[1] He worked at the Jet Propulsion Laboratory (JPL), California Institute of Technology, where he was responsible for developing techniques for sea surface temperature and soil moisture remote sensing using microwave radiometers.

[2][3] Njoku was tasked by NASA in 1983 to organize and chair a series of science community workshops to intercompare the accuracies of sea surface temperature measurements by microwave and visible spectrum-infrared instruments on polar orbiting and geostationary satellites.

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.

[9] His team successfully demonstrated the feasibility of a 6-meter mesh reflector antenna system for low microwave frequency (L-band) soil moisture sensing.

Njoku was elected a Fellow of the Institute of Electrical and Electronics Engineers in 1995 and served on the administrative committee of the IEEE Geoscience and Remote Sensing Society becoming vice-president for professional activities in 1996-97.