The Study On The Subsurface Feature Detection And The Environment Evolution Of Juyanze Based On Remote Sensing Technology

Arid- Semi-arid region contains precious natural resources, being more sensitive to the global change. As one of the inland lakes with quite rich water storage capacity, the Jun yan Lake is deep in the hinterland of Eurasia, and it used to be a whole with the Gaxun Nur and the Sogo Nur. Since its drying up in the Ming Dynasty, the research area has been suffered from sand erosion, and the climate there turned out to be the extremely dry temperate continental desert climate with the exceedingly fragile ecological environment. Its environmental changes and basin evolution reflect the general rule of the arid area lakes‘ evolution, so to be significant to the study of global climate change and ecological reconstruction of ancient lake.This article started from the variation rule of the water and salt different from the lake shore to the lake center, and then established a water-salt dielectric model using the measured data based on the surface roughness quantification and regional surface temperature inversion. Through the comprehensive analysis of the water, salt and particle size distribution of the sample points, we revealed the dielectric properties of the ancient lake. With the help of radar remote sensing technology and optical remote sensing technology, we then quantitatively characterized the radar penetrating phenomena after the evaluation of the radar penetration depth on the basis of dielectric permittivity. This evaluation work was based on the mechanism of radar electromagnetic wave propagation and the backscattering coefficient analysis. For the next, we used the SRTM DEM data and Optical Stimulated Luminescence Dating dating(OSL) data with the ArcGIS Spatial Analyst tools to complete the quantitative reconstruction of the Chak transitional area. After the study, the main conclusions are listed below:(1) Both from the surface to the subsurface in the vertical direction, and the lake shore to the lake center in the horizontal direction, the water and salt content show an increasing trend with the significant step. But the change is more obvious in the horizontal direction than in the horizontal direction. This result links directly which the low rainfall and strong evapotranspiration climate in the research area. The roughness calculation result shows that the research area is the rough ground surface kind, and the RMS(mean square root) height ranged 0.1913 cm ~ 3.8101 cm, the correlation length ranged 2.7708 cm ~ 29.6745cm; The particle size analytical result(medium mechanical composition) indicates that the regional sedimentary environment is more complex and more seriously eroded by wind and sand. So the surface roughness is not appropriate to be the fundamental indicator of the research on the causes of the environment.(2) To get a more accurate dielectric constant of the surface and the subsurface, this article established a model suitable for medium dielectric model of the research area combining the Dobson semi-empirical model and the Stogryn model. The major factors of the water and salt medium dielectric properties were analyzed using theory, simulation data and measured data. And we found that salinity has little effect on the real part of the dielectric constant, and it is consistent with the change of water content. Besides, both the moisture content and the salt content can affect the imaginary part of the dielectric constant, in which the dielectric constant is more sensitive to the salinity.(3)We used the actual sample point monitoring parameter values to launch the extended application of a universal penetration depth quantitative model that based on the disseminate basic theory and the actual conditions of the area. The result show that, the C-band Radarsat-2 radar signals can penetrate the surface and reach the subsurface interface. The maximum vertical penetration depth is 55.1cm. By comparison with the backscattering coefficient and water content, the depth of penetration is of a weak negative correlation with the HV polarization backscatter coefficient and the water content. This illuminates that the backscatter energy of the synthetic aperture radar is under the help of the subsurface media.(4) Comparing comprehensively the shore levee elevation measuring data and OSL dating data, based on the SRTM DEM data of 90-meter resolution, and using GIS spatial analysis method, the environmental evolution of Juyanze ancient lake basin district can be divided into the following several stages: middle Pleistocene(~400ka) had high lake-level and only the area of Juyanze was 3933 km2; late Pleistocene epoch(~35ka BP) had uniform large lake covering Juyanze, Sogo Nur and Gaxun Nur(~926m), whose area was 6475.4789 km2; When it was Early Holocene epoch, the lakes were drought and there weren‘t any lacustrine embankments; Mid-holocene(4.59~2.73 ka BP) Jyanze, Sogo Nur and Gaxun Nur were mutual independent, and the water in the lakes reduced to 917 m around; uniform lake wasn‘t formed until Late Holocene, and the area was 6689.1204 km2, which is obvious that the climate was moist and the environment of lakes were good.(5) Juyanze had tended to dry up in the Ming dynasty period, and the center of the lake had a salt precipitation with a serious desertification. Gaxun Nur had dried up until modern age(1961 autumn), and the bigger lake than others in the researching district were Sogo Nur and Swan Lake whose natural environment was not cheerful. The author holds that this is the result of comprehensive function of topography depositing, tectonic uplifting, climate changing and human activity and predicts the future environment in Juyanze according to local climate features and scientific survey. If there isn‘t any human ntervention, it might be covered by flowing sand dune.