Sea Ice MEaSUREs

Sea ice is the central player in a dynamic system that affects the planet’s oceans and climate. Sea ice is also a force to be reckoned with as polar waters open to human activity, such as shipping that is already taking place through the Northern Route along the coast of Russia and is potentially slated for the fabled Northwest Passage along the coast of Canada. Sea-ice motion, revealed in the data available here, is a critical factor in the thinning and melting of Arctic sea ice as it forms, rafts, ridges, and opens into leads and polynyas — and as winds and currents move it through and out of the Arctic.The sea-ice imagery and data products available through the ASF DAAC are supported under NASA’s Making Earth Science Data Records for Use in Research Environments (MEaSUREs) program. Sea Ice Measures OverviewSea ice is the central player in a dynamic system that affects the planet’s oceans and climate. Sea ice is also a force to be reckoned with as polar waters open to human activity, such as shipping that is already taking place through the Northern Route along the coast of Russia and is potentially slated for the fabled Northwest Passage along the coast of Canada. Sea-ice motion, revealed in the data available here, is a critical factor in the thinning and melting of Arctic sea ice as it forms, rafts, ridges, and opens into leads and polynyas — and as winds and currents move it through and out of the Arctic.Video: Sea Ice Moves: Radar helps reveal the global effects of sea-ice motion.  Video: Sea Ice in the Bering Strait: See an animation of synthetic aperture radar (SAR) images of the Bering Strait from 2007 and 2008. Dramatic changes: Though the extent of sea ice fluctuates, overall it is shrinking and substantially thinner than in past decades, and in spring and summer it is retreating earlier and faster. The melting, along with the absorption of solar energy by newly exposed, darker water, alters the circulations of oceans and the atmosphere, affecting climate and weather globally. Observable through remote sensing: Remote sensing has been central to observing and researching changes in sea ice. Synthetic aperture radar (SAR), used to create the majority of the imagery available in the ASF archive, is among the power tools of remote sensing and has been used extensively in the science of sea ice. SAR bounces a microwave radar signal off the Earth’s surface, including water and ice, to detect physical properties. Unlike optical technology, SAR can “see” through darkness, clouds, and rain. Critical for seafood: Sea ice also plays a substantial role in feeding the world. The ice serves as a farm for tiny organisms that drive the entire ecosystem. Seasonal sea ice in the Bering Sea is an integral part of an international fishery that provides more than half of the U.S. seafood catch. In addition, sea ice provides wildlife nurseries, molting sites, dens, hiding places, feeding grounds, resting platforms, and even transportation for Pacific walruses that migrate by riding on melting ice floes.Sea-ice data, images, and data products available through the Alaska Satellite Facility (ASF) are supported under NASA’s Making Earth System data records for Use in Research Environments (MEaSUREs) program.Sea Ice MEaSUREs productsSea-ice imagery and data products are supported under NASA’s Making Earth System data records for Use in Research Environments program. These data have been used in a variety of applications.Arctic and Southern Ocean imagery, data, and data products available at no cost from the ASF DAAC include:More than 11 years of RADARSAT-1, nearly uninterrupted, three-day radar snapshots of Arctic and Southern Ocean sea ice.Original synthetic aperture radar (SAR) images.RADARSAT-1 data have been processed to:Construct a near-decadal record of small-scale ice motion of the Arctic and Southern Oceans.Produce a record of ice motion of the northern Bering Sea.Assemble monthly high-resolution image mosaics of the Arctic Ocean.These datasets are available from the ASF DAAC and NASA’s Jet Propulsion Laboratory (JPL) through the project’s principal investigator, Ron Kwok. The original RADARSAT-1 images used to generate the products are available for download at no cost from the Alaska Satellite Facility datapool. Through ASF’s datapool, products such as Seasat, RADARSAT-1, ERS-1, ERS-2, JERS, and PALSAR sea ice images are free to approved users. To become an approved user, please submit the required Research Agreement. Additional sea ice data is offered through Polar Year 07-08, a part of the Global Inter-agency International Polar-Snapshot Year (GIIPSY), which contains satellite snapshots of polar regions.MEaSUREs supports the NASA Earth-science research community in providing Earth science data products and services driven by NASA’s Earth-science goals. MEaSUREs projects focus on the creation of Earth System Data Records (ESDRs), including Climate Data Records. An ESDR is a unified and coherent set of observations of a given parameter of the Earth system that is optimized to meet specific requirements in addressing science questions.These records are critical to understanding Earth system processes, assessing variability, long-term trends, and changes in the Earth system, and providing input and validation means for modeling efforts. Explanation of the Data Product Terms LagrangianThe Lagrangian sea-ice data products contain monthly measurements of dynamic and kinematic parameters over the Arctic Ocean sea-ice cover. “Lagrangian” is a mathematical way to study ice dynamics by noting changes in position and velocity of points over time. The sea-ice analysis in the dataset available here is initialized by laying a 10km-by-10km grid over a set of RADARSAT images of the sea ice during an initial 3-day period of a season. The grid forms cells for which several properties can be derived that describe the sea-ice dynamics. The grid points of the sea ice and related cell properties are then tracked throughout the season.Four data products result from these measurements:Map graphic: This image illustrates sea-ice-motion magnitude, one of the parameters in the Lagrangian products, at three points in time in the Arctic Ocean basin. Dark blue indicates the most motion, more than 30 km a day. The spatial extent of the data illustrated here is the typical extent of the winter products. 1) Ice Motion – a record of the time and location of each point within the initial grid as tracked on RADARSAT images at approximately 3-day intervals. Note that a small fraction of the points may be lost during the season through advection out of the Arctic basin, loss of ice, or untrackability of the ice cover. 2) Deformation – a record of each cell’s divergence, vorticity, and shear. As the vertices of each cell move within a time step, the kinematic properties can be calculated to characterize the response of the ice cover to stresses induced by wind and ocean currents. 3) Ice Age and Thickness – a record of the area, age, and thickness of new and ridged ice resulting from cell area changes. A spatial and temporal distribution of these ice areas is kept for each cell. If the area of a cell increases within a time step, an area of new ice is created. The ice thickness within all the new ice areas created during the season is increased using air temperature information. The thinnest ice areas are rafted or ridged when the cell area decreases, depending on their thickness. The thickness of areas of ridged ice also grows over time. 4) Backscatter Histogram – a record of the radiometric properties of the ice within each cell. A histogram of the radar brightness is kept within each cell at each time step, allowing the user to deduce multi-year ice fractions of the ice cover.Note that in earlier winter products, we use a 10km-resolution grid over the existing ice cover, beginning sometime near the beginning of November. In later products, we used a hybrid grid of 10km resolution over the multi-year ice pack and a 20km grid over the seasonal ice. We began our analysis in early December to permit the tracking of the seasonal ice regions. 3-Day GriddedThe 3-day gridded datasets are produced from the Lagrangian products. Parameters from the Lagrangian dataset are processed to produce fields with constant grid spacing. The gridded parameters are ice age, ice thickness, backscatter histogram, divergence, vorticity, and shear. Data values cover a 3-day period on a 12.5km-x-12.5-km grid. Each of the downloadable files contains one month of these 3-day product files. Melt OnsetThe melt onset product consists of a gridded field containing the date of surface melt at each grid location. This date is derived from changes in the radar backscatter signature within the Lagrangian cells between April and June. The grid is at 10km resolution within the interior of the Arctic basin and 25km resolution near the coasts. EulerianMaps:Eulerian data in the Sea Ice MEaSUREs North collection falls within the red bounding box visible in this image.Eulerian data in the Sea Ice MEaSUREs South collection falls within the red bounding box visible in this image.Between 2008 and 2012, an archive of Envisat SAR imagery of the Arctic and Southern Oceans was created. In a project, conducted by Senior Research Scientist Ron Kwok of the Jet Propulsion Laboratory, the SAR imagery from Envisat was used to produce a high-resolution dataset of small-scale sea ice kinematics and deformation. This work is supported under NASA’s Making Earth System Data Records for Use in Research Environments (MEaSUREs) program. The motion field is sampled in Eulerian mode. 

The objectives are to:Process the Envisat data stream to construct ESDRs of small-scale ice motion of the Arctic and Southern Oceans;Develop products that take advantage of the temporal (daily observations) and spatial sampling scheme of the Envisat mission;Produce mosaics of the Envisat images of the Arctic Ocean and Southern Ocean.

海冰是影响地球海洋和气候的动态系统中的核心参与者。随着北极水域向人类活动开放，如俄罗斯沿岸已进行的通过北方航道航运以及可能规划中的穿越加拿大沿岸的传奇西北航道，海冰也成为不容忽视的力量。本数据集中揭示的海冰运动是北极海冰在形成、漂移、形成脊和开口形成航道与开阔水域，以及随风向和洋流在北极内外移动过程中的变薄和融化的关键因素。通过美国航天局（NASA）的“构建用于研究环境的地球科学数据记录”（MEaSUREs）计划支持，美国航天局分布式活动数据档案馆（ASF DAAC）提供的海冰图像和数据产品。海冰措施概述：海冰是影响地球海洋和气候的动态系统中的核心参与者。随着北极水域向人类活动开放，如俄罗斯沿岸已进行的通过北方航道航运以及可能规划中的穿越加拿大沿岸的传奇西北航道，海冰也成为不容忽视的力量。本数据集中揭示的海冰运动是北极海冰在形成、漂移、形成脊和开口形成航道与开阔水域，以及随风向和洋流在北极内外移动过程中的变薄和融化的关键因素。视频：海冰移动：雷达有助于揭示海冰运动的全球影响。视频：白令海峡海冰：观看2007年和2008年合成孔径雷达（SAR）图像的白令海峡动画。显著变化：尽管海冰面积波动，但总体而言，海冰面积正在缩小，且比过去几十年薄得多，春季和夏季海冰退缩得早且速度更快。融化和新暴露的较暗水域吸收太阳能量，改变了海洋和大气环流，影响全球气候和天气。可通过遥感观测：遥感在观测和研究海冰变化中发挥了核心作用。合成孔径雷达（SAR），用于创建ASF存档中的大部分图像，是遥感的有力工具之一，已在海冰科学中得到了广泛的应用。SAR通过地球表面（包括水和冰）反射微波雷达信号，以检测物理属性。与光学技术不同，SAR可以穿透黑暗、云层和雨水。对海鲜至关重要：海冰还在养活世界方面发挥着重要作用。冰层为微小生物提供农场，这些生物推动着整个生态系统。白令海的季节性海冰是国际渔业的组成部分，该渔业提供了美国海鲜捕捞量的一半以上。此外，海冰为野生动物提供了育儿所、换羽地点、巢穴、藏身之处、觅食场所、休息平台，甚至为迁移的太平洋海豹提供了在融化的冰块上骑行的交通方式。通过阿拉斯加卫星设施（ASF）提供的数据，包括SeaSat、RADARSAT-1、ERS-1、ERS-2、JERS和PALSAR海冰图像等，均对经过批准的用户免费提供。要成为批准用户，请提交所需的研究协议。通过北极年07-08，这是全球机构国际极地快照年（GIIPSY）的一部分，提供了极地地区的卫星快照。MEaSUREs支持NASA地球科学研究社区，提供由NASA地球科学目标驱动的地球科学数据产品和服务的地球科学数据记录（ESDRs），包括气候数据记录。ESDR是一组统一的、协调一致的地球系统给定参数的观测，旨在满足解决科学问题的特定要求。这些记录对于理解地球系统过程、评估变异性、长期趋势和地球系统变化至关重要，并为建模工作提供输入和验证手段。数据产品术语解释：拉格朗日：拉格朗日海冰数据产品包含对北极洋海冰覆盖动态和运动参数的月度测量。‘拉格朗日’是一种通过记录随时间变化的位置和速度来研究冰动态的数学方法。本数据集中海冰分析是通过在季节初期3天的一个季节内对海冰的RADARSAT图像上放置一个10公里×10公里的网格进行初始化的。网格形成单元格，可以从中导出描述海冰动态的几个属性。海冰网格点和相关单元格属性在整个季节中跟踪。从这些测量中产生了四个数据产品：地图图形：此图像展示了北极洋盆中拉格朗日产品中的一个参数——海冰运动幅度，在三个时间点的情景。深蓝色表示运动最剧烈，每天超过30公里。这里所示的数据的空间范围是冬季产品的典型范围。1）冰运动——记录初始网格内每个点的时间和位置，这些点在约3天的间隔内通过RADARSAT图像进行跟踪。请注意，由于在季节中通过平流出北极盆地、冰层损失或冰层的不可追踪性，一小部分点可能会丢失。2）变形——记录每个单元格的散度、涡度和剪切。随着每个单元格的顶点在每个时间步长内移动，可以计算出运动学属性，以表征冰层对风和洋流引起的应力的响应。3）冰龄和厚度——记录由单元格面积变化产生的新冰和脊冰的面积、年龄和厚度。对每个单元格保持这些冰面积的空间和时间分布。如果一个单元格的面积在一个时间步长内增加，就会创建一个新的冰面积。在整个季节中创建的所有新冰区域内的冰厚度使用空气温度信息增加。当单元格面积减少时，最薄的冰区域会漂浮或形成脊，具体取决于它们的厚度。脊冰区域的厚度也会随时间增长。4）后向散射直方图——记录每个单元格内冰的辐射特性。在每个时间步长内，每个单元格都保存雷达亮度的直方图，使用户可以推断出冰层中的多年冰分数。请注意，在早期的冬季产品中，我们在现有的冰盖上使用了一个10公里分辨率的网格，开始时间大约在11月初附近。在后来的产品中，我们使用了一个混合网格，10公里分辨率覆盖多年冰层，20公里网格覆盖季节性冰层。我们在12月初开始分析，以便跟踪季节性冰区。3天网格：从拉格朗日产品中产生3天网格数据集。从拉格朗日数据集中处理参数以产生具有恒定网格间距的字段。网格化参数为冰龄、冰厚度、后向散射直方图、散度、涡度和剪切。数据值覆盖了一个3天周期在12.5公里×12.5公里的网格上。每个可下载的文件包含一个月的这些3天产品文件。融化和开始：融化和开始产品由一个网格化字段组成，包含每个网格位置表面融化的日期。这个日期是通过4月到6月之间拉格朗日单元格中雷达后向散射特征的变化导出的。网格在北极盆地的内部为10公里分辨率，在沿海地区为25公里分辨率。欧拉：在本Sea Ice MEaSUREs北集合中的欧拉数据位于图像中可见的红色边界框内。在本Sea Ice MEaSUREs南集合中的欧拉数据位于图像中可见的红色边界框内。在2008年至2012年期间，创建了一个北极和南大洋Envisat SAR图像的存档。在喷气推进实验室（JPL）的高级研究员Ron Kwok领导的项目中，使用Envisat的SAR图像生成了一个小尺度海冰运动学和变形的高分辨率数据集。这项工作是在NASA的“构建用于研究环境的地球系统数据记录”（MEaSUREs）计划的支持下进行的。运动场以欧拉模式采样。目标包括：处理Envisat数据流以构建北极和南大洋小尺度冰运动的ESDR；开发利用Envisat任务的时空（每日观测）和空间采样方案的产品；生成北极洋和南大洋的Envisat图像拼图。