Dear Colleagues,

Space-borne observations of land surfaces aim to ensure the global monitoring of bio-geophysical variables in order to model and predict their changes in response to natural and anthropogenic forces. To this purpose, space missions shall provide continuous, global, and consistent measurements of the Earth’s surface at spatial resolutions suitable for driving the relevant bio-geochemical models. Likewise, associated retrieval algorithms, used to extract the variables of interest from the space observations, shall be spatially and temporally consistent across the Earth’s various ecosystems and along the satellite mission’s lifetime. These basic requirements are underpinning the European strategy for land surface global monitoring, both the space component and the services.

On the space component side, the European Space Agency (ESA), through the Copernicus Programme, is committed to guaranteeing long-term sustained and continuous global observations at a moderate resolution (100–300m) in the visible to short-wave infrared, to support these requirements. In this context, the PROBA-V mission, successfully operated by ESA since 2013, plays a crucial role by ensuring continuity to the SPOT-VGT long-term data record of global/daily land observations. In the coming years, the Sentinel-3 twin satellite mission will progressively take over this continuity requirement, additionally extending spectral coverage to the thermal infrared. The transition phase between these two missions is currently on-going and it is expected to be completed by Spring 2020, when PROBA-V nominal operations will be discontinued. This transition phase is challenging, owing to the diversity of the relevant sensors. Extreme care is then paid to ensure the radiometric and spectral consistency of the relevant surface observations.

With respect to services, the Copernicus Global Land Service (CGLS) has been a champion user of SPOT-VGT and PROBA-V data, which is employed to derive a large set of bio-geophysical variables for operational global monitoring of the vegetation dynamic, the water cycle, the energy budget, and the cryosphere status. The CGLS products’ portfolio encompasses notably most of the terrestrial Essential Climate Variables (ECVs), such as land cover, Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), Leaf Area Index (LAI), fire disturbance, and snow cover. Nowadays, the CGLS is highly committed to ensuring continuous and seamless near-real-time provision of such variables during the transition phase from PROBA-V to Sentinel-3. However, this commitment poses significant scientific and practical challenges, namely, for adapting relevant retrieval algorithms to new sensor specifications and minimizing the potential spatio-temporal biases in derived products.

Considering the number of projects and studies currently running to ensure that the continuity requirement is fully met during the transition from PROBA-V to Sentinel-3 missions, and the relevance of this long-term dataset for the science community, we wish to compile knowledge of the current status of these projects, including examples of major achievements with a focus on land applications. We therefore invite you to submit manuscripts about your recent research, with respect to but not limited to the following topics:

• Mission status, algorithm, and data quality for PROBA-V and Sentinel-3;
• Cal/Val and cross-calibration activities between PROBA-V and Sentinel-3;
• Approaches for adapting land products’ algorithms from PROBA-V to Sentinel-3;
• Advances in retrieval and validation of terrestrial ECVs time series;
• Applications of CGLS variables for monitoring, modeling, and forecasting land surface state.

Dr. Fabrizio Niro
Dr. Roselyne Lacaze
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.