Frank D. Eaton

A new frequency‐modulated continuous wave radar for studying planetary boundary layer morphology

This paper describes a new generation frequency-modulated continuous wave (FMCW) radar using state-of-the-art electronics and computerized data processing that greatly enhance the use of the radar as a practical tool for atmospheric research. The system senses at high resolution (∼2-m range and 12 s for obtaining each profile), has ultrasensitivity (< −165 dBm), and is accurately calibrated for the refractive index structure parameter (C2n). The authors present salient features, discuss the calibration procedure, and present and discuss examples of various types of fine detail wave and frontal activity, boundary layer convection, and a light winter storm sensed by the radar over the last 2 years. The authors also show associated data from radiosonde and tower-mounted sensors that are relevant to the episodal events shown from the FMCW radar observations. Since the FMCW radar technique can resolve and sense individual insects, these point targets are shown to act as tracers and enhance flow visualization.

Preliminary estimates of the vertical profiles of inner and outer scales from White Sands Missile Range, New Mexico, VHF radar observations

There are very few reliable results of the inner and outer scales of turbulence in the remote atmosphere. Knowledge of these parameters is of high interest to the propagation and remote sensing communities. Seasonal profiles from 5 to 20 km above mean sea level of the inner scale have been estimated based on the kinematic viscosity and eddy dissipation rates which were determined from 5 years of nearly continuous 49.25-MHz radar observations at White Sands Missile Range, New Mexico. Inner scale values were found to increase from about 1 cm at 5 km to near 7 cm at 19 km altitude. Outer scale profile determinations were made using a method proposed by Tatarskii [1971] that involves vertical wind shear and the eddy dissipation rate, both derived from the longterm VHF radar measurements. The outer scale decreased from about 60 m at 5 km altitude for all seasons to 12–20 m at 15 km (depending on season) and then increased to 22 m at 19 km. Seasonal differences in the inner and outer scales and background meteorological conditions are also presented and discussed.

Short term variability of atmospheric turbidity and optical turbulence in a desert environment

SummaryVariability of atmospheric turbidity calculated from direct beam solar radiation measurements and the transverse coherence length,r0, derived from differential image motion of stellar sources show pronounced fluctuations on the order of a few minutes under convectively unstable conditions in a desert environment. The quiescent periods, “neutral” events, when local near surface adiabatic conditions occur show substantial reductions in the fluctuations of the same quantities. Image motion results for nighttime (stable) conditions display slowing varying patterns with reduced short term (few minutes) variations.The measurements were taken using a suite of instrumentation probing the same volume of atmosphere. The instrumentation used includes a pyrheliometer, Atmospheric Turbulence Measurement and Observation System (ATMOS), a sodar, a scintillometer, and tower- mounted sensors. A time-height display of sodar data calibrated for the refractive index structure parameter,Cn2, coupled with scintillometer measurements show the diurnal evolution of the boundary layer responding to the local heating-cooling cycle and drainage flows from the surrounding mountains. Several atmospheric features are seen and discussed in these results as they affect the nature of the patterns of turbidity andr0. Of particular interests are the development of convection, changes in the capping inversion, thermal plume structures, neutral events, and wave-turbulence interactions. Sinusoidal oscillations, identified as internal gravity waves, are seen in the nighttime laminated structures.

EXPOSURE-TIME EFFECTS ON DIFFERENTIAL R0 MEASUREMENTS

Experimental results are presented indicating a causal effect between exposure time of the detection system and variations in measured differential stellar image motion. The variability is also dependent on atmospheric winds encountered along the entire propagation path at the precise time of measurement, making explicit comparison of experimental results with theory impractical. Earlier theoretical development is recast in terms of Frieds seeing parameter r0, and collected data is tested for conformance to stationarity criteria. It is recommended that atmospheric turbulence seeing monitors based on differential image motion measurements be restricted to exposure times of not more than two milliseconds.

Phase Structure Function Measurements With Multiple Apertures

A newly-developed Atmospheric Turbulence Measurement and Observation System (ATMOS) was equipped with multiple apertures, allowing the phase structure function to be determined experimentally. Data was obtained with the ATMOS under two conditions: (a) over a horizontal path with a laser source, and (b) from near-vertical viewing of stellar sources. This data was compared to measurements of the refractive index structure parameter (Cn2) obtained from scintillometers, spatially separated temperature probes, and anemometers. The existence of the Kolmogorov spectrum of turbulence during the measurement period will be discussed as well as the relevance of the results on the transverse coherence length, r0. The optical arrangement, as well as data collection and analysis methods, are also outlined.

Anew High Speed Two-Dimensional Ccd Atmospheric Turbulence Monitor

A new atmospheric turbulence monitor utilizes relative motion between dual images of a single star, formed by two subapertures of a Schmidt-Cassegrain telescope, to calculate Frieds atmospheric seeing parameter, r0. Dual images are formed on a two-dimensional CCD array, and intensity at each pixel location is digitized for calculations by the host computer. Flexibility in frame rate, exposure time, and data processing are incorporated into the system design through extensive use of programmable array logic, state machines, and microcomputer control. The equipment eliminates many problems characteristic of current systems which use one-dimensional detectors and a single image.

The U.S. Army atmospheric profiler research facility - A preliminary view

The U.S. Army Atmospheric Sciences Laboratory has established a unique atmospheric research facility at White Sands Missile Range (WSMR), New Mexico. The Atmospheric Profiler Research Facility (APRF) monitors three primary atmospheric parameters: wind (speed and direction), refractive index structure parameter C-squared(n), and ambient temperature. The APRF includes a suite of high-performance (temporal and spatial resolution) phased-array, multiple reflector, and multiple aperture type atmospheric profilers. Specialized and standard surface and balloon-borne instrumentation are deployed to provide local ground truth, comparison, and calibration data. The Facility achieves a high-resolution height coverage to about 20 km. The products of the APRF support research applications, including research and development testbed analyses, imaging and propagation system design and testing, meteorological and earth-observation satellite ground comparison, and environmental forecasting improvement at WSMR. The design and capabilities of the APRF are described. Preliminary measured and derived atmospheric parameters as well as initial comparisons are presented.

Atmospheric measurements of Cn2 and comparisons between atmospheric profiler and aircraft anemometer measurements for clear, daytime conditions

A joint radar/aircraft optical turbulence measurement is discussed. The joint measurement was made over White Sands, New Mexico with a KC135E aircraft equipped with fiber film temperature probes and a ground-based atmospheric profiler. General meteorological conditions were such that the turbulence on the day of the experiment was fairly weak. Emphasis was placed on the 36,000 ft to 42,000 ft altitude regime. Results showed good agreement between the atmospheric profiler and the aircraft-based measurements.

Wind measurements from Doppler radar profilers and rawinsondes: a comparison of 50-MHz and 404-MHz profilers and rawinsonde data at White Sands Missile Range

Wind measurements derived from collocated VHF and UHF Doppler radar profilers were analyzed for statistical trends in vertical and horizontal variability. Nearly continuous-6-min data from 20 March through 30 April 1991 are analyzed and also compared with rawinsonde data. Consistency of wind data from these three sources is discussed.