Ira Gehman Nolt, a highly regarded pioneer of far-IR astronomical and atmospheric measurements, passed away on 22 August 2024 at the age of 87, after an extended battle with Parkinson’s disease. The asteroid (13910) Iranolt is his namesake.
Nolt was born on 12 March 1937 in Lancaster County, Pennsylvania, the second of 13 children of Milton and Margie Nolt. Ira received a BS degree in 1960 from Franklin & Marshall College, worked three years at Armstrong Lancaster Labs, and then entered graduate school at Cornell University to pursue his passion for research. He graduated in 1967 with PhD research describing the construction of the first university-developed sub-millimeter-wave lamellar interferometer, heralding the demise of FIR monochromators. An additional significant increase in spectroscopic sensitivity was achieved with a helium-3 cooled bolometer invented by fellow student Dennis Drew.
In 1967, Ira joined the University of Hawaii Institute for Astronomy as a postdoctoral associate. An important question at that time related to the possible increase in atmospheric transmission in the sub-mm wave region gained by using a high-altitude observing site such as Mauna Kea. To make such measurements, Ira needed an FIR interferometer, a diffusion pump–driven closed-cycle 3He refrigerator to cool the bolometric detector to 0.37 K, and associated support systems that he transported with a large truck to the top of the mountain. Using the Sun as a source, he successfully showed that the atmosphere was more transparent to IR radiation than anyone had expected. It was also the first application of a 3He-cooled bolometer for astronomical measurements.
In 1970, Ira moved to the University of Oregon physics department, where he continued his development, with Jim Radostitz, of a portable 3He-cooled bolometer system. He and David Tanner (Cornell) introduced the idea of adsorption pumping of 3He with cooled charcoal to maintain an ultralow detector temperature. This more practical 3He refrigeration system had no moving parts, with the 3He gas stored in the cryostat body.
An immensely fruitful collaboration with the Queen Mary College (London) group began when Peter Ade met Ira and Jim at a conference in 1977. The QMC team was developing composite bolometers which, when combined with the portable cryostat, made a unique sub-mm photometer system for the UKIRT telescope on Mauna Kea. The new instrument immediately realized a gain in sensitivity of a factor of 20 over competitors at the time. In true Ira style, the instrument was shared with experts in star formation, galaxies, quasars, planets, and asteroids. The QMC/Oregon photometer made many pioneering measurements, gained international scientific recognition, and became a pathfinder for the facility instrument SCUBA: the world’s first sub-mm camera built for the 15-meter-diameter James Clerk Maxwell Telescope also sited on Mauna Kea. This latter system led the development of sub-mm astronomy from a fledgling technique to a well-established observing method for the crucial gap between IR and radio observations.
This astronomical work was impressive, but Ira maintained a strong interest in atmospheric physics and chemistry. He and the QMC group joined forces with Bruno Carli at the University of Florence in Italy, who had a very high-resolution balloon-borne FTS system capable of measuring ultralow concentrations of molecules in the stratosphere. Using a modified photometer system with Bruno’s FTS, the QMC/Oregon instrument could be applied to ozone depletion and climate change, urgent research issues in the 1980s. The enhanced balloon instrument successfully identified the hydrogen, oxygen, and chlorine compounds involved in ozone chemistry and crucially detected hydrogen bromide, a key ozone-destroying chemical in the stratosphere. A later aircraft version of this instrument allowed these types of measurements to be made in the tropics and in the Arctic to better understand the complex flows of polluting chemicals in the atmosphere. This work led to international agreements to limit aerosols and the use of agricultural fumigants based on assessments by the Intergovernmental Panel on Climate Change.
Ira was also aware of the importance of cirrus clouds in weather and climate processes. He worked with Frank Evans at NIST to design a FIR radiometer system for cirrus clouds (FIRSC), which was able to measure the ice water path and particle size to provide input to global climate models. Ira’s work pioneered measurements employed in the latest Earth-observation satellites and enabled quantification of chemical processes vital to understanding and predicting global climate change.
We remember Ira as a wonderful collaborator and friend, always patient, sensitive, and thoughtful in his dealings with people at all levels. Several students whom he worked with at the University of Oregon more than 50 years ago credit him with having a profound, positive influence on their careers. Ira had a deep knowledge of physics, cryogenics, Earth’s atmosphere, and astrophysics, and he willingly shared his expertise very openly. He will be greatly missed by all who were fortunate enough to know and to work with him.
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