**1. Introduction**

The CYGNSS Science Team [1–5] is composed of a wide variety of researchers, working in a collaborative and coordinated manner to further advance the use of CYGNSS for Global Navigation Satellite Systems Reflectometry (GNSS-R) Earth remote sensing [6–8].

GNSS-R is a type of L-band passive multi-bistatic radar, which uses the navigation spacecrafts which are in view as transmitters. GNSS-R provides global coverage, full temporal availability, and sampling of the Earth's surface over several tracks within a wide area up to ~1500 km. One potential disadvantage is the degraded spatial resolution under the incoherent scattering regime. The use of GNSS radio-navigation signals for Earth remote sensing has been investigated since it was originally proposed for mesoscale ocean altimetry by the European Space Agency (ESA) [9]. The first in-orbit proof-of-concept study was an experiment performed at the Jet Propulsion Laboratory (JPL) using the Space-borne Imaging Radar-C (SIR-C) on-board the Space Shuttle [10]. This experiment motivated the development of GNSS-R. At present, several GNSS-R space-borne studies have been

**Citation:** Carreno-Luengo, H.; Crespo, J.A.; Akbar, R.; Bringer, A.; Warnock, A.; Morris, M.; Ruf, C. The CYGNSS Mission: On-Going Science Team Investigations. *Remote Sens.* **2021**, *13*, 1814. https://doi.org/ 10.3390/rs13091814

Academic Editor: Emanuele Santi

Received: 1 March 2021 Accepted: 1 May 2021 Published: 6 May 2021

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performed with several satellites, including United Kingdom (UK) Disaster Monitoring System-1 (DMC-1) [11], UK Techdemosat-1 (TDS-1) [12], Soil Moisture Active Passive (SMAP) [13], and the CYGNSS 8 microsatellites constellation [3] which is the first-ever operational GNSS-R mission.

The CYGNSS Science Team (Figure 1, Table 1) holds two Science Team meetings every year to coordinate such activities, and to share our most recent results. The last 2020 conference was held in UM (virtual conference) in June 2020 (Figure 1). This conference was structured along six different sessions covering all of our research topics: Session 1 (CYGNSS Mission Overview and Data Products I), Session 2 (CYGNSS Data Products II), Session 3 (Land Processes I), Session 4 (Land Processes II), Session 5 (Altimetry and Tropical Cyclones and Tropical Convection I), and Session 6 (Tropical Cyclones and Tropical Convection II). This article provides a synoptic overview of the meeting.

**Table 1.** Some key-members of the CYGNSS Science Team. The full list is available in [14].


**Figure 1.** Zoom-derived photo of some Science Team members attending the June 2020 CYGNSS meeting.
