Assessing Scale Dependence on Local Sea Level Retrievals from Laser Altimetry Data over Sea Ice
Assessing Scale Dependence on Local Sea Level Retrievals from Laser Altimetry Data over Sea Ice
复制标题
DOI：
10.3390/rs12223732
复制
发表时间：
2020-11
期刊：
影响因子：
--
通讯作者：
Liuxi Tian;H. Xie;S. Ackley;Alberto M. Mestas-Nuñez
中科院分区：
文献类型：
--
作者：
Liuxi Tian;H. Xie;S. Ackley;Alberto M. Mestas-Nuñez
测量海冰高于海平面或“干舷”的高度取决于对当地海平面的准确恢复。当地海平面以前是通过最低高程方法仅从测高数据中提取的，其中使用了特定段长度尺度上最低海拔的百分比。在这里，我们使用美国宇航局2013年在罗斯海进行的冰桥行动(OIB)的数据，对这些当地海平面反演的尺度依赖性进行了评估。这是来自机载地形图测绘仪(ATM)的五个轨道上的激光高度计测量的独特数据集，巧合地具有来自数字测绘系统(DMS)的高空间分辨率图像，从而允许独立的海平面验证。首先通过使用通过使用相应的DMS图像识别的导线上的ATM L1B数据的平均海拔来计算当地海平面。然后，将所得到的本地海平面参考用作地面真实，以验证从ATM L2检索的本地海平面，方法是在五个ATM轨道中的每一个的七个不同分段长度尺度(1、5、10、15、20、25和50公里)下使用最低海拔的九个不同百分比(0.1%、0.5%、1%、1.5%、2%、2.5%、3%、3.5%和4%)。用与1：1直线的贴近度、R2和均方根误差(RMSE)来量化反演的准确性。结果发现，对于所有被测数据，所有线性最小二乘拟合度在每个尺度上都具有统计学意义(p<；0.05)。一般情况下，当分段长度尺度从1公里或5公里增加到50公里时，海平面反演离1：1线较远。我们发现，分段长度尺度比百分比尺度对检索精度的影响更大。根据我们的结果，大多数反演低估了当地的海平面；使用的分段长度(从1到50公里)越长，特别是在小百分比尺度上，误差往往越大。基于较高的R2和较小的RMSE，通过使用1-5公里路段长度处最低海拔的0.1-2%来反演所有轨道组合的最佳局部海平面。
The measurement of sea ice elevation above sea level or the “freeboard” depends upon an accurate retrieval of the local sea level. The local sea level has been previously retrieved from altimetry data alone by the lowest elevation method, where the percentage of the lowest elevations over a particular segment length scale was used. Here, we provide an evaluation of the scale dependence on these local sea level retrievals using data from NASA Operation IceBridge (OIB) which took place in the Ross Sea in 2013. This is a unique dataset of laser altimeter measurements over five tracks from the Airborne Topographic Mapper (ATM), with coincidently high-spatial resolution images from the Digital Mapping System (DMS), that allows for an independent sea level validation. The local sea level is first calculated by using the mean elevation of ATM L1B data over leads identified by using the corresponding DMS imagery. The resulting local sea level reference is then used as ground truth to validate the local sea levels retrieved from ATM L2 by using nine different percentages of the lowest elevation (0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, and 4%) at seven different segment length scales (1, 5, 10, 15, 20, 25, and 50 km) for each of the five ATM tracks. The closeness to the 1:1 line, R2, and root mean square error (RMSE) is used to quantify the accuracy of the retrievals. It is found that all linear least square fits are statistically significant (p < 0.05) using an F test at every scale for all tested data. In general, the sea level retrievals are farther away from the 1:1 line when the segment length scale increases from 1 or 5 to 50 km. We find that the retrieval accuracy is affected more by the segment length scale than the percentage scale. Based on our results, most retrievals underestimate the local sea level; the longer the segment length (from 1 to 50 km) used, especially at small percentage scales, the larger the error tends to be. The best local sea level based on a higher R2 and smaller RMSE for all the tracks combined is retrieved by using 0.1–2% of the lowest elevations at the 1–5 km segment lengths.