How NISAR Uses L-Band and S-Band Radar to See Earth
The joint NASA-ISRO NISAR satellite combines longer-wavelength L-band radar with shorter-wavelength S-band radar. Their different interactions with vegetation, soil, snow and ice help researchers map surface change in darkness and through clouds.
Timeline
- 2025-07-30: NISAR launched from India aboard an ISRO GSLV-F16 rocket.
- Evergreen: The satellite’s planned observing pattern repeats its orbit every 12 days, with ascending and descending passes producing an average revisit of roughly six days.
NISAR, short for NASA-ISRO Synthetic Aperture Radar, is a joint Earth-observing mission built around two radar wavelengths. NASA supplied an L-band system with a wavelength of about 24 centimeters, while the Indian Space Research Organisation supplied an S-band system with a wavelength of about 10 centimeters. NISAR launched from the Satish Dhawan Space Centre on July 30, 2025, aboard ISRO’s GSLV-F16 rocket. [1][4]
Radar instruments transmit microwave pulses and measure the energy scattered back from Earth. Synthetic-aperture processing combines measurements collected as the spacecraft moves along its orbit, producing much finer images than the physical antenna alone would ordinarily allow. Because NISAR supplies its own microwave illumination, it can observe during day or night. Its wavelengths also pass through clouds, giving it a major advantage over visible-light cameras in persistently cloudy regions. [1][2]
Wavelength determines how a radar signal interacts with a landscape. NISAR’s longer L-band waves can penetrate farther into many vegetation canopies and respond to relatively large structures such as branches and woody biomass. They are also useful for detecting subtle ground movement by comparing the phase of radar observations from different dates, a technique called interferometry. These properties support studies of earthquakes, volcanoes, landslides, groundwater change and forests. [2][3]
The shorter S-band waves interact more strongly with smaller-scale features nearer the surface, including light vegetation, crop structure, surface roughness and moisture in snow. JPL also notes that S-band observations are less affected by ionospheric disturbances in polar regions. Comparing the two frequencies gives scientists complementary measurements that can help interpret which parts of a scene are changing, although the pairing does not automatically remove every ambiguity. [2][3]
NISAR’s observing geometry is designed for repeated change detection. The satellite follows a 12-day exact repeat orbit and observes on both ascending and descending passes. NASA describes that combination as an average revisit of about six days. That does not mean every location receives identical coverage every six days: viewing geometry, instrument mode and the mission’s observation plan determine when a particular area is measured. The radar can image a swath wider than 240 kilometers. [1][2]
The dual-frequency design supports several kinds of public-interest science. Repeated measurements can reveal centimeters or smaller changes in the ground after tectonic strain, subsidence or volcanic activity. Over ice sheets and glaciers, the data can track movement and changes in frozen surfaces. Over farms, wetlands and forests, the two wavelengths provide different clues about vegetation structure, water and biomass, helping researchers build more complete interpretations than a single frequency can provide. [1][2][3]
Coverage differs between the instruments. NASA’s mission overview says the L-band system provides global measurements, while S-band observations focus on India and selected science sites. NISAR science data are intended to be free and openly available, allowing researchers and agencies to combine the observations with ground measurements and other satellites. NASA planned a baseline three-year science mission, so users should consult the current mission portal for operating status, coverage and data-product updates. [1][2][4]
Sources
- NASA Science: NISAR Mission Overview
- NASA JPL: NISAR Mission Concept
- NASA JPL: NISAR Radars
- ISRO: GSLV-F16 / NISAR Mission