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 Water and Carbon Cycles: People
Eni Njoku's Picture
Jet Propulsion Laboratory
M/S 300-329F
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 hydrology and the global water cycle. He served as project scientist of the Soil Moisture Active Passive (SMAP) mission and is a member of the EOS/Aqua Advanced Microwave Scanning Radiometer (AMSR) science team, investigating surface soil moisture and its role in hydrologic and ecologic modeling, weather and climate prediction, and monitoring of floods and droughts.

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

Water cycle science and applications using microwave remote sensing.


SMAP - Soil Moisture Active & Passive Icon SMAP - Soil Moisture Active & Passive
SMAP, launched in 2015, provides global measurements of soil moisture and other hydrologic variables for a variety of science and applications benefits.

Professional Experience
  • Jet Propulsion Laboratory (1977-Present)
    • Project Scientist, SMAP Mission (2008-2013)
    • 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 Assoc. (1976)
  • NASA Group Achievement Awards (1980, 1982, 1985, 2013)
  • NASA Exceptional Service Medal (1985)
  • Fellow, Institute of Electrical and Electronics Engineers (IEEE) (1995)
  • Visiting Fellow, Massachusetts Institute of Technology (2001-02)

Selected Publications
  1. Das, N., D. Entekhabi, E. Njoku, J. Shi, J. Johnson, A. Colliander (2014): Tests of the SMAP combined radar and radiometer algorithm using airborne field campaign observations and simulated data, IEEE Trans. Geosci. Rem. Sens., 52, 2018-2028.
  2. Kim, S., M. Moghaddam, L. Tsang, M. Burgin, X. Xu, E. Njoku (2014): Models of L-band radar backscattering coefficients over global terrain for soil moisture retrieval, IEEE Trans. Geosci. Rem. Sens., 52, 1381-1396.
  3. Das, N., A. Colliander, S. Chan, E. Njoku, L. Li (2014): Intercomparisons of brightness temperature observations over land from AMSR-E and Windsat, IEEE Trans. Geosci. Rem. Sens., 52, 452-464.
  4. Tsang, L. I-S. Koh, T-H. Liao, S. Huang, X. Xu, E. Njoku, and Y. Kerr (2013): Active and passive vegetated surface models with rough surface boundary conditions from NMM3D, IEEE J. of Selected Topics in Appl. Earth Obs. and Rem. Sens., 6, 1698-1709.
  5. 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.
  6. Colliander, A., K. McDonald, R. Zimmermann, T. Linke, R. Schroeder, J. Kimball, and E. Njoku (2012): Application of QuikSCAT backscatter to SMAP validation planning: Freeze/thaw state over ALECTRA sites in Alaska from 2000 to 2007, IEEE Trans. Geosci. Rem. Sens., 50, 461-468.
  7. Colliander, A., S. Chan, S. Kim, N. Das, S. Yueh, M. Cosh, R. Bindlish, T. Jackson, and E. Njoku (2011):  Long term analysis of PALS soil moisture campaign measurements for global soil moisture algorithm development, Rem. Sens. of Environ., 121, 309-322.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. Entekhabi, D., E. Njoku, et al. (2010): The Soil Moisture Active Passive (SMAP) Mission, Proceedings of the IEEE, 98, 704-716.
  13. Li, L., P. Gaiser, B. Gao, R. Bevilacqua, T. Jackson, E. Njoku, C. Rudiger, J.-C. Calvet, and R. Bindlish (2010):  WindSat global soil moisture retrieval and validation, IEEE Trans. on Geosci. Rem. Sens., 48, 2224-2241.
  14. Das, N. N., B. P. Mohanty, and E. G. Njoku (2008):  An MCMC algorithm for upscaled SVAT modeling to evaluate satellite-based soil moisture measurements, Water Resources Res., 44, W05416, doi:10.1029/2007WR006472.
  15. Piepmeier, J. R., D. G. Long and E. G. Njoku (2008): Stokes antenna temperatures, IEEE Trans. Geosci. Rem. Sens., 46, 516-527.
  16. 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.
  17. 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.
  18. 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.
  19. Njoku, E.G. and T. K. Chan (2006): Vegetation and surface roughness effects on AMSR-E land observations, Rem. Sens. Environ., 100, 190-199.
  20. 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.
  21. 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.
  22. 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.
  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. 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.
  25. 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.
  26. 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.
  27. 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.
  28. 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.
  29. 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.
  30. Njoku, E. G. and D. Entekhabi (1996): Passive microwave remote sensing of soil moisture, J. Hydrology, 184, 101-129.
  31. 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.
  32. 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.
  33. 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.

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