Water States - Corrected Reflectance (VIIRS / NOAA-20)

Overview and Intended Use This visualization represents a "false color" band combination (Red = M3, Green = I3, Blue = M11) of data collected by the VIIRS instrument on NOAA’s Joint Polar Satellite System (JPSS-1) satellite, which was renamed to NOAA-20 once on orbit. The imagery is most useful for distinguishing water in its various states (e.g. liquid, ice, and snow). For example, clouds over snow, ice cloud versus water cloud; or floods from dense vegetation. At its highest resolution, this visualization represents the underlying data scaled to a resolution of 250m per pixel at the equator. The VIIRS Corrected Reflectance product retains visible aerosols for a natural-looking visualization, though gross atmospheric effects (e.g. Rayleigh scattering) have been removed. The following guidelines will aid in understanding this visualization. See here for additional information on how this "false color" band combination highlights these physical characteristics of the Earth. Thick ice and snow appear a vivid red (or dark pink), while ice crystals in clouds will appear pinkish. Vegetation will appear green. Naturally bare soil, like a desert, will appear bright cyan. Liquid water on the ground will appear very dark, while water droplets in clouds will appear white. Sediments in water will appear dark red. Multi-Spectral Bands The following table lists the VIIRS bands that are utilized to create this visualization. See here for a full description of all VIIRS bands. Band Description Wavelength (µm) Resolution (m) I3 Shortwave IR (Red) 1.58 - 1.64 375 M3 Visible (reflective) 0.478 - 0.488 750 M11 Shortwave IR 2.23 - 2.28 750 Temporal Coverage and Limitations of Use By default, this layer will display the imagery currently available for today’s date. The update frequency of the imagery is a "daily composite" that is assembled from hundreds of individual data files. When viewing imagery for “today,” you may notice that only a portion of the map has imagery. This is because the visualization is continually updated as the satellite collects more data. To view imagery over time, you can update the layer properties to enable time animation and configure time settings. The current version of this layer is available from present back to April 25th, 2020. In the coming months, this will be extended to the start of the mission (November 18th, 2017). Source: NASA Global Imagery Browse Services (GIBS), NASA Worldview, & NASA LANCE This visualization is provided through the NASA Global Imagery Browse Services (GIBS), which are a set of standard services to deliver global, full-resolution satellite imagery for hundreds of NASA Earth science datasets and science parameters. Through its services, and the NASA Worldview client, GIBS enables interactive exploration of NASA's Earth imagery for a broad range of users. The data and imagery are generated within 3 hours of acquisition through the NASA LANCE capability. Esri and NASA Collaborative Services This visualization is made available through an ArcGIS image service hosted on Esri servers and facilitates access to a NASA GIBS service endpoint. For each image service request, the Esri server issues multiple requests to the GIBS service, processes and assembles the responses, and returns a proper mosaic image to the user. Processing occurs on-the-fly for each and every request to ensure that any update to the GIBS imagery is immediately available to the user. As such, availability of this visualization is dependent on both the Esri and the NASA GIBS services.### 概述与预期用途 本可视化图像呈现的是美国国家海洋和大气管理局（NOAA）联合极地卫星系统-1（JPSS-1）卫星（入轨后更名为NOAA-20）搭载的可见光红外成像辐射仪（VIIRS）所采集数据的假彩色（false color）波段组合（红通道对应M3波段、绿通道对应I3波段、蓝通道对应M11波段）。该图像可用于区分不同形态的水体（如液态水、冰与积雪），例如区分积雪上空的云、冰云与水云，或是区分洪水与茂密植被。在最高分辨率下，该可视化图像基于原始数据缩放至赤道处每像素对应250米的分辨率。 VIIRS校正反射率产品（VIIRS Corrected Reflectance Product）保留了可见气溶胶以实现自然的视觉效果，但已去除显著大气效应（如瑞利散射）。以下指南将帮助您理解本可视化图像。点击此处可了解该假彩色波段组合如何凸显地球这些物理特征的更多信息： - 厚冰与积雪呈现鲜亮红色（或深粉色），云层中的冰晶则呈偏粉色； - 植被呈现绿色； - 自然裸露土壤（如沙漠）呈亮青色； - 地表液态水呈深暗色，而云层中的水滴则呈白色； - 水体中的沉积物呈暗红色。 ### 多光谱波段 下表列出了用于生成本可视化图像的VIIRS波段。完整的VIIRS波段说明请点击此处。 | 波段 | 描述 | 波长（μm） | 分辨率（米） | |------|------|------------|--------------| | I3 | 短波红外（红色通道） | 1.58 - 1.64 | 375 | | M3 | 可见光（反射型） | 0.478 - 0.488 | 750 | | M11 | 短波红外 | 2.23 - 2.28 | 750 | ### 时间覆盖范围与使用限制 默认情况下，该图层将显示当前日期可用的图像。该图像的更新频率为每日合成产品，由数百份独立数据文件拼接而成。当查看“今日”图像时，您可能会发现仅部分地图区域有图像覆盖，这是因为该可视化图像会随着卫星采集更多数据而持续更新。若需查看随时间变化的图像，您可以更改图层属性以启用时间动画并配置时间参数。当前版本的该图层可查看的时间范围为2020年4月25日至今，未来数月内将扩展至任务起始日（2017年11月18日）。 ### 数据来源 本可视化图像由NASA全球图像浏览服务（GIBS）提供，该服务是一套标准化服务，可为数百项NASA地球科学数据集与科学参数提供全球全分辨率卫星图像。通过其服务与NASA Worldview客户端，GIBS可支持广大用户交互式探索NASA地球图像。借助NASA LANCE功能，数据与图像可在采集后3小时内生成。 ### Esri与NASA合作服务 本可视化图像通过托管于Esri服务器的ArcGIS图像服务提供，便于用户访问NASA GIBS服务端点。针对每一次图像服务请求，Esri服务器会向GIBS服务发起多次请求，对响应结果进行处理与拼接后，向用户返回完整的镶嵌图像。所有请求均会实时处理，以确保GIBS图像的任何更新均可立即为用户所用。因此，本可视化图像的可用性同时依赖于Esri与NASA GIBS两项服务。