Coherent lidar design and performance verification

The verification of LAWS beam alignment in space can be achieved by a measurement of heterodyne efficiency using the surface return. The crucial element is a direct detection signal that can be identified for each surface return. This should be satisfied for LAWS but will not be satisfied for descoped LAWS. The performance of algorithms for velocity estimation can be described with two basic parameters: the number of coherently detected photo-electrons per estimate and the number of independent signal samples per estimate. The average error of spectral domain velocity estimation algorithms are bounded by a new periodogram Cramer-Rao Bound. Comparison of the periodogram CRB with the exact CRB indicates a factor of two improvement in velocity accuracy is possible using non-spectral domain estimators. This improvement has been demonstrated with a maximum-likelihood estimator. The comparison of velocity estimation algorithms for 2 and 10 micron coherent lidar was performed by assuming all the system design parameters are fixed and the signal statistics are dominated by a 1 m/s rms wind fluctuation over the range gate. The beam alignment requirements for 2 micron are much more severe than for a 10 micron lidar. The effects of the random backscattered field on estimating the alignment error is a major problem for space based lidar operation, especially if the heterodyne efficiency cannot be estimated. For LAWS, the biggest science payoff would result from a short transmitted pulse, on the order of 0.5 microseconds instead of 3 microseconds. The numerically errors for simulation of laser propagation in the atmosphere have been determined as a joint project with the University of California, San Diego. Useful scaling laws were obtained for Kolmogorov atmospheric refractive turbulence and an atmospheric refractive turbulence characterized with an inner scale. This permits verification of the simulation procedure which is essential for the evaluation of the effects of refractive turbulence on coherent Doppler lidar systems. The analysis of 2 micron Doppler lidar data from Coherent Technologies, Inc. (CTI) has demonstrated many of the advantages of doppler lidar measurements of boundary layer winds. The effects of wind shear and wind turbulence over the pulse volume are probably the dominant source of the reduced performance. The effects of wind shear and wind turbulence on the statistical description of doppler lidar data has been derived and calculated

The Novel Nonlinear Adaptive Doppler Shift Estimation Technique and the Coherent Doppler Lidar System Validation Lidar

The signal processing aspect of a 2-m wavelength coherent Doppler lidar system under development at NASA Langley Research Center in Virginia is investigated in this paper. The lidar system is named VALIDAR (validation lidar) and its signal processing program estimates and displays various wind parameters in real-time as data acquisition occurs. The goal is to improve the quality of the current estimates such as power, Doppler shift, wind speed, and wind direction, especially in low signal-to-noise-ratio (SNR) regime. A novel Nonlinear Adaptive Doppler Shift Estimation Technique (NADSET) is developed on such behalf and its performance is analyzed using the wind data acquired over a long period of time by VALIDAR. The quality of Doppler shift and power estimations by conventional Fourier-transform-based spectrum estimation methods deteriorates rapidly as SNR decreases. NADSET compensates such deterioration in the quality of wind parameter estimates by adaptively utilizing the statistics of Doppler shift estimate in a strong SNR range and identifying sporadic range bins where good Doppler shift estimates are found. The authenticity of NADSET is established by comparing the trend of wind parameters with and without NADSET applied to the long-period lidar return data

Coherent Doppler lidar signal covariance including wind shear and wind turbulence

The performance of coherent Doppler lidar is determined by the statistics of the coherent Doppler signal. The derivation and calculation of the covariance of the Doppler lidar signal is presented for random atmospheric wind fields with wind shear. The random component is described by a Kolmogorov turbulence spectrum. The signal parameters are clarified for a general coherent Doppler lidar system. There are two distinct physical regimes: one where the transmitted pulse determines the signal statistics and the other where the wind field dominates the signal statistics. The Doppler shift of the signal is identified in terms of the wind field and system parameters

Computer simulation of coherent Doppler lidar measurement of wind velocity and retrieval of turbulent wind statistics

We describe the algorithms for the simulation of cw and pulsed coherent Doppler wind lidar operation in a turbulent atmosphere and the methods to estimate the mean wind and the parameters of small-scale wind turbulence from lidar data. The algorithms are realized as LabView computer codes, which include parts simulating the atmospheric turbulent wind fields based on the Karman model, lidar signal, and data processing. The errors for lidar measurement of turbulent parameters and the retrieval of the wind vertical profiles are estimated based on a computer simulation of the coherent Doppler lidar system operation

Innovative Applications of Laser Remote Sensing of Gases, Aerosols and Wind

Over the years, a major component of the research carried out at the Optical Remote Sensing Laboratory of the City College of New York has been on active sensing technologies and their different applications in atmospheric studies. This thesis builds upon and looks to further advance this field by demonstrating innovative applications of laser remote sensing technologies for studies involving trace gases, aerosol particles and wind; which are key components of the Earth’s atmosphere. First, we present the demonstration of gas concentration measurements using a quantum cascade laser open path system with characteristics that make it promising for mobile and/or multidirectional remote detection of gas leaks. This work looks to address an important environmental concern as fugitive methane emissions from industrial plants and pipelines can contribute to the global increase of greenhouse gas concentration and are a security and safety issue because of the risk of fire, explosion or toxicity. Second, we present horizontal measurements of the spatial distribution of aerosols over New York City using a scanning eye-safe elastic micro-pulse lidar system. Two case studies are presented in which different methodologies are applied in order to estimate the backscatter and extinction coefficients. These observations demonstrate capabilities to monitor local emission sources and rapid transport of aerosols, which are of great importance for air quality monitoring in urban areas due to the harmful effects of particulate pollution on human health. Lastly, we present the analysis of airborne wind measurements using a micro pulse Doppler lidar and comparison against ground measurements. Moreover, in order to evaluate the performance of the airborne system, we investigate some of the factors that may influence wind measurement uncertainty and provide insights on how to improve measurement precision while minimizing errors

Identification of patterns in long-term observations of the cloudy boundary layer

Understanding atmospheric boundary layer (ABL) processes is a key aspect in improving parameterizations in weather forecast and climate prediction models, but also for renewable energy and air quality studies. The ABL, as the lowest part of the atmosphere, can be directly affected by heterogeneities in land surface properties like soil, vegetation and topography, creating patterns at different temporal and spatial scales. In this context, turbulent mixing plays an important role in connecting the atmosphere to the Earth's surface. The turbulent motions are responsible for the thermodynamic structure of the ABL by redistributing heat and moisture and the transport of constituents like aerosols and pollutants away from the surface. These processes are the main drivers for the development of ABL clouds, which in turn feed back to the ABL and surface through interaction with solar radiation, coupling to the large-scale circulation and precipitation formation. This links back to the aim of model improvement, since clouds are one of the largest source of uncertainty in global models. Therefore interdisciplinary research is required to capture the interplay between the different compartments of the Earth. The Transregional Collaborative Research Centre 32 (TR32) in its third phase is dedicated to find these patterns in the soil-vegetation-atmosphere system by a monitoring, modelling and data assimilation approach. Within the TR32 project D2 special emphasis is on measuring, modelling and understanding the spatio-temporal structures in land surface-atmosphere exchange at the Jülich ObservatorY for Cloud Evolution (JOYCE). For the typical ABL process scales of seconds to hours and meters to kilometers, ground-based remote sensing observations are well suited to continuously gather comprehensive information on the atmospheric state in a long-term perspective. With additional model simulations the conceptual process understanding can be improved. This study focuses on the long-term characterisation of the cloudy boundary layer to identify patterns that can be further linked to surface properties at JOYCE. For this purpose, a classification for characterizing ABL turbulence is developed (Publication I). The classification, based on Doppler wind lidar (DWL) data, identifies turbulence regions in the ABL and assigns a mixing source using multiple DWL quantities. In this way, convective, wind shear and cloud driven turbulence can be distinguished under most atmospheric conditions. The method is applied at two research sites, showing a distinct behavior for different climate regimes in terms of the diurnal and seasonal cycle of ABL development. In the analysis of the long-term data sets, nocturnal low-level jets (LLJ) are identified as an important source of shear generated mixing. Therefore, a long-term record of LLJ periods, compiled with DWL observations, is investigated in Publication II. The high frequency of occurrence and wind speeds, associated with significant turbulence close to the surface, reveal the relevance of LLJs for wind energy applications. In addition, a strong interaction of the wind field with the surrounding topography can be seen in the DWL measurements, as well as in the results of a high-resolution large-eddy simulation (LES). Also during the day, when the buoyancy production represents the main factor of convective ABL mixing, the interaction between the land surface and the atmosphere is strongly influenced by surface properties. In particular, the local transport of water vapor in moist thermals is a key mechanism for the coupling of clouds to the underlying land surface and a spatially heterogeneous distribution of land use types can lead to patterns in atmospheric water vapor fields (Publication III). Besides a scanning microwave radiometer (MWR), also satellite and LES data are taken into account, showing a good agreement in identifying the direction of water vapor sources. Convective clouds, that are frequently forming in the ABL due to this convective humidity transport, often contain small amounts of liquid water. These thin liquid water clouds, with a low liquid water path (LWP), are important in terms of their interaction with radiation. In the range of low LWP values, the radiative fluxes are very sensitive to small changes in the amount liquid water contained in the clouds. For a correct representation of the cloud microphysical and optical properties, statistical retrievals using a neural network approach are developed in Publication IV. The retrievals with low computational demand are derived from ground-based observations and make use of the distinct sensitivities in different spectral regimes. While the microwave regime suffers from high uncertainties in low LWP situations, the infrared regime reveals saturation effects for higher LWP. A combination of both spectral regimes yields the best results for the whole range of LWP values

Sekoituskerroksen korkeuden arviointi eri menetelmin Loviisan ydinvoimalaitoksen läheisyydessä

Työssä tarkastellaan ilmakehän sekoituskorkeuden arvioimista eri menetelmin Loviisan ydinvoimalaitoksen läheisyydessä. Sekoituskorkeus on keskeinen parametri arvioitaessa voimalaitokselta ilmaan tapahtuvien radioaktiivisten aineiden leviämistä ilmakehässä sekä niiden vaikutuksia voimalaitoksen lähialueella. Sekoituskorkeus arvioidaan LIDAR-mittausten perusteella sekä Loviisan ydinvoimalaitoksen säähavaintojärjestelmän mittauksista parametrisoimalla aikavälillä 10.4. - 5.6.2015. Käytettävän parametrisointiyhtälön muoto riippuu rajakerroksen stabiiliusolosuhteista. Stabiiliusolosuhteiden erottelu tehdään säähavaintojärjestelmältä saatavan Obukhov-pituuteen perustuvan Pasquill-stabiiliusluokan perusteella. Stabiileissa ja neutraaleissa olosuhteissa parametrisointiyhtälön kertoimet arvioidaan LIDAR-mittausten avulla. Eri menetelmin arvioituja sekoituskorkeuksia verrataan Loviisan ydinvoimalaitoksella käytettyyn Pasquill-stabiiliusluokkaan perustuvaan lähestymistapaan. Työn tulosten mukaan LIDAR-mittauksista saadaan melko harvoin arvio sekoituskorkeudesta ja saantoon liittyy vuorokaudenaikaista vaihtelua. LIDAR-mittausten tulokset eivät myöskään vastaa Pasquill-stabiiliusluokan mukaan labiileissa olosuhteissa parametrisoitua sekoituskorkeutta. Voimakkaan sekoittumisen tilanteissa LIDAR-mittauksien avulla ei pystytty arvioimaan sekoituskorkeutta luotettavasti. Lisäksi Pasquill-stabiiliusluokan mukaan olosuhteet ovat toisinaan labiilit, vaikka ne todellisuudessa ovat neutraalit tai stabiilit. Näiden epävarmuustekijöiden vuoksi sekoituskorkeuden tyypillisestä käyttäytymisestä ei voida tehdä johtopäätöksiä labiileiden tilanteiden osalta. Tulokset osoittavat, että neutraaleissa ja stabiileissa olosuhteissa eri menetelmin arvioidut sekoituskorkeudet käyttäytyvät samaan tapaan Loviisan ydinvoimalaitoksella sovelletun menetelmän kanssa, joskin LIDAR-mittausten ja parametrisointiyhtälön mukaiset sekoituskorkeudet ovat erityisesti neutraaleissa ja lievästi stabiileissa olosuhteissa selvästi matalampia. Tämä on merkittävää, koska rajakerros on Loviisan mittausympäristössä useimmiten likimain neutraalisti kerrostunut. Keväisen mittausjakson tuloksien perusteella Loviisan ydinvoimalaitoksen käyttämä sekoituskorkeuden arviointimenetelmä vaikuttaa yliarvioivan sekoituskorkeutta rantaviivan läheisyydessä stabiileissa ja neutraaleissa olosuhteissa. Mahdollisen vuodenaikaisen vaihtelun selvittämiseksi tulisi tarkastella sekoituskorkeuden käyttäytymistä muina vuodenaikoina tehtyjen LIDAR-mittausten perusteella. Pasquill-stabiiliusluokkiin perustuvia sekoituskorkeusarvioita on syytä tarkentaa, tai vaihtoehtoisesti arvioida sekoituskorkeus jollain toisella menetelmällä. Parametrisointi vaikuttaa työn tulosten perusteella lupaavalta vaihtoehdolta sekoituskorkeuden arvioinnille ainakin neutraaleissa ja stabiileissa olosuhteissa

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion