Retrieval of aerosol optical depth (AOD) using NOAA AVHRR data in an alpine environment

摘要

The aim of this study is the retrieval of aerosol optical depth from the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) sensor over land. The region of interest covers central Europe ranging from 50°N to 40.5°N and from 0°E to 17°E including the European Alps. On the temporal scale, we limit the data set to afternoon NOAA-16 passes of the entire year 2002. In this region, there are sixteen stations from the Aerosol Robotic Network (AERONET) at which we can compare the ground based versus the space borne measurements. The most crucial parameter in the retrieval procedure is the estimate of a correct surface reflectance since inaccuracies of 0.01 can result in AOD variations of ±0.1. Surface reflectance has been estimated by extracting the minimum reflectance within 10° intervals of the satellite zenith angle within two-month intervals. This method eliminates the varying reflectance with varying satellite zenith angle but the extracted surface reflectance still contains an aerosol signal. Most stations show a clear relationship between the AVHRR and the AERONET data. In case of a weak or non-existing relationship, we were able to identify reasons for this behavior. The standard error of estimate is about 0.18. The largest potential for increasing the accuracy of this product posses an improvement of the cloud mask. We can conclude that aerosol retrieval over land using AVHRR is a challenging task but it is possible to extract some valuable results.