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By NASA
Advancing Single-Photon Sensing Image Sensors to Enable the Search for Life Beyond Earth
A NASA-sponsored team is advancing single-photon sensing Complementary Metal-Oxide-Semiconductor (CMOS) detector technology that will enable future NASA astrophysics space missions to search for life on other planets. As part of their detector maturation program, the team is characterizing sensors before, during, and after high-energy radiation exposure; developing novel readout modes to mitigate radiation-induced damage; and simulating a near-infrared CMOS pixel prototype capable of detecting individual photons.
Single-photon sensing and photon-number resolving CMOS image sensors: a 9.4 Mpixel sensor (left) and a 16.7 Mpixel sensor (right). Credit: CfD, RIT Are we alone in the universe? This age-old question has inspired scientific exploration for centuries. If life on other planets evolves similarly to life on Earth, it can imprint its presence in atmospheric spectral features known asbiosignatures. They include absorption and emission lines in the spectrum produced by oxygen, carbon dioxide, methane, and other molecules that could indicate conditions which can support life. A future NASA astrophysics mission, the Habitable Worlds Observatory (HWO), will seek to find biosignatures in the ultraviolet, optical, and near-infrared (NIR) spectra of exoplanet atmospheres to look for evidence that life may exist elsewhere in the universe.
HWO will need highly sensitive detector technology to detect these faint biosignatures on distant exoplanets. The Single-Photon Sensing Complementary Metal-Oxide-Semiconductor (SPSCMOS) image sensor is a promising technology for this application. These silicon-based sensors can detect and resolve individual optical-wavelength photons using a low-capacitance, high-gain floating diffusion sense node. They operate effectively over a broad temperature range, including at room temperature. They have near-zero read noise, are tolerant to radiation, and generate very little unwanted signal—such as dark current. When cooled to 250 K, the dark current drops to just one electron every half-hour. If either the read noise or dark current is too high, the sensor will fail to detect the faint signals that biosignatures produce.
A research team at the Rochester Institute of Technology (RIT) Center for Detectors (CfD) is accelerating the readiness of these SPSCMOS sensors for use in space missions through detector technology maturation programs funded by NASA’s Strategic Astrophysics Technology and Early Stage Innovations solicitations. These development programs include several key goals:
Characterize critical detector performance metrics like dark current, quantum efficiency, and read noise before, during, and after exposure to high-energy radiation Develop new readout modes for these sensors to mitigate effects from short-term and long-term radiation damage Design a new NIR version of the sensor using Technology Computer-Aided Design (TCAD) software SPSCMOS sensors operate similarly to traditional CMOS image sensors but are optimized to detect individual photons—an essential capability for ultra-sensitive space-based observations, such as measuring the gases in the atmospheres of exoplanets. Incoming photons enter the sensor and generate free charges (electrons) in the sensor material. These charges collect in a pixel’s storage well and eventually transfer to a low-capacitance component called the floating diffusion (FD) sense node where each free charge causes a large and resolved voltage shift. This voltage shift is then digitized to read the signal.
Experiments that measure sensor performance in a space relevant environment use a vacuum Dewar and a thermally-controlled mount to allow precise tuning of the sensors temperature. The Dewar enables testing at conditions that match the expected thermal environment of the HWO instrument, and can even cool the sensor and its on-chip circuits to temperatures colder than any prior testing reported for this detector family. These tests are critical for revealing performance limitations with respect to detector metrics like dark current, quantum efficiency, and read noise. As temperatures change, the electrical properties of on-chip circuits can also change, which affects the read out of charge in a pixel.
The two figures show results for SPSCMOS devices. The figure on the left shows a photon counting histogram with peaks that correspond to photon number. The figure on the right shows the dark current for a SPSCMOS device before and after exposure to 50 krad of 60 MeV protons. Credit: CfD, RIT The radiation-rich environment for HWO will cause temporary and permanent effects in the sensor. These effects can corrupt the signal measured in a pixel, interrupt sensor clocking and digital logic, and can cause cumulative damage that gradually degrades sensor performance. To mitigate the loss of detector sensitivity throughout a mission lifetime, the RIT team is developing new readout modes that are not available in commercial CMOS sensors. These custom modes sample the signal over time (a “ramp” acquisition) to enable the detection and removal of cosmic ray artifacts. In one mode, when the system identifies an artifact, it segments the signal ramp and selectively averages the segments to reconstruct the original signal—preserving scientific data that would otherwise be lost. In addition, a real-time data acquisition system monitors the detector’s power consumption, which may change from the accumulation of damage throughout a mission. The acquisition system records these shifts and communicates with the detector electronics to adjust voltages and maintain nominal operation. These radiation damage mitigation strategies will be evaluated during a number of test programs at ground-based radiation facilities. The tests will help identify unique failure mechanisms that impact SPSCMOS technology when it is exposed to radiation equivalent to the dose expected for HWO.
Custom acquisition electronics (left) that will control the sensors during radiation tests, and an image captured using this system (right). Credit: CfD, RIT While existing SPSCMOS sensors are limited to detecting visible light due to their silicon-based design, the RIT team is developing the world’s first NIR single-photon photodiode based on the architecture used in the optical sensors. The photodiode design starts as a simulation in TCAD software to model the optical and electrical properties of the low-capacitance CMOS architecture. The model simulates light-sensitive circuits using both silicon and Mercury Cadmium Telluride (HgCdTe or MCT) material to determine how well the pixel would measure photo-generated charge if a semiconductor foundry physically fabricated it. It has 2D and 3D device structures that convert light into electrical charge, and circuits to control charge transfer and signal readout with virtual probes that can measure current flow and electric potential. These simulations help to evaluate the key mechanisms like the conversion of light into electrons, storing and transferring the electrons, and the output voltage of the photodiode sampling circuit.
In addition to laboratory testing, the project includes performance evaluations at a ground-based telescope. These tests allow the sensor to observe astronomical targets that cannot be fully replicated in lab. Star fields and diffuse nebulae challenge the detector’s full signal chain under real sky backgrounds with faint flux levels, field-dependent aberrations, and varying seeing conditions. These observations help identify performance limitations that may not be apparent in controlled laboratory measurements.
In January 2025, a team of researchers led by PhD student Edwin Alexani used an SPSCMOS-based camera at the C.E.K. Mees Observatory in Ontario County, New York. They observed star cluster M36 to evaluate the sensor’s photometric precision, and the Bubble Nebula in a narrow-band H-alpha filter. The measured dark current and read noise were consistent with laboratory results.
The team observed photometric reference stars to estimate the quantum efficiency (QE) or the ability for the detector to convert photons into signal. The calculated QE agreed with laboratory measurements, despite differences in calibration methods.
The team also observed the satellite STARLINK-32727 as it passed through the telescope’s field of view and measured negligible persistent charge—residual signal that can remain in detector pixels after exposure to a bright source. Although the satellite briefly produced a bright streak across several pixels due to reflected sunlight, the average latent charge in affected pixels was only 0.03 e–/pix – well below both the sky-background and sensor’s read noise.
Images captured at the C.E.K. Mees Observatory. Left: The color image shows M36 in the Johnson color filters B (blue), V (green), and R (red) bands (left). Right: Edwin Alexani and the SPSCMOS camera (right). Credit: : CfD, RIT As NASA advances and matures the HWO mission, SPSCMOS technology promises to be a game-changer for exoplanet and general astrophysics research. These sensors will enhance our ability to detect and analyze distant worlds, bringing us one step closer to answering one of humanity’s most profound questions: are we alone?
For additional details, see the entry for this project on NASA TechPort.
Project Lead(s): Dr. Donald F. Figer, Future Photon Initiative and Center for Detectors, Rochester Institute of Technology (RIT), supported by engineer Justin Gallagher and a team of students.
Sponsoring Organization(s): NASA Astrophysics Division, Strategic Astrophysics Technology (SAT) Program and NASA Space Technology Mission Directorate (STMD), Early Stage Innovations (ESI) Program
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Last Updated Sep 02, 2025 Related Terms
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By NASA
A new online portal by NASA and the Alaska Satellite Facility maps satellite radar meas-urements across North America, enabling users to track land movement since 2016 caused by earthquakes, landslides, volcanoes, and other phenomena.USGS An online tool maps measurements and enables non-experts to understand earthquakes, subsidence, landslides, and other types of land motion.
NASA is collaborating with the Alaska Satellite Facility in Fairbanks to create a powerful web-based tool that will show the movement of land across North America down to less than an inch. The online portal and its underlying dataset unlock a trove of satellite radar measurements that can help anyone identify where and by how much the land beneath their feet may be moving — whether from earthquakes, volcanoes, landslides, or the extraction of underground natural resources such as groundwater.
Spearheaded by NASA’s Observational Products for End-Users from Remote Sensing Analysis (OPERA) project at the agency’s Jet Propulsion Laboratory in Southern California, the effort equips users with information that would otherwise take years of training to produce. The project builds on measurements from spaceborne synthetic aperture radars, or SARs, to generate high-resolution data on how Earth’s surface is moving.
The OPERA portal shows how land is sinking in Freshkills Park, which is being built on the site of a former landfill on Staten Island, New York. Landfills tend to sink over time as waste decomposes and settles. The blue dot marks the spot where the portal is showing movement in the graph.Alaska Satellite Facility Formally called the North America Surface Displacement Product Suite, the new dataset comes ready to use with measurements dating to 2016, and the portal allows users to view those measurements at a local, state, and regional scales in a few seconds. For someone not using the dataset or website, it could take days or longer to do a similar analysis.
“You can zoom in to your country, your state, your city block, and look at how the land there is moving over time,” said David Bekaert, the OPERA project manager and a JPL radar scientist. “You can see that by a simple mouse click.”
The portal currently includes measurements for millions of pixels across the U.S. Southwest, northern Mexico, and the New York metropolitan region, each representing a 200-foot-by-200-foot (60-meter-by-60-meter) area on the ground. By the end of 2025, OPERA will add data to cover the rest of the United States, Central America, and Canada within 120 miles (200 kilometers) of the U.S. border. When a user clicks on a pixel, the system pulls measurements from hundreds of files to create a graph visualizing the land surface’s cumulative movement over time.
Land is rising at the Colorado River’s outlet to the Gulf of California, as indicated in this screenshot from the OPERA portal. The uplift is due to the sediment from the river building up over time. The graph shows that the land at the blue dot has risen about 8 inches (20 centimeters) since 2016.Alaska Satellite Facility “The OPERA project automated the end-to-end SAR data processing system such that users and decision-makers can focus on discovering where the land surface may be moving in their areas of interest,” said Gerald Bawden, program scientist responsible for OPERA at NASA Headquarters in Washington. “This will provide a significant advancement in identifying and understanding potential threats to the end users, while providing cost and time savings for agencies.”
For example, water-management bureaus and state geological surveys will be able to directly use the OPERA products without needing to make big investments in data storage, software engineering expertise, and computing muscle.
How It Works
To create the displacement product, the OPERA team continuously draws data from the ESA (European Space Agency) Sentinel-1 radar satellites, the first of which launched in 2014. Data from NISAR, the NASA-ISRO (Indian Space Research Organisation) Synthetic Aperture Radar mission, will be added to the mix after that spacecraft launches later this year.
The OPERA portal shows that land near Willcox, Arizona, subsided about 8 inches (20 centimeters) since between 2016 and 2021, in large part due to groundwater pumping. The region is part of an area being managed by state water officials.Alaska Satellite Facility Satellite-borne radars work by emitting microwave pulses at Earth’s surface. The signals scatter when they hit land and water surfaces, buildings, and other objects. Raw data consists of the strength and time delay of the signals that echo back to the sensor.
To understand how land in a given area is moving, OPERA algorithms automate steps in an otherwise painstaking process. Without OPERA, a researcher would first download hundreds or thousands of data files, each representing a pass of the radar over the point of interest, then make sure the data aligned geographically over time and had precise coordinates.
Then they would use a computationally intensive technique called radar interferometry to gauge how much the land moved, if at all, and in which direction — towards the satellite, which would indicate the land rose, or away from the satellite, which would mean it sank.
“The OPERA project has helped bring that capability to the masses, making it more accessible to state and federal agencies, and also users wondering, ‘What’s going on around my house?’” said Franz Meyer, chief scientist of the Alaska Satellite Facility, a part of the University of Alaska Fairbanks Geophysical Institute.
Monitoring Groundwater
Sinking land is a top priority to the Arizona Department of Water Resources. From the 1950s through the 1980s, it was the main form of ground movement officials saw, as groundwater pumping increased alongside growth in the state’s population and agricultural industry. In 1980, the state enacted the Groundwater Management Act, which reduced its reliance on groundwater in highly populated areas and included requirements to monitor its use.
The department began to measure this sinking, called subsidence, with radar data from various satellites in the early 2000s, using a combination of SAR, GPS-based monitoring, and traditional surveying to inform groundwater-management decisions.
Now, the OPERA dataset and portal will help the agency share subsidence information with officials and community members, said Brian Conway, the department’s principal hydrogeologist and supervisor of its geophysics unit. They won’t replace the SAR analysis he performs, but they will offer points of comparison for his calculations. Because the dataset and portal will cover the entire state, they also could identify areas not yet known to be subsiding.
“It’s a great tool to say, ‘Let’s look at those areas more intensely with our own SAR processing,’” Conway said.
The displacement product is part of a series of data products OPERA has released since 2023. The project began in 2020 with a multidisciplinary team of scientists at JPL working to address satellite data needs across different federal agencies. Through the Satellite Needs Working Group, those agencies submitted their requests, and the OPERA team worked to improve access to information to aid a range of efforts such as disaster response, deforestation tracking, and wildfire monitoring.
NASA-Led Project Tracking Changes to Water, Ecosystems, Land Surface News Media Contacts
Andrew Wang / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
626-379-6874 / 818-354-0307
andrew.wang@jpl.nasa.gov / jane.j.lee@jpl.nasa.gov
2025-076
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Last Updated Jun 06, 2025 Related Terms
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