressure flame.

Photothermoelectric p–n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films

Light polarization is used in the animal kingdom for communication, navigation, and enhanced scene interpretation and also plays an important role in astronomy, remote sensing, and military applications. To date, there have been few photodetector materials demonstrated to have direct polarization sensitivity, as is usually the case in nature. Here, we report the realization of a carbon-based broadband photodetector, where the polarimetry is intrinsic to the active photodetector material. The detector is based on p-n junctions formed between two macroscopic films of single-wall carbon nanotubes. A responsivity up to ~1 V/W was observed in these devices, with a broadband spectral response spanning the visible to the mid-infrared. This responsivity is about 35 times larger than previous devices without p-n junctions. A combination of experiment and theory is used to demonstrate the photothermoelectric origin of the responsivity and to discuss the performance attributes of such devices.

Imaging of atomic hydrogen in flames with two-step saturated fluorescence detection

The hydrogen profile in a laminar hydrogen-air diffusion flame is mapped from a study of the Balmer-..cap alpha.. emission. (AIP)

Demonstration of pattern transfer into sub-100 nm polysilicon line/space features patterned with extreme ultraviolet lithography

In two separate experiments, we have successfully demonstrated the transfer of dense- and loose-pitch line/space (L/S) photoresist features, patterned with extreme ultraviolet (EUV) lithography, into an underlying hard mask material. In both experiments, a deep-UV photoresist (∼90 nm thick) was spin cast in bilayer format onto a hard mask (50–90 nm thick) and was subsequently exposed to EUV radiation using a 10× reduction EUV exposure system. The EUV reticle was fabricated at Motorola (Tempe, AZ) using a subtractive process with Ta-based absorbers on Mo/Si multilayer mask blanks. In the first set of experiments, following the EUV exposures, the L/S patterns were transferred first into a SiO2 hard mask (60 nm thick) using a reactive ion etch (RIE), and then into polysilicon (350 nm thick) using a triode-coupled plasma RIE etcher at the University of California, Berkeley, microfabrication facilities. The latter etch process, which produced steep (>85°) sidewalls, employed a HBr/Cl chemistry with a large (>1...

Comparison of Hydroxyl Concentration Profiles using Five Laser-Induced Fluorescence Methods in a Lean Subatmospheric-Pressure H2/O2/Ar Flame

Abstract We have assessed the relative consistency among laser-based fluorescence methods for kinetic studies in flames by comparing the OH concentration profiles determined by five such methods in a lean H2/O2/Ar flame at 72Torr. For all the methods, a single rovibronic transition is excited within the A 2Σ+−X2 Π system of OH. Relative OH concentrations are determined by monitoring the resulting fluorescence using: (1) single-photon excitation within the (0,0) band followed by broadband detection of the (0,0) rovibronic manifold; (2) single-photon excitation within the (0,0) band followed by detection of the (0,1) manifold; (3) single-photon excitation within the (1,0) band followed by broadband detection of the (1,1) rovibronic manifold; (4) two-photon excitation within the (0,0) band followed by detection of the (0,0) manifold; and (5) saturated single-photon excitation within the (0,0) band followed by narrowband detection of one rovibronic transition in the (0,0) manifold. In each case, good agreemen...

Long-Term Evaluation of Temperature Profiles Measured by an Operational Raman Lidar

AbstractThis study investigates the accuracy and calibration stability of temperature profiles derived from an operational Raman lidar over a 2-yr period from 1 January 2009 to 31 December 2010. The lidar, which uses the rotational Raman technique for temperature measurement, is located at the U.S. Department of Energys Atmospheric Radiation Measurement site near Billings, Oklahoma. The lidar performance specifications, data processing algorithms, and the results of several test runs are described. Calibration and overlap correction of the lidar is achieved using simultaneous and collocated radiosonde measurements. Results show that the calibration coefficients exhibit no significant long-term or seasonal variation but do show a distinct diurnal variation. When the diurnal variation in the calibration is not resolved the lidar temperature bias exhibits a significant diurnal variation. Test runs in which only nighttime radiosonde measurements are used for calibration show that the lidar exhibits a daytime...

Raman Lidar Profiling of Atmospheric Water Vapor: Simultaneous Measurements with Two Collocated Systems

Abstract Raman lidar is a loading candidate for providing the detailed space-and time-resolved measurements of water vapor needed by a variety of atmospheric studies. Simultaneous measurements of atmospheric watervapor are described using two collocated Raman lidar systems. These lidar systems, developed at the NASA/Goddard Space Flight Center and Sandia National Laboratories, acquired approximately 12 hours of simultaneous water vapor data during three nights in November 1992 while the systems were collocated at the Goddard Space Flight Center. Although these lidar systems differ substantially in their design, measured water vapor profiles agreed within 0.159 g Kg−1 between altitudes of 1 and 5 km. Comparisons with coincident radiosondes showed all instruments agreed within 0.2 g kg−1 in this same altitude range. Both lidars also clearly showed the advection of water vapor in the middle troposphere and the pronounced increase in water vapor in the nocturnal boundary layer that occurred during one night.