P-band for measuring glacier and ice sheet velocities

The ESA Biomass Mission and Its Role in Measuring Glacier and Ice-Sheet Velocities

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The European Space Agency (ESA) Biomass mission is an advanced Earth observation initiative aimed primarily at quantifying global forest biomass using P-band synthetic aperture radar (SAR). However, its capabilities extend beyond terrestrial applications, offering significant potential for cryospheric research, particularly in assessing glacier and ice-sheet dynamics. This paper examines the technical aspects of the Biomass mission, the advantages of P-band SAR, and its role in monitoring ice-sheet velocities and glacier movement.

The ESA Biomass Mission: Overview

Biomass is the seventh Earth Explorer mission under ESA’s Living Planet Programme, with a planned launch in 2024. It is the first satellite to operate a fully polarimetric P-band SAR system (wavelength ~70 cm, frequency ~435 MHz), optimized for deep penetration of dense vegetation and ice. While the mission’s primary objective is to improve our understanding of the carbon cycle by estimating forest biomass and structure, its unique radar characteristics make it an invaluable tool for subsurface imaging, including ice-sheet monitoring.

Unlike previous SAR missions operating at C- or X-band frequencies, Biomass’s P-band radar allows for deeper penetration into ice masses, making it particularly suited for assessing subsurface ice properties, detecting basal conditions, and mapping internal ice flow structures. These data are essential for refining ice-sheet stability models and improving projections of sea-level rise.

P-band SAR and Its Application in Cryospheric Science

P-band SAR operates at significantly lower frequencies than most existing SAR missions, which enables it to penetrate deeper into materials such as ice, snow, and vegetation. This makes it an excellent tool for studying the internal dynamics of ice masses and monitoring their response to climate change.

The key benefits of P-band SAR for glacier and ice-sheet velocity measurements include:

• Deep Penetration: Unlike shorter-wavelength SAR systems, P-band waves can propagate through the upper snowpack and reach deeper ice layers, providing velocity measurements that reflect internal ice flow rather than just surface displacement.
• Interferometric SAR (InSAR) Capability: Biomass’s ability to acquire repeat-pass images enables differential InSAR analysis, allowing researchers to infer ice velocity by measuring phase differences between consecutive acquisitions.
• Temporal Coherence Stability: The long wavelength of P-band SAR reduces temporal decorrelation, which enhances the accuracy of long-term ice velocity monitoring.
• Subsurface and Basal Ice Characterization: The ability to detect subglacial structures and basal conditions is crucial for understanding ice dynamics, particularly in areas where basal lubrication influences ice flow rates.

Measuring Glacier and Ice-Sheet Velocities with Biomass

Glaciers and ice sheets play a fundamental role in regulating global sea levels and oceanic circulation patterns. Biomass contributes to their study through the following methodologies:

1. Interferometric SAR (InSAR) Analysis:

• By obtaining repeat-pass SAR images, Biomass can measure phase shifts between acquisitions, allowing for precise estimations of glacier surface displacement and velocity.
• P-band penetration ensures that motion measurements extend beyond surface features, offering insights into internal ice flow dynamics.
• This capability is particularly valuable for tracking fast-flowing ice streams, which are key contributors to ice mass loss in Greenland and Antarctica.

1. Polarimetric SAR (PolSAR) Techniques:

• Biomass’s fully polarimetric SAR system enables the differentiation of ice types and surface conditions.
• Polarimetric decomposition techniques allow for the classification of firn, compact ice, and fresh snow, providing valuable information on accumulation and melting rates.
• PolSAR can also help identify areas of active crevasse formation, which may indicate zones of ice instability or rapid deformation.

1. Subsurface Ice and Basal Condition Monitoring:

• P-band SAR can reveal internal layering within ice sheets, offering critical insights into historical accumulation patterns and deformation processes.
• The radar’s ability to sense basal conditions can help distinguish between frozen and melting ice-bed interfaces, which are key factors influencing ice-sheet dynamics.
• Identifying areas of basal meltwater production is crucial for understanding ice flow acceleration and potential contributions to sea-level rise.

Challenges and Limitations

Despite its unique advantages, the application of Biomass’s P-band SAR to glaciology comes with certain challenges:

• Signal Attenuation in Wet Ice and Snow: P-band SAR, while capable of deep penetration, may experience significant signal loss in areas with high water content, limiting its effectiveness in wet or melting ice conditions.
• Potential Interference Issues: The P-band frequency range overlaps with certain telecommunication and military applications, necessitating careful frequency allocation and signal processing to minimize interference.
• Complex Data Interpretation: Deriving accurate ice flow velocities from deep ice layers requires sophisticated modeling and cross-validation with complementary datasets, such as optical, altimetry, and gravimetric measurements.
• Integration with Other Observations: To maximize its effectiveness, Biomass data must be combined with observations from other missions, such as Sentinel-1 (C-band SAR), ICESat-2 (laser altimetry), and GRACE-FO (gravitational measurements), to provide a comprehensive view of ice-sheet mass balance and dynamics.

Future Perspectives and Synergies with Other Missions

The contribution of Biomass to cryospheric research will be further enhanced through synergies with other satellite missions and in situ observations. Sentinel-1, operating at C-band, provides high-resolution surface velocity measurements that, when combined with Biomass’s deeper penetration capabilities, offer a more complete understanding of ice-sheet motion. Similarly, ICESat-2’s laser altimetry can complement Biomass by providing precise elevation change data, helping to quantify ice mass loss.

Upcoming missions such as the NASA-ISRO Synthetic Aperture Radar (NISAR) will provide L-band SAR data, which, when integrated with P-band observations, can refine estimates of ice dynamics and detect subtle variations in ice flow over time. The combination of these datasets will lead to improved modeling of ice-sheet behavior and its implications for global climate change.

Conclusion

Although originally designed for forest biomass mapping, the ESA Biomass mission has the potential to make significant contributions to glaciology and cryospheric science. Its P-band SAR system offers unique advantages for measuring glacier and ice-sheet velocities by penetrating deeper into ice masses, maintaining long-term coherence for InSAR applications, and providing insights into subglacial conditions. By integrating Biomass data with other Earth observation missions, researchers will gain a more detailed and accurate understanding of ice-sheet stability, glacier dynamics, and their impact on global sea levels. As remote sensing technology advances, Biomass’s role in cryospheric research is expected to grow, enabling better predictions of ice-sheet responses to climate change and helping to refine future climate models.

Expand Your Knowledge – Dive Deeper

• The ESA BIOMASS mission in EO-College
• Sea Ice & Icebergs
• Glaciers & Ice Sheets

Further Reading

• Dall, J., Nielsen, U., Kusk, A., & van de Wal, R. S. (2013, July). Ice flow mapping with P-band SAR. In 2013 IEEE International Geoscience and Remote Sensing Symposium-IGARSS (pp. 251-254). IEEE.
• Banda, F., Dall, J., & Tebaldini, S. (2015). Single and multipolarimetric P-band SAR tomography of subsurface ice structure. IEEE Transactions on Geoscience and Remote Sensing, 54(5), 2832-2845.
• Biomass beyond forests