Leroy L. Cogger: A Pioneer in Optical Observations From Space

This perspective is in memory of Leroy Leonard Cogger, a pioneer in optical imaging of the aurora and the airglow, who passed away in October 2022 in Canada at the age of 85. In his 40‐plus‐year career, which spans both space and ground‐based optical instrumentation and observations, Dr. Cogger has made significant contributions to the development of instruments for several space missions and ground observatories, including the world's first truly digital (charge‐coupled device) camera to be used in the field, the UV auroral imagers for the Swedish Viking and Freja satellites, the NASA IMAGE satellite, and the Russian INTERBALL‐2 satellite, respectively, and the fast near‐infrared auroral imager on the Canadian CASSIOPE/Enhanced Polar Outflow Probe satellite. He has also collaborated and mentored the next generation of space scientists in Canada and Europe in many areas of auroral and airglow research; he was particularly adept at combining diverse observations to provide insight into a wide array of atmospheric phenomena. His legacies go well beyond his contributions in the peer‐reviewed literature and innovative instrumentation: his scientific vision and leadership played an indispensable role in the Canadian space science research agenda, and his commitment to mentoring has left an indelible mark on many of his students and associates. He exemplified AGU's motto of “Unselfish cooperation in research.” His gentle and quiet spirit, his passion for research and in making a difference in life will be very much missed by his many friends and colleagues in Canada and abroad alike, as will his great sense of humor.

The significant scientific impact of Cogger's pioneering measurements at Arecibo is two-fold.The studies illustrated the value of combining radar and optical data to achieve the broader scope of measurements needed to understand fully the nighttime oxygen ionospheric chemistry.Moreover, they led to our firm understanding of the underlying dissociative recombination mechanism for the production of the 630 nm nightglow emission: the technique of Doppler shift and broadening measurements with Fabry-Pérot interferometers is widely used nowadays for observing the dynamics of the thermosphere.
After his move to Calgary from Arecibo, Dr. Cogger shifted his research focus to the analysis of airglow and auroral observations at 557.7 and 391.4 nm from the scanning photometer on the Canadian ISIS 2 satellite.Using limb observations, initial analysis revealed and resolved for the first time both the E-region and F-region components of the OI 557.7 nm nightglow (L.L. Cogger & Anger, 1973), which points to their different underlying drivers.Subsequent limb studies provided a wealth of information on OI 557.7 nm airglow including its midlatitude maximum (L.L. Cogger & Khaneja, 1979), its spatial and temporal variations (L.L. Cogger et al., 1981), and its utilization in determining atomic oxygen density, local turbulence, and global circulation (Elphinstone et al., 1984).Access to the ISIS 2 auroral data provided the opportunity for Dr. Cogger to lend his optical expertise to the analysis of the auroral distribution and its various features including dayside aurora (L.L. Cogger et al., 1977) and polar cap arcs (Murphree & Cogger, 1981).Then with the availability of satellite UV images from the Swedish Viking satellite he continued to make significant contributions to the signatures of magnetospheric processes as seen in the UV aurora such as the impulsive changes in the dayside aurora and their effects on the high-latitude thermosphere (L.L. Cogger & Murphree, 1990).
Dr. Cogger was particularly adept at combining diverse observations to provide insight into atmospheric phenomena.Satellite observations, ground-based optical systems, and radar facilities, etc. were all utilized to extract key information on processes as diverse as radio aurora (Prikryl & Cogger, 1992), lower thermospheric neutral winds (L.L. Cogger et al., 1985), and gravity waves (Giers et al., 1997).
Dr. Cogger has made significant contributions to the development of instruments for several space missions and ground observatories in his career.In 1979 he led a team that, in conjunction with Fairchild Semiconductor, developed the world's first truly digital (charge-coupled device [CCD]) camera to be used in the field, the Fairchild All-Sky Camera.The later application of CCD imaging in space revolutionized the field of auroral imaging, akin to the way microchannel plate detectors revolutionized the measurements of space plasma by enabling the imaging of their energy and angular distributions.He later contributed to the development of UV auroral imagers for the Swedish Viking and Freja satellites as well as the NASA IMAGE satellite.In addition, he served as Principal Investigator (PI) for the auroral imagers on the Russian INTERBALL-2 (Lyatsky et al., 2001;Zelenyi & Sauvaud, 1998) and Canadian CASSIOPE Enhanced Polar Outflow Probe (e-POP) satellites (L.Cogger et al., 2015;Yau & James, 2015).
The CASSIOPE/e-POP Fast Auroral Imager (FAI) exemplifies Dr. Cogger's innovative, outside-of-the-box approach to space instrumentation.It consists of two CCD cameras for measuring the 630.0 nm emission of atomic oxygen in the aurora and enhanced nightglow, and the prompt auroral emissions at 650-1,000 nm, respectively, using fast lens systems (f/0.8) and high quantum-efficiency (>90% max) CCDs to achieve high sensitivity.Despite the severe resource and budgetary constraints for the cost-capped e-POP instruments and given the state of spaceborne auroral imagery at the time, Dr. Cogger was convinced of the technical feasibility of the FAI design and its scientific potential.
The legacy of Dr. Cogger's vision is a unique, 7-year data set of near-infrared auroral images of 0.1-s exposure and few-km spatial resolution.It has allowed the spatiotemporal study of the dynamic (second-scale) and small-scale (<10 km) auroral phenomena (as well as those of airglows), from pulsating aurora (Lui et al., 2015), to ion heating in active aurora (Shen et al., 2018), to km-scale structuring in discrete auroral arcs and associated Alfvénic dynamics (Miles et al., 2018).Figure 2 shows an example of the observed pre-midnight aurora (at 19:18 MLT) in the near infrared by FAI over the Canadian Arctic, showing its highly dynamic characteristics.

Beyond the Science and the Instruments
Dr. Cogger's legacies in airglow and auroral research go well beyond his contributions in the peer-reviewed literature and his many innovative instruments.
In 1989 Dr. Cogger founded the Institute for Space Research and served as Director until 2002.During that time, he led a successful bid to form the Canadian Network for Space Research (CNSR), a National Center of Excellence that operated from 1990 to 1995.The creation and management of CNSR represented a massive administrative effort, and it made possible the recruitment and retention of an entire generation of new space researchers in Canada, many of whom are now scientific leaders-and former mentors of current leaders-in Canadian universities, government laboratories, and space industry.
In addition to being the driving force behind the CNSR, Dr. Cogger led the development of the NORSTAR All-Sky Imager (ASI) array, paving the way for its subsequent expansion and its later evolution into the Canadian In the late 1990s Dr. Cogger initiated a series of community-led space environment workshops that led to a new community vision captured in his extensive report "The Canadian Space Environment Program: Toward a Better Future," elements of which continue to guide the trajectory of space environment research in Canada.In the words of a Canadian Space Agency official at the time, "Leroy Cogger is the conscience of Canadian Space Science." On the international stage, Dr. Cogger has actively and specifically cultivated scientific collaborations in developing nations throughout his career, for example, through a sabbatical stay in Bulgaria, and through the donation of a tilting-filter photometer, shown in Figure 3, which he installed and helped maintain outside Ho Chi Minh City, Vietnam.
Dr. Cogger's commitment to mentoring has left many an indelible mark on his students and research associates over half a century.His mentoring style was one of uncommon kindness that went beyond the expected boundaries of acceptance and care-many Sunday evenings were spent connecting with his graduate students over dinner at his home.This style proved very effective at propelling many of his students to long and productive careers in space science.
He also played an instrumental role in both the development of the Portable All-Sky Imager (PAI) by Trond S. Trondsen, in his role as thesis advisor, and Dr. Trondsen's subsequent establishment of Keo Scientific Ltd.The PAI has enabled the studies of a wide array of dynamic and small-scale auroral phenomena at high spatial and temporal resolution, such as the black aurora (Trondsen & Cogger, 1997), asymmetric multiple auroral arcs and associated inertial Alfvén waves (Trondsen et al., 1997), and mesoscale auroral arcs (Knudsen et al., 2001).Keo Scientific Ltd. has become a major provider of state-of-the-art all-sky imagers and Fabry-Pérot interferometers for geophysical observatories around the globe.
Dr. Cogger's commitment to furthering the careers and lives of others is evident not only professionally but also in his private life: He and his wife Marilyn are principals in a group of founders and benefactors of the Good Samaritan's India/Calgary Health and Training Centre in rural India, which provides training in typing, computing, sewing, and printing.This group purchases sewing machines and provides training for young widows who have no other sources of income.During the years of the INTERBALL-2 mission, when he traveled frequently to the former Soviet Union for instrument integration and testing, Dr. Cogger would often fill his suitcase with medicine acquired from pharmaceutical companies in Canada, for distribution to the local poor with the help of his friend, the late Prof. Yuri Galperin.
In his personal life, Dr. Cogger enjoyed traveling, fly fishing, and photography.His curiosity for other cultures led him to travel to over 60 countries in his lifetime, including many places in Europe, Asia, and Africa in his retirement; see Figure 4, for example, His technical expertise in space imaging was mirrored in his personal life by a fascination of cameras and photography, particularly when on vacation.

A Closing Thought
Dr. Cogger enjoyed wonderful collegial relations with many scientists in aeronomy and space physics around the world, including China, Japan, Russia (and the former Soviet Union), Sweden, and the Americas.His gentle and quiet spirit, his passion for research and in making a difference in life will be very much missed by his many friends and colleagues in Canada and abroad alike, as will his great sense of humor.
Dr. Cogger devoted his whole life to the advancement of space science and the betterment of his fellow human beings.Above all, he was a kind, soft-spoken gentleman, and a shining example of AGU's motto: Unselfish Cooperation in Research!

Figure 1 .
Figure 1.(a) Photograph of assembled Fabry-Pérot spectrometer.(b) Measured twilight emission rate of atomic oxygen (OI) at 557.7 nm as a function of the solar depression angle.The length of the instrument including the mirror system is approximately 4.3 m.The measurements showed the occurrence of twilight enhancements and their possible magnetic activity dependence, which were an important open question at the time.Reproduced from Figures 2.3 and 5.3 of L. L. Cogger (1968).

Figure 2 .
Figure 2. Image of the pre-midnight aurora in the near-infrared taken by Fast Auroral Imager on CASSIOPE/Enhanced Polar Outflow Probe over the Canadian Arctic (71.06°N, 130.79°W, 1,372 km altitude) on 2 October 2015, at 05:40:00 UT.

Figure 3 .
Figure 3. Tilting-filter photometer donated by Dr. Leroy Cogger to the Vietnamese scientific community and installed at Hoc Mon Observatory (10.9°N, 106.6°E) outside Ho Chi Minh City, Vietnam.

Figure 4 .
Figure 4.This photo captures Dr. Cogger's characteristic contemplative side.It was taken outside Sanya on Hainan Island, China, in January 2007 while he was attending an international science conference.(Photo: Dr. T.S. Trondsen).