remote sensing Review Small-Satellite Synthetic Aperture Radar for Continuous Global Biospheric Monitoring: A Review Sung Wook Paek 1,* , Sivagaminathan Balasubramanian 1, Sangtae Kim 2 and Olivier de Weck 3 1 Samsung SDI Co., Ltd. 130 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16678, Korea;
[email protected] 2 Department of Nuclear Engineering, Hangyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea;
[email protected] 3 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;
[email protected] * Correspondence:
[email protected] Received: 26 June 2020; Accepted: 2 August 2020; Published: 7 August 2020 Abstract: Space-based radar sensors have transformed Earth observation since their first use by Seasat in 1978. Radar instruments are less affected by daylight or weather conditions than optical counterparts, suitable for continually monitoring the global biosphere. The current trends in synthetic aperture radar (SAR) platform design are distinct from traditional approaches in that miniaturized satellites carrying SAR are launched in multiples to form a SAR constellation. A systems engineering perspective is presented in this paper to track the transitioning of space-based SAR platforms from large satellites to small satellites. Technological advances therein are analyzed in terms of subsystem components, standalone satellites, and satellite constellations. The availability of commercial satellite constellations, ground stations, and launch services together enable real-time SAR observations with unprecedented details, which will help reveal the global biomass and their changes owing to anthropogenic drivers. The possible roles of small satellites in global biospheric monitoring and the subsequent research areas are also discussed. Keywords: synthetic aperture radar; small satellite; biospheric monitoring; satellite constellation 1.