John Ralph Apel, a physicist and oceanographer who pioneered the use of satellite remote sensing in the study of Earth’s oceans, died on 16 August 2001 of pancreatic cancer at a hospital in Bethesda, Maryland. His home had been in Rockville, Maryland.
Apel was born on 14 June 1930 in Absecon, New Jersey, near Atlantic City. Born into a family of boat designers and builders, a love of the sea came naturally. He spent two years at the Westlawn School of Yacht Design, followed by two years in the US Navy. He then entered the University of Maryland, from which he earned a bachelor’s degree in physics and mathematics in 1957 and a master’s degree in theoretical physics in 1961. During his years at Maryland, Apel authored or coauthored several key papers dealing with the existence and behavior of the then newly discovered Van Allen radiation belts. In 1970, Apel earned his PhD in applied physics from the Johns Hopkins University while working at the university’s Applied Physics Laboratory (APL).
Following a term as a visiting scholar at the Woods Hole Oceanographic Institution in Massachusetts, Apel joined the National Oceanographic and Atmospheric Administration in 1971. There, he was the director of the Ocean Remote Sensing Laboratory, a research entity within NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) in Miami, Florida.
In 1976, Apel moved to Seattle, Washington, to serve as director of NOAA’s Pacific Marine Environmental Laboratory. The move to this laboratory provided Apel with the opportunity to combine his education, interests, and unique talents to pursue what would become his lifelong passion: the development and use of remote-sensing techniques to study ocean characteristics and behavior. With coworkers from AOML, he used acoustic echo sounders to show that packets of coastal internal waves found on the continental shelf along the East Coast of the US had waveforms and propagation characteristics of nonlinear solitary waves. These new and important findings were later confirmed by observations from the Landsat satellite.
Apel also was directly responsible for including an ocean wave height measurement capability on the NASA geodetic satellite GEOS-3. By 1979, the data produced with this capability were being used by the National Weather Service in its operational marine forecasts.
Fascinated by airborne radar images of ocean wave patterns and internal wavepackets along the West Coast of the US, Apel became one of the principal advocates for including a synthetic aperture radar on NASA’s Seasat satellite, which was launched in 1978. While director of the Ocean Remote Sensing Laboratory, Apel was assigned to NASA headquarters from 1973 to 1975. During that period, he provided scientific leadership and mission design concepts for the Seasat mission. This highly successful, forward-looking mission paved the way for following generations of ocean-viewing satellites that have provided improved measuring and monitoring of the world’s oceans.
Continuing his studies of internal ocean waves, Apel led a major oceanic expedition in 1980 on the NOAA research ship Oceanographer to study large amplitude internal waves in the Sulu Sea. This expertly designed and skillfully executed experiment yielded comprehensive and unprecedented data for testing theories of the generation, propagation, and dissipation of nonlinear internal ocean waves.
In 1982, Apel returned to APL, where, along with his new duties as a laboratory assistant director, he continued his research on remote sensing of internal waves. Always eager to go to sea, he participated in numerous field experiments with collaborators at APL, at institutions in Norway and the UK, and at the Institute for Space Research in Moscow. He retired from APL in 1996 as the chief scientist of the laboratory’s research center and formed Global Ocean Associates, an R&D company in Rockville, Maryland.
A prolific author, Apel wrote the highly successful textbook Principles of Ocean Physics (Academic Press, 1987). He was elected a foreign member of the Norwegian Academy of Technical Sciences and was awarded the NASA/US Department of the Interior’s William T. Pecora Award in 1988. Throughout his career, Apel advocated and practiced the use of basic physics principles in the study of the world’s oceans. His excellent grounding in physics coupled with his love of the sea provided him with a unique opportunity to successfully pursue his goal.
Apel also was a gifted sculptor, a talented gardener, and an excellent and enthusiastic boatsman. His seamanship and navigation skills with a sextant were amazing to behold. Drawing from the knowledge and experience of his earlier years, Apel designed and built (in his basement) a classic, all-mahogany powerboat (known as a Sweet-16 runabout) that he, his family, and his friends enjoyed sailing for many years. Those who knew and worked with Apel found him to be a dedicated researcher, a visionary leader, and a delightful companion. He leaves a void that will be difficult to fill.