Newsletter January 2025

A Deeper Look

A Newsletter of Innovative Imaging & Research Corporation

January 2025

Happy New Year from I2R!

For those unfamiliar with our regular updates, the I2R Newsletter highlights our advancements in scientific imaging technologies and analysis. You can explore past newsletters, including the November 2024 edition, at I2R Resources.

Here in the northern hemisphere, the long January nights offer ample opportunities for stargazing, a suitable activity to match the topic of our first newsletter of 2025: our star photometer, Angstrom. Angstrom images stars to measure atmospheric properties, enabling new science and improved night imaging.

Angstrom: Expanding Fieldable Imaging Technology

Angstrom represents a significant evolution in fieldable scientific imaging. Specifically designed for nighttime atmospheric measurements, Angstrom employs advanced software-driven data collection and simplified hardware to tackle complex environmental challenges.

Angstrom Unit with Electronic Box and Cellular Antennas Fielded at Stennis Space Center

The Challenge

Photometers measure the amount of light from the sun, moon, or stars that reaches Earth’s surface. The difference between the amount of light reaching the top of the Earth’s atmosphere and the light measured by a sensor on the surface offers valuable information about the atmosphere.

Most photometers currently in use measure atmospheric quantities via light from the sun or moon. For example, Aeronet, a worldwide cooperative and standardized network of photometers, largely relies on sun photometers and only sometimes includes lunar-based instruments. Aeronet provides a vital, consistent, and global long-term aerosol data record to better understand the aerosol impact on climate, improve aerosol transport models, and bound lidar-derived aerosol products. A few star photometers also exist, typically only in academic contexts.

Despite scientific and commercial interest, very few photometers make measurements at night, missing the opportunity to study the effects of nighttime aerosols, which can vary significantly from daytime aerosols.

Aerosol Optical Depth from December 8, 2024

Measured by Aeronet Sensors Around the World

(Source: https://aeronet.gsfc.nasa.gov/)

The Solution

I2R’s Angstrom star photometer combines a sun photometer’s aerosol optical depth (AOD) accuracy with a simplified design that enables measurements over a large portion of the night sky and features that allow for easy installation and fielding in remote locations. Angstrom amplifies a star’s signal through software rather than relying on specialized hardware like conventional star photometers, facilitating wider fieldability at a lower cost. Angstrom’s potential to offer more spatially and temporally dense aerosol data will contribute to understanding aerosols’ impact on air pollution, precipitation, and other research areas.

Nighttime Star Imagery Acquired by Angstrom

on January 6 - 7, 2022

Algorithm-Driven Performance

Angstrom operates primarily via software algorithms to track and process star signals across an imaging sensor rather than precision star-pointing and tracking hardware. Its algorithms apply calibrations, identify night stars, track them through time and air mass, determine their brightness, and estimate the AOD and Angstrom parameters. The software also controls Angstrom’s hardware, including camera command, control, and inter-component communication. The diagram below shows Angstrom’s algorithm workflow and data products:

Angstrom's Algorithm Workflow

Simplified Hardware

Angstrom’s hardware design emphasizes accessibility and efficiency:

Constructed with high quantum efficiency, low read noise sensors, low-distortion lenses, and high-performance computers
Measures within four spectral bandpasses (450, 470, 490, and 520 nm) that
- - Optimize functionality and cost
  - Avoid variable atmospheric molecular water absorption
  - Allow for determining the Angstrom exponent to estimate the aerosol size
Includes a single-board computer to control the cameras and perform initial on-board image processing, including cloud screening

Optimized Wide FOV

Angstrom has a wider field of view than traditional solar or lunar photometers, allowing it to

Acquire a single star quickly across a wide patch of sky
Simultaneously capture multiple stars throughout the sky
Improve the probability of cloud-free observations
Optimize sensor signal-to-noise ratio (SNR)

Angstrom's FOV compared to traditional photometers

High Sensitivity

The brightest star is a trillion times dimmer than the sun. Conventional star photometers use complex hardware to track and amplify star signals to boost their SNR. In contrast, Angstrom achieves high sensitivity using carefully selected high-sensitivity sensors, calibrations, long exposures, and signal processing. Langley regressions maintain proper calibration, and AODs are determined through additional processing. Angstrom’s AOD accuracy approaches 0.01 (comparable to sun photometers).

Angstrom was initially fielded at South Dakota State University (SDSU). We also currently have systems operating at the Stennis Space Center in Mississippi and Colorado State University (CSU).

Angstrom Fielded at SDSU

Angstrom's Applications

Angstrom’s enhanced capabilities make nighttime imaging across diverse applications significantly more reliable by improving the understanding of nighttime atmospheric properties. Knowledge of these atmospheric properties can enhance quantitative night imaging, correcting for atmospheric transmission between Earth’s surface and space. Some of Angstrom’s applications include

Environmental Monitoring: Facilitating the analysis of light and atmospheric pollution
Disaster Response: Supporting damage assessments based on nighttime lights after hurricanes, ice storms, and earthquakes
Socioeconomic Analysis: Delivering insights into urban population changes, economic trends, and electrical power usage
Scientific Research: Improving nighttime atmospheric monitoring for accurate radiometric corrections and reduced noise in time-series analyses

If you are interested in quantitative night imaging or atmospheric monitoring, contact us at info@i2rcorp.com. We welcome collaboration opportunities to expand Angstrom’s potential applications.

Angstrom's development was funded through a NASA Small Business Innovation Research Phase II contract.

A Deeper Read

Wikipedia article on the Angstrom exponent
I2R’s Presentation on Angstrom at JACIE 2024: Angstrom: An Imaging Star Photometer
Aeronet: https://aeronet.gsfc.nasa.gov/

Thank you for staying connected! Look for future updates as we continue to innovate in imaging technology.

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