Validating MODIS Above-Cloud Aerosol Optical Depth Retrieved from Color Ratio Algorithm Using Direct Measurements Made by NASA's Airborne AATS and 4STAR Sensors

• Published in: Atmospheric measurement techniques 2016-10, Vol.9 (10), p.5053-5062
• Main Authors: Jethva, Hiren, Torres, Omar, Remer, Lorraine, Redemann, Jens, Livingston, John, Dunagan, Stephen, Shinozuka, Yohei, Kacenelenbogen, Meloe, Segal Rozenhaimer, Michal, Spurr, Rob
• Format: Article
• Language: English
• Subjects: Aerosol optical depth; Aerosol optical properties; Aerosols; Airborne remote sensing; Airborne sensing; Aircraft; Algorithms; Atmospheric particulates; Atmospheric research; Biomass burning; Burning; Cloud optical depth; Clouds; Color; Colour; Datasets; Decks; Depth; Dust storms; Earth Resources And Remote Sensing; Experiments; Field tests; Geophysics; MODIS; Optical analysis; Optical properties; Optical thickness; Photometers; Reflectance; Satellites; Sensors; Sky; Tracking; Uncertainty; Wildfires; Wildlife tourism
• ISSN: 1867-1381; 1867-8548; 1867-8548
• DOI: 10.5194/amt-9-5053-2016

We present the validation analysis of above-cloud aerosol optical depth (ACAOD) retrieved from the color ratio method applied to MODIS cloudy-sky reflectance measurements using the limited direct measurements made by NASAs airborne Ames Airborne Tracking Sunphotometer (AATS) and Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) sensors. A thorough search of the airborne database collection revealed a total of five significant events in which an airborne sun photometer, coincident with the MODIS overpass, observed partially absorbing aerosols emitted from agricultural biomass burning, dust, and wildfires over a low-level cloud deck during SAFARI-2000, ACE-ASIA 2001, and SEAC4RS 2013 campaigns, respectively. The co-located satellite-airborne match ups revealed a good agreement (root-mean-square difference less than 0.1), with most match ups falling within the estimated uncertainties associated with the MODIS retrievals (about -10 to +50 ). The co-retrieved cloud optical depth was comparable to that of the MODIS operational cloud product for ACE-ASIA and SEAC4RS, however, higher by 30-50% for the SAFARI-2000 case study. The reason for this discrepancy could be attributed to the distinct aerosol optical properties encountered during respective campaigns. A brief discussion on the sources of uncertainty in the satellite-based ACAOD retrieval and co-location procedure is presented. Field experiments dedicated to making direct measurements of aerosols above cloud are needed for the extensive validation of satellite based retrievals.