Modern Topics in Microwave Propagation and Air-Sea Interaction

Long-term measurements of field strength have been performed over a 160 km path entirely over sea in the Baltic area. For short periods the radio measurements have been combined with meteorolo gical measurements in order to describe the structure of the re fractive index field. The heigth of layers was continously deter mined by remote sensing techniques and their thickness and inten sity by airborne and balloonborne instruments. From these data, field strengths have been calculated for scatter, reflection and duct propagation. It will be shown that reflection propagation dominates at the low frequency end. Whilst at higher frequencies, very sharp layers are required for reflection propagation. At these frequencies, high signals are generally caused by duct propagation. 1.1 Instruments and plan for the experiments. The radio measurements were performed with the following equipment. 5000 MHz: Transmitted power 500 kW (pulsed). Reflector antennas. Free space field strength over the path + 15 dBm. 460 MHz: Transmitted power 10 W (CW) 8 element Yagi antennas. Free space field strength over the path - 65 dBm. 170 MHz: Transmitted power 10, W(CW). 8 element Yagi antennas. Free space field strength over the path - 60 dBm. The antenna heights for the transmitters and receivers were 100 m above sea level. The field strengths were recorded on ink recorders and simul taneously sampled, digitized and evaluated on line in a minicom puter. For the meteorological measurements, the following equipment were used: Airborne microwave refractometer and thermistor, flown up to 2000 m.

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Proceedings of the NATO Advanced Study Institute, Sorrento, Italy, June 5-14, 1973

Contenu
Opening Session.- Introductory speech.- Welcome address.- Introductory lecture/Some aspects of modern radiometeorology.- I Group / Air-Sea Interaction and Ducting: Meteorological and Radiometeorological Aspects.- The physical processes of air-sea interactions: a review.- Present state of knowledge on evaporation from the sea and numerical analysis/forecasting of water vapor pressure in the surface layers of the air.- Preliminary observation of the evaporation duct in the I.M.S.T. air-sea wind tunnel.- The dynamics of water vapor flux in the marine boundary layer.- The structure of the atmospheric boundary layer at sea.- About the need of a standard technique to compute atmospheric refractive index from radiosonde data.- Determination of the wind stratification by scatter propagation methods on 7 and 16 GHz.- Turbulent transport and refractive index structure immediately above the air-sea interface.- II Group / Air-Sea Interaction and Ducting: Radiopropagation Aspects.- The structure of moisture and temperature profiles in the near-surface layers, their variability and effects on radar propagation as demonstrated with ray tracing techniques.- State and limits of prediction methods of radar wave propagation conditions over sea.- Characteristics and applications of line- of-sight duct propagation.- Propagation theory for the evaporation duct.- Oceanic duct and its effects on microwave propagation in the Mediterranean Sea.- Transmission of millimeter radio waves in over water ducts.- Diffraction of radio waves by terrain obstacles in radio ducts.- Interference lobes pattern connected to a ground based radar duct.- The Occurrence of very high field strengths at beyond the horizon propagation over sea in the frequency range 605000 MHZ.- III Group / Atmospheric Influence onRadio Propagation Above 10 GHz: Communication Aspects.- Communications requirements at frequencies above 10 GHz and their correlation with propagation aspects.- Aspects in using frequencies bands above 10 GHz for satellite communication systems.- IV Group / Atmospheric Influence on Radio Propagation Above 10 GHz: E.M. Propagation Phenomena and Results.- Attenuation by rainfall in the sub-millimetre wave region.- Recent studies of visibility and atmospheric attenuation at optical wavelengths.- Some recent lidar experiments on particle scattering in the lower troposphere.- Radiometry, the structure of atmospheric spectrum lines, and related experiments.- Depolarization phenomena on electromagnetic waves through rain.- Analysis of the influence of the various parameters on the attenuation-rain rate relation.- Quantitative analysis of precipitations through radar techniques.- Reports of Working Groups.- Group A: Some general comments on the exchange and stability processes in the surface layer.- Group B: Concerning evaporation and intermittency.