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1.
《中国科学:地球科学》2021,(7)
北极海冰是地球气候系统的重要因子,获取精确的海冰厚度及其变化信息对于开展北极和全球变化研究等有着重要的意义.卫星测高是获取连续、大范围海冰厚度的主要方法之一.冰间水道识别是卫星测高方法估算海冰厚度的关键之一.基于CryoSat-2数据,利用遥感影像对两种主要的冰间水道识别方法进行了对比,发现波形特征法能够更好地识别冰间水道.考虑到雷达信号对海冰表面积雪的不完全穿透,对海冰干舷-厚度转化模型进行了优化,通过选取合适的输入参数,获取了2010年11月至2019年12月北极海冰厚度,并利用IceBridge海冰厚度产品和仰视声呐数据对计算结果进行了验证,结果表明本文海冰厚度解算精度优于0.2m.最后,结合PIOMAS海冰模式数据、北极气温和海表面温度数据对北极海冰厚度变化特征进行了分析,发现2014年北极海冰厚度出现剧烈增长的现象. 相似文献
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水库冰气泡含量和密度对探地雷达测厚的影响分析(英文) 总被引：2，自引：0，他引：2
在水库现场试验了RIS K2型探地雷达探测水库冰厚度的能力,试验时所用天线频率为600MHz;同步钻孔测量雷达探测处的冰厚度;以及在一个点上取样测试分析冰晶体、冰内气泡和冰密度。试验时冰面积雪厚度0.03-0.05m,冰层上部有0.24m粒状冰,其下均为柱状冰;冰内气泡含量呈表层高底层低分布;冰密度随气泡含量变化;冰厚度在平面内不均一。通过探测厚度和实测厚度的对比分析以及气泡含量对介电系数影响的理论分析,建立了积雪、粒状冰和柱状冰三层介质模型,获取雷达波在冰内的理论传递时间。结果发现:能够利用等效介电常数或等效传播速度评价雷达波传递时间,结冰期冰层1/3深度处的对应介电常数或传递速度可以作为等效值;另外因冰内大气泡造成的理论传递时间大于雷达探测时间,其差值随理论传递时间或冰厚的增加呈非线性增加。 相似文献
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北冰洋海冰厚度穿透雷达探测与下表面形态特征分析 总被引：10，自引：2，他引：10
通过对北冰洋海冰穿透雷达的探测与分析, 讨论了雷达电磁波探测海冰厚度和海冰下表面形态特征的能力. 结果表明, 雷达波可穿透超过6 m厚度的北极盛夏海冰, 雷达波在海冰内的传播速度是0.142~0.154 m/ns. 雷达图像表现出海冰下表面粗糙起伏的微形态特征, 这种微形态特征与海冰类型关系紧密, 反映出雷达探测有助于识别和划分海冰类型. 基于雷达图像同时显示海冰上、下界线的特点, 统计分析了二者界线实际长度的差异, 提出一个新的长度因子数值概念, 可用于海冰上、下表面面积差异的研究. 相似文献
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基于2019—2020期间在盘锦市含章湖利用浮式观测平台开展湖冰原型观测试验,分析不同因素对湖冰变化造成的影响.结果表明:99 d冰期内湖冰的生消过程可概述为:湖泊封冻(3 d)—稳定生长(62 d)—冰厚稳定(7 d)—加速消融(24 d)—破碎分解(3d).生长期冰厚的平均增长速率为0.4 cm/d,最大冰厚为30.7 cm;不同深度(5～17 cm)冰温对气温变化的响应存在滞后性,滞后时间为70～158 min,冰温与气温的最大相关系数为0.52～0.89;降雨过程造成冰面反照率由0.22降至0.09,影响了冰内温度以及冰下40 cm以内的浅层水温,但14 mm的降雨量并未引起表面冰厚增加;降雪过程造成冰面反照率由0.25升至0.90,同时阻碍了 5 cm以内的浅层冰温对气温变化的响应,但风速长时间大于8 m/s时会导致冰面积雪被吹散,冰面重新裸露;消融期冰厚的衰减过程呈抛物线趋势,存在显著的加速过程,融化速率由0.3 cm/d逐渐增加到2.7 cm/d;湖冰生长期的冰底热通量均值为4.8 W/m~2;到消融期增加至8.1 W/m~2,为生长期的1.7倍;太阳辐射与湖冰边界侧向融化是导致湖冰加速融化的关键因素.本研究填补了国内湖冰冻融全过程实测资料的空缺,为湖冰热力学模型的改进提供了科学支撑. 相似文献
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冰盖厚度是研究南极冰盖质量、建立冰盖动力学模型的基本参数,对于冰川均衡调整、冰盖物质平衡及全球气候变化研究具有重要意义.基于地震学的远震接收函数和H-Kappa格网搜索方法可以用于地震台站下方冰盖厚度的可靠探测,不仅能与冰雷达获得的冰盖厚度进行独立对比,还可以与冰雷达方法相互补充,进一步填补南极大陆冰盖厚度探测空白区.本文利用布设于南极大陆冰盖上方的流动地震台阵记录到的远震波形数据,基于接收函数方法对台阵下方的冰盖厚度进行了研究.结果显示:基于远震接收函数方法的冰盖厚度与Bedmap2冰厚格网模型相比,二者差别大多在200 m以内;少数台站差值达到600 m左右,这一差别可能与Bedmap2测线分布空区、冰雷达测深不确定性以及冰盖内部复杂波速结构等因素有关.本文研究结果表明:利用南极大陆冰盖上方的流动地震台阵,基于远震接收函数方法可以获得比较可靠的南极冰盖厚度,为独立验证冰雷达的探测结果并弥补冰雷达探测空白区提供了有效方法.同时,部分台站接收函数波形的复杂性可能暗示了南极大陆数千米厚的冰盖内部结构不是均一的,仍然存在比较复杂的内部结构变化.因此,有必要进一步利用包括接收函数波形拟合、地震面波反演等方法对南极大陆冰盖厚度及其内部精细结构进行更为深入的研究. 相似文献
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湖冰厚度是湖泊在封冻期的重要物理参数,明晰其时空变化特征对于认识气候变暖背景下的湖冰响应规律具有重要的理论价值和现实意义.基于ERA5 Climate Reanalysis气温数据集、MODIS MOD09GQ数据产品和2019年湖冰钻孔测厚数据及雷达测厚数据,重建2000—2019年青海湖冰厚时间序列并分析其时空变化特征.结果表明:①2019年3月实测青海湖湖冰厚度平均增长速率为0.30 cm/d,高于2月份(0.12 cm/d).基于度日法湖冰生长模型模拟的2018年11月—2019年3月青海湖冰厚平均增长速率为0.34 cm/d,与实际观测数据相比,模拟冰厚误差为±2 cm,但在河流入湖口处和湖区南侧误差较大,且冰厚模拟数值在3月中旬前高估而之后有所低估.②青海湖多年平均冰厚介于32～37 cm,其中2008—2016年湖冰厚度年际变化剧烈,呈现先增大再稳定后减小的趋势.冻结初期湖冰厚度增长迅速,12月和1月湖冰增长速率分别为0.45和0.41 cm/d,2月后冰厚增长速率放缓,2月和3月分别为0.29和0.14 cm/d.③2000—2019年冰厚整体呈现北厚南薄、东厚西薄的空间格局,多年冰厚变化幅度湖区西部较东部稳定,湖冰平均厚度与完全封冻时长及封冻期呈正相关. 相似文献
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《地球物理学进展》2017,(6)
为了检验自主研发的地面瞬变电磁探测系统(GPTEM)的稳定性和实际野外工作性能,在吉林省公主岭市附近开展了地面瞬变电磁探测系统与国外商业仪器系统各组成部分的全面对比试验.试验中,进行了两套仪器使用各自的常规装置展开单点传感器噪声对比、实测数据对比和整套仪器系统的稳定性和一致性对比.并在同一感应电动势-衰减时间(V-T)的坐标下考察两者的关断时间、感应电动势的幅值、曲线的光滑程度和衰减速率以及尾期信号的抗干扰度等硬性指标来衡量仪器的性能.试验分别进行了以下对比方案:(1)GPTEM和GDP-32Ⅱ传感器静态噪声对比;(2)GPTEM和GDP-32Ⅱ传感器实测数据对比;(3)GPTEM和GDP-32Ⅱ整套发射-接收系统性能对比.最后对GPTEM和GDP-32Ⅱ系统采集数据进行反演,并通过和测井资料对比,验证了采集结果的正确性.试验分析表明,自主研发的地面瞬变电磁探测系统具有稳定性较好、抗干扰能力强、对异常体具有较强的分辨能力等优点,已经达到和在某些方面已经优于国外同类产品的性能,能够很好胜任野外实际勘察工作. 相似文献
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本文对大地电磁感应的场源效应进行了较详细的研究.用线电流为场源,均匀大地和三层结构为构造模型进行了计算,其结果与均匀场源的感应作了对比.场源效应受场源高度、信号周期、电阻率、测点距离等的影响.为了能更深入的了解和控制这影响,本文提出了“阻抗平均法”,该方法对消减场源效应有一定作用,使平面波的解释继续有效. 相似文献
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利用中国第4~6次北极考察获得的北冰洋中心区(80°~88°N))GPS探空资料和NCEP再分析资料,分析了大气垂直结构、边界层参数的变化特征及其与海冰和温度变化的关系.结果表明,2010、2012和2014年夏季北冰洋中心区的对流层顶、边界层高度、逆温强度及风速和风向的垂直结构均存在明显差异.通过分析1979~2014年9月温度与海冰范围变化的关系,解释了其差异的原因.2012年9月北极海冰范围最小,减少了44%,具有明显的增温过程.2010年和2014海冰分别减少了22.6%和17%,出现的是降温过程.对比2种过程反映出海冰变化对大气边界层结构有重要影响.近30年北冰洋中心区(80°~90°N)1000和850hPa的温度变化呈显著的升温趋势,并与海冰范围呈显著的负相关.表明北极海冰的持续减少,会使地表至对流层中层持续增温. 相似文献
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Guo Jingxue Sun Bo Tian Gang 《应用地球物理》2007,4(3):214-220
As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m. 相似文献
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Lasse Rabenstein Stefan HendricksJohn Lobach Christian Haas 《Journal of Applied Geophysics》2011,75(1):87-98
In this paper, the noise sources of an airborne electromagnetic frequency domain instrument used to measure sea-ice thickness are studied. The antennas are mounted on the wings of an aircraft. The paper presents real data examples showing that strong noise limited the accuracy of the thickness measurement to ± 0.5 m in the best case. Even drift correction and frequency ?ltering did not reduce the noise to a level necessary for sea ice thickness measurements with an accuracy of 0.1 m. We show results of 3D ?nite element modeling of the coupling between transmitter and receiver coils and the aircraft, which indicate that wing ?exure is the primary cause of the strong noise. Wing de?ection angles below 5° relative to the fuselage are large enough to cause changes higher than the wanted signal from the seawater under the ice. Wing ?exure noise can be divided into an inductive and geometric contribution, both of the same order. Most of the wing ?exure signal appears on the inphase component only, hence the quadrature component should be taken for sea ice thickness retrievals when wing ?exure is present even when the inphase produces a larger ocean signal. Results also show that pitch and roll movements of the aircraft and electromagnetic coupling between seawater and aircraft can contribute signi?cantly to the total noise. For ?ight heights of 30 m over the ocean these effects can change the signal by about 10% or more. For highly quantitative measurements like sea-ice thickness all these effects must be taken into account. We conclude that a ?xed wing electromagnetic instrument for the purpose of measurements in a centimeter scale must include instrumentation to measure the relative position of the antenna coils with an accuracy of 1/10 mm. Furthermore the antenna separation distance should be as large as possible in order to increase the measured ratio of secondary to primary magnetic field strength. 相似文献
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We investigate helicopter electromagnetic (HEM) inversion schemes applied to synthetic and measured HEM sea ice profiling data. Direct HEM data-to-ice-thickness inversion is compared to three different formal, least squares layered earth inversion algorithms.By making several approximations, it is possible to directly invert a single channel measurement (i.e., the in-phase or quadrature component of a single frequency measurement) to obtain an estimate of sea ice thickness. Measurements from multiple input channels, however, can be used in a layered earth inversion to simultaneously recover several model parameters such as sea ice thickness, sea ice conductivity and sub-ice bathymetry. Synthetic data sets for a particular two-frequency HEM system showed that simple least squares inversion algorithms produce reliable estimates of sea ice thickness in cases where the ice is thicker than 3 m. These methods could also recover acceptable estimates of sea ice thickness when a thin, conductive, partially melted sea ice layer was present, and could determine shallow, sub-ice bathymetry in brackish water. As expected, 1D transformations and inversions of synthetic data for a three-dimensional pressure ridge keel structure contained artifacts, notably broadening of the apparent width of the keel.Prior to inverting a field data set acquired over rather thin (~ 0.5 m) Antarctic sea ice, we found it necessary to recalibrate the phase angle of the measurements using a phasor diagram-based method. Direct transformation of a single channel from the recalibrated data set produced more accurate estimates of sea-ice thickness than formal inversion of multi-channel data. We suggest that the least squares inversion methods are inferior in this situation because of the particular characteristics of the two-frequency HEM system used in this evaluation; the extreme differences in sensitivity of high and low frequency data components, the overall low sensitivity to sea ice conductivity (especially for thin ice), and the partially low signal-to noise ratios of the measurements. The data sets used in this study will be made available to the public to allow alternate inversion approaches to be applied and evaluated. It is suggested that inclusion of parameter bounds and other forms of regularization could help to improve the inversion results. 相似文献
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Characteristics and distribution patterns of snow and meteoric ice in the Weddell Sea and their contribution to the mass balance of sea ice 总被引：2，自引：0，他引：2
Based on snow- and ice-thickness measurements at >11 000 points augmented by snow- and icecore studies during 4 expeditions from 1986 - 92 in the Weddell Sea, we describe characteristics and distribution patterns of snow and meteoric ice and assess their importance for the mass balance of sea ice. For first-year ice (FY) in the central and eastern Weddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker snow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepage into the snow pack, snow salinities averaged 4‰. Through 18O measurements the distribution of meteoric ice (i.e. precipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean density of 290 kg/m3, the snow cover itself contributes 8% to total ice mass (7% FY, 11% SY). Analysis of
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JERRY C. RITCHIE THOMAS J. JACKSON JURGEN D. GARBRECHT EARL H. GRISSINGER JOSEPH B. MURPHEY JAMES H. EVERITT 《水文科学杂志》2013,58(5):403-416
Abstract Vertical surface properties of the landscape were measured using a laser altimeter mounted in a small twin-engine aeroplane. The laser altimeter makes 4000 measurements per second with a vertical recording precision of 0.05 m for a single measurement. These airborne laser measurements were analysed to provide information on topography, vegetation canopy and stream and gully cross-sections. Laser altimeter data were used to measure small (less than 0.20 m deep) and large gullies and stream cross-sections. Vegetation canopy heights, cover, structure and distribution were determined in studies in Texas and Arizona. Laser measurements of vegetation cover and height were significantly correlated with ground measurements made with line-intercept methods. While conventional ground-based techniques may be used to make all these measurements, airborne laser altimeter techniques allow the data to be collected in a quick and efficient way over large and inaccessible areas. The airborne laser altimeter data can also help quantify various land surface parameters needed for natural resource and landscape management or required by hydrological simulation models. Measurements of landscape properties over large areas provide a better understanding of landscape functions and can lead to the development of better management plans to conserve and improve the productivity of natural resources. 相似文献
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Observational estimation of heat budgets on drifting ice and open water over the Arctic Ocean 总被引：9，自引：0，他引：9
It is of major scientific interests to determine the parameters of momentum, heat and vapor exchange in the planetary boundary layer in order to study the effects of ocean-ice-atmosphere interactions and their feedback mechanisms on global climate[1]. Lin… 相似文献
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The effect of sea-ice on various aspects of the Southern Hemisphere (SH) extratropical climate is examined. Two simulations using the LMD GCM are performed: a control run with the observed sea-ice distribution and an anomaly run in which all SH sea-ice is replaced by open ocean. When sea-ice is removed, the mean sea level pressure displays anomalies predominantly negatives near the Antarctic coast. In general, the meridional temperature gradient is reduced over most of the Southern Ocean, the polar jet is weaker and the sea level pressure rises equatorward of the control ice edge. The high frequency filtered standard deviation of both the sea level pressure and the 300-hPa geopotential height decreases over the southern Pacific and southwestern Atlantic oceans, especially to the north of the ice edge (as prescribed in the control). In contrast, over the Indian Ocean the perturbed simulation exhibits less variability equatorward of about 50°S and increased variability to the south. The zonal averages of the zonal and eddy potential and kinetic energies were evaluated. The effect of removing sea-ice is to diminish the available potential energy of the mean zonal flow, the available potential energy of the perturbations, the kinetic energy of the growing disturbances and the kinetic energy of the mean zonal flow over most of the Southern Ocean. The zonally averaged intensity of the subpolar trough and the rate of the baroclinic energy conversions are also weaker. 相似文献
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To model ice conditions in the eastern Gulf of Finland, a high-resolution three-dimensional hydrodynamic model is coupled with the advanced sea-ice model HELMI (Haapala et al., 2005). To test the model in extreme situations, the ice pattern in the eastern Gulf of Finland was simulated for a mild ice winter (2007–2008) and for a moderate one (2003–2004). The reference runs were performed on the assumption that the ice in the model domain is fast ice if the sea depth is less than 10 m. Using this assumption, the ice thickness averaged over the Neva Bay (the easternmost part of the Gulf of Finland) is overestimated by the model for almost the entire wintertime in the mild winter and during the ice formation and melting periods in the moderate winter, as compared with the thickness reported in ice charts. 相似文献
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Changes of mean annual net accumulation at the surface on the grounded ice sheets of East Antarctica, West Antarctica and Greenland in response to variations in sea ice extent are estimated using grid-point values 100 km apart. The data bases are assembled principally by bilinear interpolation of remotely sensed brightness temperature (Nimbus-5 ESMR, Nimbus-7 SMMR), surface temperature (Nimbus-7 THIR), and surface elevation (ERS-1 radar altimeter). These data, complemented by field data where remotely sensed data are not available, are used in multivariate analyses in which mean annual accumulation (derived from firn emissivity) is the dependent variable; the independent variables are latitude, surface elevation, mean annual surface temperature, and mean annual distance to open ocean (as a source of energy and moisture). The last is the shortest distance measured between a grid point and the mean annual position of the 10% sea ice concentration boundary, and is used as an index of changes in sea ice extent as well as of mean concentration. Stepwise correlation analyses indicate that variations in sea ice extent of ± 50 km would lead to changes in accumulation inversely of ± 4% on East Antarctica, ± 10% on West Antarctica, and ±4% on Greenland. These results are compared with those obtained in a previous study using visually interpolated values from contoured compilations of field data; they substantiate the findings for the Antarctic ice sheets (±4% on East Antarctica, ±9% in West Antarctica), and suggest a reduction by one half of the probable change of accumulation on Greenland (from ±8%). The results also suggest a reduction of the combined contribution to sea level variability to ±0.19 mm a-1 (from ±0.22 mm a-1). 相似文献