Future performance of ground-based and airborne water-vapor differential absorption lidar. I. Overview and theory.
TL;DR: The most important features of the DIAL technique are introduced: its clear-air measurement capability, its flexibility, and its simultaneous high resolution and accuracy.
Abstract: The performance of a future advanced water-vapor differential absorption lidar (DIAL) system is discussed. It is shown that the system has to be a direct-detection system operating in the rhovarsigmatau band of water vapor in the 940-nm wavelength region. The most important features of the DIAL technique are introduced: its clear-air measurement capability, its flexibility, and its simultaneous high resolution and accuracy. It is demonstrated that such a DIAL system can contribute to atmospheric sciences over a large range of scales and over a large variety of humidity conditions. An extended error analysis is performed, and errors (e.g., speckle noise) are included that previously were not been discussed in detail and that become important for certain system designs and measurement conditions. The applicability of the derived equation is investigated by comparisons with real data. Excellent agreement is found.
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University of Hohenheim1, Karlsruhe Institute of Technology2, German Aerospace Center3, Leibniz Association4, MeteoSwiss5, University of Leeds6, Delft University of Technology7, University of Montpellier8, University of Cologne9, University of Potsdam10, University of Vienna11, University of Bayreuth12, Centre national de la recherche scientifique13, University of Fribourg14, Deutscher Wetterdienst15, EUMETSAT16, Pacific Northwest National Laboratory17, University of Hamburg18, University of Toulouse19, University of Innsbruck20, University of Wisconsin-Madison21, Blaise Pascal University22, National Center for Atmospheric Research23, ETH Zurich24
TL;DR: The COPS field phase was performed from 1 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains.
Abstract: Within the framework of the international field campaign COPS (Convective and Orographically induced Precipitation Study), a large suite of state-of-the-art meteorological instrumentation was operated, partially combined for the first time. This includes networks of in situ and remote-sensing systems such as the Global Positioning System as well as a synergy of multi-wavelength passive and active remote-sensing instruments such as advanced radar and lidar systems. The COPS field phase was performed from 01 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains. The collected dataset covers the entire evolution of convective precipitation events in complex terrain from their initiation, to their development and mature phase until their decay. Eighteen Intensive Observations Periods with 37 operation days and eight additional Special Observations Periods were performed, providing a comprehensive dataset covering different forcing conditions. In this article, an overview of the COPS scientific strategy, the field phase, and its first accomplishments is given. Highlights of the campaign are illustrated with several measurement examples. It is demonstrated that COPS research provides new insight into key processes leading to convection initiation and to the modification of precipitation by orography, in the improvement of quantitative precipitation forecasting by the assimilation of new observations, and in the performance of ensembles of convection-permitting models in complex terrain.
215 citations
TL;DR: In this article, a review of remote sensing technology for lower-tropospheric thermodynamic profiling is presented with focus on high accuracy and high temporal-vertical resolution, and the contributions of these instruments to the understanding of the Earth system are assessed with respect to radiative transfer, land-surface-atmosphere feedback, convection initiation, and data assimilation.
Abstract: A review of remote sensing technology for lower-tropospheric thermodynamic (TD) profiling is presented with focus on high accuracy and high temporal-vertical resolution. The contributions of these instruments to the understanding of the Earth system are assessed with respect to radiative transfer, land-surface-atmosphere feedback, convection initiation, and data assimilation. We demonstrate that for progress in weather and climate research, TD profilers are essential. These observational systems must resolve gradients of humidity and temperature in the stable or unstable atmospheric surface layer close to the ground, in the mixed layer, in the interfacial layer – usually characterized by an inversion – and the lower troposphere. A thorough analysis of the current observing systems is performed revealing significant gaps that must be addressed to fulfill existing needs. We analyze whether current and future passive and active remote sensing systems can close these gaps. A methodological analysis and demonstration of measurement capabilities with respect to bias and precision is executed both for passive and active remote sensing including passive infrared and microwave spectroscopy, the global positioning system as well as water-vapor and temperature Raman lidar and water-vapor differential absorption lidar. Whereas passive remote sensing systems are already mature with respect to operational applications, active more » remote sensing systems require further engineering to become operational in networks. However, active remote sensing systems provide a smaller bias as well as higher temporal and vertical resolutions. For a suitable mesoscale network design, TD profiler system developments should be intensified and dedicated observing system simulation experiments should be performed. « less
171 citations
Cites background from "Future performance of ground-based ..."
...D studies of CI, need even higher resolution and large range [Wulfmeyer and Walther, 2001a, 2001b]....
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...The single-scattering lidar equation describes the power of the elastic backscatter signal PS in dependence of range r and reads [Wulfmeyer and Walther, 2001a, 2001b] PS;ν0 rð Þ ¼ P0 ξν0 cΔt 2 Atel r2 O rð Þ βpar;ν0 rð Þ þ βmol;ν0 rð Þ n o Γ2ν0 rð Þ þ PB;ν0 with Γ2ν0 rð Þ ¼ exp 2∫ r 0 αpar;ν0 r’ð Þ…...
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TL;DR: In this paper, a field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested.
Abstract: . A field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested. Significant advances are discussed, including a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with optomechanical and thermal stability; multistage optical filtering enabling measurement during daytime bright-cloud conditions; rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions; and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing, and intercomparisons are performed and discussed. In general, the instrument has a 150 m range resolution with a 10 min temporal resolution; 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument is shown capable of autonomous long-term field operation – 50 days with a > 95% uptime – under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.
99 citations
Cites background from "Future performance of ground-based ..."
...The differential optical depth, 1τ , needed to retrieve the water vapor number density (Wulfmeyer and Walther, 2001a) is 1τ = nσon1R ≈ 0.03–0.1, where n is the water vapor number density, σon is the absorption cross section at the online wavelength, andR is the range bin size....
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...Second, wavelength switching on timescales of several seconds can result in errors due to decorrelation between the online and offline signals from fluctuations in the backscatter coefficient, as discussed in Wulfmeyer and Walther (2001a)....
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TL;DR: In this article, high-resolution water vapour measurements made by the Atmospheric Radiation Measurement (ARM) Raman lidar operated at the Southern Great Plains Climate Research Facility site near Lamont, Oklahoma, U.S.A. are presented.
Abstract: High-resolution water vapour measurements made by the Atmospheric Radiation Measurement (ARM) Raman lidar operated at the Southern Great Plains Climate Research Facility site near Lamont, Oklahoma, U.S.A. are presented. Using a 2-h measurement period for the convective boundary layer (CBL) on 13 September 2005, with temporal and spatial resolutions of 10 s and 75 m, respectively, spectral and autocovariance analyses of water vapour mixing ratio time series are performed. It is demonstrated that the major part of the inertial subrange was detected and that the integral scale was significantly larger than the time resolution. Consequently, the major part of the turbulent fluctuations was resolved. Different methods to retrieve noise error profiles yield consistent results and compare well with noise profiles estimated using Poisson statistics of the Raman lidar signals. Integral scale, mixing-ratio variance, skewness, and kurtosis profiles were determined including error bars with respect to statistical and sampling errors. The integral scale ranges between 70 and 130 s at the top of the CBL. Within the CBL, up to the third order, noise errors are significantly smaller than sampling errors and the absolute values of turbulent variables, respectively. The mixing-ratio variance profile rises monotonically from ≈0.07 to ≈3.7 g2 kg−2 in the entrainment zone. The skewness is nearly zero up to 0.6 z/z
i
, becomes −1 around 0.7–0.8 z/z
i
, crosses zero at about 0.95 z/z
i
, and reaches about 1.7 at 1.1 z/z
i
(here, z is the height and z
i
is the CBL depth). The noise errors are too large to derive fourth-order moments with sufficient accuracy. Consequently, to the best of our knowledge, the ARM Raman lidar is the first water vapour Raman lidar with demonstrated capability to retrieve profiles of turbulent variables up to the third order during daytime throughout the atmospheric CBL.
79 citations
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TL;DR: The HITRAN molecular absorption database as mentioned in this paper contains line parameters for 31 species and their isotopomers that are significant for terrestrial atmospheric studies, including chlorofluorocarbons and other molecular species that are not amenable to line-by-line representation.
Abstract: We describe in this paper the modifications, improvements, and enhancements to the HITRAN molecular absorption database that have occurred in the two editions of 1991 and 1992 The current database includes line parameters for 31 species and their isotopomers that are significant for terrestrial atmospheric studies This line-by-line portion of HITRAN presently contains about 709,000 transitions between 0 and 23,000/cm and contains three molecules not present in earlier versions: COF2, SF6, and H2S The HITRAN compilation has substantially more information on chlorofluorocarbons and other molecular species that exhibit dense spectra which are not amenable to line-by-line representation The user access of the database has been advanced, and new media forms are now available for use on personal computers
1,442 citations
Journal Article•
TL;DR: In this article, the authors describe work done to increase the spectral resolution from 20 to 2 1/cm (FWHM) using the MODTRAN computer code, which is a moderate resolution version of the low-power low-voltage spectrum analyzer (LOWTRAN).
Abstract: : The LOWTRAN computer codes, with LOWTRAN 7 being the most current version, are widely used to calculate atmospheric transmittance and/or radiance in the infrared, visible and near ultraviolet spectral regions; LOWTRAN 7 has been extended to include the microwave spectral region The code is easily used, runs quickly and provides the user with a wide variety of atmospheric models and options Its spectral resolution is 20 1/cm Full Width/Half Maximum (FWHM) with calculations being done in 5 1/cm increments This report describes work done to increase LOWTRAN's spectral resolution from 20 to 2 1/cm (FWHM) Specifically, the technical objectives for this program were: 1) to develop algorithms providing 2 1/cm resolution (FWHM); 2) to model molecular absorption of atmospheric molecules as a function of temperature and pressure; 3) to calculate band model parameters for twelve LOWTRAN molecular species; and 4) to integrate the LOWTRAN 7 capabilities into the new algorithms, maintaining compatibility with the multiple scattering option MODTRAN, the final product of this effort, is a moderate resolution LOWTRAN code Molecular absorption is calculated in 1 1/cm spectral bins, while the other parts of the calculation remain unchanged The molecular species affected are: water vapor, carbon dioxide, ozone, nitrous oxide, carbon monoxide, methane, oxygen, nitric oxide, sulfur dioxide, nitrogen dioxide, ammonia and nitric acid
846 citations
TL;DR: The Atmospheric Radiation Measurement (ARM) Program, supported by the U.S. Department of Energy, is a major new program of atmospheric measurement and modeling as discussed by the authors.The program is intended to improve the understanding of processes that affect atmospheric radiation and the description of these processes in climate models.
Abstract: The Atmospheric Radiation Measurement (ARM) Program, supported by the U.S. Department of Energy, is a major new program of atmospheric measurement and modeling. The program is intended to improve the understanding of processes that affect atmospheric radiation and the description of these processes in climate models. An accurate description of atmospheric radiation and its interaction with clouds and cloud processes is necessary to improve the performance of and confidence in models used to study and predict climate change. The ARM Program will employ five (this paper was prepared prior to a decision to limit the number of primary measurement sites to three) highly instrumented primary measurement sites for up to 10 years at land and ocean locations, from the Tropics to the Arctic, and will conduct observations for shorter periods at additional sites and in specialized campaigns. Quantities to be measured at these sites include longwave and shortwave radiation, the spatial and temporal distributi...
836 citations
TL;DR: A nighttime operating Raman lidar system that is designed for the measurement of high vertical and temporal resolution profiles of the water vapor mixing ratio and the aerosol backscattering ratio is described.
Abstract: A nighttime operating Raman lidar system that is designed for the measurement of high vertical and temporal resolution profiles of the water vapor mixing ratio and the aerosol backscattering ratio is described. The theory of the measurements is presented. Particular attention is given to operational problems that have been solved during the development of the system. Data are presented from Sept. 1987 and described in their meteorological context.
439 citations
TL;DR: In this paper, a combined Raman elastic-backscatter lidar has been developed, where a XeCl excimer laser is used as the radiation source and inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator.
Abstract: A combined Raman elastic-backscatter lidar has been developed. A XeCl excimer laser is used as the radiation source. Inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator. Raman channels can be chosen to register signals from CO2, O2, N2, and H2O. Algorithms for the calculation of the water-vapor mixing ratio from the Raman signals and the particle extinction and backscatter coefficients from both elastic and inelastic backscatter signals are given. Nighttime measurements of the vertical humidity distribution up to the tropopause and of particle extinction, backscatter, and lidar ratio profiles in the boundary layer, in high-altitude water and ice clouds, and in the stratospheric aerosol layer are presented. Daytime boundary-layer measurements of moisture and particle extinction are made possible by the improved daylight suppression of the grating polychromator. Test measurements of the CO2 mixing ratio indicate the problems for the Raman lidar technique in monitoring other trace gases than water vapor.
415 citations