15 Jun 2021
Field Line of sight Automated Radiance Exposure (FLARE) technique improves optical calibration for satellite and drone imaging.
Optics and lighting metrology specialist Labsphere is to locate a high-tech system of mirrors at Arizona State University (ASU) for optical calibration of remote sensing imagery captured by satellites and drones.
The planned site, in Mesa, will enable students at the university to gain experience of Labsphere’s “Field Line of sight Automated Radiance Exposure” (FLARE) system - described by the firm as a revolutionary new approach to assessing the spatial, geometric, and radiometric performance of imaging sensors.
Based around technology initially developed to calibrate telescopes using light from stars, FLARE’s mirror targets are effectively controlled, automated, adjustable “stars” located on the ground - for calibrating satellite imagers pointed at Earth, rather than at the night sky.
“Labsphere is using this robust technique and making it available to telescopes imaging the Earth so they can perform the same verification and testing in real time,” states the firm, which has also partnered with Raytheon’s intelligence and space division on the mirror hardware used by FLARE.
Chris Durell, Labsphere’s director of business development, said in a company release: “The ASU location, students and outstanding staff afford Labsphere a very agile resource to conduct satellite testing and explore new technology avenues for FLARE.”
Projects carried out by ASU students learning the fundamental skills of remote sensing and Earth observation will support the development of new ways to assess satellite testing tools and techniques.
“The ASU environment will be a fantastic incubator for new ideas and services,” added Durrell.
Labsphere and ASU say that they have agreed on the manual deployment of geometric mirror arrays for satellite image quality testing, while a fully automated FLARE system installation is envisaged at some point in the future.
According to a Labsphere website dedicated to the FLARE system, current issues with satellite imaging and remote sensing calibration include mismatched radiometry data, and the high costs of maintaining calibration and image processing teams.
Large-area targets require a managed radiometric model over time, while it is difficult to maintain co-registration across all imaging platforms, explains the firm. No single method has been developed for airborne to space calibration, it adds.
FLARE data collection
Aiming to improve matters, the FLARE system opens up when tasked, orienting its mirrors to point the sun towards the satellite, and start collecting radiometric data.
“When open, FLARE measures the direct solar radiance and atmospheric transmission, the mirror, and surrounding reflectance,” reports the firm, with the collected data then delivered to the cloud.
When combined with a satellite image, that calibration data package is said to provide “unprecedented” information regarding the point-spread function [i.e. optical quality] of the sensor, the radiometric response, and atmospheric conditions.
“FLARE advances conventional calibration because it is specific to each imager’s optical performance, provides world-class [levels of] uncertainty, [and] serves UAVs [and] airborne or satellite platforms.”
Potential applications of the technology include better observation of algal blooms from space - current approaches tend to become “contaminated” by blue light scattered more effectively by the atmosphere.
“Small differences in ratios of green to blue, and red to green [light] can be used to distinguish harmless algae from toxic species,” suggests Labsphere.
Detailed analysis of spectral channels could also aid farmers by evaluating more accurately vegetation health, soil moisture, plant emergence and yields, adds the firm, while FLARE-corrected images ought to be more accurately and easily processed using machine learning techniques.