Jingfeng Huang

Preliminary evaluation of S‐NPP VIIRS aerosol optical thickness

The Visible Infrared Imaging Radiometer Suite (VIIRS) is the next-generation polar-orbiting operational environmental sensor with a capability for global aerosol observations. The VIIRS aerosol Environmental Data Record (EDR) is expected to continue the decade-long successful multispectral aerosol retrieval from the NASAs Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) for scientific research and applications. Since the launch of the Suomi National Polar-orbiting Partnership (S-NPP), the VIIRS aerosol calibration/validation team has been continuously monitoring, evaluating, and improving the performance of VIIRS aerosol retrievals. In this study, the VIIRS aerosol optical thickness (AOT) at 550 nm EDR at current Provisional maturity level is evaluated by comparing it with MODIS retrievals and measurements from the Aerosol Robotic Network (AERONET) and the Maritime Aerosol Network (MAN). The VIIRS global mean AOT at 550 nm differs from that of MODIS by approximately −0.01 over ocean and 0.03 over land (0.00 and −0.01 for the collocated retrievals) but shows larger regional biases. Global validation with AERONET and with MAN measurements shows biases of 0.01 over ocean and −0.01 over land, with about 64% and 71% of retrievals falling within the expected uncertainty range established by MODIS over ocean (±(0.03 + 0.05AOT)) and over land (±(0.05 + 0.15AOT)), respectively. The VIIRS retrievals over land exhibit slight overestimation over vegetated surfaces and underestimation over soil-dominated surfaces. These results show that the VIIRS AOT at 550 nm product provides a solid global data set for quantitative scientific investigations and environmental monitoring.

CALIPSO inferred most probable heights of global dust and smoke layers

The vertical location of aerosol layers is critical for determining predominance of aerosol radiative and microphysical effects in aerosol-cloud-precipitation-climate interaction. The spaceborne lidar system, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), provides an unprecedented opportunity to observe vertical distributions of global aerosol layers. In this study we examine the most probable height (MPH) of dust and smoke layers, which are calculated either from aerosol occurrence frequency (OF) in vertical feature mask or aerosol extinction profile. The study focuses on six high-aerosol-loading regions where aerosols are of great interest in a range of scientific topics: Saharan Air Layer (SAL) over Tropical Atlantic, West African Monsoon region (WAM), Southeast Atlantic Ocean (SAO), Southeast Asia (SEA) and South China Sea, Amazon (AMZ), and Northwestern Pacific (NWP). The analysis revealed interesting spatial and seasonal variability of different vertical mixture features over these regions: seasonal migration of dust layers over SAL, separation and mixture of dust and smoke layers over WAM and NWP, and smoke layer above clouds over SAO, SEA, and AMZ. Results also indicated that the OF-based MPH tends to be much higher than the aerosol optical depth (AOD)-based MPH, owing to the predominating near-surface sources. Within the same vertical resolution grid of CALIPSO, aerosols are found with higher OF at higher levels but AOD tends to increase toward lower levels, because most aerosol sources are near the surface and the aerosol layers transported to high altitudes are generally much more diluted over larger spatial domain than those near the surface.

An enhanced VIIRS aerosol optical thickness (AOT) retrieval algorithm over land using a global surface reflectance ratio database

The Visible/Infrared Imager Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (S-NPP) satellite has been retrieving aerosol optical thickness (AOT), operationally and globally, over ocean and land since shortly after S-NPP launch in 2011. However, the current operational VIIRS AOT retrieval algorithm over land has two limitations in its assumptions for land surfaces: (1) it only retrieves AOT over the dark surfaces and (2) it assumes that the global surface reflectance ratios between VIIRS bands are constants. In this work, we develop a surface reflectance ratio database over land with a spatial resolution 0.1° × 0.1° using 2 years of VIIRS top of atmosphere reflectances. We enhance the current operational VIIRS AOT retrieval algorithm by applying the surface reflectance ratio database in the algorithm. The enhanced algorithm is able to retrieve AOT over both dark and bright surfaces. Over bright surfaces, the VIIRS AOT retrievals from the enhanced algorithm have a correlation of 0.79, mean bias of −0.008, and standard deviation (STD) of error of 0.139 when compared against the ground-based observations at the global AERONET (Aerosol Robotic Network) sites. Over dark surfaces, the VIIRS AOT retrievals using the surface reflectance ratio database improve the root-mean-square error from 0.150 to 0.123. The use of the surface reflectance ratio database also increases the data coverage of more than 20% over dark surfaces. The AOT retrievals over bright surfaces are comparable to MODIS Deep Blue AOT retrievals.