Pointcatcher software: analysis of glacial time-lapse photography and integration with multitemporal digital elevation models
Pointcatcher software: analysis of glacial time-lapse photography and integration with multitemporal digital elevation models
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DOI：
10.1017/jog.2016.27
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发表时间：
2016-02
影响因子：
3.4
通讯作者：
M. James;P. How;P. Wynn
中科院分区：
文献类型：
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作者：
M. James;P. How;P. Wynn
地面延时摄影通过高空间和时间分辨率的图像提供了对冰川过程的深入了解。然而，倾斜的相机视图使地理坐标中的测量复杂化，并且导致依赖于特定的成像几何形状或简化用于计算参数（例如冰速度）的假设。我们开发了一种新的方法，将延时图像与多时相DEM相结合，以获得整个单视场图像序列中跟踪的自然特征的完整三维坐标。这使得每天能够独立测量水平（冰流）和垂直（冰融）速度。通过将两个地面激光扫描仪测量与冰岛Sólheimajökull的73天序列相结合，在~25天的时间尺度内确定了~10%的水平冰速度变化。约3.0 m的表面高程的整体下降显示出与水平速度变化不同步的速率变化，表明冰面下降过程与冰川运动机制之间存在时间上的脱节。我们的软件，“Pointcatcher”，是免费提供的用户友好的一般时间推移序列的交互式处理，包括蒙特卡洛误差分析和不确定性投影到DEM表面。它特别适合于具有挑战性的倾斜冰川图像的分析，我们讨论了良好的功能跟踪，无论是校正相机运动和推导冰的速度。
ABSTRACT Terrestrial time-lapse photography offers insight into glacial processes through high spatial and temporal resolution imagery. However, oblique camera views complicate measurement in geographic coordinates, and lead to reliance on specific imaging geometries or simplifying assumptions for calculating parameters such as ice velocity. We develop a novel approach that integrates time-lapse imagery with multitemporal DEMs to derive full three-dimensional coordinates for natural features tracked throughout a monoscopic image sequence. This enables daily independent measurement of horizontal (ice flow) and vertical (ice melt) velocities. By combining two terrestrial laser scanner surveys with a 73 days sequence from Sólheimajökull, Iceland, variations in horizontal ice velocity of ~10% were identified over timescales of ~25 days. An overall decrease of ~3.0 m surface elevation showed asynchronous rate changes with the horizontal velocity variations, demonstrating a temporal disconnect between the processes of ice surface lowering and mechanisms of glacier movement. Our software, ‘Pointcatcher’, is freely available for user-friendly interactive processing of general time-lapse sequences and includes Monte Carlo error analysis and uncertainty in projection onto DEM surfaces. It is particularly suited for analysis of challenging oblique glacial imagery, and we discuss good features to track, both for correction of camera motion and for deriving ice velocities.