Abstract
The Atmospheric Correction Inter-comparison eXercise (ACIX) is an international initiative with the aim to analyse the Surface Reflectance (SR) products of various state-of-the-art atmospheric correction (AC) processors. The Aerosol Optical Thickness (AOT) and Water Vapour (WV) are also examined in ACIX as additional outputs of an AC processing. In this paper, the general ACIX framework is discussed; special mention is made of the motivation to initiate this challenge, the inter-comparison protocol and the principal results. ACIX is free and open and every developer was welcome to participate. Eventually, 12 participants applied their approaches to various Landsat-8 and Sentinel-2 image datasets acquired over sites around the world. The current results diverge depending on the sensors, products and sites, indicating their strengths and weaknesses. Indeed, this first implementation of processor inter-comparison was proven to be a good lesson for the developers to learn the advantages and limitations of their approaches. Various algorithm improvements are expected, if not already implemented, and the enhanced performances are yet to be investigated in future ACIX experiments.
Highlights
Today, free and open data policy allows access to a large amount of remote sensing data, which together with the advanced cloud computing services, significantly facilitate the analysis of long time series
Atmospheric Correction Inter-comparison eXercise (ACIX) was only initiated to inter-compare the performance of atmospheric correction (AC) processors over land, five coastal and inland water sites were included in the analysis, in order to examine the performance over diverse sites
These quality-approved pixels were the result of the intersection of the Quality Assessment (QA) band estimated by LaSRC and each processor’s quality flags in every analysis case
Summary
Free and open data policy allows access to a large amount of remote sensing data, which together with the advanced cloud computing services, significantly facilitate the analysis of long time series. In the international framework of the Committee on Earth Observation Satellites (CEOS), the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) initiated the Atmospheric Correction Inter-comparison Exercise (ACIX) to explore the different aspects of every AC processor and the quality of the SR products. In order to obtain an accurate SR product, ready to use for land or water applications, two main steps are required: first, the detection of cloud and cloud shadow and the correction for atmospheric effects. Both parts of the process have equal importance, ACIX only concentrated on the atmospheric correction in this first experiment. The analysis performed per test site is not presented in this paper, but all the results can be found on the ACIX web site hosted on the CEOS Cal/Val portal (http://calvalportal.ceos.org/projects/acix)
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