Profile for Miguel Román
|Title:||Research Physical Scientist|
Terrestrial Information Systems Laboratory
Mail Code 619, Bldg 32, S-036F
Greenbelt, MD 20771
Office Phone: 301-614-5498
Google Scholar Profile: ~507 citations, h-index 12 as of July 2014.
Summary: My research focuses on the development and application of satellite remote sensing to produce stable, well calibrated, and scientifically validated products from a series of earth observing satellites. My focus is on the quantiﬁcation of uncertainty in satellite-derived products through a combination of quality assessment and validation techniques including day/night visible, near-infrared, and multi-angle imagery and measurements acquired from in-situ and airborne platforms.
At NASA Goddard, I am a member of the Land Product Evaluation and Test Element (PEATE) and the Joint Polar Satellite System's (JPSS) Land discipline teams. As part of this joint NASA/NOAA effort, our team is currently tasked with evaluating the operational Land algorithms that are being used for the Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (NPP) satellite. I am also the Land scientist for NASA’s Cloud Absorption Radiometer (CAR), considered the most frequently used airborne instrument built in-house at NASA Goddard, and an associate member (Co-I) of the MODIS science team.
I have also participated in several field campaign programs (e.g., FluxNet, NACP, ARM-DoE, and BSRN) and intense observing periods (e.g., ChEAS’06, CLASIC'07, ARCTAS'08, ECO3D'11, and DISCOVER-AQ'14) to coordinate the production of in-depth accuracy and variability assessments for current and future reprocessing of global land and cryosphere products.
At the international level, my work focuses on addressing the challenges associated with the validation of Essential Climate Variables (ECVs) derived from satellite data by coordinating major field and airborne campaigns, managing a global network of validation sites, developing internationally-recognized validation protocols and standards, and ensuring that validation data and results are made available for free within the global user community.
EDUCATION- Ph.D. in Geography, Boston University, 2009. (Major: Remote Sensing and GIS) Dissertation Title: “Use of in situ and airborne data to assess satellite-based estimates of directional reflectance and albedo”. Advisor: Crystal B. Schaaf.
ACTIVITIES AND PROJECTS (CURRENT)
Recent Meetings, Interviews, and Presentations
M Román was the primary author on the following paper presented at the 2014 International Geosciences and Remote Sensing Symposium (IGARSS) in Quebec City, Canada: 'Land, Cryosphere, and Nighttime Environmental Products from Suomi NPP VIIRS: Overview and Status'. Román was also the Chair of Oral Session TH3.03: Land Use and Land Cover Change I.
M. Román's Samuel J. Heyman Service to America Medals (Sammies) finalist profile was featured in El Nuevo Día (the most widely read newspaper in Puerto Rico, with a daily circulation of 155,000: link: http://tinyurl.com/nshn2un). The June 22, 2014 article focused on various highlights from projects at GSFC Code 619; including MODAPS, MODIS Rapid Response, and the Suomi-NPP and JPSS missions. The article also mentioned Román's recent work using the Suomi-NPP VIIRS Day/Night Band in Global Land Change Science and Applications.
M. Román was interviewed on a national broadcast of “Zona Política con Helen Aguirre Ferre” on Univision America Radio (http://tinyurl.com/keb6v4s). The live interview on June 13, 2014 focused on impacts of climate change in Latin America and the Caribbean.
M. Román "CEOS Working Group on Cal/Val Land Product Validation (LPV) Sub Group: Essential Climate Variables and the Sustainable Land Imaging Program”. 4th Annual HyspIRI Product Symposium, June 4-5. The HyspIRI Symposium included 42 talks, 6 posters, and 2 demonstration sessions on the HyspIRI Mission and new approaches and potential products for land and coastal imaging (http://hyspiri.jpl.nasa.gov).
M. Román was interviewed on ABC7 (WJLA) by Capital Insider’s Morris Jones. The interview, released on May 29, 2014 (link: http://wj.la/1hku6uh), focused on the use of Suomi-NPP data and products in satellite research and policy.
M. Román was interviewed on a live broadcast on Federal News Radio conducted by Federal Drive’s Tom Temin and Emily Kopp. The broadcast, conducted on May 19, 2014, focused on innovative techniques, using data from Suomi-NPP, in a variety of global land change science and applications (Radio podcast).
M. Román was interviewed by the Washington Post's Joe Davidson for a news article focusing on Public Service Recognition Week (URL: http://goo.gl/1AGV85).
M. Román attended the STAR JPSS Annual Meeting at the NOAA Center for Weather and Climate Prediction (NCWCP) in College Park, Maryland. The goals for the meeting were to present the accomplishments of the JPSS program over the past year and to highlight the transitions in algorithms, management, and the algorithm change process that are planned as NASA and NOAA advance towards the launch of JPSS-1. Román co-chaired the VIIRS Land Products breakout session, and gave a talk entitled: "An Overview of Innovative Approaches using Suomi-NPP Data for Global Land Change Science and Applications" during the closing plenary session.
M. Román attended the Global Vegetation Monitoring and Modeling International Conference (GV2M) in Avignon, France, February 3-7, 2014. The primary goal of this meeting was to bring researchers together to discuss new developments in the use of remote sensing observations and Earth system modeling with emphasis on applications related to water, carbon and nitrogen cycles, climate processes and change, agriculture and forest monitoring over large spatial domains using possibly long time series of satellite observations. Román presented a plenary talk entitled: "Assessment of Satellite-Derived Terrestrial Essential Climate Variables: An Overview of the Land Product Validation (LPV) sub-group of the CEOS Working Group on Calibration and Validation (WGCV)."
M. Román attended the ESA/ESRIN Land Product Validation and Evolution Workshop in Frascati Italy (Jan 28-30, 2014). The primary goal of this workshop was to foster continued coordination between scientists, national space agencies, national research programmes, and ESA with respect to global land product algorithm development and calibration/validation activities. Román presented a talk entitled: "Land, Cryosphere, and Nighttime Environmental Products from Suomi NPP VIIRS: Overview and Status". Following the ESA/ESRIN workshop, the Land Product Validation Subgroup of the CEOS Working Group on Calibration and Validation convened their 2nd subgroup leads workshop at ESA/ESRIN (Jan 30-31, 2014). During this workshop, Román (LPV co-chair) led the discussion panel on exchange on validation methods used for Land Essential Climate Variables (ECVs).
M. Román attended the Fall Meeting of the American Geophysical Union and presented the following poster: Román, M. (NASA/619), J. Nickeson (Sigma/619), G. Schaepman-Strub (U. Zurich), "Assessment of Satellite-Derived Essential Climate Variables in the Terrestrial Domain: An Overview of the CEOS LPV Subgroup". Román also presented a talk entitled: "Land and Cryosphere Products from Suomi NPP VIIRS: Overview and Status", coauthors (various institutions): C. Justice; I. Csiszar; L. Giglio; W. Schroeder; J. Coen; E. Vermote; R. Wolfe; S. Hook; M. Friedl; C. Schaaf; T. Miura; M. Vargas, M. Tschudi; G. Riggs; D. Hall; A. Lyapustin; R. Myneni; S. Devadiga; C. Davidson; E. Masuoka.
M. Román served as distinguished speaker for the 10th anniversary celebration of PROMISE: Maryland’s Alliance for Graduate Education and the Professoriate (AGEP), celebrated at the University of Maryland Baltimore SMC Campus Center. PROMISE: Maryland’s AGEP is an alliance of UMBC, the University of Maryland College Park, and the University of Maryland Baltimore (UMB, the Founding Campus), dedicated to the increasing the number and diversity of Ph.D. graduates in the sciences and engineering who go on to academic careers. AGEP is a program of the National Science Foundation.
M. Román attended the 36th CEOS Working Group on Calibration and Validation Plenary (WGCV-36) in Shanghai, China, May 13-17, 2013. The ultimate goal of the WGCV is to ensure long-term confidence in the accuracy and quality of Earth observation data and products through (1) sensor-specific calibration and validation and (2) geophysical parameter and derived-product validation. The WGCV-36 plenary provided a forum for the exchange of information on calibration and validation and international cooperative activities between CEOS member agencies. Román presented a status report on the CEOS-WGCV Land Product Validation (LPV) sub-group (http://lpvs.gsfc.nasa.gov/) of which he now serves as vice-chair. Román also presented the NASA agency report. Xiong, who is an standing member of the Infrared and Visible Optical Sensors Subgroup of WGCV (http://ceoswgcv-ivos.org/), presented a status report on the MODIS (Terra/Aqua) and VIIRS (Suomi-NPP) on-orbit calibration.
M. Román attended the Suomi NPP (S-NPP) Science Status Review Meeting and VIIRS Calibration workshop. The primary focus of the meeting was on evaluations of the S-NPP products and progress reports with an emphasis on the major findings and results to date for each activity, and the implications for proposing the next steps for NASA use of S-NPP data.
M. Román was interviewed on a live national broadcast on Univision Radio conducted by Dr. Isabel Gomez-Bassols. The one hour broadcast, conducted on October 16, 2012, focused on Earth Science careers as well as a discussion on NASA's Earth Science projects and research activities (Radio podcast).
M. Román, "The Suomi National Polar Orbiting Partnership (NPP) Day/Night Visible Sensor: Unleashing A New Era of Nighttime Remote Sensing Applications." Yale School of Forestry and Environmental Studies, 1 October, 2012, in New Haven, CT.
M. Román, "Assessing Satellite-Based Estimates of Surface Reflectance Anisotropy (BRDF) and Albedo Under Conditions of Rapid Surface Change." University of Massachusetts Boston Environmental, Coastal and Ocean Sciences Graduate Department Seminar Series, 24 September, 2012, in Boston, MA.
M. Román, Ivan Csiszar, Chris Justice, Jeffrey Key, Jeff Privette, Sadashiva Devadiga, Carol Davidson, Robert E. Wolfe, and Edward J. Masuoka "Status of the Suomi NPP Visible/Infrared Imager Radiometer Suite’s (VIIRS) Land Environmental Data Records (EDRs) after Early Evaluation of On-orbit Performance." IEEE Geoscience and Remote Sensing Symposium (IGARSS'12), 22-27 July, 2012, in Munich, Germany.
M. Román, "Use of In-Situ and Airborne Multiangle Data to Assess MODIS, VIIRS, and Landsat-based Estimates of Directional Reflectance And Albedo." 12th Science and Review Workshop of the World Climate Research Programme (WCRP) Global Energy and Water Cycle Experiment (GEWEX) and Global Climate Observing System (GCOS) Baseline Surface Radiation Network (BSRN) in Potsdam, Germany on 2 August, 2012.
M. Román, "Evaluation and Validation of Global Land Surface Products Derived from NASA and CNES Satellite Sensors." Laboratoire d'Optique Atmosphérique, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France on 30 July, 2012.
M. Román, "Evaluation and validation of global land surface products derived from Landsat, MODIS, and VIIRS." NASA-GSFC Climate & Radiation Laboratory seminar, Feb 01, 2012, in Greenbelt, MD.
M. Román, "Pre-launch evaluation of the NPP VIIRS Land and Cryosphere EDRs to meet NASA's science requirements." IEEE Geoscience and Remote Sensing Symposium (IGARSS'11), 24-29 July, 2011, in Vancouver, BC.
M. Román, “Overview of NASA Earth System Science.” South Dakota School of Mines and Technology (SDSMT) Open House, October 17, 2011, held at the NASA-GSFC Visitor Center in Greenbelt, MD.
M. Román and J. Nightingale, "CEOS-WGCV Land Product Validation Sub-Group Activities: Current and Potential Roles in Future Decadal Survey Missions” and poster entitled: “The Role of Scale and Spatial Heterogeneity in Retrieval of BRDF/Albedo Products.” HyspIRI Symposium, 17-18 May, 2011, held at the NASA-GSFC Visitor Center in Greenbelt, MD.
M. Román, “Roles and Responsibilities of NASA Earth System Scientists.” Explore@NASA Goddard open house event: Greatness@Goddard Session, May 14, 2011, in Greenbelt, MD.
Z. Wang, C. Schaaf, and M. Román, “Geostatistical Analysis of AmeriFlux Validation Sites for Assessment of Moderate Resolution Satellite-Derived Albedo Products.” AmeriFlux Science Meeting & 3rd NACP All-Investigators Meeting, January 31-February 4, 2011 in New Orleans, Louisiana.
M. Román, “Characterization of Surface Directional Reflectance Properties over the SGP Site from Airborne Measurements and Surface Observations.” IEEE Geoscience and Remote Sensing Symposium (IGARSS’10), July 25-30, 2010 in Honolulu, HI.
M. Román, “Characterization of Surface Directional Reflectance Properties from Airborne Angular Reflectance Measurements to Improve the Accuracy and Consistency of Long-Term Data Records.” 32nd Review of Atmospheric Transmission Models Meeting, 14-15 June 2010, held at the National Heritage Museum in Lexington, Massachusetts.
M. Román, “Use of In-Situ and Airborne Data to Assess Satellite Estimates of Directional Surface Reflectance and Albedo.” NOAA-NESDIS STAR Science Forum, Nov. 3, 2009, in Camp Springs, MD.
February, 2014: Global Leaf Area Index Product Validation Good Practices
January, 2014: Observations of Bioluminescence in Arctic and Antarctic Regions from VIIRS Nighttime Visible Data during the Polar Winter
August, 2013: Land and cryosphere products from Suomi NPP VIIRS: Overview and Status
January, 2013: Use of in situ and airborne multiangle data to assess MODIS- and Landsat-based estimates of directional reflectance and albedo
June, 2012: Detection of Light Outages using the VIIRS Day/Night Band: An Early Case Study on the D.C. Derecho Storm
March, 2012: Intercomparison of MODIS Albedo Retrievals and In-Situ Measurements across the Global FLUXNET Network
February, 2012: Software Tools for Data Manipulation, Visualization, and Analysis of Suomi-VIIRS Land and Cryosphere Products
November, 2011: Evaluation of MODIS snow albedo product (MDC43) over tundra
June, 2011: Variability in the BRDF at different spatial scales over a mixed agricultural landscape as retrieved from airborne and satellite spectral measurements
March, 2011: Monitoring savanna dynamics using the MODIS BRDF/albedo product
May, 2010: NASA’s Cloud Absorption Radiometer (CAR): Understanding surface bidirectional reflectance variability at sub-pixel scales
March, 2010: Characterization of surface directional reflectance properties at the Chesapeake Bay Watershed (CBW)
February, 2010: Assessing the coupling between surface albedo derived from MODIS and the fraction of diffuse skylight over NSA-Barrow
Education and Outreach
Gatebe, C. K., Ichoku, C. M., Poudyal, R. , Román, M.O., and Wilcox, E. (2014): Surface Albedo Darkening from Wildfires in Northern Sub-Saharan Africa, Environmental Research Letters., 9, doi:10.1088/1748-9326/9/6/065003.
Wang, Z., Schaaf, C.B., Strahler, A.H., Chopping, M.J., Román, M.O., Shuai, Y., Woodcock, C.E., Hollinger, D.Y., & Fitzjarrald, D.R. (2014). Evaluation of MODIS albedo product (MCD43A) over grassland, agriculture and forest surface types during dormant and snow-covered periods. Remote Sensing of Environment, 140, 60-77, doi:10.1016/j.rse.2013.08.025.
Justice, C.O., Román, M.O., Csiszar, I., Vermote, E., Wolfe, R., Hook, S.J., Friedl, M., Wang, Z., Schaaf, C., Miura, T., Tschudi, M., Riggs, G., Hall, D.K., Lyapustin, A., Devadiga, S., Davidson, C., & Masuoka, E. (2013). Land and Cryosphere Products from Suomi NPP VIIRS: Overview and Status. Journal of Geophysical Research-Atmospheres, 118, 1-13, doi:10.1002/jgrd.50771.
Gatebe, C., Ichoku C., Poudyal R., M.O. Román, and Wilcox E. (2014). Surface Albedo Darkening from Wildfires in Northern Sub-Saharan Africa Environmental Research Letters, 9.
Wang, Z., Schaaf C., Strahler A., Chopping M., M.O. Román, Shuai Y., Woodcock C., Hollinger D., and Fitzjarrald D. (2014). Evaluation of MODIS albedo product (MCD43A) over grassland, agriculture and forest surface types during dormant and snow-covered periods Remote Sensing of Environment, 14, 60-77
F. Zhao, X. Yang, A. H. Strahler, C. B. Schaaf, T. Yao, Z. Wang, M.O. Román, C. E. Woodcock, W. Ni-Meister, D.L.B. Jupp, J. L. Lovell, D. S. Culvenor, G. J. Newnham, H. Tang, and R. O. Dubayah (2013). A comparison of foliage profiles in the Sierra National Forest obtained with a full-waveform under-canopy EVI lidar system with the foliage profiles obtained with an airborne full-waveform LVIS lidar system Remote Sensing of Environment, 136, 330–341
Román, M.O., Gatebe, C.K., Shuai, Y., Wang, Z., Gao, F., J. Masek, He, T., Liang, S., and Schaaf, C.B. (2013). Use of in situ and airborne multiangle data to assess MODIS- and Landsat-based estimates of directional reflectance and surface albedo IEEE Transactions on Geoscience and Remote Sensing.
Alessandro Cescatti, Barbara Marcolla, Suresh K. Santhana Vannan, Jerry Yun Pan, M.O. Román, Xiaoyuan Yang, Philippe Ciais, Robert B. Cook, Beverly E. Law, Giorgio Matteucci, Mirco Migliavacca, Eddy Moors, Andrew D. Richardson, Günther Seufert, and Crystal B. Schaaf (2012). Intercomparison of MODIS albedo retrievals and in situ measurements across the global FLUXNET network Remote Sensing of Environment, 121, 323–334
Fatoyinbo Agueh, T.E., Rincon, Rafael, Harding, David, Gatebe, Charles, J. Ranson, G. Sun, Dabney, Phillip, and M.O. Román (2012). The 2011 Eco3D Flight Campaign: Vegetation Structure and Biomass Estimation from Simultaneous SAR, Lidar and Radiometer Measurements IEEE Geoscience and Remote Sensing Symposium (IGARSS) 2012
Román, M.O., Csiszar, I, Justice, C, , Key, J., Privette, J., Devadiga, S., Davidson, C., R.E. Wolfe, and E.J. Masuoka (2012). Status of the Suomi NPP Visible/Infrared Imager Radiometer Suite's (VIITS) Land Environmental Data Redords (EDRs) After Early Evaluation of On-Orbit Performance IEEE International Geoscience and Remote Sensing Symposium, 1084-1087
Zhuosen Wang, Crystal B. Schaaf, Mark J. Chopping, Alan H. Strahler, Jindi Wang, M.O. Román, Adrian V. Rocha, Curtis E. Woodcock, and Yanmin Shuai (2012). Evaluation of Moderate-resolution Imaging Spectroradiometer (MODIS) snow albedo product (MCD43A) over tundra Remote Sensing of Environment, 117, 264–280
Hill, M. J., M.O. Román, Schaaf C. B., Hutley L., Brannstrom C., Etter A., and Hanan N. P. (2011). Characterizing vegetation cover in global savannas with an annual foliage clumping index derived from the MODIS BRDF product Remote Sensing of Environment, 115, 2008-2024
Hill, M. J., M.O. Román, and C. B. Schaaf (2011). Dynamics of vegetation indices in tropical and subtropical savannas defined by ecoregions and Moderate Resolution Imaging Spectroradiometer (MODIS) land cover Geocarto International, 1-39
Román, M.O., C. K. Gatebe, C. Schaaf, R. Poudyal, Z. Wang, and M. D. King (2011). Variability in surface BRDF at different spatial scales (30 m–500 m) over a mixed agricultural landscape as retrieved from airborne and satellite spectral measurements Remote Sensing of Environment, 115, 2184-2203
Román, M.O., Justice, C., Csiszar, I., Key, J. R., Devadiga, S., Davidson, C., R.E. Wolfe, and Privette, J. (2011). Pre-Launch evaluation of the NPP VIIRS Land and Cryosphere EDRs to meet NASA's science requirements Geoscience and Remote Sensing Symposium (IGARSS), 2011 IEEE International , 154-157
Román, M.O., Justice, C., Csiszar, I., Key, J>R., Devadiga, S., Davidson, C., R.E. Wolfe, and Privette, J. (2011). Pre-launch evaluation of the NPP VIIRS Land and Cryosphere EDRs to meet NASA's science requirements Geoscience and Remote Sensing Symposium (IGARSS), 2011 IEEE International
Román, M.O., Gatebe, C., Schaff, C., Poudyal, R., Wang, Z., and King, M. (2011). Variability in surface BRDF at different spatial scales (30 m-500 m) over a mixed agricultural landscape as retrieved from airborne and satellite spectral measurements Remote Sensing of Environment, 115(9), 2184–2203
Zhao, F., Yang, X., Schull, M. A., M.O. Román, Yao, T., Wang, Z., Q. Zhang, Jupp, D. L. B., Lovell, J. l., Culvenor, D.s., Newnham, G. J., Richardson, A. D., W. Ni-Meister, Schaaf, C. B., Woodcock, C. E., and Strahler, A. H. (2011). Measuring effective leaf area index, foliage profile, and stand height in New England forest stands using a full-waveform ground-based lidar Remote Sensing of Environment, 115(11), 2954-2964
Hill, Michael J., M.O. Román, and Crystal B. Schaaf (2010). Biogeography, Ecology andDynamics of Global Savanna: A Geospatial View. In Ecosystems Function in Savannas. M.J. Hill and N.P. Hanan (Ed.). Ecosystem Function in Savannas: Measurement and Modeling at Landscape to Global Scales: CRC Taylor and Francis.
Román, M.O., C.B. Schaaf, P. Lewis, F. Gao, G.P. Anderson, J.L. Privette, A.H. Strahler, C.E. Woodcock, and M. Barnsley (2010). Assessing the Coupling between Surface Albedo derived from MODIS and the Fraction of Diffuse Skylight over Spatially-Characterized Landscapes Remote Sens. Environ., 114, 738-760
Lewis, P.E., G.P. Anderson, S.S. Shen, J. Chetwynd, M.O. Román, C.B. Schaaf, D.D. Turner, D.A. Rutan, A. Berk, D.P. Miller, and R. Kroutil (2009). MODTRAN5 analysis of clear-sky, co-located space- and ground-based infrared atmospheric measurements: AERI, AIRS, CERES, MODIS. Proc. SPIE, 7334(733410)
Liu, J., C.B. Schaaf, A.H. Strahler, Z. Jiao, Y. Shuai, Q. Zhang, M.O. Román, J.A. Augustine, and E.G. Dutton (2009). Validation of Moderate Resolution Imaging Spectroradiometer (MODIS) albedo retrieval algorithm: Dependence of albedo on solar zenith angle J. Geophys. Res., 114(D01106).
Román, M.O., C.B. Schaaf, C.E. Woodcock, A.H. Strahler, X. Yang, R.H. Braswell, P.S. Curtis, K.J. Davis, D. Dragoni, L. Gu, M.L. Goulden, D.Y. Hollinger, T.E. Kolb, T.P. Meyers, J.W. Munger, J.L. Privette, A.D. Richardson, T.B. Wilson, and S.C. Wofsy (2009). The MODIS (Collection V005) BRDF/albedo product: Assessment of spatial representativeness over forested landscapes Remote Sensing of Environment, 113, 2476-2498
Rutan, D., F. Rose, M.O. Román, N. Manalo-Smith, C. Schaaf, and T. Charlock (2009). Development and assessment of broadband surface albedo from Clouds and the Earth's Radiant Energy System Clouds and Radiation Swath data product J. Geophys. Res., 114(D08125).
Anderson, G.P., C.B. Schaaf, K. Loukachine, R.S. Stone, E. Andrews, E.P. Shettle, E.G. Dutton, M.O. Román, A. Stohl, and A. Berk (2008). Assessing the radiative impact of aerosol smoke using MODTRAN5. Proc. SPIE, 6966(696617).
Coddington, O., K.S. Schmidt, P. Pilewskie, W.J. Gore, R.W. Bergstrom, M.O. Román, J. Redemann, P.B. Russell, J. Liu, and C.C. Schaaf (2008). Aircraft measurements of spectral surface albedo and its consistency with ground-based and space-borne observations J. Geophys. Res., 113(D14S16).
Knobelspiesse, K.D., B. Cairns, B. Schmid, M.O. Román, and C.B. Schaaf (2008). Surface BRDF estimation from an aircraft compared to MODIS and ground estimates at the Southern Great Plains site J. Geophys. Res., 113(D20105).
Stone, R.S., G.P. Anderson, E.P. Shettle, E. Andrews, K. Loukachine, E.G. Dutton, C. Schaaf, and M.O. Román (2008). Radiative impact of boreal smoke in the Arctic: Observed and modeled J. Geophys. Res., 113(D14S16).