Scientists’ ability to see changes in solid Earth and its surface features has been revolutionized by JPL’s invention of geodetic measurement techniques such as spaceborne Interferometric Synthetic Aperture Radar (InSAR). This method compares differences in the phase of radar measurements to accurately detect changes in Earth's geometric shape. By comparing and contrasting two or more SAR images taken from the same space-based vantage point at different times, an interferogram can be produced capable of detecting surface deformation changes in a centimeter or less.
Using its Advanced Rapid Imaging and Analysis (ARIA) system, JPL currently tracks surface deformation by applying interferometry to SAR data from Japan’s ALOS/PALSAR, Italy’s COSMO SkyMed, and Canada’s RADARSAT missions and ground truthing this with GPS data. ARIA automates large-scale data processing and produces data products of unprecedented detail by pioneering the latest computing technologies. These products are relied upon by both the science community and those responding to earthquakes, tsunamis, volcanoes, landslides, fires, and other natural disasters around the world.
In order to expand this capability to some of the hardest to monitor places on Earth, JPL is collaborating with India’s space agency to build and launch the NASA-ISRO Synthetic Aperture Radar (NISAR) mission in 2022. This mission will employ L-band and S-band Polarimetric Synthetic Aperture Radar with 12-meter deployable antenna. The technology will be uniquely suited to measuring all types of terrain, including slopes, heavily vegetated areas, ecosystem disturbances and ice sheet collapse. NISAR will produce radar imaging of the entire U.S. and most of the rest of the world four to six times each month with resolutions of several tens of meters, greatly enhancing the science and application benefits of SAR satellite capabilities.
In the 1980s, JPL began pioneering measurement of atmospheric carbon at various altitudes with sufficient spatial and temporal resolution to revolutionize our understanding of the carbon cycle. To meet the complex technical challenges involved in this study — especially measurement of shifts in and fluxes among the most swiftly changing carbon reservoirs — JPL designed and fabricated three crucial technologies: grating-based spectrometers, low-cost cryocoolers, and hyperspectral imaging sensors.
These high-spectral instruments first came together as the Orbiting Carbon Observatory (OCO-2) mission aboard the International Space Station with the ability to diffract incoming light into a spectrum of component colors so finely resolved that the reflective signatures of different gases could be detected and precisely measured. For example, OCO-2 could detect carbon dioxide concentrations in the atmosphere with one-part-per-million accuracy. OCO-3 will continue and build on this achievement, quantifying and differentiating the amount of carbon being absorbed by different plants and ecosystem types around the world. It will be the first space-based instrument to measure Solar-Induced Fluorescence — an indicator of photosynthesis efficiency — in high definition from dawn to dusk. This capability will be a complement to JPL’s ongoing airborne and planned spaceborne hyperspectral imagers. As new detectors and grating technology advances, JPL is developing an imaging spectrometer to image and detect methane from high-emitting sources.
And when NISAR launches in 2022, its synthetic aperture radar interferograms will enable calculation of changes in above-ground biomass short- and long-term.
Since 1978, when it launched the world’s first satellite-based ocean altimetry radar, JPL has been pioneering the technologies that allow scientists to monitor and understand sea-level rise. Through a decades-long collaboration with the French space agency (CNES), JPL has combined unique antenna designs, innovative power supplies, and precision navigation tools to create the radar systems aboard the TOPEX/Jason satellite series. These instruments measure global trends in sea-level change with accuracies in millimeters per year from 700 kilometers above the Earth.
JPL has also been pioneering the measurement of Earth mass changes for nearly two decades. The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) missions, launched in partnership with the German Aerospace Center (DLR), circle the globe 15 times a day, sensing minute variations in Earth’s gravitational pull. When the first satellite passes over a zone of slightly stronger gravity, it is pulled ahead of its trailing satellite. By tracking changes in the relative positions of the two satellites to within one micron — a fraction of the thickness of a human hair —the GRACE missions allow researchers to detect subtle regional changes in Earth’s gravitational field. These measurements can then be used to calculate shifts in water mass in that region.
The combination of data on ocean surface height from TOPEX and data on ocean water mass from GRACE has made it possible to calculate the relative contributions of ice melt and ocean thermal expansion to sea-level rise.
JPL’s next major contribution to understanding this complex cycle will launch in 2021, when the unique radar interferometer, microwave radiometer, radar altimeter, and other instruments aboard the Surface Water and Ocean Topography (SWOT) mission begin measuring the level of the world’s lakes, reservoirs, wetlands, and rivers.
Because the water cycle involves multiple reservoirs in solid, liquid, and gaseous forms, its components cannot all be characterized using any single technology or instrument. To meet this challenge, JPL has pioneered a suite of different approaches and miniaturizations that enable the scientific community to both track and deepen understanding of the movement of water around the planet.
For example, radar is used by CloudSat to measure cloud liquid and ice in the atmosphere and by CubeSat to measure precipitation. The Soil Moisture Active Passive (SMAP) satellite uses a first-of-its-kind, combined radar and radiometer antenna to measure soil moisture, and the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) uses innovative multispectral infrared instruments to study evapotranspiration. The Atmospheric Infrared Sounder (AIRS) uses high spectral resolution infrared “sounders” to measure profiles of atmospheric water vapor. The Gravity Recovery and Climate Experiment (GRACE) missions use gravity sensing to monitor changes in underground water storage, and the Airborne Snow Observatory (ASO) uses lidar and spectrometry to make fine-scale measurements of snow depth and brightness to advance understanding of mountain snowpack. Combined, this suite of complementary technologies allows scientists to investigate the many facets of the water cycle.
This capability will be a complement to JPL’s recently launched ECOSTRESS mission. With a new type of hardware specifically developed to reduce the cost and risk for thermal infrared radiometers, ECOSTRESS provides the most detailed temperature images of Earth’s surface ever acquired from space and can be used to precisely quantify evapotranspiration at resolutions as fine as an individual farm field.
Air quality and weather
Measuring specific trace gases in the atmosphere requires the ability to distinguish their faint signals amidst much stronger background noise. JPL first overcame this challenge three decades ago by pioneering the Schottky diode signal-switching technology that enabled the first Microwave Limb Sounder (MLS). At the heart of the current generation of MLS is a more advanced Monolithic Microwave Integrated Circuit (MMIC) signal isolation and amplification technology.
JPL’s Tropospheric Emissions Spectrometer (TES) was the first satellite instrument to use spectrometers — which use dispersive prisms to analyze the spectral content of incident electromagnetic radiation — to provide simultaneous measurement of carbon monoxide (CO), ozone (O3), water vapor (H2O), and methane (CH4) concentrations throughout Earth’s lower atmosphere. TES has the highest spectral resolution of any thermal infrared sounder launched to date and has allowed first-ever profiling of the amounts and placement of tropospheric gases.
JPL has also created unique technologies to characterize the size, composition, and quantity of particulate matter by measuring the polarization of sunlight scattered by atmospheric aerosols. When it launches in 2022, the Multi-Angle Imager for Aerosols (MAIA) mission will take polarimetric measurements using a JPL-developed photoelastic modulator (PEM) system. The High-resolution Imaging Multiple-species Atmospheric Profiler (HiMAP), in an earlier stage of development, will employ a metalens — a flat, achromatic optical surface thinner than a sheet of paper — to make multiple-angle, spectrally resolved polarimetric measurements.
For weather, JPL’s pioneering work also extends into the miniaturization of radar and radiometer technology. Miniature satellites — built into a 6U CubeSat (RainCube and TEMPEST-D) and enabled by deployable antennas, advanced digital signal processors, and high-efficiency InP-based MMIC power amplifiers—measure ice and water movement through cloud layers, improving measurement of convection processes. Producible at a tenth of the cost of traditional weather satellites, these miniature instruments can be affordably built to fly in constellations that enable simultaneous and temporally sequenced sampling of the formation and behavior of severe weather patterns.
JPL atmospheric measurement instruments like TES and MAIA, working in lockstep with constellations of miniature weather satellites, will power the next decade’s investigation of the interplay of weather and air quality.