Georadar survey of the crash site Chebarkul of the meteorite fragment "Chelyabinsk"

V.V. Kopeikin, P.A. Morozov A.V. Popov (IZMIRAN), S.V. Merkulov (VNIISMI), V.A. Alekseev (TRINITY)

According to witnesses one of the largest meteorite fragments "Chelyabinsk" February 15, 2013 fell in the western part of the lake Chebarkul, leaving in the ice oval wormwood sized 6x8 meters.

Attempts to find a meteorite in the bottom of the lake in the vicinity of open water were unsuccessful, although scientists and local residents removed from the hole using a magnet small fragments with significant iron content. The depth of the lake in the vicinity of a meteorite about 10 meters, divers made it difficult to work the thick layer of loose silt, reaching at their estimated depth two or more meters.

To clarify the probable location of the Chebarcul fragment, was carried out a remote sensing of the lake bottom with GPR "Loza-H", developed at the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation. NV Pushkov (IZMIRAN) Ltd. and produced by VNIISMI

The principle of operation is based on the GPR radiation of ultra-wideband electromagnetic pulses in the underlying environment and recording their reflections from the interfaces between the layers or objects

A distinctive feature of the instrument series "LOZA", compared with foreign and domestic counterparts, is a great energy potential, allowing to work in environments with high conductivity, such as clay loam or wet

The probe pulse is generated by high-voltage gas discharge tube (5-10 kV) and radiated resistor loaded dipole antenna length of 0.5 to 6 meters.A similar antenna is used in the receiver

«LOZA-В»,

«LOZA-Н»,

Depending on the model of the device and environment settings probing depth ranges from a few to hundreds of meters

During the three days of field work (12-14 March 2013) the expedition IZMIRAN-VNIISMI produced 36 GPR profiles length of 100-150 m in the area of the meteorite. The grid covers the wormwood and the area of 100x100 m to the west of it. Sounding produced from the surface of the ice allowed restore a detailed picture of the bottom topography and indicate the most likely place of occurrence of a meteorite or its fragments

Furthermore, in the area of incidence, water samples and the fine fraction of the ice fragments were collected for further analysis of the physico-chemical

Below is a sample representation of the raw data of GPR sensing program "Krot1301" developed VNIISMI. The right panel is a waveform pulses detected by the receiver in the selected GPR profile point (A-scan). With the passage of the track are formed in vertical sections (B-scan), shown in the two left panels. Horizontal postponed distance in meters vertically - the time of arrival of the reflected pulse in nanoseconds (right scale) and the estimated depth of the reflecting boundary (left scale)

Р602 Р603

Bands in the top of the picture correspond to the direct signal propagating from the transmitting to the receiving antenna at different speeds - in the air, in the thick snow and in the water beneath the ice. Underlying the broad bands correspond lengthy unipolar pulses reflected from a smooth transition from the sludge to the bottom of the solid rocks. Bands in the top of the picture correspond to the direct signal propagating from the transmitting to the receiving antenna at different speeds - in the air, in the thick snow and in the water beneath the ice. Underlying the broad bands correspond lengthy unipolar pulses reflected from a smooth transition from the sludge to the bottom of the solid rocks.

Noteworthy is a violation of the structure of the ice cover and a sharp drop in the bottom topography on the profile P602 at the intersection with the profile of R603.We interpret this anomaly as the result of a meteorite impact on the bottom of the lake. Noteworthy is a violation of the structure of the ice cover and a sharp drop in the bottom topography on the profile P602 at the intersection with the profile of R603.

Further confirmation of this hypothesis are the observational facts. Apparently, it is generally accepted that the Chebarkul meteorite fragments approached the lake in the north-east direction with an azimuth of 280-290 degrees inclined path. Therefore, look for it at the bottom of tracks necessary to the west of the polynya  (open areas in frozen seas). A small amount of the ejected ice around polynyas suggests that the bulk of its mass was infatuated with a meteorite, and then surfaced, breaking the structure of the ice cover over the funnel.

Based on this fact, we conducted a detailed areal sensing portion bottom situated between the shore and wormwood. Linear profiles processed by the program "Krot" and 3D reconstruction of the bottom topography reveal a dramatic deepening in this sector is likely caused by the fall of a meteorite fragment. Further confidence can give a comparison with the magnetic measurements