The 3rd Northern Forum FWG Meeting:
Investigation of Ice River Cover With Radio Echo Sounding And Gps Technology
By Professor A.V.Omelyanenko,
Chief of Geophisics
The N.V. Cherskiy Institute of Mining in the North of SD of RAS
Each year floods and consequences of ice-blockings cause big losses to the economics, especially to agricultural areas, which lie in the valleys of large rivers flowing into northern seas. Therefore, organization of monitoring of ice-cover condition using hydrological and geophysical services is extremely urgent topic of today.
Nowadays, the appropriate services have no effective methods to look under the blocked ice and study its structure. It is impossible to realize the well-known methods of measuring when studying the thin, destructed, and pack ice under real conditions. And there is no another way of measuring but using remote methods when studying the moving ice. Besides, watching of quickly changing situations, with formation of long and vast ice-blocks, require reliable information to make quick technological decisions on ice-blocks prevention and liquidation.
In the world practice of remote geophysical studies of ice, the method of georadiolocation is counted for the most prospective. For the last two decades, a large amount of work was done to create underground and underwater sounding radiolocators. The current georadiolocation systems are mostly for sounding from the surface of the medium being studied.
The scientific research institute named after Tikhomirov is famous in the field of inventing and industrial production of modern georadiolocation equipment. The specialized aero-ice-measuring georadiolocator invented in the research institute is an advanced model of OKO-M1 georadiolocators (GPR). It has magnetic antennas, which create H z and E ? field of rotating polarization. This allows to study the ice of exterior and interior hummocking, as well as to receive signals reflected from the upper and lower ends of plunged ice-block more than 20- 60 meters thick. The invention of high-speed receive-and-report canal, high-speed hindrance protective protocol of information exchange between antenna signal processor and microprocessor of analysis block made it possible to make aerial shooting with the flight speed of up to 160 km/h .
A complex system georadiolocator – GPS – was invented to realize monitoring of ice-cover condition and to compound measuring data bank. In this way, as a result of improved parameters of the equipment and scientifically proved choice of georadiolocational sounding regimes, it is possible to provide effective research of ice-cover construction and thickness during floods.
The research of snow cover influence on the results of radiolocational soundings was made on test profile 1 300 m long, and laid across the river Lena in the region of hydrological post “Tabaga”. Soundings on this profile were made with the antennas hanging 0,8 m above the ice surface. The results of radiolocational soundings show that the ice thickness varies along the profile from 125 to 178 cm . Also, there is a tendency of ice getting thicker from the coastal zones to fairway. Along with this, it was noted that signal reflected from the border of air-snow is 3-4 times fainter than the one reflected from the border of snow-ice. Consequently, snow-cover is not an obstacle to radiolocational measurement of ice covers of rivers and water bodies. The repeated ice drilling and hydrological analysis show that radiolocation measuring of ice thickness is recorded to within 1%.
The analysis of spectral characteristics of georadiolocational signals proved the possibility of effective discern of structure and construction of ice-cover of rivers according to the peculiarities of amplitude and frequency - phase spectrum of signals.
Large-scale aero-ice-measuring georadiolocational shooting of the rivers Lena and Olekma were made in the springs of 2002-2005. The measuring was made along the fairway and many transverse profiles.
In the picture No. 3 you can see a general result of ice-blocking research on the river Lena in the spring of 2003. the three mutually crossed profiles illustrate the ice-block. The ice thickness increases two times in the distance of 150 m . The measuring of pack ice formations thicknesses allows to estimate the mass of the ice in ice-blocking process. On the left part of the illustration you can see geophysical presentation of the profile's part with thick pack ice.
The need to receive the information on ice situation during floods, quick and comfortable in use, determined the invention of specialized data process algorithm and a package of programs for real-time receipt of the measuring results, i.e. during the flight, in the process of measuring. The algorithm of software includes the blocks of collation procedures, visualization, and editing, selecting upper and lower borders of ice, corrections reflected signals time delay, counting the flight trajectory, printing out the results of measuring as a chart of the ice thickness distribution along the route.
The results of georadiolocation measuring are put into the data base for comparative analysis with the cycles of the previous studies. The routes of studies in years and seasons are put on the map of the studied part of the river. The routes are divided into pieces presented as the sailing directions with the indication of bar charts of ice thickness in years and seasons. The bar charts are presented on the most crucial parts of the route, usually along coasts and fairway. When it is needed to study the structure if ice, the parts of the route are given as radar charts with the deciphering of results. The further detailed elaboration is made on the level of reprocessing of data and statistical analysis of data base.
The aero-ice-measuring shooting equipment was tested under natural conditions and adopted on production base of the scientific research institute of Tikhomirov .
The methods of the work went through industrial approbation in 2002 and was introduced in industry in 2003. Georadiolocation monitoring technologies are recommended for broad introduction in practice of Emergency Control Ministry of Russia. |
