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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L18814, doi:10.1029/2006GL026626, 2006

Assessment of MODIS-derived visible and near-IR aerosol optical properties and their spatial variability in the presence of mineral dust

J. Redemann

BAER Institute, Sonoma, California, USA


Q. Zhang

BAER Institute, Sonoma, California, USA


B. Schmid

BAER Institute, Sonoma, California, USA


P. B. Russell

NASA Ames Research Center, Moffett Field, California, USA


J. M. Livingston

SRI International, Menlo Park, California, USA


H. Jonsson

CIRPAS, Marina, California, USA


L. A. Remer

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


Abstract

Mineral dust aerosol is among the most difficult aerosol species to measure quantitatively from space. In this paper, we evaluate MODIS retrievals of spectral aerosol optical depth (AOD) from the visible to the near-IR off the US West Coast using measurements taken by the NASA Ames Airborne Tracking Sunphotometer, AATS-14, during the EVE (Extended-MODIS-λ Validation Experiment, 2004) campaign in April of 2004. In EVE, a total of 35 and 49 coincident over-ocean suborbital measurements at the nominal level-2 retrieval scale of 10 km × 10 km were collected for Terra and Aqua, respectively. For MODIS-Terra about 80% of the AOD retrievals are within the estimated uncertainty, Δτ = ±0.03 ± 0.05τ; this is true for both the visible (here defined to include 466–855 nm) and near-IR (here defined to include 1243–2119 nm) retrievals. For MODIS-Aqua about 45% of the AOD retrievals are within Δτ = ±0.03 ± 0.05τ; the fraction of near-IR retrievals that fall within this uncertainty range is about 27%. We found an rms difference of 0.71 between the sunphotometer and MODIS-Aqua estimates of the visible (553–855 nm) Ångstrom exponent, while the MODIS-Terra visible Ångstrom exponents show an rms difference of only 0.29 when compared to AATS. The cause of the differences in performance between MODIS-Terra and MODIS-Aqua could be instrument calibration and needs to be explored further. The spatial variability of AOD between retrieval boxes as derived by MODIS is generally larger than that indicated by the sunphotometer data.

Received 19 April 2006; accepted 24 August 2006; published 30 September 2006.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 1640 Global Change: Remote sensing (1855); 3311 Atmospheric Processes: Clouds and aerosols.

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Citation: Redemann, J., Q. Zhang, B. Schmid, P. B. Russell, J. M. Livingston, H. Jonsson, and L. A. Remer (2006), Assessment of MODIS-derived visible and near-IR aerosol optical properties and their spatial variability in the presence of mineral dust, Geophys. Res. Lett., 33, L18814, doi:10.1029/2006GL026626.