干旱区湖泊古环境多源重建与耦合研究

The process and mechanism of environmental change in paleolakes in arid regions of China are important as they involve the variation of regional water resource. Limited by chronological and geomorphological techniques,some scientific issues such as the age and extent of the megapaleolake in arid China during late Quaternary are still in debate. The project selects Lake Juyanze,a paleolake in the northwestern margin of the Badanjilin desert in Inner Mongolia,as the research object. The well preserved paleoshorelines and extensive Quaternary lacustrine sediments will be studied systematically in combination of geological and geomorphological investigations to confirm the spatial distribution and sedimentary characteristics.Optically Stimulated Luminescence(OSL) and AMS C-14 dating technologies will be integrated to determine the age of this paleolake.Furthermore,digital image processing technology will be introduced.Spectrum, backscattering coefficients, and polarization parameters based on optical and PolSAR images will be extracted to analyze the features of surface and subsurface in the paleolake basin.Image extracted parameters and measured parameters from horizontal and vertical dimensions will be compared to investigate the paleoenvironmental indications of the extracted parameters and their coupling relationships with measured parameters.Finally,DEM data will be analyzed by means of GIS spatial analysis technologies to reconstruct the lake level fluctuation history as well as the temporal and spatial evolution processes of Lake Juyanze.The evolutionary mechanisms will be presented by analyzing various climatic proxies and image extracted parameters.The research combines the advantages of both optical and PolSAR images, through visual interpretation and parameter extraction, being promising to explore a new clue for paleoenvironmental reconstruction.This project has significant implications not only for improving our knowledge of paleolake evolution and environmental change in Juyan region,but also for the sustainable development and utilization of water resource in this region.

干旱区湖泊环境变化的过程和机制涉及区域水资源变化，受年代学和传统地貌学等手段的限制，晚第四纪高湖面出现的年代与范围等方面存在争议。本项目选择内蒙古额济纳旗居延泽古湖湖岸地貌与湖泊沉积为研究对象，通过传统地貌调查和沉积岩芯代用指标分析，研究湖岸地貌和湖相沉积的空间分布及沉积特征，结合光释光和14C测年建立古湖岸线年代序列；在此基础上引入数字图像分析技术，基于光学和全极化雷达图像，提取影像光谱、后向散射系数和极化特征参数，分析各参数的变化特征，深化对地表、次地表特性的认识；通过影像提取参数与水平尺度研究剖面实测参数、与纵向尺度岩芯实测参数对比，探讨影像提取参数的古环境指示意义，寻求其与实测参数间的耦合关系；同时，利用DEM和GIS空间分析手段三维重建晚第四纪居延泽湖泊演化的时空过程，探讨湖泊演化的机制。研究对于深入理解干旱区晚第四纪环境演变的历史和机制、探索湖泊古环境重建的新途径具有重要意义。

以内蒙古额济纳旗居延泽古湖湖岸地貌与湖泊沉积为研究对象，综合利用地质地貌调查、释光测年、差分GPS（DGPS）测量和遥感数字图像分析等技术手段，研究居延泽湖岸地貌和湖相沉积的空间分布及沉积特征，确认居延泽大湖期和高湖面的形成年代、湖泊范围及中全新世的气候特点，重建晚第四纪居延泽湖泊演化的时空过程，探讨古湖盆区地表/次地表特征，分析影像提取参数与各实测参数间的内在联系，为揭示影像提取参数的古环境意义、深入理解干旱区晚第四纪环境演变的历史和机制提供参考。.研究表明，居延泽地区主要存在海拔~927 m、~924 m、~920 m、~918 m、~914 m 和~912 m共六个级别的古湖岸线。在覆盖深海氧同位素第5阶段（MIS5）大部分时段的 ~122 到73 ka期间，存在三次湖湘沉积序列。当湖面海拔为~927 m、深度为~33 m时，居延泽古湖范围可以达到1800 km2，湖面波动频繁，MIS5巨大古湖的存在可能是对末次间冰期湿润气候的一种响应。在末次冰期包括深海氧同位素第3阶段晚期并不存在稳定大湖，早全新世干涸、中晚全新世湖泊较稳定发育，呈现出与季风区湖泊演化模式明显不同的全新世成湖模式。基于RADARSAT-2雷达影像的土壤水分反演和极化分析表明，居延泽地区土壤水分在0.1% - 25% 之间，土壤含水量整体偏低，大部分地区低于10%。区域地表散射机制较为复杂，相对于湖盆边缘沙丘分布区而言，湖岸线分布区和湖盆内部区域散射机制相对简单，Cloude分解和Freeman-Durden分解均能较好地反映区域地表/次地表特征。单一极化参数与实测土壤水分和地表粗糙度之间的相关性并不明显，随着极化参数个数的增加，极化参数与实测参数之间的相关性稳步增加。组合极化参数和非线性拟合方法仅能够从一定程度上提高相关性，但 C波段雷达图像的极化参数并不适用于土壤水分和地表粗糙度等参数的精确推算。.由于居延泽地处无人区，自然条件极端恶劣，深入湖心的剖面线长度有限，影像提取参数与土壤参数等实测参数间的相关分析结果不甚理想，影像提取参数的环境指示意义尚需要进一步深入开展。