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Advancing Earth Observation with SPACEBEAM: Photonics-Powered Radar Receivers

Earth observation (EO) has been a crucial tool in fields like cartography and environmental monitoring, particularly in addressing global warming. In the world of Earth observation (EO), spaceborne Synthetic Aperture Radars (SARs) have long played a vital role. They have been instrumental in applications like cartography, elevation mapping, and, more recently, environmental monitoring to combat the effects of global warming.

However, the ever-increasing demand for higher performance in terms of resolution and sensitivity has led to continuous research for innovative techniques to enhance SAR systems. One groundbreaking development is the scan-on-receive (SCORE) mode, which is part of the SPACEBEAM project, revolutionizing SAR performance.

Understanding the Limitations of Conventional SARs

In conventional stripmap SAR systems, the spatial resolution along the track is inversely related to the swath width across the track. To achieve high-resolution imaging, multiple satellite passes are often necessary, making it an inefficient process.

The Innovation: Scan-on-Receive (SCORE) SAR

Traditional stripmap SAR systems have limitations, notably the trade-off between spatial resolution along the track and the swath width across the track. To achieve fine-resolution imaging, multiple satellite passes are often required, making the process inefficient. However, the SPACEBEAM project introduced an innovative approach: the Scan-on-Receive (SCORE) mode.

SCORE-SAR overcomes the limitations of conventional SARs by employing a wide swath in transmission while receiving radar echoes through multiple, smaller, and higher-gain receive beams steered across the track. This approach significantly enhances imaging resolution without necessitating multiple satellite passes, making it an efficient and promising solution for EO applications.

 

Challenges in Implementing SCORE-SAR

To enable SCORE-SAR at higher frequencies and onboard small satellites, certain challenges must be addressed. Implementing real-time digital beamforming, capable of handling multi-channel, wide bandwidth (from a few hundred MHz to 1.2 GHz per channel), within constraints like size, weight, power, and cost (SWaP-C) poses a significant technical challenge.

Photonics-Powered Solutions

Photonics technology has emerged as a potential solution to address these challenges. Its inherent characteristics, such as broadband nature, immunity to electromagnetic interference, low loss, and data-transparent link capacity, make it well-suited for advanced radar systems. Within photonics, microwave photonics, which involves applying photonics to microwave systems, offers the capability to process radio frequency (RF) signals across various spectrums.

Photonic Integrated Circuits (PICs) for Beamforming

The SPACEBEAM receiver is based on an optical beamforming network realized as a photonic integrated circuit (PIC). PICs are miniaturized optical devices that can perform complex optical functions, such as beamforming, filtering, and switching.

The SPACEBEAM PIC is able to perform continuous and accurate beamforming of wideband signals. It can also perform frequency-agnostic photonic down-conversion, which means that the output signals can be directly digitized.

Integrated photonics is a rapidly developing field that utilizes light to transmit and process information. By employing integrated photonics, the SPACEBEAM project aimed to create a radar receiver that was significantly smaller, lighter, and more power-efficient than conventional receivers. Additionally, the project sought to develop a reconfigurable beamforming capability, enabling the receiver to adapt its focus and resolution to specific observation tasks.

Photonic integrated circuit (PIC) technologies, which involve integrating photonic components on a single chip, can be used to implement beamforming networks (BFNs). These BFNs have applications not only in radar systems but also in areas like 5G communications.

The SPACEBEAM Project: Pioneering Photonics-Powered SCORE-SAR

The SPACEBEAM project represents a pioneering effort in developing and testing the first photonics-assisted SCORE-SAR receiver module designed for Earth observation from space. The project, funded by the European Commission under the H2020 program, aimed to create a compact and power-efficient beamforming solution, making SCORE-SAR observation modes feasible for smaller SAR missions and higher frequencies.

The SPACEBEAM project involved a consortium of leading European research institutions and industrial partners, bringing together expertise in photonics, microwave engineering, and EO applications. The project’s primary objectives included:

  1. Design and development of a photonic integrated circuit (PIC) for radar beamforming.

  2. Integration of the PIC with other receiver components, such as antennas and signal processing units.

  3. Demonstration of the receiver’s performance in a laboratory setting and under simulated space conditions.

  4. Development of a roadmap for the commercialization of the SPACEBEAM technology.

The SPACEBEAM project successfully achieved its objectives, demonstrating the feasibility of using integrated photonics for advanced EO applications. The project’s outcomes have the potential to revolutionize EO technology, enabling smaller, lighter, and more versatile satellites for Earth observation.

Hybrid Photonic Integrated Circuits

At the core of the SPACEBEAM system lies an extremely compact hybrid Photonic Integrated Circuit (PIC), achieved through advanced integration of a Silicon Nitride (SiN) chip and Indium Phosphide (InP) chips. The hybrid PICs, designed and assembled by Lionix, play a pivotal role in the project. A unique feature of these PICs is the use of piezo-electric actuators in lead zirconate titanate (PZT), known for their low power consumption, making them suitable for space applications.

Impressive Performance

The SPACEBEAM photonics-assisted receiver demonstrates the capability to process 12 incoming RF signals in the optical domain. An analogue reconfigurable optical Beamforming Network (BFN) is used to dynamically synthesize and steer three independent beams with continuity. This hybrid PIC represents one of the most advanced photonic integrated circuits developed to date, offering a combination of functionality and input/output ports.

Testing and Harsh Environmental Conditions

Two versions of the SPACEBEAM receiver were developed: a functional model and a hermetic packaged PIC. Rigorous testing, including exposure to radiation and thermal cycling in a vacuum environment, was conducted in compliance with European Space Agency standards. These tests validated the robustness of the hybrid PIC in space conditions.

Potential for Earth Observation

The SPACEBEAM project has showcased the potential of integrated photonics in implementing complex beamforming networks with precise analogue control, resulting in a significant SWaP reduction in the challenging space environment. Additionally, the broad bandwidth of photonic technologies allows for radar applications at higher frequencies, expanding the possibilities for Earth observation and SAR systems. The innovative developments within the SPACEBEAM project are expected to open new opportunities for EO applications based on integrated microwave photonics techniques.

SPACEBEAM radar receivers are also more sensitive than traditional radar receivers, allowing them to detect weaker signals. This makes SPACEBEAM radar receivers ideal for a variety of EO applications, such as:

  • Monitoring polar ice caps: SPACEBEAM radar receivers can be used to monitor the thickness and extent of polar ice caps, which is important for understanding climate change.
  • Detecting deforestation: SPACEBEAM radar receivers can be used to detect deforestation, which is important for protecting forests and mitigating climate change.
  • Monitoring natural disasters: SPACEBEAM radar receivers can be used to monitor natural disasters, such as floods, hurricanes, and earthquakes.
  • Tracking ships and aircraft: SPACEBEAM radar receivers can be used to track ships and aircraft, which is important for maritime safety and national security.

Conclusion

SPACEBEAM radar receivers are a new and exciting technology with the potential to revolutionize Earth Observation. SPACEBEAM radar receivers are smaller, lighter, and more sensitive than traditional radar receivers, making them ideal for a variety of EO applications.

The development of SPACEBEAM radar receivers is a significant step forward in EO technology, and it is likely to have a major impact on the way we monitor our planet.

About Rajesh Uppal

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