MODIS/Terra+Aqua L3 Value-added Aerosol Optical Depth - NRT

MODIS was launched aboard the Terra satellite on December 18, 1999 (10:30 am equator crossing time) as part of NASA's Earth Observing System (EOS) mission. MODIS with its 2330 km viewing swath width provides almost daily global coverage. It acquires data in 36 high spectral resolution bands between 0.415 to 14.235 micron with spatial resolutions of 250m(2 bands), 500m(5 bands),and 1000m (29 bands). MODIS sensor counts, calibrated radiances, geolocation products and all derived geophysical atmospheric and ocean products are archived at various DAACs and has been made available to public since April 2000.

The shortname for this level-3 MODIS aerosol product is MCDAODHD. The Naval Research Laboratory and the University of North Dakota developed this value-added aerosol optical depth dataset based on MODIS Level 2 aerosol products. MCDAODHD is a gridded product and is specifically designed for quantitative applications including data assimilation and model validation. It is available through LANCE-MODIS. It offers several enhancements over the MODIS Level 2 data on which it is based. These enhancements include stringent filtering to reduce outliers, eliminate cloud contamination, and exclude conditions where aerosol detection is likely to be inaccurate; reduction of systematic biases over land and ocean by empirical corrections; reduction of random variation in AOD values by spatial averaging; quantitative estimation of uncertainty for each AOD data point.

The MxDAODHD granules are produced every six hours, and time-stamped 00:00, 06:00, 12:00, and 18:00 (all times UTC). Each granule includes MODIS observations from +/-3 hours from the timestamp (e.g. 12:00 product includes MODIS data from 09:00-15:00 UTC). Production is initiated as soon as the Level 2 inputs become available in the LANCE system.

See the LANCE-MODIS page for more dataset information:

https://earthdata.nasa.gov/earth-observation-data/near-real-time/downlo…

MODIS于1999年12月18日（当地时间上午10:30，赤道穿越时间）搭载Terra卫星发射升空，作为美国宇航局地球观测系统（EOS）任务的一部分。MODIS以其2330公里的观测带宽度，几乎每日实现对全球的覆盖。它采集了0.415至14.235微米范围内的36个高光谱分辨率波段的数据，空间分辨率分别为250米（2个波段）、500米（5个波段）和1000米（29个波段）。MODIS传感器计数、校准辐射亮度、地理定位产品和所有派生的地球物理大气和海洋产品均存档于各数据存档与分配中心（DAACs），并于2000年4月起向公众开放。

该三级MODIS气溶胶产品的简称是MCDAODHD。海军研究实验室和北达科他大学基于MODIS二级气溶胶产品开发了这一增值气溶胶光学深度数据集。MCDAODHD是一个网格化产品，专门设计用于定量应用，包括数据同化和模型验证。它可通过LANCE-MODIS获取。它在基于的MODIS二级数据的基础上提供了多项改进。这些改进包括严格的过滤以减少异常值、消除云污染和排除气溶胶检测可能不准确的条件；通过经验校正减少陆地和海洋的系统偏差；通过空间平均减少AOD值中的随机变化；对每个AOD数据点的不确定性进行定量估计。

MxDAODHD数据块每六小时生成一次，时间戳为00:00、06:00、12:00和18:00（均为UTC时间）。每个数据块包括从时间戳前后的±3小时内的MODIS观测数据（例如，12:00的产品包括从09:00至15:00 UTC的MODIS数据）。生产启动的时间是LANCE系统中二级输入可用后。

有关数据集的更多信息，请参阅LANCE-MODIS页面：

https://earthdata.nasa.gov/earth-observation-data/near-real-time/downlo…