Differential absorption lidar sensing of ozone

The differential absorption lidar (DIAL) technique for deriving O/sub 3/ profiles from lidar measurements is discussed. The US National Aeronautics and Space Administration's airborne DIAL system is described, and examples of a broad range of O/sub 3/ and aerosol measurements are presented from a number of field experiments. The airborne and ground-based DIAL measurements discussed demonstrate the outstanding capability of lidar for conducting O/sub 3/ investigations throughout the troposphere and lower stratosphere under widely different atmospheric conditions.<>     

生态景观设计40年

本文简要总结了英国生态景观设计的历史,阐述了在景观设计中如何纳入生态设计原则。通过对位于爱丁堡郊区里卡顿的一所新大学校园的规划与建设的案例研究,阐明了生态景观理论在景观设计中的实践。     

NASA multipurpose airborne DIAL system and measurements of ozone and aerosol profiles

An airborne differential absorption lidar (DIAL) system has been developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. The multipurpose DIAL system can operate from 280 to 1064 nm for measurements of ozone, sulfur dioxide, nitrogen dioxide, water vapor, temperature,pressure, and aerosol backscattering. The laser transmitter consists of two narrow linewidth Nd: YAG pumped dye lasers with automatic wavelength control. The DIAL wavelengths are transmitted with a 00-,usec temporal separation to reduce receiver system complexity. A coaxial receiver system is used to collect and optically separate the DIAL and aerosol lidar returns. Photomultiplier tubes detect the backscattered laser returns after optical filtering, and the analog signals from three tubes are digitized and stored on high-speed magnetic tape. Real-time gas concentration profiles or aerosol backscatter distributions are calculated and displayed for experiment control. Operational parameters for the airborne DIAL system are presented for measurements of ozone, water vapor, and aerosols in the 290-, 720-, and 600-nm wavelength regions, respectively. The first ozone profile measurements from an aircraft using the DIAL technique are discussed in this paper. Comparisons between DIAL and in situ ozone measurements show agreement to within +/-5 ppbv in the lower troposphere. Lidar aerosol data obtained simultaneously with DIAL ozone measurements are presented for a flight over Virginia and the Chesapeake Bay. DIAL system performance for profiling ozone in a tropopause folding experiment is evaluated, and the applications of the DIAL system to regional and global-scale tropospheric investigations are discussed.     

Atmospheric CO2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection

We report airborne measurements of CO(2) column abundance conducted during two 2009 campaigns using a 2.05 μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO(2) column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO(2) measurements from low Earth orbit pertinent to the NASA Active Sensing of CO(2) Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO(2) 2 μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO(2). The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.     

LASSO vector autoregression structures for very short‐term wind power forecasting

The deployment of smart grids and renewable energy dispatch centers motivates the development of forecasting techniques that take advantage of near real‐time measurements collected from geographically distributed sensors. This paper describes a forecasting methodology that explores a set of different sparse structures for the vector autoregression (VAR) model using the least absolute shrinkage and selection operator (LASSO) framework. The alternating direction method of multipliers is applied to fit the different LASSO‐VAR variants and create a scalable forecasting method supported by parallel computing and fast convergence, which can be used by system operators and renewable power plant operators. A test case with 66 wind power plants is used to show the improvement in forecasting skill from exploring distributed sparse structures. The proposed solution outperformed the conventional autoregressive and vector autoregressive models, as well as a sparse VAR model from the state of the art. Copyright © 2016 John Wiley & Sons, Ltd.     

A spatial and temporal correlation analysis of aggregate wind power in an ideally interconnected Europe

Studies have shown that a large geographic spread of installed capacity can reduce wind power variability and smooth production. This could be achieved by using electricity interconnections and storage systems. However, interconnections and storage are not totally flexible, so it is essential to understand the wind power correlation in order to address power system constraints in systems with large and growing wind power penetrations. In this study, the spatial and temporal correlation of wind power generation across several European Union countries was examined to understand how wind ‘travels’ across Europe. Three years of historical hourly wind power generation data from 10 countries were analysed. The results of the analysis were then compared with two other studies focused on the Nordic region and the USA. The findings show that similar general correlation characteristics do exist between European country pairs. This is of particular importance when planning and operating interconnector flows, storage optimization and cross‐border power trading. Copyright © 2017 The Authors Wind Energy Published by John Wiley & Sons Ltd     

Ultraviolet DIAL measurements of O3 profiles in regions of spatially inhomogeneous aerosols

The differential absorption lidar (DIAL) technique generally assumes that atmospheric optical scattering is the same at the two laser wavelengths used in the DIAL measurement of a gas concentration profile. Errors can arise in this approach when the wavelengths are significantly separated, and there is a range dependence in the aerosol scattering distribution. This paper discusses the errors introduced by large DIAL wavelength separations and spatial inhomogeneity of aerosols in the atmosphere. A Bernoulli solution for determining the relative distribution of aerosol backscattering in the UV region is presented, and scattering ratio boundary values for these solutions are discussed. The results of this approach are used to derive a backscatter correction to the standard DIAL analysis method. It is shown that for the worst cases of severe range dependence in aerosol backscattering, the residual errors in the corrected DIAL O3 measurements were <10 ppbv for DIAL wavelengths at 286 and 300 nm.     

Airborne differential absorption lidar system for measurements of atmospheric water vapor and aerosols

An airborne differential absorption lidar (DIAL) system has been developed at the NASA Langley Research Center for remote measurements of atmospheric water vapor (H(2)O) and aerosols. A solid-state alexandrite laser with a 1-pm linewidth and > 99.85% spectral purity was used as the on-line transmitter. Solid-state avalanche photodiode detector technology has replaced photomultiplier tubes in the receiver system, providing an average increase by a factor of 1.5-2.5 in the signal-to-noise ratio of the H(2)O measurement. By incorporating advanced diagnostic and data-acquisition instrumentation into other subsystems, we achieved additional improvements in system operational reliability and measurement accuracy. Laboratory spectroscopic measurements of H(2)O absorption-line parameters were perfo med to reduce the uncertainties in our knowledge of the absorption cross sections. Line-center H(2)O absorption cross sections were determined, with errors of 3-6%, for more than 120 lines in the 720-nm region. Flight tests of the system were conducted during 1989-1991 on the NASA Wallops Flight Facility Electra aircraft, and extensive intercomparison measurements were performed with dew-point hygrometers and H(2)O radiosondes. The H(2)O distributions measured with the DIAL system differed by ≤ 10% from the profiles determined with the in situ probes in a variety of atmospheric conditions.