Theory and Practice of Tropospheric Sounding by Radar

Friend, A. W.

doi:10.1109/jrproc.1949.230936

Cited by 37 publications

(13 citation statements)

References 6 publications

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“…On the other hand, partial reflection from stratified stable layers was also proposed (Röttger and Liu, 1978;Gage and Green, 1978;Röttger, 1980b). This mechanism was also speculated by Friend (1949), Friis et al (1957), Misme et al (1958) and Saxton et al (1964), for example, to explain radio wave propagation beyond the horizon. The theory shows that this mechanism occurs especially at low radar frequencies, primarily depending on the thickness and shape of the layer, as stressed by Woodman and Chu (1989).…”

Section: Various Interpretations Of Aspect Sensitive Echoing Layersmentioning

confidence: 77%

Temperature sheets and aspect sensitive radar echoes

Luce

Crochet

Dalaudier³

2001

Ann. Geophys.

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Abstract. There have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution insitu temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very highresolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d'Aéronomie (CNRS, France) for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or meso-scale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics of the ST radar echoes with a particular emphasis on recent works. Their possible coupling with stable sheets is then presented and their known characteristics are described with some hypotheses concernCorrespondence to: H. Luce (luce@kurasc.kyoto-u.ac.jp) ing their generation mechanisms. Finally, measurement campaigns that took recently place or will be carried out in the near future for improving our knowledge of these small-scale structures are presented briefly.

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Section: Various Interpretations Of Aspect Sensitive Echoing Layersmentioning

confidence: 77%

Temperature sheets and aspect sensitive radar echoes

Luce

Crochet

Dalaudier³

2001

Ann. Geophys.

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“…If the horizontal dimension of a single stratified layer extends beyond the first Fresnel zone, the received power P• at vertical incidence from a flat and horizontal reflecting layer at r range is given by the basic relation [Friend, 1949] ...................... Table 1).…”

Section: Limited Horizontal Extent Effectsmentioning

confidence: 99%

Interpretation of VHF ST radar vertical echoes from in situ temperature sheet observations

Luce¹,

Crochet²,

Dalaudier³

et al. 1995

Radio Science

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The interpretation of the radar aspect sensitivity observed at VHF frequencies in the lower atmosphere is still a subject of controversy in the radar community. Indeed, scattering from anisotropic turbulence layers and partial reflection from stable thin horizontally stratified layers are generally proposed without leading to a definitive conclusion. A cause of this persistent discussion has been a lack of in situ high‐resolution observations which could identify and describe accurately the atmospheric structures at the origin of the radar aspect sensitivity. The Radars, Scidar and Balloons (RASCIBA 90) campaign (February‐March 1990, Aire sur l'Adour, France) was performed using simultaneously colocated VHF ST radars and balloon experiments. The objective was to obtain information about the small‐scale structures of the lower atmosphere and then to identify the origin of radar echoes. The main result was produced by the high vertical resolution (20 cm) temperature measurements. For the first time, very strong (positive) temperature gradients within thin layers were detected in the lower atmosphere (at least up to 27 km). Such an observation allowed then investigation of the partial reflection interpretation using available bifrequency radar measurements: a 45‐MHz radar for which typical 15‐dB vertical enhancement is observed just above the tropopause and a 72.5‐MHz radar for which an aspect sensitivity of the same order is presented for the first time at this frequency. A simple model considering flat and very extended sheets was assumed to estimate quantitatively the possible contribution of these temperature gradients to the VHF radar vertical power. Radar and reconstructed power reflection coefficient profiles are in good agreement in shape and in level showing that partial reflection from atmospheric sheets is an important and generally dominant process at vertical incidence. Furthermore, the effect of sheets of limited extent is investigated using simple theoretical considerations, and this model shows that the correction to the infinite sheet approximation is probably weak. The sheet distortion effect is also approximately evaluated applying Gaussian rough models. The power loss from the flat sheet case at VHF in the vertical direction is weak for a mean roughness height lower than a few tens of centimeters and for larger heights if the correlation length of the irregularities is larger than a few hundreds of meters. Sheet generation mechanisms are also briefly discussed using two previously published models: the viscosity wave model (Hocking et al., 1991) and “sheet and layer” model (Gossard et al., 1985). Neither of the models in their present forms seems to be able to account for the observations.

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“…Alternatively, the scattering can be from sharp changes in the index of refraction over distances of the order of a radar wavelength. The distinction between these types of scattering becomes less clear as the dimension of the scattering volume along the radar line of sight is reduced, as might be the case in a narrow turbulent layer (see Booker and Gordon [1950] and Friend [1949] for detailed discussions of EM scattering).…”

Section: Scattering From Neutralsmentioning

confidence: 99%

A review of radar studies of the middle atmosphere

Harper¹,

Gordon²

1980

Radio Science

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This paper reviews radar studies of the middle atmosphere at VHF and UHF frequencies. The mechanisms responsible for the scattering at both stratospheric and mesospheric heights are qualitatively discussed, and an attempt is made to evaluate the potential of the technique for inferring atmospheric parameters. A few applications of the technique to the study of atmospheric dynamics are then presented. Finally, some recommendations are made for future work.

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Theory and Practice of Tropospheric Sounding by Radar

Cited by 37 publications

References 6 publications

Temperature sheets and aspect sensitive radar echoes

Temperature sheets and aspect sensitive radar echoes

Interpretation of VHF ST radar vertical echoes from in situ temperature sheet observations

A review of radar studies of the middle atmosphere

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