ENVIRONMENT/ENERGY


percentage of the overall light that the big telescope is collecting. That stray light, or deadband, massively reduces the performance of the IFUs. “The absolutely critical thing was to cut all of these pieces of aluminium such that the edges were incredibly sharp and precisely positioned,” Shore continued. The main enabler in achieving this


was finding a way to control temperature. Shore said: “The key innovation probably wasn’t anything to do with the optics. The key innovation was the machine built at Cranfield where we could temperature- control to about 0.005K. So, we were able to control a significant machine over a two-week duration where the movement of laser-controlled axes were stable to an optical imaging system that checked the position of the near-atomically sharp diamond tools. And because we had thermal control at 1mK resolution and 5mK temperature control, it allowed us to make these things. So, probably the biggest innovation from the Cranfield side was our


FRONTIERS PHOTONICS


“The absolutely critical thing was to cut all of these pieces of aluminium such that the edges were incredibly sharp and precisely positioned”


The James Webb image slicer manufactured by the Cranfield University team


ability to control the temperature in the machinery.” Thanks to the innovations made by the


Cranfield team, it takes a couple of weeks to make the parts today, compared with years in the early 2000s. Most of the tooling and micromachining


knowledge developed at Cranfield during the James Webb project now exists in spin-


out companies, notably Loxham Precision and Ultra-Precision Structured Surfaces (UPS2). Winning high-profile contracts can seem impossible to many organisations. But rather than having the most groundbreaking or novel process, it was simplicity and repeatability that mattered the most in securing the project, said Shore. “Our process was really quite simple –


compared to other organisations that had much more complicated ways of doing it, it actually looked rather routine. But it was completely based on us being able to do the same thing over many hours to construct the mirror arrays.” l


ORBITAL IMAGING


Satellite imagery aids natural disaster relief efforts


T


he days following the destructive 7.8- and 7.5-magnitude


earthquakes in southern Turkey and western Syria in February saw rescuers scramble to search for survivors trapped beneath the rubble.


Assessing areas affected


by natural disasters is crucial for prioritising and directing emergency services, and satellite images helped determine the extent of damage in addition to the risk of secondary dangers such as landslides. Images captured by the


Operational Land Imager-2 (OLI-2) on NASA’s Landsat 9 satellite, for example, allowed scientists to identify more than 100 landslides, which were included in maps provided to


“Images captured by OLI-2, on NASA’s Landsat 9 satellite, allowed scientists to identify more than 100 landslides”


World Central Kitchen to help the aid group deliver food and water to earthquake victims. The OLI instrument was also


able to identify flooded farmland and communities along the Orontes (Asi) river. Much of the flooding occurred about 100km south of the epicentre of the quake in the Idlib governorate of Syria.


The Operational Land


Imager (OLI), built by the Ball Aerospace and Technologies Corporation, measures in the visible, near-infrared, and shortwave infrared (SWIR) portions of the spectrum. Its images have 15m panchromatic and 30m multispectral spatial resolutions along a 185km-wide (115-mile) swath, covering large areas of the Earth’s landscape while providing sufficient resolution to distinguish features such as urban centres, farms, forests and other land uses. The entire Earth falls within view once every 16 days thanks to Landsat 8’s near- polar orbit. OLI’s design uses an


NASA Earth Observatory satellite image showing flooding along the Orontes River


approach demonstrated by the Advanced Land Imager sensor flown on NASA’s experimental EO-1 satellite. Instruments on earlier Landsat satellites employed scan mirrors to sweep the instrument fields of view across the surface swath and transmit light to a few detectors. The OLI instead uses long detector arrays, with more than 7,000 detectors per spectral


band, aligned across its focal plane to view across the swath. This ‘push-broom’ design results in a more sensitive instrument, providing improved land surface information with fewer moving parts. With an improved signal-to-noise ratio compared with past Landsat instruments, OLI is more reliable and provides improved performance. l


Photonics Frontiers 2023 7


Loxham Precision


Lauren Dauphin/ NASA Earth Observatory/ US Geological Survey


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