A. Satellite Communications, Navigation, and Observation Research on Earth Observation Sensor Systems

Earth observation sensor systems encompass a wide range of technologies, distinguished by the electromagnetic spectrum they utilize (such as optical or microwave) and by their respective observation methodologies.

Building on JAXA’s extensive expertise in sensor system design and development, this research aims to investigate and advance both elemental-level technologies and advanced sensor systems with a long-term perspective extending 10 to 20 years into the future. In parallel, potential mission concepts that leverage these advanced sensor systems are being studied in collaboration with internal and external stakeholders.

The ultimate objective of this research is to mature these technologies and realize their application in future Earth observation missions.

Significance of the Research

Satellite-based Earth observation is increasingly becoming an essential infrastructure that supports society, and observation sensors are the core systems that directly enable this capability. These sensor systems observe electromagnetic radiation reflected from or emitted by the Earth, providing critical information about the planet’s atmosphere, oceans, land surfaces, and ecosystems. To achieve highly precise observations with enhanced spatial, temporal, and spectral resolution across a broad range of the electromagnetic spectrum, this research focuses on the development of advanced sensor systems and satellite constellations that integrate state-of-the-art technologies.

The resulting capabilities will contribute to addressing global and societal challenges by providing reliable data to address global challenges such as climate change and extreme weather, reduce damage from natural disasters, and support daily life and industry.

Research Objectives

Active Optical Sensors (Laser Radar / Lidar)

ISS-mounted lidar demonstration (MOLI)

As a sensor system for the near future, JAXA is conducting research on active optical sensor technologies, an area in which operational experience has been relatively limited compared with other Earth observation instruments. Lidar offers unique capabilities for acquiring vertical profile information that cannot be readily obtained using conventional passive optical sensors, making it a highly promising technology for future three-dimensional Earth observation.
As part of this research program, JAXA is developing the spaceborne vegetation lidar system MOLI (Multi-sensing Observation Lidar and Imager Demonstration). MOLI is designed to improve the accuracy of forest biomass estimation through the measurement of forest height and structural characteristics from space.
JAXA has also begun studying future lidar systems that can derive information such as wind direction, wind speed, and surface conditions from aerosol altitude distributions and surface observations.

Passive Optical Sensors

JAXA is researching systems that use larger telescopes to enable detailed observations from geostationary orbit.

Radio-Frequency Sensors

Unlike optical sensors, whose observations are often limited by cloud cover and atmospheric conditions, radio-frequency sensors can penetrate clouds and acquire observations of the Earth’s surface under a wide range of weather conditions.

Within the Earth observation sensor research program, both core and next-generation technologies are being advanced for Synthetic Aperture Radar (SAR) and related radio-frequency sensing systems. The core research includes the estimation of physical target properties using polarimetric scattering information obtained from SAR observations, as well as the development of holographic and tomographic observation techniques using ground-based SAR systems. We are also pursuing wider swath coverage through multibeam technologies. In addition, the observable frequency ranges are being expanded toward both lower and higher frequency bands. For radiometer systems, this includes exploration of submillimeter-wave and terahertz-wave frequencies approaching the optical spectrum. Research is also underway on wide-area SAR technologies capable of simultaneous multi-frequency observations, which will enhance observation flexibility and improve the performance of onboard receiver systems for space-based Automatic Identification System (AIS) used to identify ships.

Elemental Technologies

Prototype of a lightweight, high-precision composite antenna for terahertz applications

As part of the Earth observation sensor research, JAXA is advancing a range of foundational technologies that are expected to expand the capabilities of future sensor systems through advanced technology studies, including high-power pulsed laser transmitters, new Type II superlattice* infrared area sensors capable of operating without cooling, lightweight and high-precision composite antennas for terahertz applications, and metamaterials expected to see wider use in the years ahead.
In parallel, JAXA is developing infrared calibration technologies that extend existing calibration and performance-evaluation methods used for the radiometric characterization of observational cameras and radiometers into the thermal infrared region. These technologies will help ensure the accuracy, reliability, and traceability required of a space agency.

*Type II superlattice infrared sensor: a new type of infrared sensor formed by alternately stacking InAs and GaSb. These sensors are expected to achieve sensitivity comparable to that of conventional HgCdTe sensors, while enabling operation at higher temperatures.