用雷达电磁波探测研究南极冰盖浅层散射特征：以中山站至Dome A冰盖断面为例

SCATTERING FEATURES ANALYSES OF THE SHALLOW ANTARCTIC ICE SHEET BASED ON ICE-PENETRATING RADAR METHOD:A CASE-STUDY ALONG THE ZHONGSHAN STATION-DOME A TRANSECT

本研究运用双频雷达(60MHz和179MHz)获取的南极中山站—Dome A断面的雷达回波探测数据,对冰盖浅部100—700m的雷达内部反射层和接收功率变化定量计算分析表明,60MHz的雷达回波能量比179MHz衰减得更快;中山站—Dome A断面冰盖浅层700m以上的雷达反射层形成的主导原因是冰密度的变化;断面上不同测站点间同一深度的接收功率差值达到10dB,表明冰盖浅层散射存在显著差异。

Radio-echo detecting ice sheet is one of the most significant progresses in Antarctic ice sheet researches in recent 20 years. Ice-penetrating radar is a convenient and significant method to image and analyze the properties of Antarctic ice sheet internal structure. This research used the two-frequency （60 MHz and 179 MHz） radar to detect the radar internal reflection strata. The variations of the received power within 100--700 m of the ice sheet surface along the Zhongshan-Dome A transect showed that： the received power PR for both frequencies de- creased with depth; comparing to 179 MHz, the radar echo energy attenuation of 60 MHz radar antenna was greater; PR form the same depth fluctuated along the transect： at 60 MHz, the fluctuation was within 5 dB from Dome A site to DT401 site, increased to about 10 dB from DT401 site to ZStation site, at 179 MHz, the trend was the same, but the amplitude was smaller. The radar reflection strata could be traced to several kilometers, even to several tens of kil- ometers, the radar reflection strata of 60 MHz was clearer comparing to 179 MHz in all region along Zhongshan-Dome A transect; the continuity and horizontal uniformity of the radar reflec- tion strata was clear in the vicinity of the dome; the strata in the DT085 region was distorted, which indicated that the interference pattern had changed, resulting in the non-linear change of depth and thickness of the strata; the ice-bedrock interface was obvious in the vicinity of ZSta- tion region as the thickness in this area was only 367 m. The dominant cause of the reflection within top 100--700 m region was changes in ice density across strata： at 400 m, APR is con- sistently to 10dB, with fluctuations of a few dB, which meant that the permittivity-based reflections dominated ; at 700 m, the mean tendency of APa is between 0 dB and 10 dB, suggesting that both the density and acidity variations affected the reflection pattern ; at 1000 m, the aver- age tendency was almost the same as in 700 m, because I000 m depth area belongs to deep ice sheet, the leading cause of the reflection were acidity and crystal-orientation fabrics changes. The research conducted the correlation analyses between scattering variations and the deposi- tional environment condition of ice sheet surface, including different ice thickness, changes in the surface slope and ice surface accumulation rate. The resuhs showed that the correlation was not very close. And the correlation between variations of Radarsat-1 backscatter values and the received power was not very strong. The conclusions were valuable and significative to many Antarctic Glaciology researches, such as determining suitable ice-coring locations and under- standing the scattering mechanism that dominates in the ice sheet along the Zhongshan-Dome A transect.