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 Water and Carbon Cycles: People
Eni Njoku's Picture
Jet Propulsion Laboratory
M/S 300-229
4800 Oak Grove Drive
Pasadena, CA 91109

Eni Njoku
Group Supervisor
Senior Research Scientist

Dr. Eni Njoku is a senior research scientist and supervisor of the Water and Carbon Cycles Group. His research interests focus on applications of spaceborne microwave sensing to studies of land surface hydrologic processes and the global water cycle. He is the project scientist of the Soil Moisture Active Passive (SMAP) mission and a member of the EOS/Aqua Advanced Microwave Scanning Radiometer (AMSR-E) science team, investigating surface soil moisture and its role in hydrologic and ecologic modeling, weather and climate prediction, and monitoring of natural hazards.

Dr. Njoku's other activities have included development of microwave remote sensing retrieval algorithms for land, ocean, atmosphere, and cryospheric investigations; technology studies utilizing large deployable antennas for spaceborne microwave sensing; and field campaigns using airborne microwave radiometers and radar systems.

  • Ph.D., Electrical Engineering, Massachusetts Inst. of Technology (1976)
  • M.S., Electrical Engineering, Massachusetts Inst. of Technology (1974)
  • B.A., Natural Sciences/Electrical Sciences, Cambridge University (1972)

Research Interests
Global hydrology and climate studies using microwave remote sensing.


SMAP - Soil Moisture Active & Passive Icon SMAP - Soil Moisture Active & Passive
SMAP will provide global measurements of soil moisture and its freeze/thaw state.

Professional Experience
  • Jet Propulsion Laboratory (1977-Present)
    • Project Scientist, SMAP Mission (2008-Present)
    • Senior Research Scientist (2006-present)
    • Project Scientist, Hydros Mission (2001-2006)
    • Principal Scientist (2001-2006)
    • Research Scientist (1977-2001)
    • Aqua/AMSR-E science team member for soil moisture (1996-present)
    • Section Manager, Geology and Planetology Section (1993-1994)
    • National Academy of Sciences/National Research Council Postdoctoral Research Associate, (1976-1977)
  • Visiting Professor, Dept. of Civil & Environ. Engineering, MIT. (2001-2002)
  • Program Scientist, Ocean Processes Branch and Earth Science Data and Information Systems, NASA Headquarters (1986-1990)
  • Associate Professor, Dept. of Engineering, Harvey Mudd College, Claremont, CA (1984-1986)
  • Senior Lecturer, Dept. of Electrical Engineering, Institute of Management & Technology, Enugu, Nigeria (1980-1981)

Selected Awards
  • English-Speaking Union, King George VI Memorial Scholarship (1972)
  • National Acad. of Sciences/NRC, Resident Research Associateship (1976)
  • NASA Group Achievement Awards (1980, 1982, 1985)
  • NASA Exceptional Service Medal (1985)
  • Fellow, Institute of Electrical and Electronics Engineers (IEEE) (1995)
  • Visiting Fellow, Massachusetts Institute of Technology (2001-02)
  • NASA Group Achievement Award SMAPVEX12 Field Campaign Team (2013)

Selected Publications
  1. Tsang, L., E. Njoku, and J. A. Kong (1975): Microwave thermal emission from a stratified medium with nonuniform temperature distribution, J. Appl. Phys., 46, 5127-5133.
  2. Njoku, E. G. and J. A. Kong (1977): Theory for passive microwave remote sensing of near-surface soil moisture, J. Geophys. Res., 82, 3108-3118.
  3. Tsang, L., J. A. Kong, E. G. Njoku, D. H. Staelin, and J. W. Waters (1977): Theory for microwave thermal emission from a layer of cloud or rain, IEEE Trans. Ant. & Propagat., AP-25, 650-657.
  4. Njoku, E. G. (1980): Antenna pattern correction procedures for the Scanning Multichannel Microwave Radiometer (SMMR), Boundary-Layer Meteorol., 18, 79-98.
  5. Njoku, E. G., J. M. Stacey, and F. T. Barath (1980): The Seasat Scanning Microwave Radiometer (SMMR): Instrument description and performance, IEEE J. Oceanic Eng., OE-5, 100-115.
  6. Hofer, R., E. G. Njoku, and J. W. Waters (1981): Microwave radiometric measurements of sea surface temperature from satellite: First results, Science, 212, 1385-1387.
  7. Njoku, E. G. (1982): Passive microwave remote sensing of the Earth from space - A review, Proc. IEEE, 70, 728-750.
  8. Njoku, E. G. (1983): Reflection of electromagnetic waves at a biaxial/isotropic interface, J. Appl. Phys., 54, 524-530.
  9. Njoku, E. G. and L. Swanson (1983): Global measurements of sea surface temperature, wind speed, and atmospheric water content from satellite microwave radiometry, Mon. Wea. Rev., 111, 1977-1987.
  10. Njoku, E. G. (1985): Satellite-derived sea surface temperature: Workshop comparisons, Bull. Am. Met. Soc., 66, 274-281.
  11. Njoku, E. G. and E. K. Smith (1985): Microwave antenna temperature of the Earth from geostationary orbit, Radio Science, 20, 591-599.
  12. Njoku, E. G., T. P. Barnett, R. M. Laurs, and A. C. Vastano (1985): Advances in satellite sea surface temperature measurement and oceanographic applications, J. Geophys. Res., 90, 11573-11586.
  13. Kerr, Y. and E. G. Njoku (1990): A semiempirical model for interpreting microwave emission from semiarid land surfaces as seen from space, IEEE Trans. Geosci. Rem. Sens., 28, 384-393.
  14. Entekhabi, D., H. Nakamura, and E. G. Njoku (1994): Solving the inverse problem for soil moisture and temperature profiles by sequential assimilation of multifrequency remotely sensed observations, IEEE Trans. Geosci. Rem. Sens., 32, 438-448.
  15. Davis, D. T., Z. Chen, J.-N. Hwang, L. Tsang, and E. G. Njoku (1995): Solving inverse problems by Bayesian iterative inversion of a forward model with applications to parameter mapping using SMMR remote sensing data, IEEE Trans. Geosci. Rem. Sens., 33, 1182-1193.
  16. Njoku, E. G. and D. Entekhabi (1996): Passive microwave remote sensing of soil moisture, J. Hydrology, 184, 101-129.
  17. Chehbouni, A., D. Lo Seen, E. G. Njoku, J. P. Lhomme, A. B. Monteny, and Y. H. Kerr (1997): Estimation of sensible heat flux over sparsely vegetated surfaces, J. Hydrology, 188-189, 855-868.
  18. Njoku, E., Y. Rahmat-Samii, J. Sercel, W. Wilson, and M. Moghaddam (1999): Evaluation of an inflatable antenna concept for microwave sensing of soil moisture and ocean salinity, IEEE Trans. Geosci. Rem. Sens., 37, 63-78.
  19. Njoku, E. and L. Li (1999): Retrieval of land surface parameters using passive microwave measurements at 6 to 18 GHz, IEEE Trans. Geosci. Rem. Sens., 37, 79-93.
  20. Njoku, E. G., W. J. Wilson, S. H. Yueh, and Y. Rahmat-Samii (2000): A large-antenna microwave radiometer-scatterometer concept for ocean salinity and soil moisture sensing, IEEE Trans. Geosci. Rem. Sens., 38, 2645-2655.
  21. Njoku, E., W. Wilson, S. Yueh, S. Dinardo, F. Li, T. Jackson, V. Lakshmi, and J. Bolten (2002): Observations of soil moisture using a passive and active low frequency microwave airborne sensor during SGP99, IEEE Trans. Geosci. Rem. Sens. 40, 2659-2673.
  22. Njoku, E., T. Jackson, V. Lakshmi, T. Chan, and S. V. Nghiem (2003): Soil moisture retrieval from AMSR-E, IEEE Trans. Geosci. Rem. Sens., 41, 215-229.
  23. Li., L., E. Njoku, E. Im, P. Chang, and K. St. Germain (2004): A preliminary survey of radio-frequency interference over the U. S. in Aqua AMSR-E data, IEEE Trans. Geosci. Rem. Sens., 42, 380-390.
  24. Entekhabi, D., E. Njoku, P. Houser, M. Spencer, T. Doiron, J. Smith, R. Girard, S. Belair, W. Crow, T. Jackson, Y. Kerr, J. Kimball, R. Koster, K. McDonald, P. O'Neill, T. Pulz, S. Running, J. Shi, E. Wood, and J. van Zyl (2004): The Hydrosphere State mission (HYDROS): An earth system pathfinder for global mapping of soil moisture and land freeze/thaw, IEEE Trans. Geosci. Rem. Sens., 42, 2184-2195.
  25. Njoku, E., P. Ashcroft, and L. Li (2005): Statistics and global survey of radio-frequency interference in AMSR-E land observations, IEEE Trans. Geosci. Rem. Sens., 43, 938-947.
  26. Crow, W., T. Chan, D. Entekhabi, P. Houser, A. Hsu, T. Jackson, E. Njoku, P. O'Neill, J. Shi, and X. Zhan (2005): An observing system simulation experiment for Hydros radiometer-only soil moisture products, IEEE Trans. Geosci. Rem. Sens., 43, 1239-1303.
  27. Njoku, E.G. and T. K. Chan (2006): Vegetation and surface roughness effects on AMSR-E land observations, Rem. Sens. Environ., 100, 190-199.
  28. Dunne, S., D. Entekhabi, and E. Njoku (2007): Impact of multi-resolution active and passive microwave measurements on soil moisture estimation using the ensemble Kalman smoother, IEEE Trans. Geosci. Rem. Sens., 45, 1016-1028.
  29. Reichle, R. H., R. D. Koster, P. Liu, S. P. Mahanama, E. G. Njoku and M. Owe (2007): Comparison and assimilation of global soil moisture retrievals from AMSR-E and SMMR, J. Geophys. Res., 112, D09108, doi:10.1029/2006JD008033.
  30. Waliser, D., K.-W. Seo, S. Schubert and E. Njoku (2007): Global water cycle agreement in the climate models assessed in the IPCC AR4, Geophys. Res. Lett., 34, L16705, doi:10.1029/2007GL030675.
  31. Piepmeier, J. R., D. G. Long and E. G. Njoku (2008): Stokes antenna temperatures, IEEE Trans. Geosci. Rem. Sens., 46, 516-527.
  32. Entekhabi, D., E. Njoku, et al. (2010): The Soil Moisture Active Passive (SMAP) Mission, Proceedings of the IEEE, 98, 704-716.
  33. Das, N. N., B. P. Mohanty, and E. G. Njoku (2010): Profile soil moisture across spatial scales under different hydroclimatic conditions, Soil Science, 175, 315-319.
  34. Huang, S., L. Tsang, E. Njoku, and K. Chan (2010): Backscattering coefficients, coherent reflectivities and emissivities of randomly rough soil surfaces at L-band for SMAP applications based on numerical solutions of Maxwell Equations in three-dimensional simulations, IEEE Trans. Geosci. Rem. Sens., 48, 2557-2568.
  35. Das, N. N., D. Entekhabi, and E. G. Njoku (2011): An algorithm for merging SMAP radiometer and radar data for high resolution soil moisture retrieval, IEEE Trans. Geosci. Rem. Sens., 49, 1504-1512.
  36. Konings, A. G., D. Entekhabi, S. K. Chan, E. G. Njoku (2011): Effect of radiative transfer uncertainty on L-band radiometric soil moisture retrieval, IEEE Trans. Geosci. Rem. Sens., 49, 2686-2698.
  37. Kim, S., L. Tsang, J. T. Johnson, S. Huang, J. J. van Zyl, E. G. Njoku (2012): Soil moisture retrieval using time-series radar observations over bare surfaces, IEEE Trans. Geosci. Rem. Sens., 50, 1853-1863.

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