Characteristics of Sunset radar

Located in a narrow canyon 15 km west of Boulder, Colorado, the Sunset pulsed Doppler radar was the first radar designed and constructed specifically as a VHF ST radar. The antenna system is a phased array of coaxial-colinear dopoles with computer-controlled phase shifters for each line of dipoles. It operates at a frequency of 40.475 MHz and a wavelength of 7.41M. Peak transmitter power is 100 kW. Aperture efficiency is 0.58 and resistive loss is 0.30 for its 3600 sq m area. The practical steering rate is 1 record/minute/position to any arbitrary antenna beam position. The first clear-air turbulence echoes and wind velocity measurements were obtained in 1974. Significant accomplishments are listed

An example of scaling MST Doppler spectra using median spectra, spectral smoothing, and velocity tracing

Although automatic, computer scaling methods appeared at the start of the MST (mesosphere stratosphere troposphere) radar technique, there is a continuing need for scaling algorithms that perform editing functions and increase the sensitivity of radar by post processing. The scaling method presented is an adaptation of the method of scaling MST Doppler spectra presented by Rastogi (1984). A brief overview of this method is as follows: a median spectrum is calculated from several sequential spectra; the median noise value is subtracted from this derived spectrum; the median spectrum is smoothed; the detection/nondetection decision is made by comparing the smoothed spectrum to the variance of the smoothed noise; and if a signal is detected, then the half-power points of the smoothed echo spectrum are used to place limits on the evaluation of the first two moments of the unsmoothed median spectrum. In all of the above steps, the algorithm is guided by tracing the expected velocity range upward from the lowest range as far as possible. The method is discussed in more detail

Range gate dependence of specular echoes

Some controversy has surrounded the interpretation of the enhancement of VHF radar echoes at vertical incidence (also known as partial reflections, specular reflections and Fresnel scattering) since they were reported by the Sunset and the SOUSY radars. There is little doubt as to the observational fact of this enhancement since it was observed by experimenters using at least eleven MST or ST radars. In addition to the Sunset and SOUSY radars, this result was obtained in the lower atmosphere at the Platteville, Poker Flat, Jicamarca Arecibo radars as well as the three radars of the ALPEX experiments. In the upper atmosphere, specular or partial reflections were observed. These vertical enhancements were associated with increases in the static stability of the atmosphere, with a temperature gradient in the stratosphere, were used to monitor the height of the tropopause, and were associated with the passage of fronts

Determination of U, V, and W from single station Doppler radar radial velocities

The ST/MST (stratosphere troposphere/mesosphere stratosphere troposphere) clear air Doppler radar, or wind profiler, is an important tool in observational meteorology because of its capability to remote observe dynamic parameters of the atmosphere. There are difficulties in transforming the observed radial velocities into meteorological wind components. How this problem has been treated in the past is reviewed, and some of the analysis is recast to a form more suited to the high diagnostic abilities of a number of fixed beam configurations with reference to a linear wind field. The results, in conjunction with other works which treats problems such as the effects of finite sample volumes in the presence of nonhomogeneous atmospheric reflectivity, have implications important to the design of both individual MST/ST radars and MST/ST radar networks. The key parameters to uncoupling terms in the scaling equations are w sub x and w sub y. Whenever the stratiform condition, which states that these two parameters are negligible, is satisfied, a five beam ST radar may determine unbiased values of u, v, and w for sample volumes directly above the radar. The divergence and partial deformation of the flow may also be determined. Three beam systems can determine w and w sub z, but are unable to obtain u and v wind components uncontaminated by vertical sheer terms, even when the stratiform condition is satisfied

Preliminary estimates of vertical momentum flux

Preliminary results of themomentum flux and flux divergence during a transient episode, as a jet stream moved over the radar are given. The zonal and meridional momentum flux and flux divergences displayed remarkable continuity with altitude in time, increasing in intensity as lee waves and other gravity-wave activity developed while the jet stream approached. The momentum flux values observed compare favorably with aircraft measurements made over similar topography, at least during the early part of the day. The accelerations due to the momentum flux divergence seem rather large at first glance, especially for the late part of the day. However, there may be compensating forces due to effects not considered here, such as transverse circulations or, scales of motion to small to be resolved by these data

From bedside to bench: Comroe and dripps revisited

Twenty-five years ago a paper published in Science by Julius Comroe and Robert Dripps purported to demonstrate that 41 per cent of all articles judged to be essential for later clinical advances were not clinically oriented at the time of the study and 62 per cent of key articles were the result of basic research. Since that analysis, support for basic research has increased in the G7 countries. In the UK, Research Council expenditure on basic research has increased from a low of £444 million (or 42 per cent of total civil R&D) in 1991/92 to £769 million (or 61 per cent of total civil R&D) in 1998/99. Although it would be difficult to argue that Comroe and Dripps were directly responsible for a strategic shift (or drift) in the type of science supported by research funders, their arguments are often cited (albeit at times implicitly) in support of the increased funding for basic biomedical research. In 1987 Richard Smith wrote a critical paper reassessing Comroe and Dripps. His main argument was that the original study was in itself ‘unscientific’ and that it should be “followed by bigger and better studies”. This study is, in part, an answer to that challenge. Given the increased support for basic research, and the apparent importance based on the work of Comroe and Dripps, we felt it was important to investigate Smith’s comments by replicating Comroe and Dripps’s study and at the same time try to improve upon the methodology. The current project had two objectives: 1. To see if the original Comroe and Dripps’s methodology was ‘replicable’. 2. To validate the key findings of Comroe and Dripps. By looking at neonatal intensive care (NIC), we concluded that Comroe and Dripps’ study – as reported – is not repeatable, reliable or valid, and thus is an insufficient evidence base for increased expenditure on basic biomedical research. We did, however, develop an alternative methodology which used bibliographic databases and bibliometric techniques to describe the research underpinning five of the most important clinical advances in NIC, as identified through a Delphi survey. Using the revised bibliometric protocol, we demonstrated that after a time-lag of about 17 years, between 2 and 21 per cent of research underpinning the clinical advances could be described as basic. This observation is at odds with Comroe and Dripps’s finding that 62 per cent of key research articles judged to be essential for latter clinical advance were the result of basic research. In reaching this conclusion we are acutely aware of the significant limitations to the revised methodology and, therefore, we caution against the over-interpretation of our results. However, we would argue that there needs to be a greater understanding of how basic research supports healthcare and hope this report will inform part of this wider debate.R&D Directorate of the NHS Executive London; Wellcome Trus

Practicality of electronic beam steering for MST/ST radars, part 6.2A

Electronic beam steering is described as complex and expensive. The Sunset implementation of electronic steering is described, and it is demonstrated that such systems are cost effective, versatile, and no more complex than fixed beam alternatives, provided three or more beams are needed. The problem of determining accurate meteorological wind components in the presence of spatial variation is considered. A cost comparison of steerable and fixed systems allowing solution of this problem is given. The concepts and relations involved in phase steering are given, followed by the description of the Sunset ST radar steering system. The implications are discussed, references to the competing SAD method are provided, and a recommendation concerning the design of the future Doppler ST/MST systems is made

Testing and optimizing MST coaxial collinear arrays, part 6.4A

Many clear-air VHF wind profiles use coaxial collinear (COCO) arrays for their antenna. A COCO array is composed of long lines of half-wave dipoles spaced one-half wavelength apart. An inexpensive method of checking a COCO array is described and its performance is optimized by measuring and then correcting the relative rf phase among its lines at their feed point. This method also gives an estimate of the rf current amplitude among the lines. The strength and location of the sidelobes in the H-plane of the array can be estimated