STAR / SMCD / EMB Aerosol Remote Sensing

Analysis of AVHRR Aerosol Data

Aerosol optical depth (AOD) were retrieved from the nearly 25-year record of inter-calibrated radiances in the AVHRR Pathfinder Atmosphere-Extended (PATMOS-x) data set. The PATMOS-x radiance dataset was recalibrated using MODIS radiances [Heidinger et al., 2002]. The aerosol algorithm used to retrieve AOD was the independent two-channel algorithm also employed in the operational processing. A description of the algorithm is accessible from the Products/AVHRR page.

The long-term trend of AOD over the global oceans has been studied from the PATMOS-x aerosol record. A linear decadal change of -0.01 is obtained for globally and monthly averaged AOD. This negative tendency is even more evident in globally and annually averaged AOD; the magnitude can be up to -0.03/decade. The decreasing trend is consistent with that found from the GACP data. Seasonal patterns in the AOD regional long-term trend are also evident. In general, negative tendencies are observed for seasonally averaged AOD in the regions influenced by emissions from industrialized countries and the magnitude can be up to -0.10/decade. Positive tendencies are observed in regions influenced by emissions from fast developing countries; their magnitude can be up to as large as +0.04/decade. For regions heavily influenced by Saharan desert particles, a negative trend with a maximum magnitude of -0.03/decade is detected. However, over regions influenced by smoke from biomass burning, positive tendencies with a maximum magnitude of +0.04/decade are found [Zhao et al., 2008].

The mean of monthly-average aerosol optical depths for the period of Apr 2004 -May 2008 is shown in Figure 1, along with the total number of samples available for calculating the mean. Monthly mean AOD values in PATMOS-x were also compared to those available in the standard MODIS aerosol products. The time series of monthly AOD from PATMOS-x and from MODIS/Terra and MODIS/Aqua is shown in Figure 2.

Figure 1. Mean of monthly averaged AOD in the PATMOS-x data for Apr 2004-May 2008 (left), and the total number of AOD samples available for calulating the mean (right).

Figure 2. Time series of monthly average AOD estimated from the afternoon ascending orbits of AVHRR in PATMOS-x, and those from MODIS instrument on the NASA/EOS Terra and Aqua patforms.

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