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

The new Collection 6.1 (C61) MOD04_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 new 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 attemptes 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

新版本集合6.1（C61）MOD04_3K产品系基于暗目标（DT）城市区域气溶胶反演算法改进与深蓝（DB）气溶胶反演不确定性估算的优化版本。该MODIS二级大气气溶胶产品在全球范围内，无论是海洋还是陆地，均提供了环境气溶胶的光学特性反演、质量保证以及其他参数。在集合5及之前版本中，仅有一个10公里（正午点）空间分辨率的气溶胶产品（MOD04_L2）。自C6版本起，暗目标（DT）气溶胶算法团队提供了新的3公里空间分辨率产品（MOD04_3k），旨在服务于空气质量领域。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，检索像素选择和质控方面存在细微差异。现有10公里算法与新的3公里算法之间的主要区别包括：1）定义每个检索框的像素阵列大小（3公里算法采用6x6检索框，即36个像素，分辨率为0.5公里，相对于10公里产品的20x20检索框，即400个像素，分辨率为0.5公里）；2）要求检索中良好像素的最小百分比（海洋区域至少5个像素，陆地区域至少6个像素，而10公里产品的检索则要求至少10个像素在海洋或12个像素在陆地）；3）10公里算法尝试进行低质量检索，而3公里算法则不进行。除了上述三点外，两种产品在其他方面均保持一致。有关C6.1版本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。