V.A. Malyshev – Dr.Sc.(Eng.), Professor, 

Department of Common Military Discipline, MESC «Zhukovsky–Gagarin Air Force Academy» (Voronezh) E-mail: vamalyshev@list.ru

V.G. Mashkov – Ph.D.(Eng.), Associate Professor, Dr.Sc.Candidate, 

Department of Operation of Radio Equipment (Flight Support), MESC «Zhukovsky–Gagarin Air Force Academy» (Voronezh) E-mail: mvgblaze@mail.ru

The accuracy of measuring the depth of snow and the thickness of the ice cover when landing a helicopter type aircraft (HTA) on an unprepared snow and the ice pad directly affects the level flight safety. Landing on the snow-covered pond with snow depth above the permissible or thickness the ice cover below the permissible may lead to falling through the snow, ice, or overturn HTA day and night in simple and adverse weather conditions (fog, haze, rain, snow, dust, or smoke the atmosphere), and also in conditions of raised snow rotating screw. The need for such a landing may be caused, for example, by the delivery goods, search and rescue operations, and the evacuation the wounded.

When measuring the depth snow and ice cover thickness using radar, its accuracy will depend on the accuracy measuring the time delay and the propagation speed the electromagnetic wave (EW) in a medium other than the EW propagation speed in a vacuum c  2,99792458 10 8 m/s, depending on its dielectric constant. A snow-ice surface is a three-component medium that is a mixture ice

with water and air inclusions. In turn, the dielectric constant the snow-ice underlying surface, depending on the density and proportion water content, will vary significantly. Since, for example, the actual part the static permittivity melt water mw s  87,9 , and dry dense ice (without air inclusions) di 3,200,02 .

The results calculations the electromagnetic wave propagation velocity in dry snow Vds  278,1...212,7 m/µs, dry firn

Vdf  212,7...189,0 m/µs and dry ice Vdi 189,0...167,9 m/µs showed a very noticeable change depending on the density, the percentage water content, the preferred orientation and the form ice and air inclusions in the snow.

The estimates the complex relative permittivity the medium that determines the speed EW propagation show a noticeable influence the density, the percentage water content, and structure of the underlying surface (snow, firn, and ice), which makes it possible to identify the layers the underlying surface in order to remotely determine the possibility landing the HTA on an unprepared site with snow and ice cover.

When the percentage water content in the medium Pw  0 , which is typical for negative temperatures, the rate EW propagation in the medium will depend only on the density the medium and the structure this medium, for dry ice in the small range 1 m/µs from the temperature Tdi  1...40C . In dry snow, vertical and horizontal elongated or spherical inclusions make a significant contribution to changing the EW propagation rate. At zero temperature, in the frequency range f  2...8 GHz , will play a decisive role in the rate EW propagation in the medium Vr the percentage water content in the medium Pw , the density r and structure the medium.

The purpose this article is determine the change ranges speed electromagnetic waves in a snow-icy the underlying surface depending on the density, structure, percentage water content to restore the structure the snow and ice according to radar sensing, a more accurate determination the depth snow and thickness ice cover used in the assessment the ability to perform a safe landing HTA on an unprepared ground with snow-ice cover.

Thus, the knowledge EW propagation velocity intervals for dry snow, firn, and ice and the availability remote measurement propagation velocity EW propagation speed in the medium Vr , the average density the medium r а , as well as the average percentage water content in the medium Pw а can be estimated, which will allow remote identification the medium (underlying surface), more accurately determine the depth the snow and the thickness the ice cover, in order to perform a safe landing the HTA on an unprepared site with snow and ice cover.

When the percentage water content in the medium Pw  0 , for medium temperature Tr  0C , which is typical, for example, for

Arctic territories, the task identifying the medium (underlying surface) is simplified, since the speed EW propagation in the medium Vr will depend only on the density the r and the structure these mediums.

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