08/11/2022 Final Review Meeting

The CIRCAS Final review meeting took place online through Microsoft Teams. The positive impact of the improved calibration of SLSTR has been discussed during the presentation of the validation results. The extensive validation report prepared by Brockmann Consult with the support of Rayference showed encouraging results achieved by this ambitious and innovative project. The work performed within CIRCAS will be extended within other ESA project such as Aerosol-CCI+.

22/09/2020 Acceptance Review Meeting

The CIRCAS acceptance review meeting took place online through WebEx. The objective of the meeting was to review the first validation results of the CISAR retrieval of aerosols and clouds properties, surface reflectance and solar downward fluxes.

08/05/2020 CIRCAS presented at EGU 2020

CIRCAS intermediate results on the consistent retrieval of cloud and aerosol single scattering properties and surface reflectance have been presented at the EGU 2020 (virtual meeting due to COVID). The presentation can be found here.

11/12/2019 Correction of the SLSTR solar band calibration

Rayference has been working on the verification and correction of the S3A/SLSTR solar bands. This activity has been reported in web story of the Eradiate project entitled "Estimating the accuracy of 1D radiative transfer models over the Libya-4 site". Following this study, the S3A/SLSTR Level 1b TOA BRF corrections recommended by Rayference, displayed in the following table,

will be used by the CIRCAS project. These calibration correction factors should multiply the delivered top-of-atmosphere bidirectional reflectance factor (TOA BRF) values. The complete analysis is presented in a dedicated report.

09/05/2019 CIRCAS presented at The Fifth Sentinel-3 Validation Team Meeting

The CIRCAS project has been presented at the 5th Sentinel-3 Validation Team Meeting. The presentation can be found on the event website website.

06/12/2018 Mid-Term Review

The CIRCAS mid-term review took place in Hamburg. The objective of the meeting was to review the CIRCAS progress during the first year of the project.

11/01/2018 Science Review

The CIRCAS science review took place at Rayference premises located in Brussels. The objective of the meeting was to review the Requirement Baseline Document and the draft version of the ATBD.

29/09/2017 Kick-off meeting

The CIRCAS kick-off meeting took place at ESA-ECSAT (UK).

Publication alert!

The development on the CISAR algorithm to extend the retrieval to cloud single scattering properties, initiated within the CIRCAS project and continued within the Aerosol-CCI+ ESA project, have been published on the Atmosphere MDPI journal (Luffarelli et al., 2022). The proposed approach aims at filling this gap and deepening the understanding of aerosol properties in cloudy environments. The new CISAR version is applied to Sentinel-3A/SLSTR observations and evaluated against different satellite products and ground measurements. The spatial coverage is greatly improved with respect to algorithms processing only pixels flagged as clear sky by the SLSTR cloud mask. The continuous retrieval of aerosol properties without any safety zone around clouds opens new possibilities for studying aerosol properties in cloudy environments.

2020 Godzilla Dust Storm

In June 2020, a dust plume originating from Sahara was transported towards the Caribbean islands, traveling more than 8000 km and peaking between 14 and 20 June. This dust storm was so extreme that it has been named Godzilla. This extraordinary dust plume, nearly as big as the continental United States, weighed almost 24 million tons. Godzilla was surprising not only in terms of size and weight but also in terms of its trigger. Most of the dust storm is unfortunately misclassified as cloud from the SLSTR summary cloud flag (see Figure below). Aerosol retrieval algorithms only inverting clear-sky observations would therefore completely miss such an exceptional event. Conversely, the CISAR algorithm, not relying on an external cloud mask, performs the retrieval over all SLSTR observations regardless of the cloud mask classification. The Figure below shows the false-color composite obtained from SLSTR bands S1, S2, and S3, the SLSTR summary cloud flag, the combined AOT and COT retrieval at 0.55 μm with the CISAR algorithm, and the FM fraction associated with the AOT retrieval. It can be seen that most of the dust storm, partially visible in the false-color composite, is flagged as cloud. In particular, about 85% of SLSTR observations are flagged as cloud; with a retrieval algorithm only inverting clear-sky observations, the aerosol retrieval would be performed only on the remaining 15% of the pixels. CISAR, however, retrieves valid AOT (i.e., greater than 0) over 35% of all SLSTR observations, greatly improving the spatial coverage of the AOT product.

2019 Australian Fires

In the framework of the ESA Aerosol Climate Change Initiative (Aerosol-CCI+) project, the CISAR algorithm, extended to the retrieval of clouds within the CIRCAS project, has been applied to SLSTR / Sentinel-3A observations acquired in the visible and near-infrared bands. On 6th September 2019 CNN reported over 100 wildfires over Australia, in the states of Queensland and New South Wales. CISAR retrieval during this extreme event shows that CISAR correctly discriminates between high aerosol loads and clouds, with continuity between cloudy and cloud free sky.

A webstory on the results obtained with the CISAR algorithm from SLSTR observations during the Australian fire season in 2019 has been published by ESA.

Correction of the SLSTR solar band calibration

Rayference has been working on the verification and correction of the S3A/SLSTR solar bands. This activity has been reported in web story of the Eradiate project entitled "Estimating the accuracy of 1D radiative transfer models over the Libya-4 site". Following this study, the S3A/SLSTR Level 1b TOA BRF corrections recommended by Rayference, displayed in the following table,

will be used by the CIRCAS project. These calibration correction factors should multiply the delivered top-of-atmosphere bidirectional reflectance factor (TOA BRF) values. The complete analysis is presented in a dedicated report.