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Snow water equivalent retrieval over Idaho – Part 1: Using Sentinel-1 repeat-pass interferometry 爱达荷州上空的雪水当量检索 - 第一部分:使用哨兵-1 重复通干涉测量法
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-559-2024
S. Oveisgharan, Robert Zinke, Zachary Hoppinen, Hans Peter Marshall
Abstract. Snow water equivalent (SWE) is identified as the key element of the snowpack that impacts rivers' streamflow and water cycle. Both active and passive microwave remote sensing methods have been used to retrieve SWE, but there does not currently exist a SWE product that provides useful estimates in mountainous terrain. Active sensors provide higher-resolution observations, but the suitable radar frequencies and temporal repeat intervals have not been available until recently. Interferometric synthetic aperture radar (InSAR) has been shown to have the potential to estimate SWE change. In this study, we apply this technique to a long time series of 6 d temporal repeat Sentinel-1 C-band data from the 2020–2021 winter. The retrievals show statistically significant correlations both temporally and spatially with independent in situ measurements of SWE. The SWE change measurements vary between −5.3 and 9.4 cm over the entire time series and all the in situ stations. The Pearson correlation and RMSE between retrieved SWE change observations and in situ stations measurements are 0.8 and 0.93 cm, respectively. The total retrieved SWE in the entire 2020–2021 time series shows an SWE error of less than 2 cm for the nine in situ stations in the scene. Additionally, the retrieved SWE using Sentinel-1 data is well correlated with lidar snow depth data, with correlation of more than 0.47. Low temporal coherence is identified as the main reason for degrading the performance of SWE retrieval using InSAR data. We also show that the performance of the phase unwrapping algorithm degrades in regions with low temporal coherence. A higher frequency such as L-band improves the temporal coherence and SWE ambiguity. SWE retrieval using C-band Sentinel-1 data is shown to be successful, but faster revisit is required to avoid low temporal coherence. Global SWE retrieval using radar interferometry will have a great opportunity with the upcoming L-band 12 d repeat-pass NASA-ISRO Synthetic Aperture Radar (NISAR) data and the future 6 d repeat-pass Radar Observing System for Europe in L-band (ROSE-L) data.
摘要雪水当量(SWE)被认为是影响河流流量和水循环的关键雪层要素。主动式和被动式微波遥感方法都被用来检索雪水当量,但目前还没有一种雪水当量产品能为山区地形提供有用的估算。有源传感器可提供更高分辨率的观测数据,但直到最近才有合适的雷达频率和时间重复间隔。干涉合成孔径雷达 (InSAR) 已被证明具有估算 SWE 变化的潜力。在本研究中,我们将这一技术应用于 2020-2021 年冬季的 6 天时间重复哨兵-1 C 波段长时间序列数据。检索结果表明,无论从时间上还是从空间上,SWE 都与独立的原地测量值有显著的统计相关性。在整个时间序列和所有原位站中,SWE 变化测量值在 -5.3 到 9.4 厘米之间。检索到的 SWE 变化观测值与原位站测量值之间的皮尔逊相关性和均方根误差分别为 0.8 厘米和 0.93 厘米。在整个 2020-2021 年时间序列中,9 个原地站的 SWE 误差均小于 2 厘米。此外,使用哨兵 1 号数据检索的西南降水量与激光雷达雪深数据相关性良好,相关性超过 0.47。低时间一致性被认为是降低使用 InSAR 数据检索 SWE 性能的主要原因。我们还发现,在低时间相干性区域,相位解包算法的性能也会下降。更高的频率(如 L 波段)可改善时间一致性和 SWE 模糊性。使用 C 波段哨兵-1 数据进行 SWE 检索证明是成功的,但需要更快的重访以避免低时间相干性。即将发布的 L 波段 12 d 重复通量的 NASA-ISRO 合成孔径雷达(NISAR)数据和未来的 L 波段 6 d 重复通量的欧洲雷达观测系统(ROSE-L)数据将为利用雷达干涉测量进行全球 SWE 检索提供绝佳机会。
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引用次数: 2
Coupling MAR (Modèle Atmosphérique Régional) with PISM (Parallel Ice Sheet Model) mitigates the positive melt–elevation feedback 将 MAR(区域大气模型)与 PISM(平行冰盖模型)耦合可减轻融化-海拔的正反馈作用
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-633-2024
Alison Delhasse, J. Beckmann, C. Kittel, X. Fettweis
Abstract. The Greenland Ice Sheet is a key contributor to sea level rise. By melting, the ice sheet thins, inducing higher surface melt due to lower surface elevations, accelerating the melt coming from global warming. This process is called the melt–elevation feedback and can be considered by using two types of models: either (1) atmospheric models, which can represent the surface mass balance (SMB), or SMB estimates resulting from simpler models such as positive degree day models or (2) ice sheet models representing the surface elevation evolution. The latter ones do not represent the surface mass balance explicitly as well as polar-oriented climate models. A new coupling between the MAR (Modèle Atmosphérique Régional) regional climate model and the PISM (Parallel Ice Sheet Model) ice sheet model is presented here following the CESM2 (Community Earth System Model; SSP5-8.5, Shared Socioeconomic Pathway) scenario until 2100 at the MAR lateral boundaries. The coupling is extended to 2200 with a stabilised climate (+7 ∘C compared to 1961–1990) by randomly sampling the last 10 years of CESM2 to force MAR and reaches a sea level rise contribution of 64 cm. The fully coupled simulation is compared to a one-way experiment where surface topography remains fixed in MAR. However, the surface mass balance is corrected for the melt–elevation feedback when interpolated on the PISM grid by using surface mass balance vertical gradients as a function of local elevation variations (offline correction). This method is often used to represent the melt–elevation feedback and prevents a coupling which is too expensive in computation time. In the fully coupled MAR simulation, the ice sheet morphology evolution (changing slope and reducing the orographic barrier) induces changes in local atmospheric patterns. More specifically, wind regimes are modified, as well as temperature lapse rates, influencing the melt rate through modification of sensible heat fluxes at the ice sheet margins. We highlight mitigation of the melt lapse rate on the margins by modifying the surface morphology. The lapse rates considered by the offline correction are no longer valid at the ice sheet margins. If used (one-way simulation), this correction implies an overestimation of the sea level rise contribution of 2.5 %. The mitigation of the melt lapse rate on the margins can only be corrected by using a full coupling between an ice sheet model and an atmospheric model.
摘要格陵兰冰原是导致海平面上升的主要因素。通过融化,冰盖变薄,由于地表海拔降低,导致地表融化加剧,从而加速了全球变暖带来的融化。这一过程被称为 "融化-海拔高度反馈",可以通过两类模型来考虑:(1) 大气模型,它可以代表地表质量平衡(SMB),或由正度日模型等更简单的模型得出的地表质量平衡估计值;或 (2) 冰盖模型,代表地表海拔高度演变。后者不像面向极地的气候模式那样明确表示地表质量平衡。本文介绍了 MAR(Modèle Atmosphérique Régional)区域气候模式和 PISM(Parallel Ice Sheet Model)冰盖模式之间的新耦合,该耦合是在 CESM2(Community Earth System Model;SSP5-8.5,Shared Socioeconomic Pathway)情景下进行的,直到 2100 年 MAR 的横向边界。通过随机抽样 CESM2 的最后 10 年,将耦合扩展到 2200 年的稳定气候(与 1961-1990 年相比+7 ∘C),迫使 MAR 达到 64 厘米的海平面上升。完全耦合模拟与单向实验进行了比较,在单向实验中,MAR 的地表地形保持不变。不过,在 PISM 网格上进行插值时,地表质量平衡会根据熔融-海拔反馈进行校正,将地表质量平衡垂直梯度作为当地海拔变化的函数(离线校正)。这种方法通常用于表示融化-高程反馈,并防止计算时间过于昂贵的耦合。在完全耦合的 MAR 模拟中,冰盖形态演变(改变坡度和减少地形屏障)会引起当地大气模式的变化。更具体地说,风系和温度失效率都发生了变化,通过改变冰原边缘的显热通量影响了融化率。我们强调通过改变表面形态来减缓边缘地区的融化失效率。离线校正所考虑的失效率在冰原边缘不再有效。如果使用这种校正方法(单向模拟),意味着海平面上升的贡献被高估了 2.5%。只有通过冰盖模型和大气模型之间的全面耦合,才能对边缘地区的融化失效率进行校正。
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引用次数: 0
Extreme events of snow grain size increase in East Antarctica and their relationship with meteorological conditions 南极洲东部雪粒增大的极端事件及其与气象条件的关系
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-593-2024
Claudio Stefanini, G. Macelloni, M. Leduc-Leballeur, Vincent Favier, Benjamin Pohl, G. Picard
Abstract. This study explores the seasonal variations in snow grain size on the East Antarctic Plateau, where dry metamorphism occurs, by using microwave radiometer observations from 2000 to 2022. Local meteorological conditions and large-scale atmospheric phenomena have been considered in order to explain some peculiar changes in the snow grains. We find that the highest ice divide is the region with the largest grain size in the summer, mainly because the wind speed is low. Moreover, some extreme grain size values with respect to the average (over +3σ) were identified. In these cases, the ERA5 reanalysis revealed a high-pressure blocking close to the onsets of the summer increase in the grain size. It channels moisture intrusions from the mid-latitudes, through atmospheric rivers that cause major snowfall events over the plateau. If conditions of weak wind and low temperature occur during the following weeks, dry snow metamorphism is facilitated, leading to grain growth. This determines anomalous high maximums of the snow grain size at the end of summer. These phenomena confirm the importance of moisture intrusion events in East Antarctica and their impact on the physical properties of the ice sheet surface, with a co-occurrence of atmospheric rivers and seasonal changes in the grain size with a significance of over 95 %.
摘要本研究利用 2000 年至 2022 年的微波辐射计观测数据,探讨了发生干变质作用的南极东部高原雪粒大小的季节性变化。考虑了当地气象条件和大尺度大气现象,以解释雪粒的一些特殊变化。我们发现,在夏季,冰雪分界线最高的区域粒度最大,这主要是因为风速较低。此外,我们还发现了一些相对于平均值的极端粒径值(超过 +3σ)。在这些情况下,ERA5 再分析显示,在夏季粒径增大的起始点附近存在高压阻塞。它通过大气河流引导来自中纬度地区的水汽入侵,导致高原地区出现大规模降雪事件。如果在接下来的几周内出现弱风和低温条件,就会促进干雪变质,导致雪粒增大。这就决定了在夏末雪粒尺寸会异常地达到最大值。这些现象证实了南极洲东部湿气入侵事件的重要性及其对冰原表面物理性质的影响,大气河流和雪粒大小季节性变化的共同发生率超过 95%。
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引用次数: 0
Snow water equivalent retrieval over Idaho – Part 2: Using L-band UAVSAR repeat-pass interferometry 爱达荷州上空的雪水当量检索 - 第二部分:使用 L 波段 UAVSAR 重复通量干涉测量法
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-575-2024
Zachary Hoppinen, S. Oveisgharan, Hans-Peter Marshall, Ross Mower, Kelly Elder, C. Vuyovich
Abstract. This study evaluates using interferometry on low-frequency synthetic aperture radar (SAR) images to monitor snow water equivalent (SWE) over seasonal and synoptic scales. We retrieved SWE changes from nine pairs of SAR images, mean 8 d temporal baseline, captured by an L-band aerial platform, NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), over central Idaho as part of the NASA SnowEx 2020 and 2021 campaigns. The retrieved SWE changes were compared against coincident in situ measurements (SNOTEL and snow pits from the SnowEx field campaign) and to 100 m gridded SnowModel modeled SWE changes. The comparison of in situ to retrieved measurements shows a strong Pearson correlation (R=0.80) and low RMSE (0.1 m, n=64) for snow depth change and similar results for SWE change (RMSE = 0.04 m, R=0.52, n=57). The comparison between retrieved SWE changes to SnowModel SWE change also showed good correlation (R=0.60, RMSD = 0.023 m, n=3.2×106) and especially high correlation for a subset of pixels with no modeled melt and low tree coverage (R=0.72, RMSD = 0.013 m, n=6.5×104). Finally, we bin the retrievals for a variety of factors and show decreasing correlation between the modeled and retrieved values for lower elevations, higher incidence angles, higher tree percentages and heights, and greater cumulative melt. This study builds on previous interferometry work by using a full winter season time series of L-band SAR images over a large spatial extent to evaluate the accuracy of SWE change retrievals against both in situ and modeled results and the controlling factors of the retrieval accuracy.
摘要。本研究评估了在低频合成孔径雷达(SAR)图像上使用干涉测量法监测季节和天气尺度的雪水当量(SWE)的情况。作为 NASA SnowEx 2020 年和 2021 年活动的一部分,我们从爱达荷州中部上空由 L 波段航空平台(NASA 无人驾驶飞行器合成孔径雷达 (UAVSAR))捕获的九对 SAR 图像(平均 8 天时间基线)中检索了 SWE 变化。将检索到的 SWE 变化与重合的原地测量值(SNOTEL 和 SnowEx 野外作业中的雪坑)以及 100 米网格化 SnowModel 模拟的 SWE 变化进行了比较。原位测量值与检索测量值的比较结果显示,雪深变化的皮尔逊相关性强(R=0.80),均方根误差小(0.1 米,n=64),而 SWE 变化的结果类似(均方根误差 = 0.04 米,R=0.52,n=57)。检索到的 SWE 变化与 SnowModel SWE 变化之间的比较也显示出良好的相关性(R=0.60,RMSD = 0.023 m,n=3.2×106),尤其是对于没有模型融化和树木覆盖率低的像素子集,相关性更高(R=0.72,RMSD = 0.013 m,n=6.5×104)。最后,我们对各种因素的检索结果进行了分类,结果表明,在海拔较低、入射角度较高、树木比例和高度较高以及累积融化量较大的情况下,建模值与检索值之间的相关性降低。本研究在以往干涉测量工作的基础上,利用大空间范围内整个冬季的 L 波段合成孔径雷达图像时间序列,对照原地和模拟结果,评估了 SWE 变化检索的准确性,以及检索准确性的控制因素。
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引用次数: 0
Disentangling the drivers of future Antarctic ice loss with a historically calibrated ice-sheet model 利用经历史校准的冰盖模型厘清未来南极冰层流失的驱动因素
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-653-2024
Violaine Coulon, A. Klose, C. Kittel, T. Edwards, Fiona Turner, R. Winkelmann, F. Pattyn
Abstract. We use an observationally calibrated ice-sheet model to investigate the future trajectory of the Antarctic ice sheet related to uncertainties in the future balance between sub-shelf melting and ice discharge, on the one hand, and the surface mass balance, on the other. Our ensemble of simulations, forced by a panel of climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), suggests that the ocean will be the primary driver of short-term Antarctic mass loss, initiating ice loss in West Antarctica already during this century. The atmosphere initially plays a mitigating role through increased snowfall, leading to an Antarctic contribution to global mean sea-level rise by 2100 of 6 (−8 to 15) cm under a low-emission scenario and 5.5 (−10 to 16) cm under a very high-emission scenario. However, under the very high-emission pathway, the influence of the atmosphere shifts beyond the end of the century, becoming an amplifying driver of mass loss as the ice sheet's surface mass balance decreases. We show that this transition occurs when Antarctic near-surface warming exceeds a critical threshold of +7.5 ∘C, at which the increase in surface runoff outweighs the increase in snow accumulation, a signal that is amplified by the melt–elevation feedback. Therefore, under the very high-emission scenario, oceanic and atmospheric drivers are projected to result in a complete collapse of the West Antarctic ice sheet along with significant grounding-line retreat in the marine basins of the East Antarctic ice sheet, leading to a median global mean sea-level rise of 2.75 (6.95) m by 2300 (3000). Under a more sustainable socio-economic pathway, we find that the Antarctic ice sheet may still contribute to a median global mean sea-level rise of 0.62 (1.85) m by 2300 (3000). However, the rate of sea-level rise is significantly reduced as mass loss is likely to remain confined to the Amundsen Sea Embayment, where present-day climate conditions seem sufficient to commit to a continuous retreat of Thwaites Glacier.
摘要我们利用观测校准的冰盖模型来研究南极冰盖的未来轨迹,该轨迹一方面与海底融化和冰排放之间的未来平衡的不确定性有关,另一方面与地表质量平衡的不确定性有关。我们由耦合模式相互比较项目(CMIP6)第六阶段的一组气候模式进行的集合模拟表明,海洋将是南极短期质量损失的主要驱动力,本世纪南极洲西部的冰已经开始损失。大气最初通过增加降雪量起到缓解作用,在低排放情景下,到 2100 年南极对全球平均海平面上升的贡献为 6(-8 到 15)厘米,在极高排放情景下为 5.5(-10 到 16)厘米。然而,在极高排放路径下,大气的影响会在本世纪末发生转变,随着冰盖表面质量平衡的降低,大气会成为质量损失的放大驱动力。我们的研究表明,这种转变发生在南极近地表变暖超过+7.5 ∘C临界阈值时,此时地表径流的增加超过了积雪的增加,这一信号被融化-海拔反馈放大。因此,在极高排放情景下,海洋和大气驱动因素预计将导致南极西部冰盖完全崩塌,同时南极东部冰盖海洋盆地的接地线显著后退,导致全球平均海平面到 2300 年(3000 年)上升 2.75(6.95)米。在更具可持续性的社会经济途径下,我们发现到 2300 年(3000 年),南极冰盖仍可能导致全球平均海平面上升 0.62(1.85)米。不过,海平面上升的速度会大大降低,因为质量损失可能仍然局限于阿蒙森海海湾,那里目前的气候条件似乎足以导致斯韦思冰川的持续后退。
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引用次数: 1
Coupling MAR (Modèle Atmosphérique Régional) with PISM (Parallel Ice Sheet Model) mitigates the positive melt–elevation feedback 将 MAR(区域大气模型)与 PISM(平行冰盖模型)耦合可减轻融化-海拔的正反馈作用
Pub Date : 2024-02-12 DOI: 10.5194/tc-18-633-2024
Alison Delhasse, J. Beckmann, C. Kittel, X. Fettweis
Abstract. The Greenland Ice Sheet is a key contributor to sea level rise. By melting, the ice sheet thins, inducing higher surface melt due to lower surface elevations, accelerating the melt coming from global warming. This process is called the melt–elevation feedback and can be considered by using two types of models: either (1) atmospheric models, which can represent the surface mass balance (SMB), or SMB estimates resulting from simpler models such as positive degree day models or (2) ice sheet models representing the surface elevation evolution. The latter ones do not represent the surface mass balance explicitly as well as polar-oriented climate models. A new coupling between the MAR (Modèle Atmosphérique Régional) regional climate model and the PISM (Parallel Ice Sheet Model) ice sheet model is presented here following the CESM2 (Community Earth System Model; SSP5-8.5, Shared Socioeconomic Pathway) scenario until 2100 at the MAR lateral boundaries. The coupling is extended to 2200 with a stabilised climate (+7 ∘C compared to 1961–1990) by randomly sampling the last 10 years of CESM2 to force MAR and reaches a sea level rise contribution of 64 cm. The fully coupled simulation is compared to a one-way experiment where surface topography remains fixed in MAR. However, the surface mass balance is corrected for the melt–elevation feedback when interpolated on the PISM grid by using surface mass balance vertical gradients as a function of local elevation variations (offline correction). This method is often used to represent the melt–elevation feedback and prevents a coupling which is too expensive in computation time. In the fully coupled MAR simulation, the ice sheet morphology evolution (changing slope and reducing the orographic barrier) induces changes in local atmospheric patterns. More specifically, wind regimes are modified, as well as temperature lapse rates, influencing the melt rate through modification of sensible heat fluxes at the ice sheet margins. We highlight mitigation of the melt lapse rate on the margins by modifying the surface morphology. The lapse rates considered by the offline correction are no longer valid at the ice sheet margins. If used (one-way simulation), this correction implies an overestimation of the sea level rise contribution of 2.5 %. The mitigation of the melt lapse rate on the margins can only be corrected by using a full coupling between an ice sheet model and an atmospheric model.
摘要格陵兰冰原是导致海平面上升的主要因素。通过融化,冰盖变薄,由于地表海拔降低,导致地表融化加剧,从而加速了全球变暖带来的融化。这一过程被称为 "融化-海拔高度反馈",可以通过两类模型来考虑:(1) 大气模型,它可以代表地表质量平衡(SMB),或由正度日模型等更简单的模型得出的地表质量平衡估计值;或 (2) 冰盖模型,代表地表海拔高度演变。后者不像面向极地的气候模式那样明确表示地表质量平衡。本文介绍了 MAR(Modèle Atmosphérique Régional)区域气候模式和 PISM(Parallel Ice Sheet Model)冰盖模式之间的新耦合,该耦合是在 CESM2(Community Earth System Model;SSP5-8.5,Shared Socioeconomic Pathway)情景下进行的,直到 2100 年 MAR 的横向边界。通过随机抽样 CESM2 的最后 10 年,将耦合扩展到 2200 年的稳定气候(与 1961-1990 年相比+7 ∘C),迫使 MAR 达到 64 厘米的海平面上升。完全耦合模拟与单向实验进行了比较,在单向实验中,MAR 的地表地形保持不变。不过,在 PISM 网格上进行插值时,地表质量平衡会根据熔融-海拔反馈进行校正,将地表质量平衡垂直梯度作为当地海拔变化的函数(离线校正)。这种方法通常用于表示融化-抬升反馈,并防止计算时间过于昂贵的耦合。在完全耦合的 MAR 模拟中,冰盖形态演变(改变坡度和减少地形障碍)会引起当地大气模式的变化。更具体地说,风系和温度失效率都会发生变化,通过改变冰原边缘的显热通量影响融化率。我们强调通过改变表面形态来减缓边缘地区的融化失效率。离线校正所考虑的失效率在冰原边缘不再有效。如果使用这种校正方法(单向模拟),意味着海平面上升的贡献被高估了 2.5%。只有通过冰盖模型和大气模型之间的全面耦合,才能对边缘地区的融化失效率进行修正。
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引用次数: 0
Seasonal to decadal dynamics of supraglacial lakes on debris-covered glaciers in the Khumbu region, Nepal 尼泊尔昆布地区碎屑覆盖冰川上的超冰川湖的季节至十年动态变化
Pub Date : 2024-02-08 DOI: 10.5194/tc-18-525-2024
Lucas Zeller, D. McGrath, S. McCoy, J. Jacquet
Abstract. Supraglacial lakes (SGLs) play an important role in debris-covered glacier (DCG) systems by enabling efficient interactions between the supraglacial, englacial, and subglacial environments. Developing a better understanding of the short-term and long-term development of these features is needed to constrain DCG evolution and the hazards posed to downstream communities, ecosystems, and infrastructure from rapid drainage. In this study, we present an analysis of supraglacial lakes on eight DCGs in the Khumbu region of Nepal by automating SGL identification in PlanetScope, Sentinel-2, and Landsat 5–9 images. We identify a regular annual cycle in SGL area, with lakes covering approximately twice as much area during their maximum annual extent (in the pre-monsoon season) than their minimum annual extent (in the post-monsoon season). The high spatiotemporal resolution of PlanetScope imagery (∼ daily, 3 m) shows that this cycle is driven by the appearance and expansion of small lakes in the upper debris-covered regions of these glaciers throughout the winter. Decadal-scale expansion of large, near-terminus lakes was identified on four of the glaciers (Khumbu, Lhotse, Nuptse, and Ambulapcha), while the remaining four showed no significant increases over the study period. The seasonal variation in SGL area is of comparable or greater magnitude as decadal-scale changes, highlighting the importance of accounting for this seasonality when interpreting long-term records of SGL changes from sparse observations. The complex spatiotemporal patterns revealed in our analysis are not captured in existing regional-scale glacial lake databases, suggesting that more targeted efforts are needed to capture the true variability of SGLs on large scales.
摘要。超冰川湖(SGL)在碎屑覆盖冰川(DCG)系统中发挥着重要作用,使超冰川、冰川和冰川下环境之间能够有效互动。我们需要更好地了解这些地貌的短期和长期发展,以制约DCG的演化以及快速排水对下游社区、生态系统和基础设施造成的危害。在本研究中,我们通过自动识别 PlanetScope、哨兵-2 和 Landsat 5-9 图像中的超冰川湖,对尼泊尔昆布地区 8 个 DCG 上的超冰川湖进行了分析。我们发现,SGL 面积的年周期是有规律的,湖泊面积最大年周期(季风前季节)是湖泊面积最小年周期(季风后季节)的两倍。PlanetScope 图像的高时空分辨率(每天∼ 3 米)显示,这一周期是由这些冰川上部碎屑覆盖区整个冬季出现和扩大的小湖泊所驱动的。有四条冰川(昆布冰川、洛子峰冰川、努布齐峰冰川和安布拉巴查冰川)的大型近端点湖泊出现了十年尺度的扩张,而其余四条冰川在研究期间没有出现明显的扩张。SGL面积的季节性变化与十年尺度变化的幅度相当或更大,这突出表明了在解释来自稀少观测数据的SGL长期变化记录时考虑这种季节性的重要性。现有的区域尺度冰川湖数据库无法捕捉到我们的分析所揭示的复杂时空模式,这表明需要更有针对性的努力来捕捉大尺度 SGL 的真实变化。
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引用次数: 0
Evaluation of satellite methods for estimating supraglacial lake depth in southwest Greenland 估算格陵兰西南部超冰川湖深度的卫星方法评估
Pub Date : 2024-02-08 DOI: 10.5194/tc-18-543-2024
L. Melling, A. Leeson, M. McMillan, Jennifer Maddalena, Jade S. Bowling, Emily Glen, Louise Sandberg Sørensen, M. Winstrup, Rasmus Lørup Arildsen
Abstract. Supraglacial lakes form on the Greenland ice sheet in the melt season (May to October) when meltwater collects in surface depressions on the ice. Supraglacial lakes can act as a control on ice dynamics since, given a large enough volume of water and a favourable stress regime, hydrofracture of the lake can occur, which enables water transfer from the ice surface to the bedrock, where it can lubricate the base. The depth (and thus volume) of these lakes is typically estimated by applying a radiative transfer equation (RTE) to optical satellite imagery. This method can be used at scale across entire ice sheets but is poorly validated due to a paucity of in situ depth data. Here we intercompare supraglacial lake depth detection by means of ArcticDEM digital elevation models, ICESat-2 photon refraction, and the RTE applied to Sentinel-2 images across five lakes in southwest Greenland. We found good agreement between the ArcticDEM and ICESat-2 approaches (Pearson's r=0.98) but found that the RTE overestimates lake depth by up to 153 % using the green band (543–578 nm) and underestimates lake depth by up to 63 % using the red band (650–680 nm). Parametric uncertainty in the RTE estimates is substantial and is dominated by uncertainty in estimates of reflectance at the lakebed, which are derived empirically. Uncertainty in lake depth estimates translates into a poor understanding of total lake volume, which could mean that hydrofracture likelihood is poorly constrained, in turn affecting ice velocity predictions. Further laboratory studies to constrain spectral radiance loss in the water column and investigation of the potential effects of cryoconite on lakebed reflectance could improve the RTE in its current format. However, we also suggest that future work should explore multi-sensor approaches to deriving lake depth from optical satellite imagery, which may improve depth estimates and will certainly result in better-constrained uncertainties.
摘要格陵兰冰盖上的超级冰川湖是在融化季节(5 月至 10 月)融水汇集到冰面凹陷处时形成的。超级冰川湖可以控制冰的动态,因为如果水量足够大,应力机制有利,冰湖就会发生水力断裂,从而使水从冰面转移到基岩,润滑基岩。这些湖泊的深度(也就是体积)通常是通过对光学卫星图像应用辐射传递方程(RTE)来估算的。这种方法可在整个冰原上大规模使用,但由于缺乏原位深度数据,这种方法的有效性很差。在这里,我们比较了通过 ArcticDEM 数字高程模型、ICESat-2 光子折射和应用于格陵兰西南部五个湖泊的哨兵-2 图像的 RTE 进行的超冰川湖泊深度探测。我们发现 ArcticDEM 和 ICESat-2 方法之间有很好的一致性(Pearson's r=0.98),但发现使用绿色波段(543-578 nm)时,RTE 高估湖泊深度达 153%,使用红色波段(650-680 nm)时,RTE 低估湖泊深度达 63%。RTE 估计值的参数不确定性很大,主要是湖床反射率估计值的不确定性,而湖床反射率是根据经验得出的。湖泊深度估算值的不确定性会导致对湖泊总体积的不了解,这可能意味着对水文断裂可能性的约束不足,进而影响冰速预测。通过进一步的实验室研究来限制水体中的光谱辐射损失,并调查冰晶石对湖床反射率的潜在影响,可以改进当前格式的 RTE。不过,我们也建议,未来的工作应探索从光学卫星图像中得出湖泊深度的多传感器方法,这可能会改善深度估算,并肯定会带来更好的不确定性约束。
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引用次数: 0
Evaluation of satellite methods for estimating supraglacial lake depth in southwest Greenland 估算格陵兰西南部超冰川湖深度的卫星方法评估
Pub Date : 2024-02-08 DOI: 10.5194/tc-18-543-2024
L. Melling, A. Leeson, M. McMillan, Jennifer Maddalena, Jade S. Bowling, Emily Glen, Louise Sandberg Sørensen, M. Winstrup, Rasmus Lørup Arildsen
Abstract. Supraglacial lakes form on the Greenland ice sheet in the melt season (May to October) when meltwater collects in surface depressions on the ice. Supraglacial lakes can act as a control on ice dynamics since, given a large enough volume of water and a favourable stress regime, hydrofracture of the lake can occur, which enables water transfer from the ice surface to the bedrock, where it can lubricate the base. The depth (and thus volume) of these lakes is typically estimated by applying a radiative transfer equation (RTE) to optical satellite imagery. This method can be used at scale across entire ice sheets but is poorly validated due to a paucity of in situ depth data. Here we intercompare supraglacial lake depth detection by means of ArcticDEM digital elevation models, ICESat-2 photon refraction, and the RTE applied to Sentinel-2 images across five lakes in southwest Greenland. We found good agreement between the ArcticDEM and ICESat-2 approaches (Pearson's r=0.98) but found that the RTE overestimates lake depth by up to 153 % using the green band (543–578 nm) and underestimates lake depth by up to 63 % using the red band (650–680 nm). Parametric uncertainty in the RTE estimates is substantial and is dominated by uncertainty in estimates of reflectance at the lakebed, which are derived empirically. Uncertainty in lake depth estimates translates into a poor understanding of total lake volume, which could mean that hydrofracture likelihood is poorly constrained, in turn affecting ice velocity predictions. Further laboratory studies to constrain spectral radiance loss in the water column and investigation of the potential effects of cryoconite on lakebed reflectance could improve the RTE in its current format. However, we also suggest that future work should explore multi-sensor approaches to deriving lake depth from optical satellite imagery, which may improve depth estimates and will certainly result in better-constrained uncertainties.
摘要格陵兰冰盖上的超级冰川湖是在融化季节(5 月至 10 月)融水汇集到冰面凹陷处时形成的。超级冰川湖可以控制冰的动力学,因为如果水量足够大,应力机制有利,湖泊就会发生水力断裂,从而使水从冰面转移到基岩,润滑基岩。这些湖泊的深度(也就是体积)通常是通过对光学卫星图像应用辐射传递方程(RTE)来估算的。这种方法可在整个冰原上大规模使用,但由于缺乏原位深度数据,这种方法的有效性很差。在这里,我们比较了通过 ArcticDEM 数字高程模型、ICESat-2 光子折射和应用于格陵兰西南部五个湖泊的哨兵-2 图像的 RTE 进行的超冰川湖泊深度探测。我们发现 ArcticDEM 和 ICESat-2 方法之间有很好的一致性(Pearson's r=0.98),但发现使用绿色波段(543-578 nm)时,RTE 高估湖泊深度达 153%,使用红色波段(650-680 nm)时,RTE 低估湖泊深度达 63%。RTE 估计值的参数不确定性很大,主要是湖床反射率估计值的不确定性,而湖床反射率是根据经验得出的。湖泊深度估算值的不确定性会导致对湖泊总体积的不了解,这可能意味着对水文断裂可能性的约束不足,进而影响冰速预测。通过进一步的实验室研究来限制水体中的光谱辐射损失,并调查冰晶石对湖床反射率的潜在影响,可以改进当前格式的 RTE。不过,我们也建议,未来的工作应探索从光学卫星图像中得出湖泊深度的多传感器方法,这可能会改善深度估算,并肯定会带来更好的不确定性约束。
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引用次数: 0
Seasonal to decadal dynamics of supraglacial lakes on debris-covered glaciers in the Khumbu region, Nepal 尼泊尔昆布地区碎屑覆盖冰川上的超冰川湖的季节至十年动态变化
Pub Date : 2024-02-08 DOI: 10.5194/tc-18-525-2024
Lucas Zeller, D. McGrath, S. McCoy, J. Jacquet
Abstract. Supraglacial lakes (SGLs) play an important role in debris-covered glacier (DCG) systems by enabling efficient interactions between the supraglacial, englacial, and subglacial environments. Developing a better understanding of the short-term and long-term development of these features is needed to constrain DCG evolution and the hazards posed to downstream communities, ecosystems, and infrastructure from rapid drainage. In this study, we present an analysis of supraglacial lakes on eight DCGs in the Khumbu region of Nepal by automating SGL identification in PlanetScope, Sentinel-2, and Landsat 5–9 images. We identify a regular annual cycle in SGL area, with lakes covering approximately twice as much area during their maximum annual extent (in the pre-monsoon season) than their minimum annual extent (in the post-monsoon season). The high spatiotemporal resolution of PlanetScope imagery (∼ daily, 3 m) shows that this cycle is driven by the appearance and expansion of small lakes in the upper debris-covered regions of these glaciers throughout the winter. Decadal-scale expansion of large, near-terminus lakes was identified on four of the glaciers (Khumbu, Lhotse, Nuptse, and Ambulapcha), while the remaining four showed no significant increases over the study period. The seasonal variation in SGL area is of comparable or greater magnitude as decadal-scale changes, highlighting the importance of accounting for this seasonality when interpreting long-term records of SGL changes from sparse observations. The complex spatiotemporal patterns revealed in our analysis are not captured in existing regional-scale glacial lake databases, suggesting that more targeted efforts are needed to capture the true variability of SGLs on large scales.
摘要。超冰川湖(SGL)在碎屑覆盖冰川(DCG)系统中发挥着重要作用,使超冰川、冰川和冰川下环境之间能够有效互动。我们需要更好地了解这些地貌的短期和长期发展,以制约DCG的演化以及快速排水对下游社区、生态系统和基础设施造成的危害。在本研究中,我们通过自动识别 PlanetScope、哨兵-2 和 Landsat 5-9 图像中的超冰川湖,对尼泊尔昆布地区 8 个 DCG 上的超冰川湖进行了分析。我们发现,SGL 面积的年周期是有规律的,湖泊面积最大年周期(季风前季节)是湖泊面积最小年周期(季风后季节)的两倍。PlanetScope 图像的高时空分辨率(每天∼ 3 米)显示,这一周期是由这些冰川上部碎屑覆盖区整个冬季出现和扩大的小湖泊所驱动的。有四条冰川(昆布冰川、洛子峰冰川、努布齐峰冰川和安布拉巴查冰川)的大型近端点湖泊出现了十年尺度的扩张,而其余四条冰川在研究期间没有出现明显的扩张。SGL面积的季节性变化与十年尺度变化的幅度相当或更大,这突出表明了在解释来自稀少观测数据的SGL长期变化记录时考虑这种季节性的重要性。现有的区域尺度冰川湖数据库无法捕捉到我们的分析所揭示的复杂时空模式,这表明需要更有针对性的努力来捕捉大尺度 SGL 的真实变化。
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引用次数: 0
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The Cryosphere
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