Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
复制标题
DOI：
10.5194/tc-11-2003-2017
复制
发表时间：
2017-09
期刊：
影响因子：
--
通讯作者：
J. Fürst;F. Gillet‐Chaulet;T. Benham;J. Dowdeswell;M. Grabiec;F. Navarro;R. Pettersson;G. Moholdt;C. Nuth;Björn-Lukas Saß;K. Aas;X. Fettweis;C. Lang;T. Seehaus;M. Braun
中科院分区：
文献类型：
--
作者：
J. Fürst;F. Gillet‐Chaulet;T. Benham;J. Dowdeswell;M. Grabiec;F. Navarro;R. Pettersson;G. Moholdt;C. Nuth;Björn-Lukas Saß;K. Aas;X. Fettweis;C. Lang;T. Seehaus;M. Braun
抽象。大多数冰川和冰帽下面的基底地形基本上是未知的，人们已经进行了许多尝试，以根据表面上其他更容易获得的信息来估计厚度场。在这里，我们提出了一个两步重建的方法，冰厚度，解决了质量守恒在单个或多个连接的流域。该方法适用于各种测试几何形状，丰富的厚度测量，包括海洋和陆地终止冰川以及2400平方公里的冰帽斯瓦尔巴特群岛。第一步的输入要求保持在最低限度。在这一步中，一个几何控制，非本地通量的解决方案被转换成厚度值依赖于浅冰近似（SIA）。在第二步中，厚度场更新沿着快速流动的冰川树干的速度观测的基础上。这两个步骤都考虑了可用的厚度测量。每个厚度场的误差估计地图的基础上正式传播的输入不确定性。这些误差估计指出，厚度场是最不受约束的冰分裂附近或在其他停滞区。保留厚度测量的份额，误差估计倾向于在中值意义上高估失配值。我们还必须接受在非常稀疏或没有观测的冰川的重建厚度场中至少25%的总不确定性。对于Vestfonna冰帽（维克），先前基于此处使用的相同测量记录的冰量估计值必须向上校正22%。我们还发现，13%的冰盖面积实际上是在海平面以下。从直接测量插值得到的前5%估计值超过了从此处的误差估计值推断出的6- 23%的总最大范围。
Abstract. The basal topography is largely unknown beneath most glaciers and ice caps, and many attempts have been made to estimate a thickness field from other more accessible information at the surface. Here, we present a two-step reconstruction approach for ice thickness that solves mass conservation over single or several connected drainage basins. The approach is applied to a variety of test geometries with abundant thickness measurements including marine- and land-terminating glaciers as well as a 2400 km2 ice cap on Svalbard. The input requirements are kept to a minimum for the first step. In this step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation (SIA). In a second step, the thickness field is updated along fast-flowing glacier trunks on the basis of velocity observations. Both steps account for available thickness measurements. Each thickness field is presented together with an error-estimate map based on a formal propagation of input uncertainties. These error estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. Withholding a share of the thickness measurements, error estimates tend to overestimate mismatch values in a median sense. We also have to accept an aggregate uncertainty of at least 25 % in the reconstructed thickness field for glaciers with very sparse or no observations. For Vestfonna ice cap (VIC), a previous ice volume estimate based on the same measurement record as used here has to be corrected upward by 22 %. We also find that a 13 % area fraction of the ice cap is in fact grounded below sea level. The former 5 % estimate from a direct measurement interpolation exceeds an aggregate maximum range of 6–23 % as inferred from the error estimates here.