Small-Satellite Synthetic Aperture Radar for Continuous Global Biospheric Monitoring: A Review

Sung Wook Paek,Sangtae Kim,Sivagaminathan Balasubramanian,Olivier De Weck

doi:10.3390/rs12162546

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.

Highlights

Space-based radar observation has growing potentials for monitoring the global biospheric diversity subject to anthropogenic drivers at geological scales [1]
The cost per satellite is similar between ICEYE and Capella X-synthetic aperture radar (SAR), so it can be regarded that the cost of further reducing satellite sizes seems to counterbalance the benefit of lower launch costs due to the reduced mass; in both ICEYE and Capella X-SAR missions, the second generation had a larger volume and mass than the first generation, which implies the limitations of over-downsizing
New space missions represented by small satellites, are driving cost reduction and changing the design paradigm of space-based SAR (Section 2) [158]

Summary

Introduction

Space-based radar observation has growing potentials for monitoring the global biospheric diversity subject to anthropogenic drivers at geological scales [1]. Satellites with onboard sensors can provide comprehensive coverage of remote areas or vast regions that may be too costly for unmanned aerial vehicles (UAVs) or ground-based platforms, provided that all platforms provide congruent results via calibrations [2,3,4] It was Seasat, the first satellite dedicated to remote sensing of the Earth’s oceans, that carried the first synthetic aperture radar (SAR) and other radar instruments operable in space. The imaging mode, not shown, is identical to the wave mode except that the entire 100 km wide strip is scanned for high-resolution imagery without any movement profile information This resolution-swath tradeoff is shown in Advanced Land Observing Satellite (ALOS) whose ScanSAR mode has a coarse 100 m resolution but 250–350 km wide swath. This is 3 to 5 times wider than conventional SAR images and is especially useful for monitoring sea ice and rain forest extent with expansive areas of interest [13]

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Conclusion