ACIX is an international collaborative initiative to inter-compare a set of atmospheric correction (AC) processors for high-spatial resolution optical sensors. The exercise will focus on Landsat-8 and Sentinel-2 imagery over a set of test areas. The inter-comparison of the derived Bottom-of-Atmosphere (BOA) products is expected to contribute to the understanding of the different uncertainty contributors and help in improving the AC processors.

Introduction
 

The free and open data access policy to Landsat-8 and Sentinel-2 satellite imagery has stimulated the development of atmospheric correction (AC) processors for generating Bottom-of-Atmosphere (BOA) products. Several entities have started to generate (or plan to generate in the short term) BOA reflectance products at global scale for Landsat-8 and Sentinel-2 missions. To this end, NASA and the European Space Agency are organizing this exercise on AC processors inter-comparison. The results of the exercise are expected to point out the strengths and weaknesses, as well as communalities and discrepancies of various AC processors, in order to suggest and define ways for their further improvement.

The exercise aims to bring together the developers of the available AC processors, who are invited to generate the corresponding BOA products. The input data will be Landsat-8 and Sentinel-2 imagery of various test sites, i.e. coastal, agricultural, snow/artic areas and deserts. A common and harmonised inter-comparison procedure will be agreed and followed by all the participants.

Objectives

• To elaborate concepts, protocols and guidelines for the inter-comparison and validation of BOA products

• To better understand BOA reflectance uncertainty contributors by comparing the outputs of different AC schemes
• To identify and review the different uncertainty contributors
• To propose further improvements of the available AC schemes

• Description of concept, protocols and procedures for inter-comparing and validating products
• Assessment of the relative differences among the inter-compared AC processors results
• Definition of key regions and key periods for validation and quality assessment
• Description of a coordinated plan for inter-comparison and validation activities

You can find the Programme of the 1st ACIX workshop  here

You can find the Programme of the 2nd ACIX workshop (not available yet)

The Atmospheric Correction Inter-comparison Exercise will be performed in three phases:

1. Definition of the inter-comparison protocol: The participants are invited to propose a protocol for the AC processors inter-comparison. The number and type of the test sites, the number of scenes and the metrics for models inter-comparison will be proposed before the 1st ACIX workshop. All the proposals will be discussed in the workshop and the final inter-comparison procedure will be agreed by all participants.

2. Application of the AC processors: The participants will apply their AC schemes on the test cases keeping the processing parameters constant. The results will be submitted for analysis (3rd phase) to ACIX coordinators.

3. Analysis of the results: The ACIX coordinators will analyse the submitted results from all participants and will assess the inter-comparison outputs based on the agreed metrics. All the results will be announced to participants prior to the 2nd ACIX workshop, where they will be presented and discussed.

• 1st Workshop: College Park Marriott Hotel & Conference Center, close to the University of Maryland Research Park, 21-22/6/2016.

• 2nd Workshop: ESA/ESRIN, Frascati, Italy, 11-12 April 2017.