Eni G. Njoku (born May 13, 1950) is a Nigerian-American scientist specializing in microwave radiometric remote sensing of Earth from space. He worked at the Jet Propulsion Laboratory (JPL), California Institute of Technology until 2016, where he led the scientific development of microwave soil moisture remote sensing systems and mission concepts. He was the JPL project scientist (2008-2013) of NASA’s Soil Moisture Active Passive (SMAP) mission, launched in 2015.
Early Life and Education
Njoku was born in Ibadan, Nigeria, one of four siblings. His father was a Nigerian academic and professor of botany. His mother, from Manchester, England was trained as a nurse. The family was raised on the residential campus of the University of Ibadan during pre-independence Nigeria under the British colonial administration. He began high school in 1961 at King’s College, Lagos, following the British educational system, during the period of Nigeria’s transition to independence and self-rule. He spent one year (1965/66) in the U.S. at East Lansing High School, Michigan, while his father was on sabbatical as visiting professor at Michigan State University. He went to England in 1966, just prior to the outbreak of the Nigerian civil war, to complete high school at the Leys School Cambridge. After high school he gained admission to Clare College, University of Cambridge, where he studied natural sciences and electrical sciences with a focus on physics and electromagnetics, graduating with a BA in 1972. He won an English-Speaking Union King George VI Memorial scholarship for graduate study in the U.S. where he attended the Massachusetts Institute of Technology (MIT). He earned the SM and PhD degrees in electrical engineering from MIT in 1974 and 1976, respectively. At MIT he studied under Professor John V. Harrington (for his SM thesis) and Professor Jin Au Kong (for his PhD thesis) and wrote his PhD thesis on the topic of microwave remote sensing of near-surface moisture and temperature profiles. He published his first lead-authored scientific paper on this subject in 1977.
Career:
1976-1990
Njoku began his career at JPL in 1976 as a NAS/National Research Council postdoctoral research associate, joining a group led by Dr. Joe Waters. At that time this group was developing microwave radiometers and radiative transfer models for Earth atmospheric sounding and surface imaging. Initially, Njoku conducted field experiments, using transportable truck-mounted radiometers, deployed at various agricultural sites in California and Kansas, to verify new theoretical models for soil microwave emission. He also worked on surface emissivity modeling for JPL’s Shuttle Imaging Microwave System (SIMS) proposal. At this time JPL was preparing to launch NASA’s first oceanographic satellite Seasat, which had four microwave instruments onboard, including three radars and a microwave radiometer, the Scanning Multichannel Microwave Radiometer (SMMR). Njoku was hired officially as a research scientist at JPL in 1977 and, in addition to his ongoing soil moisture research, began work on algorithms and software for the SMMR antenna pattern corrections, part of the instrument ground data processing system. Seasat was launched in mid-1978 and a second SMMR instrument was launched later the same year onboard NASA’s Nimbus-7 satellite. Njoku participated on the science teams of both Seasat and Nimbus-7 and authored papers on the first microwave measurements of sea surface temperature from space.
Seeking to find a way to contribute to his home country, Njoku returned to Nigeria briefly in 1980 as a senior lecturer in engineering at the Institute of Management and Technology, Enugu. Political instability in the country and a family illness led, however, to his early return to JPL. He was tasked by NASA in 1982 to organize and chair a series of science community workshops, hosted at JPL, to determine and intercompare the accuracies of state-of-the-art sea surface temperature measurements using microwave and visible-infrared instruments on polar-orbiting and geostationary satellites. The results of the three workshops led subsequently to improvements in the operational sea surface temperature products generated by NOAA. For this work Njoku was awarded the NASA Exceptional Service Medal in 1985.
During 1984-1986 Njoku pursued further academic endeavors as an associate professor teaching undergraduate engineering at Harvey Mudd College, Claremont. In 1986 the opportunity arose to work as a JPL detailee to NASA Headquarters in Washington, DC as a program scientist in the Ocean Processes Branch under Dr. Stanley Wilson. His responsibilities included coordination of ocean and Earth science data management activities across NASA centers and between federal agencies primarily NASA, NOAA, and USGS. He also represented NASA on international and interagency committees and science panels including the Committee on Earth Observation Satellites Working Group on Data, the US Interagency Working Group on Data Management for Global Change, the NAS/NRC Committee on Radio Frequencies, and IGBP and UNDP space conferences. During 1988-1990 he worked with Dr. Dixon Butler and the EOS science team to establish the Earth Observing System Data and Information System (EOSDIS) which would support NASA’s new Earth observing satellite missions for the coming decades.
1991-2012
On returning to JPL in 1990 Njoku focused on soil moisture remote sensing research and developing concepts for a soil moisture satellite mission. During this period, he took on JPL line-management duties as a group supervisor, and served one rotation as a section manager of the Geology and Planetology Section, responsible for approximately 100 employees. He was active in professional societies and was elected a Fellow of the IEEE in 1995. He served on the administrative committee of the IEEE Geoscience and Remote Sensing Society becoming vice-president for professional activities in 1996-1997. During 1990-2000, as an expert in space microwave remote sensing, he served on several NASA and scientific organization panels in planning for next-generation remote sensing instruments and scientific measurement capabilities. In 1996 he was selected by NASA as a US science team member for the Advanced Microwave Scanning Radiometer (AMSR), an instrument developed by Japan primarily for ocean-atmosphere-ice sensing but with some secondary soil moisture capability (limited by the operating frequencies of the instrument). Two versions of AMSR were launched, on the Aqua (NASA) and ADEOS-II (JAXA) satellites in May and December 2002, respectively.
For a desired dedicated soil moisture mission, the immaturity of large lightweight antenna technology, as required for low-frequency soil moisture sensing, was a limiting factor. During 1998-2001 Njoku was lead scientist for two technology studies investigating the use of large, deployable, inflatable and mesh antennas for Earth remote sensing. The second of these studies, the OSIRIS instrument incubator study, was a collaboration between JPL, universities and industry to demonstrate the feasibility of a large rotating 6-meter deployable mesh reflector antenna and feed system for use at low microwave frequency (L-band). This study led to successful proposal and NASA selection of the Hydrosphere State (Hydros) mission in 2002 with Njoku as project scientist. Due to NASA budget constraints Hydros was cancelled in 2005, but work continued and the concept was successfully reconfigured, and was recommended by the National Academy of Sciences Decadal Survey. The mission was approved by NASA in 2008 as the Soil Moisture Active Passive mission (SMAP), NASA’s breakthrough dedicated soil moisture mission. Njoku served as the JPL project scientist for SMAP from 2008-2013 with responsibilities for the science aspects of the mission including science team coordination, requirements analysis, science algorithm and data processing software development, and advocacy for SMAP within the US and international science and applications communities.
As part of the feasibility demonstrations for the Hydros and SMAP concepts the Passive Active L-band System (PALS), an airborne radar-radiometer instrument, was designed and built by a small team that included Njoku and JPL and university engineers. PALS was flown in a series of field measurement campaigns starting in 1999, including SGP-99, SMEX-02, CLASIC-07 and others. These field campaigns were organized as part of NASA’s broader terrestrial hydrology program activities to further land hydrologic science, to evaluate soil moisture products being generated by the AMSR, and to develop improved models and soil moisture estimation methods for future L-band space missions. Njoku was the science lead for the PALS instrument in these field campaigns and was also science lead for the NASA AMSR soil moisture product processed and made available publicly through NASA’s data center at the NSIDC. One of the key findings from analysis of the early AMSR data after its launch in 2002 was that the data contained unexpectedly high levels of radio-frequency interference (RFI) from man-made sources. Njoku and his team published landmark papers related to this finding which led to the implementation of a more robust radiometer design for the SMAP mission.
Njoku returned to MIT for a year in 2001/2002 to do research and teaching as a Martin Luther King visiting scholar, hosted by the department of civil engineering and environmental studies. Njoku’s career activities have resulted in an extensive scientific publication record covering: microwave land surface, ocean and atmosphere remote sensing theory; radiometer system concepts and technology development for airborne and spaceborne soil moisture and ocean salinity sensing; and analysis and validation of data from microwave radiometers and radars for applications in water resources, agriculture, flood and drought monitoring, and studying climate change. These activities have resulted in a total of over 100 peer-reviewed scientific journal papers, books, and book chapters on these subjects. He has served as associate editor of the IEEE Transactions on Geoscience and Remote Sensing, and the IEEE Journal of Selected Topics in Applied Earth Observations, and was on the editorial board of Remote Sensing of Environment. He is the editor-in-chief of the Encyclopedia of Remote Sensing, published by Springer in 2014, a comprehensive compendium of articles on state-of-the-art remote sensing of the Earth using all wavelengths of the electromagnetic spectrum.
In addition to his research and administrative activities Njoku has devoted significant time to teaching and mentorship. He has supervised undergraduate summer research, served on graduate thesis committees, hosted several postdoctoral scholars at JPL, and mentored junior colleagues.
2013 to present
In 2013 the SMAP project transitioned to its final year of activities in preparation for launch. In his own transition to planned retirement, Njoku handed over his SMAP responsibilities to a new project scientist, Dr. Simon Yueh, to prepare for the launch and post-launch phases of the SMAP mission. SMAP was launched in January 2015 and continues in operation as of this writing. Njoku continued to advise the SMAP mission, and participated actively as a science user in SMAP data analysis and evaluation until his official retirement from JPL in June 2016. For his service to NASA and the SMAP mission, Njoku was awarded the NASA Exceptional Public Service Medal in 2016. Njoku now lives in Pasadena, California, and pursues independent interests in research, writing and education.