New Publications are available for Atmospheric boundary layer structure and processes
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New Publications are available now online for this publication.
Please follow the links to view the publication.Adaptive sky sensor web: novel multi-instrument, multi-satellite observations of volcanic ash
http://dl-live.theiet.org/content/conferences/10.1049/cp_20081092
In this paper, selected Adaptive Sky components are combined to identify, track, and reacquire volcanic ash clouds generated by the October 2007 eruption of Bezymianny in Kamchatka. The basic strategy leverages the wide area coverage/high temporal sampling of NOAA's geostationary GOES-West satellite and the high spatial resolution/specialty instruments of NASA's polar orbiting satellites. Using GOES brightness temperature difference (BTD) image sequences to track features over time, we are able to unambiguously associate measurements made in mid-ocean by the MISR (Multi-angle Imaging SpectroRa- diometer) instrument on Terra and by the CALIOP (Cloud- Aerosol Lidar with Orthogonal Polarization) instrument on CALIPSO with volcanic ash clouds from Bezymianny despite a time separation of ≈ 30 hours and a spatial separation of ≈ 400 km from the eruption event. To our knowledge, this marks the first ever unambiguous daytime observation of a tropospheric volcanic ash cloud with CALIOP and the first joint observation by both MISR and CALIOP of the same volcanic ash cloud. In the absence of the feature correspondence and data fusion capabilities provided by Adaptive Sky, these returns likely would have been attributed to cirrus clouds. (8 pages)Measurement of the tropospheric scintillation decorrelation scale-length at millimetre wave frequencies
http://dl-live.theiet.org/content/conferences/10.1049/cp_20010410
Millimetre wave propagation for both terrestrial and satellite communications is highly dependent on the dynamic nature of the atmospheric boundary layer. Small-scale changes in temperature, pressure and humidity may result in the formation of turbulence. Turbulence can affect radiowave propagation by either scattering a small part of the signal's energy outside of the incident beam or by focusing and defocusing energy within the beam. In the former case, this redirected energy may be used to provide communications on over-the-horizon paths (typically at frequencies up to 5 GHz), or may indeed result in interference with other systems. In the latter case, turbulence may result in rapid amplitude fluctuations in signal strength scintillation. Systems that employ power control algorithms may be adversely affected by the rapid fluctuation of a scintillation event. Therefore, as the characteristics of the channel will ultimately determine the data throughput, a technique to mitigate scintillation could prove to be very useful. One such mitigation technique that could be used is spatial diversity. To achieve the diversity advantage requires the spatial coherence of events. This paper therefore investigates the spatial coherency of scintillation to determine the suitability of small-scale spatial diversity as a mitigation technique.Optimisation of the terminal Doppler weather radar in a cluttered marine environment
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971697
Discusses the Terminal Doppler Weather Radar (TDWR) for the new airport at Chek Lap Kok (CLK) of Hong Kong. This paper discusses the radar characteristics that ensure that the TDWR is able to meet its mission requirements while working in the highly cluttered marine environment of Hong Kong. The Terminal Doppler Weather Radar (TDWR) system, developed by Raytheon Company for the US Federal Aviation Administration (FAA), provides automatic detection of microbursts and low-level wind shear. The second major function of TDWR is to improve air traffic management through forecasts of wind shifts, precipitation and other weather hazards. The TDWR system generates meteorological base data and wind shear products and automatically prepares warning messages for the air traffic controllers, through the timely detection and reporting of hazardous wind shear. It collects low altitude meteorological data and performs reliably in the terminal area environment characterized by natural and man-made ground clutter. The TDWR design specifically addresses the extraction of weather information in the presence of radar returns from severe ground clutter. The TDWR radar utilizes the Doppler effect to measure the radial velocity of rain or airborne microparticulates. This paper addresses the characteristics of the TDWR system design, siting, and signal processing techniques that are critical to optimal performance in the Hong Kong environment, and discusses observations during the optimisation of the TDWR.On possibility of radar angel-echoes study with Sodar and RASS techniques
http://dl-live.theiet.org/content/conferences/10.1049/cp_19971629
The need to use the remote methods of atmosphere sounding to research the features of radiowaves propagation at near-Earth tracks has been formulated in our researches in early 70s. Such conclusion was based on results of experimental research of radiowaves refraction in the atmospheric boundary layer and also on the results of the theoretical development of the radio-meteorological model to calculate the radiowave refraction index in the atmosphere. For using the model it is required to measure the height profiles of temperature and wind speed, and also data on the characteristics of atmospheric turbulence inhomogeneities. In our radiophysical research we have begun to develop methods of remote sounding using acoustic echo-sounders (sodar) and radioacoustic sounding systems (RASS) with the objective of estimating the thermodynamical conditions and turbulence status in the radiowave propagation layer. Some results are considered for utilizing sodar and RASS for the analysis of radar angel-echo in stable state conditions of the atmospheric boundary layer.Modelling air pollution transport and deposition
http://dl-live.theiet.org/content/conferences/10.1049/ic_19951018
This paper gives an outline of the principles that are used to model atmospheric pollution. It discusses relevant ideas of the atmospheric boundary layer, its stability, and how the mixing varies with atmospheric stability. The author considers examples of modelling ranging from: (1) forecasts of urban air quality using a box model; (2) plume calculations using a Gaussian formulation and the more recent UK-ADMS model; (3) photochemical ozone arriving in the UK from Europe modelled by a chemical trajectory box model; (4) nuclear accident dispersion modelling using many particle random walk modelling (the NAME model); and (5) application of the NAME model to sulphur pollution and eventually to ozone formation chemistry. The author begins with dispersion in the atmospheric boundary layer, then considers deposition before looking at examples of models. Since the boundary layer is the lowest part of the atmosphere nearest the ground, it is strongly influenced by temperature changes at the surface, and by the drag on the flow. (7 pages)Acoustic sounder applications: remote sensing of sea breeze and radio propagation studies over tropical India
http://dl-live.theiet.org/content/conferences/10.1049/cp_19950448
Acoustic sounding is one of the remote sensing techniques that can give continuous information about some of the micro-meteorological parameters of the lower atmosphere. Microwave propagation is strongly influenced by the atmospheric boundary layer where radioclimatological phenomena such as temperature inversions, fronts, and thunderstorms cause steep refractivity gradients. An important parameter in the study of tropospheric propagation is the refractive index which causes reflection, refraction, diffraction and scattering of radio waves. In an effort to identify the causes of fading over LOS microwave links a monostatic sodar was installed at Tirupati (receiving end of the links) to probe the dynamic behavior of lower atmospheric effects on LOS propagation. The observational study has provided some basic understanding of the boundary layer characteristics affecting propagation and benefitted the development of a climatological model. The authors present some observed significant episodes pertinent to the classification of fading characteristics associated with each of the various atmospheric conditions. In addition, possibilities for the causes of fading are also discussed. It is concluded that severe fading in the early morning and late evening hours is caused due to temperature inversions observed over this region. (4 pages)A moored ‘surface-following’ buoy for spectral wind measurements with satellite and VHF data telemetry
http://dl-live.theiet.org/content/conferences/10.1049/cp_19940581
Discusses the development of a Sonic Buoy. The high quality of the results from the SWALES deployment vindicates the decision to develop the Sonic Buoy. The relation between the calculated wind stress and wind speed is much more clearly defined than in previous ship-based measurements. On the technical side, the buoy design has been proved with respect to survivability, and the redundancy built into the data logging and telemetry has proved its worth.Evaluation of the structure parameter <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub>over the sea surface
http://dl-live.theiet.org/content/journals/10.1049/ip-f-2.1990.0057
An estimate of the structure parameter <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub>is required to calculate the back-scattering of radar energy by turbulent eddies in the surface layer over sea. The theory of atmospheric boundary-layer turbulence may be applied, in conjunction with two spatial point measurements of meteorological parameters, to evaluate height profiles of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub>. The paper presents contours of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub> in the height/latitude plane using meteorological observations made on a cruise to Antarctica. Routinely monitored meteorological observations aboard ships have also been used to obtain the seasonal variations of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub> over tropical oceans. The values of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub> are found to be almost two orders of magnitude higher at heights up to 30 m at tropical latitudes compared to those at high latitudes. The values of <i xmlns="http://pub2web.metastore.ingenta.com/ns/">C</i><sup xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sup><sub xmlns="http://pub2web.metastore.ingenta.com/ns/">n</sub> are higher in the winter-summer periods, compared to postmonsoon and monsoon periods.Analysis of multipath fading on line-of-sight links in the presence of an elevated atmospheric duct
http://dl-live.theiet.org/content/journals/10.1049/ip-h-2.1987.0014
Multipath propagation on microwave line-of-sight links is analysed in the presence of an elevated inversion atmospheric layer and a reflecting earth. A bilinear height profile for the modified refractive index is adopted. Simple mathematical relations are derived for the number of rays hitting the receiver, and a graphical solution is presented for the launching and arrival angles. It is shown that path inclination tends to reduce the number of rays reaching the receiver. When more than three rays are received, signal enhancement, due to ducting, is more likely to occur. On the other hand, signal fading is more probable in the presence of two or three raysEstimation of low-level winds from upper-air data
http://dl-live.theiet.org/content/journals/10.1049/ip-a-1.1983.0079
Estimates of winds at heights of around 100 m are required for the siting of large wind turbines. Because of uncertainties often attached to the normal method of extrapolating from data at 10 m, a method of extrapolating from upper-air data has been developed. The predictions of this method are compared with measurements at several stations on land and one offshore.