MODIS/Aqua Aerosol 5-Min L2 Swath 3km - NRT

The new Collection 6.1 (C61) MYD04_3K product is an improved version based on algorithm changes in Dark Target (DT) Aerosol retrieval over urban areas and uncertainty estimates for Deep Blue (DB) Aerosol retrievals.

The MODIS level-2 atmospheric aerosol product provides retrieved ambient aerosol optical properties, quality assurance, and other parameters, globally over ocean and land. In Collection 5, and earlier collections, there was only one aerosol product (MOD04_L2) at 10km (at nadir) spatial resolution. Starting from C6, the Dark Target (DT) Aerosol algorithm team provided a new 3 km spatial resolution product (MOD04_3k) intended for the air quality community.

The MOD04_3K product is based on the same algorithm and Look up Tables as the standard Dark Target aerosol product. Because of finer resolution, subtle differences are made in selecting pixels for retrieval and in determining QA. The only differences between the existing 10km algorithm and the 3km algorithm are: 1) the size of the pixel-arrays defining each retrieval box (6x6 retrieval boxes of 36 pixels at 0.5km resolution for 3km algorithm as oppose to 20x20 retrieval boxes of 400 pixels at 0.5km resolution for 10km product); 2) the minimum percentage of good pixels required for a retrieval (a minimum of 5 pixels over ocean and 6 pixels over land instead of a minimum of 10 pixels over ocean or 12 pixels over land for 10km product retrieval); 3) the 10km algorithm attempts a poor quality retrieval while 3km algorithm does not. Everything else is same in two products.

For more information on C6.1 changes and updates, visit the MODIS Atmosphere website at:
https://modis-atmosphere.gsfc.nasa.gov/documentation/collection-61

新版的6.1（C61）MYD04_3K产品是基于对城市区域暗目标（DT）气溶胶反演算法的改进以及深蓝（DB）气溶胶反演不确定性估计的改进而推出的。MODIS二级大气气溶胶产品提供了全球范围内海洋和陆地上反演的背景气溶胶光学特性、质量保证以及其他参数。在5版及之前的版本中，仅有一个气溶胶产品（MOD04_L2）以10公里（正午）的空间分辨率提供。自C6版起，暗目标（DT）气溶胶算法团队提供了一种新的3公里空间分辨率产品（MOD04_3k），旨在服务于空气质量社区。MOD04_3K产品基于与标准暗目标气溶胶产品相同的算法和查找表。由于分辨率更高，我们在选择用于反演的像素以及在确定质量保证方面做出了细微的调整。现有10公里算法与3公里算法之间的唯一区别在于：1）定义每个反演框的像素阵列的大小（3公里算法使用6x6的反演框，包含36个像素，分辨率为0.5公里，而10公里产品使用20x20的反演框，包含400个像素，分辨率为0.5公里）；2）对于反演所需的最小良好像素百分比（海洋上至少5个像素，陆地上至少6个像素，而10公里产品反演则需要至少10个像素在海洋上或12个像素在陆地上）；3）10公里算法尝试进行低质量反演，而3公里算法则不这么做。除此之外，两个产品在其他方面保持一致。有关C6.1版变更和更新的更多信息，请访问MODIS大气网站：https://modis-atmosphere.gsfc.nasa.gov/documentation/collection-61。