In January 2024, the world is poised to witness a historic moment in the realm of space exploration as the NASA-ISRO Synthetic Aperture Radar (NISAR) mission gets launched into orbit. A joint project between the Indian Space Research Organization (ISRO) and the National Aeronautics and Space Administration (NASA) aims to systematically map the Earth's surface using advanced radar technology and provide “an Unprecedented View of Earth”.

The NISAR mission is set to observe almost all of Earth's land and ice surfaces twice every 12 days, providing highly-detailed measurements of movements. With data collection spanning three years, the mission will facilitate scientists' monitoring and understanding of natural phenomena, such as earthquakes, landslides, and sea level rise. This wealth of data is anticipated to have a broad range of benefits, encompassing both scientific and societal applications.

NISAR will be the first of its kind to map Earth systematically, employing two distinct radar frequencies (L-band and S-band) to capture changes in the planet’s surfaces, including movements as small as a centimetre! This revolutionary mission thus promises to enhance our understanding of this planet and help find solutions to some of our most pressing challenges.

Simplifying SAR: What is synthetic Aperture RADAR (SAR)?

Synthetic Aperture Radar (SAR) is a type of active remote sensing technology that uses the microwave band of the electromagnetic spectrum to generate high-resolution images of the Earth's surface. Unlike optical sensors, which rely on sunlight, SAR can operate day and night and in all weather conditions, making it an essential tool for Earth observation.

SAR systems work by transmitting microwave pulses toward the Earth's surface and then measuring the strength of the signals reflected back to the sensor. By analyzing the reflected signals, SAR can generate detailed images of the surface topography, even in areas covered by clouds or vegetation. The technique also allows for the detection of subtle surface movements, such as tectonic plate shifts or glacier movements, making it an ideal tool for monitoring environmental changes.

The electromagnetic spectrum with microwave bands inset. Source: NASA EarthData

The electromagnetic spectrum with microwave bands inset. Source: NASA EarthData

The Role of Frequency and Wavelength

SAR benefits from microwave wavelengths, making it an all-weather imaging system across a wide range of bands. The longer wavelengths in C, S, L, and P-bands enable SAR sensors to penetrate through obstacles such as clouds, fog, dust, smog, and smoke. As a result, SAR is particularly well-suited for monitoring regions with high humidity, like the tropics, and areas with high latitudes.

Band Frequency Wavelength SAR Application
Ku 12–18 GHz 2.4–1.7 cm Ku-band is well-suited for high-resolution tactical, maritime monitoring, and certain surface snow and ice observation applications.
X 8–12 GHz 3.8–2.4 cm High-resolution SAR (urban monitoring, ice, and snow, little penetration into vegetation cover, fast coherence decay in vegetated areas)
C 4–8 GHz 7.5–3.8 cm Moderate wavelength provides a good balance between spatial resolution and penetration depth, making it suitable for a variety of applications. Commonly used for land use mapping, including identifying changes in forest cover, urban areas, and agricultural fields. In addition, it can be used for geological exploration, including detecting subsurface features and mineral deposits. C-band SAR is also useful for environmental monitoring, including detecting changes in wetlands, coastal zones, and glacier movement.
S 2–4 GHz 15–7.5 cm Its shorter wavelength makes it well-suited for detecting small targets at high resolution, such as ships and oil spills in the ocean. It can also be used for disaster monitoring, including detecting and mapping floods, landslides, and urban damage after earthquakes or other natural disasters. Additionally, S-band SAR can provide high-resolution imagery for urban mapping, including building identification and land-use classification.
L 1–2 GHz 30–15 cm Its longer wavelength allows for deeper penetration into vegetation, and soil, making it ideal for mapping forest biomass and monitoring agricultural crops. It can detect subtle changes in ground elevation, making it helpful in detecting ground deformation caused by earthquakes or other geological events.
P 0.3–1 GHz 100–30 cm Due to the longer wavelength in P-band, SAR can penetrate deeper into the ground and through vegetation, providing valuable information about the subsurface and underlying structures. This makes it particularly useful for geological exploration and monitoring soil moisture levels, which can be crucial for agriculture and environmental management. In addition, P-band SAR can detect changes in forest biomass and structure, helping to monitor deforestation and land use changes.

The sensitivity of Synthetic Aperture Radar (SAR) measurements to forest structure and the ability to penetrate the canopy varies depending on the wavelength used in airborne or spaceborne remote sensing observations of the land surface. Credit: NASA SAR Handbook.

The sensitivity of Synthetic Aperture Radar (SAR) measurements to forest structure and the ability to penetrate the canopy varies depending on the wavelength used in airborne or spaceborne remote sensing observations of the land surface. Credit: NASA SAR Handbook.

The collaboration

This flagship partnership would have significant contributions from NASA and ISRO, with each agency providing some of the technology and expertise needed to develop the satellite.

  • The National Aeronautics and Space Administration (NASA) is responsible for providing the L-band synthetic aperture radar,

  • Indian Space Research Organization (ISRO) is responsible for providing the S-band synthetic aperture radar.

NISAR will be the first satellite to use both L-band and S-band frequencies for Earth observation. This will allow it to provide high-resolution images of the Earth's surface, even in areas with dense vegetation or cloud cover.

Overall, the NISAR project represents an important collaboration between two major space agencies and is expected to provide valuable data and insights into the Earth's environment and natural processes.

The data characteristics

The NISAR mission will use advanced SAR technology to generate high-resolution images of the Earth's surface, allowing scientists to study the planet in unprecedented detail. The mission's sensors will have several key characteristics that will enable them to achieve this.

  • Dual-frequency capability: The NISAR sensors will operate at two different microwave frequencies, L-band (approximately 23 cm wavelength) and S-band (approximately 12 cm wavelength). The use of dual-frequency SAR allows for more accurate measurements of surface deformation and biomass estimates.

  • Large swath width: NISAR sensors will have a large swath width of up to 240 km, which means they can cover a vast area of the Earth's surface in a single pass. This feature is especially useful for monitoring large-scale environmental changes, such as sea-level rise or deforestation.

  • High-resolution imaging: The spatial resolution would vary from 3 to 10 meters, depending on the capture mode (i.e., along-track and cross-track), allowing for detailed mapping of Earth's surface topography. This level of detail is critical for studying small-scale features such as fault lines or urban areas.

All NISAR science data (L- and S-band) will be freely available and open to the public, consistent with the long-standing NASA Earth Science open data policy. With its global acquisition strategy, cloud-penetrating capability, high spatial resolution, and 12-day repeat pattern, NISAR will provide a reliable, spatially dense time series of radar data that will be a unique resource for exploring Earth change. The research team at Blue Sky Analytics has been monitoring this mission closely and plans to incorporate the data into its intelligence systems to improve its current models.

Expected benefits

The NISAR mission has several expected benefits for Earth observation and scientific research.

The NISAR website summarises it as “NISAR's data can help people worldwide better manage natural resources and hazards, as well as providing information for scientists better to understand the effects and pace of climate change. It will also add to our understanding of our planet's hard outer layer, called its crust.

Some of the significant benefits include:

  • Improved understanding of Earth's processes: The high-resolution images generated by NISAR will allow scientists to study Earth's surface in unprecedented detail, leading to a better understanding of the planet's processes, such as earthquakes, groundwater extraction, land subsidence, and volcanic eruptions. For instance, drawing drinking water from an underground aquifer can leave signs on the surface: Take out too much water, and the ground begins to sink. The movement of magma under the surface before a volcanic eruption can also cause the ground to move. NISAR will provide high-resolution time-lapse radar imagery of such shifts.

  • Cryosphere: Understanding the flow of Earth's ice sheets and glaciers is crucial to assess the current and future impact of sea-level rise and water security of glacier-fed rivers. The NISAR project aims to measure changes in glacier and ice sheet motion, sea ice, and permafrost to determine how global climate and ice masses affect each other and how the melting of land ice contributes to sea-level rise.

  • Forest resources: L-band SAR possesses a superior capability to penetrate dense vegetation compared to S-band, making it ideal for monitoring changes on the Earth's surface, regardless of the time of day or weather conditions. This unique attribute can provide a more intricate depiction of the Earth's surface. L-band SAR would be advantageous in monitoring the extent and quality of global forests. It can furnish precise and timely data regarding forest volume and products, which can facilitate the sustainable development and management of ecosystem goods and services.

  • Agriculture and food security: The implementation of S-band frequency can aid in identifying different crop types, making it more effective in monitoring crop vitality. Soil moisture content plays a crucial role in agriculture as it affects the water availability for crops. NISAR has the potential to generate soil moisture data at the spatial scale of individual farm fields every 6 to 12 days by measuring the reflected microwave energy from the soil surface. The NISAR mission has several applications in agriculture that can help improve food security, increase productivity, and reduce environmental impact.

  • Disaster response: In disaster response scenarios, SAR technology plays a pivotal role as it can swiftly and precisely provide information about the impacted region. The high-resolution images generated by NISAR can facilitate well-informed decisions about disaster response and recovery, including targeted relief efforts, insurance claims, and land management practices. NISAR's capabilities also extend to monitoring marine hazards; it can furnish essential data to track ocean wind, waves, and sea-ice extent, which can aid weather forecasting and caution against marine hazards. Its coverage of coastal oceans is advantageous for sea transportation and coastal communities.

  • Global partnerships: The NISAR mission is a joint project between NASA and ISRO, representing a significant milestone in international cooperation in space exploration. The project will provide opportunities for collaboration and knowledge-sharing between the two agencies.

This mission is a significant step forward in our ability to study and understand the Earth's surface. It holds the potential to change our understanding of our planet and unlock new discoveries about it and its complex systems. Furthermore, the mission emphasizes the value of international collaboration in utilizing cutting-edge technologies to address some of our most urgent challenges, such as climate change and environmental degradation, which pose an existential threat to humanity.