Njoku began his career in 1976 as a National Academy of Sciences postdoctoral research associate, joining JPL in 1977. He conducted experimental studies of soil microwave emission, demonstrating the feasibility of estimating soil moisture using remote measurements. He was a member of the algorithm development team for the microwave radiometer on the Seasat satellite, NASA's first oceanographic satellite launched in 1978.[6] He produced the first microwave-derived sea surface temperature maps of the global oceans.[2][3]
Njoku worked at NASA Headquarters, Washington, DC from 1986-1990 as a program scientist for Earth science data information systems. He contributed to coordination of satellite data management across NASA data centers and between U.S. and international space agencies. He participated in establishing the Earth Observing System Data and Information System EOSDIS. Njoku served in JPL management roles after 1991, while also leading design studies for future spaceborne microwave sensing systems. He led a multiyear program of field experiments using JPL ground-based and airborne radiometers to pave the way for development of a space-based remote global soil moisture observing system.[8]
In 1996, Njoku became a science team member for the Advanced Microwave Scanning Radiometer (AMSR), launched on the Aqua (NASA) and ADEOS II (JAXA) satellites in 2002, responsible for soil moisture products. From 1998-2001, he was the lead scientist for advanced technology studies investigating the use of inflatable and mesh antennas for Earth remote sensing.[9] His team successfully demonstrated the feasibility of a 6-meter mesh reflector antenna system for low microwave frequency (L-band) soil moisture sensing.[4] This study led to proposal of the NASA Hydrosphere State (Hydros) satellite mission in 2002, but the mission was not finally approved. A follow-up proposal, recommended by the National Academy of SciencesEarth Science Decadal Survey, was approved by NASA in 2008 as Soil Moisture Active Passive (SMAP), NASA's first dedicated soil moisture mission. Njoku served as the project scientist for SMAP from 2008-2013.[5] SMAP was launched successfully into space and began its operations phase in early 2015. Njoku was awarded the NASA Exceptional Public Service Medal in 2016.