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A ruby laser radar has been constructed at Fukuoka (33° N), south-west Japan, for the purpose of probing the upper atmosphere. Observations of stratospheric aerosol layers have been carried out since October 1972. Data obtained show that the layers of enhanced optical backscattering due to aerosols in the height range of 16–30 km were found throughout the period of observation. One of the layers always appeared at about 20 km height and varied to some extent in its height, structure, and peak value of scattering, day-to-day and month-to-month. Other layers appeared in the region above 25 km and seemed more variable. Height profiles of non-Rayleigh backscattering cross section βm are calculated for each night and each month of the observation and compared with the temperature, wind velocity, and ozone concentration in the stratosphere. The individual scattering profile is most likely controlled by the large scale structure of the temperature profile of the night. The mean value of βm in the region around 20 km has its minimum in January and increases from winter to summer. Comparison is also made with the geometrical cross section of the aerosols deduced from the small ion density data and the results show that a large fraction of the aerosol mass is in the range of Aitken particles.

Auroral zone E-region neutral winds have been derived from simultaneous measurements of ion drift velocities in different altitudes by the incoherent radar facility at Chatanika, Alaska, on a quiet day before and during the great magnetospheric storm of Aug. 3-9, 1972. The neutral wind expected for a day-night pressure asymmetry appears to be strongly opposed by ion drag and local pressure gradients in the auroral oval.

Recently significant progress has been made in modeling sea return by means of a composite surface theory. All of the four-frequency radar sea return data obtained by the Naval Research Laboratory have been incorporated into this theory to provide a more accurate determination of the magnitude of sea return for vertical polarization. A value of the power law for the wave number spectrum of the sea close to that of −3.75 previously found by Kinsman (1965) was determined from the radar data. By means of this spectrum, equations have been developed that model vertically polarized sea return as a function of wind velocity and direction, radar wavelength, and depression angle. A power law dependence of sea return with wind velocity is introduced that is in agreement with the data in many cases.

A technique for the observation of radar echoes from stratospheric and mesospheric heights has been developed at the Jicamarca Radio Observatory. Signals are detected at the altitude ranges between 10–35 km and from 55–85 km with powers from many to several tens of decibels above noise level. The three most important frequency spectrum characteristics-power, Doppler shift and spectrum width-are observed in real time. The power levels as well as the spectral width are explained in terms of turbulent layers, with a thickness of the order of 100 m, in regions with a positive potential temperature or electron density vertical gradients. Continuous wind velocity records are obtained with a precision of the order of 0.02–0.2 m sec−1 for the vertical component and 0.20–2 m sec−1 for the horizontal, with a time resolution of the order of 1 min. The highest precisions are obtained at stratosphere heights. Fluctuations in velocity in the mesosphere are observed at the shortest gravity wave periods with amp...

Return tag information from a number of low-level, constant volume balloons (tetroons), tracked by radar for some tens of miles in air diffusion studies, has extended the useful horizon of these atmospheric tracers to several hundred miles. Trajectories reconstructed at several levels have shown that the best approximation to the tetroon recovery point is an adjusted surface wind trajectory. The speed adjustment factor, derived from the “power-law” wind speed profile, varied from 1.6 to 1.8, individual values being dependent upon the tetroon float level. The direction adjustment amounted to 1 deg of veering per 100 ft. The approximation breaks down in frontal systems and over mountainous terrain. The “second standard level” and surface geostrophic wind trajectories are, on the average, less representative of the low-level flow as deduced from tetroon recovery points. These results have application in determining the transport of low-level air pollutants.

The poor wind response of parachute-borne sensors at altitudes above 50 km leads to significant errors in the determination of wind speed, unless a correction is applied. Errors vary considerably, depending on the type of radar.

A series of rawins, tracked by an M-33 radar, was carried out at Palestine, Texas, in November 1965. Ascent rates of about 60 m./min. and recording of balloon coordinates at half-minute intervals were used to give fine resolution. In addition to horizontal winds, the flights were analyzed for the vertical wind component, and ascent-rate of the balloon. The results suggest that some inferences as to thermal structure in the surface layer can be drawn from precision balloon tracking. A uniform rate of ascent is associated with inversion conditions. An ascent that shows two rates, a faster one through the first few hundred meters and a slower one above, occurs when the surface layer is undergoing mixing of either convective or mechanical origin. Attempts to fit an expression of the form V1/V2 = ( z1/z2 ) p to the profile of wind speed in the surface-based layer agreed moderately well with the expectation of p≦1/7 for unstable layers and p≧1/3 for inversions. This somewhat weak indication was often s...

A coherent radar was used to measure the ‘sea clutter’ or backscattering of X-band electromagnetic energy from the sea surface. More than 200 recorded samples of clutter were analyzed to give power spectra of the clutter. Each spectrum was displayed as a function of frequency and of position on the water surface and was also averaged to give the mean spectrum of patches 3750 feet long. Five of the samples showed an anomalous downwind displacement of the clutter by as much as 7 knots. The displays indicate again, as in earlier Control Systems Laboratory measurements, that the upwind edge of the clutter spectrum is smooth for all wind speeds observed, but that the downwind edge, for sea state 3 or above, is broadened in an irregular fashion as a function of range. This irregular broadening implies a considerable variability, from patch to patch, in the downwind side of the probability distribution of velocity of scatterers on the sea surface. The width at half-power of a mean spectrum is proportional, for reasonable assumptions, to the width at half-maximum of the probability distribution of scatterer velocities. The variation of the latter width, Δ0, with sea state can be represented by the equation (expressed in consistent units) Δ0=11H1/3/Tm where the numerical factor is dimensionless, H1/3 is the significant wave height, and Tm is the period corresponding to the maximum of the energy spectrum for the water waves themselves when this spectrum is plotted as a function of frequency. This equation fits the experimental data within about 10 per cent for bandwidths in the range of 2 to 5 knots (64 to 160 cps) and wind speeds in the range of 8 to 19 knots. The bandwidth of the clutter is found to be approximately proportional to the wind speed. The relationships of clutter bandwidths to wave and whitecap velocities, radar depression angle, and wind direction are also discussed.

The ability of a forward-scatter CW radar to measure cross-path wind speed profiles is demonstrated from the results of a two-week observation period in June 1971. Radar-measured winds are compared with wind speeds measured simultaneously by radiosondes and pibals. It is concluded that forward-scatter CW radar is a sensitive atmospheric probe which can accurately measure atmospheric winds.

Recently a new model for the normalized radar cross section (NRCS) of the sea has been developed that is based on the scattering from a composite surface, i.e., one in which a slightly rough surface in the sense of Rice has been superimposed upon a large wave structure. The model predicts an upper bound (saturation value) of the NRCS with increasing wind speed and in addition yields expressions for the variation of the NRCS with frequency, polarization, and grazing angle. To verify the validity of the model in the higher sea states where spray, shadowing, and nonlinear wave interactions would be expected to influence the return, extensive measurements were made over the North Atlantic Ocean in February 1969. The instrumentation used in the program was the Naval Research Laboratory four-frequency radar system which is an experimental radar installed in an EC-121 (Super Constellation) aircraft. Nine flights were made, and data acquired in sea states with winds that varied from Beaufort Force 0 to 8 with a maximum sea state condition of a 24-m/sec wind with 8.5-meter significant wave height were observed. The results of the measurement have verified the existence of the upper bound for the NRCS that is asymptotically approached in windspeeds in excess of 5 m/sec. In addition, the data have confirmed the variation of the cross section with frequency, polarization, and grazing angle with the proviso that the ‘tilting’ of the scattering surface by the large wave structure be assumed in the region of shallow grazing angles.

An analysis is presented of low-level trajectory data obtained by means of constant level balloon flights from Cape Hatteras, N.C., during September and October 1959. An approximately constant floating level was obtained by flying the nearly constant volume Mylar balloons (tetroons) with an internal superpressure of about 100 mb. The metalized tetroons were positioned a t 1-min. intervals by means of a manually operated SP–1M radar. From knowledge of these positions, overlapping 5-min. average velocities were determined for flight durations of up to 5 hr. On some of the flights the radar return was enhanced by the addition of a radar reflective mesh to the tetroon. With the addition of this mesh, flights at altitudes of less than 5,000 ft. were tracked as far as 92 n. mi. from the radar, or approximately to the radar horizon. Spectral analysis of the velocity data obtained from the four best flights shows some evidence for a (Lagrangian) wind speed periodicity of 26-min. period, a vertical motion...

Accuracy tests have been carried out on a 3-cm Decca W.F.2 radar by simultaneously tracking a single balloon with two radars. The errors in height and wind speed and direction arising from these tracking errors are discussed. Heights and wind speed component variations of balloons levelled using a valve technique are examined in the light of the errors found above. It is shown that significant fluctuations in wind speed occur over short and long time intervals at a given height.

Techniques are described for predicting the effect of the "oceanic duct" in increasing the coverage of low-sited microwave radars. Prediction is made on a monthly basis using statistical data on sea temperature, air temperature, humidity, and wind speed. A large area in the northwest Pacific is used to illustrate the methods used. The basic prediction approach is to deduce refractive index profiles from available data parameters and to use Schelkunoff's ducting criteria to predict radar propagation effects. Monthly contours are then drawn over the area for each radar band showing the probability of extended coverage.

Mesoscale perturbations in vertical wind velocity profiles obtained from superpressure balloons tracked by FPS-16 radars

Ocean surface condition correlation to radar backscattering cross sections and wind velocity from scatterometer data

Underwater acoustic reverberation from the sea surface appears to be a combination of specular reflections and diffuse scattering, which may include, on an experimental basis, the effects of subsurface volume reverberation. This paper (1) separates these contributions as a function of incidence angle, radiation wavenumber (frequency), and sea‐surface wind speed; (2) shows the fundamental relationship between specular reflections and diffuse scattering; (3) develops a tentative spectrum of roughness at large wavenumbers for a developing sea surface; (4) points out various radiation‐wavenumber, incidence‐angle and wind‐speed regimes associated with sea‐surface returns; and (5) presents a correlation formula for acoustic reverberation from a sea surface, which is applicable as well to forwardscattering of both sound and radar waves. The results of the paper are familiar in the sense that no new mechanism for reverberation is invoked and novel in the sense that the familiar mechanisms are used to interpret acoustic, turbulence, and hydrodynamic data in a manner that predicts sea‐surface acoustic reverberation in a physically consistent way.

Roughness factor of the facets of a wind-disturbed water surface is defined as the ratio of flatness tolerance to facet length. The mean roughness factor for all facets in the upwind-down-wind direction is about 0.095 at 10 knots wind velocity and about 0.135 at 20 knots when measured by means of a short fetch water-wind tunnel. Using data presented in this paper, approximate calculations have been made on the nature of the function relating radar beam depression angle with the upwind-to-downwind ratio of radar reflection back from the rough sea surface. The results are in qualitative agreement with the meager existing experimental data. It is predicted that there is an interesting minimum in the upwind-to-downwind ratio in the region of 70° depression angle.

Constant-volume balloon (tetroon) flights tracked by radar across Columbus, Ohio, in March 1969, illustrate the effect of a city on the nighttime airflow at heights of 100–200 m. On the average, the urban influence on wind direction is small at a height of 100 m, but an anticyclonic turning of 10° is observed at 200 m. The anticyclonic turning is greater under inversion than under lapse conditions and greater after midnight than before; it appears to result both from an increase in the frictional force due to increased vertical mixing and from a mesoscale high pressure system formed aloft as the result of the warmer temperatures within the city. The decrease in wind speed across the city averages nearly 20% of the upwind speed under lapse conditions but is very small under inversion conditions. In both cases the region of maximum deceleration tilts downwind with height. The average upward air motion exceeds 4 cm sec−1 above the down-town area under light wind conditions, and increases to 1 m sec−...

A series of experimental tests have been performed in which the Doppler characteristics of radar sea return at C band were measured. Both monostatic and bistatic sea return at small depression angles with both horizontal and vertical polarizations have been measured. The mean Doppler shift of the radar sea return for horizontal polarization is 2 to 4 times as great as the Doppler shift for vertical polarization for the same or similar wind and wave conditions. The vertical-polarization Doppler shift is dependent on the wave height and is directly related to the orbital velocity of the gravity waves. The horizontal-polarization Doppler shift is dependent on the wave height and the wind velocity jointly and is directly related to the motion of a surface layer of the sea. This surface velocity is the sum of two velocities: the orbital velocity of the sea moving beneath this layer and a function of the wind velocity. For both polarizations, the mean Doppler shift is cosine-law dependent on the angle between the wind and wave direction and the radar propagation direction. The spectrum bandwidth is, however, relatively independent of this viewing angle. For small depression angles, the Doppler shift and the spectrum bandwidth is independent of the radar depression angle. For both horizontal and vertical polarizations, the spectrum bandwidth is directly dependent on the mean Doppler shift obtained looking into the wind and waves. Within the conditions measured, there is no dependence of the Doppler shift or the spectrum bandwidth on bistatic conditions. Thus, the results given above apply both to monostatic and to bistatic radar configurations within the conditions measured.

Data from a combined radar-radiometer in a satellite should permit improved prediction of surface atmospheric pressure, winds, and ocean wave spectra on a global basis, with consequent advantages to shipping. Radar returns from the sea at 2.25-cm wavelength have been measured and shown to be proportioned to windspeed. Use of a microwave radiometer should permit removing false radar data caused by atmospheric attenuation since the radiometric temperature is highly sensitive to such attenuation.

Several workers have reported enhanced radar echoes, from regions well above the freezing level, in layer-type rain clouds. Usually, there is a decrease with time in the height of these ‘upper bands,’ as Bowen has called such enhanced echoes. This paper describes an investigation into upper bands which has been made at Cambridge, using a 3-cm radar with a vertically directed beam. The mean downward velocity of upper bands at a height 9,000 ft above the freezing level is found to be about 20 ft/sec, the velocity generally decreasing systematically with time. Such velocities are much greater than the rate of fall of the ice particles which are shown to be responsible for the upper-band echoes, which, it is suggested, are produced by precipitation streaks in a region of vertical wind shear. A simple theory is worked out which gives the apparent rate of fall of an upper band in terms of vertical wind shear, the horizontal wind speed near the cloud top, and the terminal velocity of the ice particles forming the precipitation streak. Measured values of the fall speed of upper bands agree reasonably well with those predicted by this theory. A previous theory of upper bands (Bowen 1951) is shown to be untenable, though it is possible that the upper bands observed by Bowen in Australia have a different origin from those observed at Cambridge. It is proposed to make further observations to settle this question.

During May and early June of 1963, 88 tetroon-transponder flights were made at relatively low level in the Los Angeles Basin. Five different tetroon release sites were utilized, extending from Point Dume northwest of Los Angeles to Sunset Beach southeast of Los Angeles. The tetroons, and attached transponders, were positioned at 3-min. intervals by means of the newly installed Weather Bureau WSR–57 radar on Blackjack Mountain, Catalina. Through the use of transponders the problem of ground clutter was eliminated, and tetroon positions were obtained at ranges exceeding 50 mi. even when the tetroon was only a few feet above the ground. More than 400 hr. of tetroon-tracking time were obtained, with the longest single track of 21 hr. duration. In general, the wind speeds derived from successive tetroon positions were small, averaging 4.4 kt. for all flights and only 2.4 kt. for flights released from Corral Beach. Aircraft tracking on more than 20 of the flights confirmed that the mean tetroon floatin...

The paper describes a new system of meteorological sounding employing secondary-radar principles. Pressure, temperature and humidity are each telemetered to an accuracy of one-thousandth part of their operating range, although the elements at present used may not be capable of measuring the meteorological parameters to this degree of accuracy. In addition, wind speed and direction are automatically measured. The maximum slant range of the system is about 100 miles, and thus the height to which soundings and wind measurements can be made is, at present, largely limited by the height at which the balloon carrying the instruments bursts.

This paper summarizes measurements of the characteristics of precipitation clutter. The goal was to provide for the radar engineer a description of the spectrum, the spatial uniformity, and the frequency correlation properties of precipitation echoes. These experiments resulted in a more complete description of the clutter characteristics than has heretofore been available. The wind shear phenomenon was found to have a dominant effect on the spectra at distant ranges. An analytical model for the spectral width is suggested. Other results show that the mean backscatter cross section is rarely uniform in space and that the frequency correlation characteristics confirm the theory predicting that echoes from pulses separated in frequency by at least the reciprocal of the pulse width are uncorrelated.

Apart from its normal functions in aviation the applications of radar have been few. In the post-war period T.R.E., in conjunction with the Meteorological Office, have been making a study of possible uses of radar to the science of meteorology and the results of these investigations are described in this paper. In the experimental work radar has been used to: — (a) investigate precipitation, (b) detect clouds dangerous to flying, (c) measure cloud height, and (d) measure wind speed and direction. An account is given of how radar may be used to measure the density of the atmosphere at altitudes up to many tens of miles and of some problems still to be solved in the design of a radar sonde system for measuring pressure, temperature and humidity profiles. It is concluded that radar will become an established meteorological tool and some possible profitable future lines of research are indicated.

A wind tunnel with water as a lower surface has been used to obtain experimental data on the statistical distributions of facet size in relationship to wind velocity, facet slope, and flatness tolerance. Flatness tolerance is defined as one-tenth of the radar wavelength. Using the above experimental data, calculations are presented which, for the first time, relate the upwind-to-downwind ratio of radar return with radar beam depression angle for various wind velocities and radar wavelengths. Comparison with available sea-clutter measurements are made. It is concluded that the concept of facet size in relationship to flatness tolerance and slope distribution is useful for describing a rough surface from which radar waves are reflected.

THE structure of isothermal and inversion layers in the troposphere is of interest in many aspects of radiometeorology. These layers, which can often be detected by centimetric radar, are now known to occur more frequently than many workers had previously thought1,2. They are usually associated with large variations in humidity and therefore in radio refractive index. Consequently, they often cause relatively strong reflexion or scattering in very high frequency radio propagation beyond the horizon. The structure of these layers and the nature of atmospheric turbulence within and near them are, however, complex subjects on which much further research is required. We summarize here some preliminary experiments (carried out by the Radio and Space Research Station in October 1968 at Cardington, Bedfordshire) in which simultaneous soundings of elevated inversion layers were made with balloon-borne refractometers and thermometers and ground-based lidar (pulsed laser). Some earlier experiments3 showed that stratified echoes, possibly associated with inversions, could be detected by lidar probing of the troposphere. The purpose of our experiments was to study the precise location of the aerosols causing the lidar echo in relation to large changes in the vertical distribution of refractive index, temperature and wind velocity. Such information is valuable in developing improved models of tropospheric structure and in extending theories of turbulent motion.

Eight iceberg trajectories observed by the U.S. Coast Guard during 1965, 1967, and 1968 have been subjected to preliminary analysis. The data were obtained by tracking the icebergs relative to fixed reference markers using visual bearings and radar ranges. Speed ratios and drift angles were calculated for each half hour of iceberg trajectory. It was found that at low wind speeds the effects of permanent currents, older wind-driven currents, and tidal currents predominate over wind drag and new wind-driven currents, whereas at wind speeds of over 10 knots the wind has a significant effect on the drift of an iceberg. The ratio of the drag coefficient for the iceberg's above-water portion to the drag coefficient for its submerged portion was found to range from 1.5 to approximately 7.

The concept of utilizing sound waves as reflectors for pulsed Doppler radar as a means for measuring wind velocity, turbulence, and air temperature has been examined theoretically. Any extension of the initial and successful, small scale experiments performed by Midwest Research Institute to a practical system for atmospheric probing is shown to require a change in the operating concept of the acoustic system. This change involves the abandoning of the concept of coherent reflection reinforcement from a multiple wave train and the substitution of reflection from a single acoustic shock front with the introduction of coherent integration of the pulsed Doppler radar signal. A preliminary experimental approach to a practical system is proposed.

A lidar study of the dispersion of the effluent from the tall (245-m) stacks of Keystone Generating Station in western Pennsylvania was conducted with the aid of two field experiments in May and October 1968. The observations, which were mostly obtained during stable conditions in the morning hours, reveal in detail the important plume characteristics that must be included in a realistic diffusion model for plumes from tall stacks: 1. (1) fanning and tilting due to wind veering with height. 2. (2) fumigation, which brings high concentrations to ground level in a pattern which, because of the tilting, progresses with time from the left to the right of the plume looking downwind. 3. (3) plume trapping by elevated stable layers. A comparison between the predictions of the Briggs/ASME plume rise formula and the lidar observations for 17 cases when temperature profiles were available gave a mean absolute difference of 30 m. A secondary experiment involving two sets of lidar plume measurements when the electrostatic precipitators at the power plant were all and half in operation, furnished estimates of 86 and 97 per cent for the precipitator efficiency on two separate days, compared with the rated value of 99 per cent. To investigate the potential of lidar for making quantitative measurements, a sample attenuation-corrected cross section of absolute mass concentration was computed on the basis of Mie scattering theory and independent particle size measurements. The integrated mass per unit plume length represented by this cross section was 680 gm−1, compared to 875 g m−1 calculated from the power-plant data and wind speed.

Sound waves from a number of low‐energy explosions at altitudes between 175 000 and 330 000 ft were detected by a square microphone array. The sound waves were incident on the earth's surface at angles between 60 and 86 deg. The altitude of the explosion as calculated by ray‐tracing techniques agreed within 1% with the radar altitude. Frequency spectra of the detected N waves are presented. The mean wind velocity between 60–95 km was determined from the known source location and the azimuth of the detected sound wave.

A body of experimental radio and meteorological data taken over Cardigan Bay, on the British west coast, is examined to ascertain how radar propagation is affected by the microwave duct lying next to the sea surface. The boundary-layer meteorological profiles are analyzed in terms of a semi-empirical relation due to E. L. Deacon, and propagation is predicted according to a method of S. A. Schelkunoff. At three-cm wave-lengths, it is found that the agreement between observation and theory becomes steadily better as wind speed increases, until at speeds above 15 mi/hr (7 m/s) the consistency is truly striking. At lower wind speeds there is a definite tendency to follow the theoretical pattern, but a great deal of scatter is noted. Possible explanations for this scatter are offered. More scatter is observed at nine cm than at three cm, and the transition to trapping conditions is less definite. The nine-cm waves appear to “feel” the effects of the duct some time before trapping occurs. An interpretation is offered of the fact noted by McPetrie and Starnecki that, in general, high signals are associated with large positive air-sea temperature differences, while low signals are accompanied by large negative differences. Also, Jones' observation that, under unstable conditions, high winds are accompanied by high signals is nicely explained.

VARIOUS workers have tried measuring the roughness of the sea by observing wave heights at a particular position as well as by compiling wave profiles along large distances by air observations. Glitter photographs of the sea surface have also been statistically analysed for finding the relation between development of wavelets and wind velocity. It has been recognized that description of sea roughness is very difficult by any of the above means. On the other hand, it is well known that radar clutter increases in amplitude with sea roughness, and estimation of sea roughness should be possible by observations of radar clutter. Recently, one aspect of analysis of sea roughness became imperative in view of the hypothesis that microseisms may be caused by means of interaction of wind and sea roughness. According to such ideas, the periods observed in microseisms should correspond to any autocorrelativ periods in sea roughness.