Comparative analysis of MODIS, MISR, and AERONET climatology over the Middle East and North Africa

Ashraf Farahat

doi:10.5194/angeo-37-49-2019

Abstract

Abstract. Comparative analysis of Multi-angle Imaging SpectroRadiometer (MISR), Moderate Resolution Imaging Spectroradiometer (MODIS), and Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) products is performed over seven AERONET stations located in the Middle East and North Africa for the period of 2000–2015. Sites are categorized into dust, biomass burning, and mixed aerosol conditions. MISR and MODIS AOD agree during high-dust seasons but MODIS tends to underestimate AOD during low-dust seasons. Over dust-dominated sites, MODIS/Terra AODs indicate a negative trend over time, while MODIS/Aqua, MISR, and AERONET depict a positive trend. A deviation between MODIS/Aqua and MODIS/Terra was observed regardless of the geographic location and data sampling. The performance of MODIS is similar over the entire region with ∼64 % of AOD within the Δτ=±0.05±0.15τAERO confidence range. MISR AOD retrievals fall within 84 % of the same confidence range for all sites examined here. Both MISR and MODIS capture aerosol climatology; however few cases were observed where one of the two sensors better captures the climatology over a certain location or AOD range than the other sensor. AERONET Level 2.0 version 3, MODIS Collection 6.1, and MISR V23 data have been used in analyzing the results presented in this study.

Highlights

The Middle East and North Africa host the largest dust source in the world, the Sahara desert in North Africa that may be responsible for up to 18 % of global dust emission (Todd et al, 2007; Bou Karam et al, 2010; Schepanski et al., 2016)
Similar correlation coefficient values were found in region 2 where Multi-angle Imaging SpectroRadiometer (MISR)–Aerosol Robotic Network (AERONET) Aerosol optical depth (AOD) shows smaller deviations from the Moderate Resolution Imaging Spectroradiometer (MODIS) data (Figs. 2 and 3 and Table 3)
The lowest MODIS–AERONET AOD correlation coefficient was found over Cairo but could be attributed to the lack of data availability at this location (Fig. 3e–h)

Summary

Introduction

The Middle East and North Africa host the largest dust source in the world, the Sahara desert in North Africa that may be responsible for up to 18 % of global dust emission (Todd et al, 2007; Bou Karam et al, 2010; Schepanski et al., 2016). The vast 650 000 km Rub’ al Khali (Empty Quarter) sand desert is a major source of frequent dust outbreaks and severe dust storms that have a major effect on human activity in the Arabian Peninsula (Böer, 1997; Elagib and Addin, 1997; Farahat et al, 2015). Blowing dust storms play a significant role in pollutant transport over the Arabian Peninsula, and major environmental pollution events such as burning of Kuwait oil fields during the 1991 Gulf War resulted in a large environmental impact on the Arabian Gulf area (Sadiq and McCain, 1993; Farahat, 2016). Aerosol optical depth (AOD; called aerosol optical thickness, AOT) as a parameter indicates the extinction of a beam of radiation as it passes through a layer of atmosphere that contains aerosols. Both satellites and ground-based instruments can be used to measure AOD in the atmosphere, but within the same temporal coordinates and geographic location different instruments could generate different retrievals (Kahn et al, 2007; Kokhanovsky et al, 2007; Liu and Mishchenko, 2008; Mishchenko et al, 2009)

Methods

Results

Conclusion