The atmosphere over the Northeastern region of Brazil (NEB) contains a variety of different aerosol types: marine, soil dust, biomass burning, urban pollution, as well as mixed species. However, very few reliable information on aerosols is available for the region. Satellite data provides spatial and temporal coverage in places with low density ground-based observational networks, with Aerosol Optical Depth (AOD) products as most important information on the atmospheric aerosol load. To find out how different AOD products from satellites behave over the NEB region we compared AOD at 550 nm from MODIS retrievals aboard both NASA's Terra and Aqua satellites, and ground-based derived AOD 550 nm from the two Aerosol Robotic Network (AERONET) sites in the region, located in cities of Petrolina and Natal, between 2015 and 2018. We based our analysis on the following MODIS AOD retrievals products: Dark Target (DT), Deep Blue (DB), the combined product (DTDB), DT 3 km resolution product (MxD3k) and MAIAC at 1 km resolution. Additionally, we used AOD from MERRA2 reanalysis for another comparison that may provide additional insight on which products perform best over the region. We also analyze and compare the seasonality of the AOD products to the four biomes of NEB, which are Amazon rainforest, Atlantic Forest, Cerrado and Caatinga (wooded savannah-like) biomes. Petrolina is located in the NEB largest biome, the Caatinga, while Natal is a coastal city in the Atlantic Forest. The results show that DB yields the best results for the Petrolina site. The analyses also show that in all biomes the AOD monthly averages decrease during austral autumn and winter and increase during spring and summer. The compared products show some differences in AOD, even though with similar patterns. MAIAC and DB show very similar values in all four biomes throughout the year, recommending the use of DB and MAIAC for studies in the Caatinga region.

中文翻译：

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巴西东北部气溶胶光学厚度：多平台比较研究


巴西东北部地区 （NEB） 的大气包含各种不同类型的气溶胶：海洋、土壤灰尘、生物质燃烧、城市污染以及混合物种。然而，关于该地区的气溶胶的可靠信息很少。卫星数据在低密度地面观测网络的地方提供空间和时间覆盖，气溶胶光学厚度 （AOD） 产品是大气气溶胶负荷的最重要信息。为了了解来自卫星的不同 AOD 产品在 NEB 区域的行为，我们比较了 2015 年至 2018 年间 NASA 的 Terra 和 Aqua 卫星上的 MODIS 检索的 550 nm 处的 AOD，以及来自该地区位于佩特罗利纳市和纳塔尔市的两个气溶胶机器人网络 （AERONET） 站点的地基衍生 AOD 550 海里。我们的分析基于以下 MODIS AOD 检索产品：暗目标 （DT）、深蓝 （DB）、组合产品 （DTDB）、DT 3 公里分辨率产品 （MxD3k） 和 1 公里分辨率的 MAIAC。此外，我们使用 MERRA2 再分析的 AOD 进行另一项比较，这可能会为哪些产品在该地区表现最佳提供更多见解。我们还将 AOD 产品的季节性与 NEB 的四个生物群落进行了分析和比较，即亚马逊雨林、大西洋森林、塞拉多和卡廷加（树木繁茂的稀树草原状）生物群落。Petrolina 位于 NEB 最大的生物群落 Caatinga，而纳塔尔是大西洋森林中的沿海城市。结果表明，DB 为 Petrolina 站点生成了最佳结果。分析还表明，在所有生物群落中，AOD 月平均值在南方秋季和冬季下降，在春季和夏季增加。比较的产品显示出 AOD 的一些差异，即使具有相似的模式。 MAIAC 和 DB 在全年所有四个生物群落中都显示出非常相似的值，建议在 Caatinga 地区使用 DB 和 MAIAC 进行研究。