ИСТИНА

Massive ice sheets (Antarctic, Greenland etc.) play a key role in terrestrial climate due to accumulation of huge mass of water and heat, and also significantly contribute in radiative balance due to their high albedo. In addition, their stratigraphy keeps record of climate of past millenia, which can provide valuable insight in the climatic evolution and history of Earth. For these reasons, deep interior of ice sheets is extensively studied. Ground Penetrating Radar (GPR) [1] is a wellestablished geophysical technique employed for that for more than five decades. Mars, as a planet of terrestrial group, has its own water cycle and its polar ice caps, like terrestrial ones, are thought to carry a record of Martian climatic history for several millions of Martian years. The long period climatic variations are in turn related to secular evolution of the orbital elements of Mars, which is of interest for astronomical applications. In addition, the polar caps are considered as a possible water source for future manned missions. Since beginning of this century, orbital GPR experiments MARSIS and SHARAD are in operation. Besides of research objectives mentioned above, Martian polar layered deposits (PLD) proved to be very attractive radar targets for several reasons. Unlike all the rest of Martian surface, they appeared to be very penetrable for radar signals. Surface of the PLDs, especially the North one, is remarkably smooth, greatly reducing the radar clutter. Nearly horizontal solar incidence angles, typical for polar latitudes, result in rather thin ionosphere which distorts wide band radar signals not too much and allows radar operation at relatively low frequencies. In addition, polar areas are prevalently observed due to highly inclined orbits of the spacecrafts. Because of that, these two martian radar experiments stimulated encouraging progress in martian polar science resulting in many published papers. Currently, significant interest of the planetary community is attracted to the icy moons of giant planets. According to modern geological views, many of them are covered with many kilometers thick icy crust with a global liquid water layer (i.e. ocean) beneath. Immediate radar probing of these icy crusts is a great challenge for the planetology and radar science. Since the end of the last century, the problem has been repeatedly discussed. Successful probing of Jovian icy moons at relatively high frequencies (several MHz) can be prevented by high signal loss in thick lossy ice and side echoes coming from rough icy surface. Operation at lower frequencies would require a large antenna system, which may be impossible for interplanetary spacecraft. However, these limitations can be overcome with a passive radar using Jovian magnetospheric noise as a source [2]. In this talk, theoretical simulations of passive and active radar sounding of Jovian icy moons are presented. In addition, radiative transfer approach to the radar probing of Martian PLD is discussed with application to the SHARAD experimental data. The research is carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University [3]. Support from Russian Science Foundation with the grant 17-77-20087, MPS and DAAD is kindly acknowledged. REFERENCES 1. Bogorodsky, V., C. Bentley, and P. Gudmandsen, Radioglaciology, Reidel, Dordrecht, 1985. 2. Hartogh, P., and Y. A. Ilyushin, “A passive low frequency instrument for radio wave sounding the subsurface oceans of the Jovian icy moons: An instrument concept: Planetary and Space Science, Vol. 130, 30–39, 2016. 3. Sadovnichy, V. A., A. Tikhonravov, Vl. Voevodin, and V. Opanasenko “Lomonosov”: Supercomputing at Moscow State University”. In Contemporary High Performance Computing: From Petascale toward Exascale, Boca Raton, USA, 2013.