8 results on '"O'Neill, Peggy"'
Search Results
2. SMAP Detects Soil Moisture Under Temperate Forest Canopies.
- Author
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Colliander, Andreas, Cosh, Michael H., Kelly, Vicky R., Kraatz, Simon, Bourgeau‐Chavez, Laura, Siqueira, Paul, Roy, Alexandre, Konings, Alexandra G., Holtzman, Natan, Misra, Sidharth, Entekhabi, Dara, O'Neill, Peggy, and Yueh, Simon H.
- Subjects
FOREST canopies ,TEMPERATE forests ,BIOGEOCHEMICAL cycles ,SOIL dynamics ,BRIGHTNESS temperature ,FORESTED wetlands ,SOIL moisture - Abstract
Soil moisture dynamics in the presence of dense vegetation canopies are determinants of ecosystem function and biogeochemical cycles, but the capability of existing spaceborne sensors to support reliable and useful estimates is not known. New results from a recently initiated field experiment in the northeast United States show that the National Aeronautics and Space Administration (NASA) SMAP (Soil Moisture Active Passive) satellite is capable of retrieving soil moisture under temperate forest canopies. We present an analysis demonstrating that a parameterized emission model with the SMAP morning overpass brightness temperature resulted in a RMSD (root‐mean‐square difference) range of 0.047–0.057 m3/m3 and a Pearson correlation range of 0.75–0.85 depending on the experiment location and the SMAP polarization. The inversion approach included a minimal amount of ancillary data. This result demonstrates unequivocally that spaceborne L‐band radiometry is sensitive to soil moisture under temperate forest canopies, which has been uncertain because of lack of representative reference data. Key Points: Soil moisture monitoring networks were deployed at two forested sites for SMAP validation experimentSMAP brightness temperature was used to retrieve soil moisture over predominantly forested sitesThe study demonstrates the capability of spaceborne L‐band radiometry to retrieve soil moisture under forest canopies [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
3. First application of regression analysis to retrieve soil moisture from SMAP brightness temperature observations consistent with SMOS soil moisture
- Author
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Al Yaari, Amen, Wigneron, Jean-Pierre, Kerr, Yann, Rodriguez-Fernandez, Nemesio, O'Neill, Peggy, Jackson, Thomas, De Lannoy, Gabrielle, Al Bitar, Ahmad, Mialon, Arnaud, Richaume, Philippe, Yueh, Simon, Interactions Sol Plante Atmosphère (UMR ISPA), Institut National de la Recherche Agronomique (INRA)-Ecole Nationale Supérieure des Sciences Agronomiques de Bordeaux-Aquitaine (Bordeaux Sciences Agro), Department of Earth and Environmental Sciences [Leuven] (EES), Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), United States Department of Agriculture, Jet Propulsion Laboratory (JPL), California Institute of Technology (CALTECH)-NASA, and Interactions Sol Plante Atmosphère (ISPA)
- Subjects
remote sensing ,télédétection ,modèle de transfert radiatif ,projet smos ,équation de régression ,donnée satellite ,[SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing - Abstract
Two dedicated soil moisture (SM) spaceborne missions, ESA’s Soil Moisture and Ocean Salinity (SMOS) and NASA’s Soil Moisture Active Passive (SMAP) satellites, were launched in 2009 and 2015, respectively. Both satellites have been providing microwave brightness temperature (TB) observations and SM retrievals at L-band since then (Entekhabi et al., 2010; Kerr et al., 2012). A recent study demonstrated the efficiency of physically-based multiple-linear regression equations (Wigneron et al., 2004) to retrieve SM from AMSR-E TB observations. The regression equations were derived analytically from the radiative transfer model. The purpose of that initial study was to extend the SMOS SM product into the past i.e., 2003-2009, using AMSR-E TB observations. The current study follows the same strategy to retrieve SM from SMAP TB observations with a purpose to extend the SMOS SM product into the future at the global scale. Regression coefficients were calibrated using SMOS horizontal and vertical TB observations and SM level 3 (SMOSL3 as a training data), over the 2013 - 2014 period. Based on these calibrated coefficients, global SM maps were produced from the SMAP TB observations during the 31/03-08/09/2015 period (referred here to as SMAP-reg). The SM data set obtained from SMAP TBs using the regression equations has been compared to the SMAP SM dataset computed withthe single channel algorithm and both exhibit the same temporal dynamics. For instance, figure 1 shows the (Pearson) correlation coefficient (R) between SMAP-reg and SMAP original SM over 31/03-08/09/2015. A remarkable agreement, R (mostly > 0.8), was obtained between the SMAP-reg and SMAP original SM products.Ongoing evaluations of the SMAP-reg SM product, with comparison to the SMAP original SM, against the global MERRA-Land SM simulations and in situ measurements will be presented. The main interest in the SMAP-reg SM product is that it is fully consistent with the SMOS Level 3 SM product. One of the key remaining tasks is toensure the consistent relative calibration between SMOS and SMAP TBs.
- Published
- 2016
4. SCoBi-Veg: A Generalized Bistatic Scattering Model of Reflectometry From Vegetation for Signals of Opportunity Applications.
- Author
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Kurum, Mehmet, Deshpande, Manohar, Joseph, Alicia T., O'Neill, Peggy E., Lang, Roger H., and Eroglu, Orhan
- Subjects
VEGETATION monitoring ,TELECOMMUNICATION satellites ,REMOTE sensing ,SOIL moisture ,BIOMASS ,RECEIVING antennas - Abstract
SCoBi-Veg stands for Signals of opportunity Coherent Bistatic scattering model for Vegetated terrains. It simulates polarimetric reflectometry of vegetation canopy over a flat ground using a Monte Carlo scheme. The model is aimed at assessing the value of navigation and communication satellite Signals of Opportunity in a range of frequencies from P- to S-bands for remote sensing of a number of geophysical land parameters such as soil moisture and biomass. A fully polarimetric expression for bistatic scattering from a vegetation canopy is first formulated for a general case and is then specialized to the practical case of ground-based/low-altitude platforms with passive receivers overlooking vegetation using the signals transmitted from large distances. Using analytical wave theory in conjunction with distorted Born approximation, the transmit and receive antenna effects (i.e., polarization crosstalk/mismatch, orientation, and altitude) are explicitly accounted for. The forward model developed here enables the understanding of the effect of different geophysical parameters and system configurations on the coherent and incoherent components of the reflected signatures. It can thus help developing robust inverse algorithm for extraction of soil moisture and biomass. The model is applied to P-band signals of geostationary communication satellites to describe polarimetric reflections from tree canopies as observed from down-looking platforms at various altitudes. The relative contributions of diffuse and specular scattering on total reflected power and reflectivity are quantified for various observing scenarios. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
5. The Soil Moisture Active Passive (SMAP) Mission.
- Author
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ENTEKHABI, DARA, NJOKU, ENI G., O'NEILL, PEGGY E., KELLOGG, KENT H., CROW, WADE T., EDELSTEIN, WENDY N., ENTIN, JARED K., GOODMAN, SHAWN D., JACKSON, THOMAS J., JOHNSON, JOEL, KIMBALL, JOHN, PIEPMEIER, JEFFREY R., KOSTER, RANDAL D., MARTIN, NEIL, MCDONALD, KYLE C., MOGHADDAM, MAHTA, MORAN, SUSAN, REICHLE, ROLF, SHI, J. C., and SPENCER, MICHAEL W.
- Subjects
SOIL moisture measurement instruments ,SOIL infiltration measurement -- Instruments ,ARTIFICIAL satellites ,REMOTE sensing ,SURFACE of the earth ,ATMOSPHERE ,EARTH (Planet) - Abstract
The Soil Moisture Active Passive (SMAP) mission is one of the first Earth observation satellites being developed by NASA in response to the National Research Council's Decadal Survey. SMAP will make global measurements of the soil moisture present at the Earth's land surface and will distinguish frozen from thawed land surfaces. Direct observations of soil moisture and freeze/thaw state from space will allow significantly improved estimates of water, energy, and carbon transfers between the land and the atmosphere. The accuracy of numerical models of the atmosphere used in weather prediction and climate projections are critically dependent on the correct characterization of these transfers. Soil moisture measurements are also directly applicable to flood assessment and drought monitoring. SMAP observations can help monitor these natural hazards, resulting in potentially great economic and social benefits. SMAP observations of soil moisture and freeze/thaw timing will also reduce a major uncertainty in quantifying the global carbon balance by helping to resolve an apparent missing carbon sink on land over the boreal latitudes. The SMAP mission concept will utilize L-band radar and radiometer instruments sharing a rotating 6-m mesh reflector antenna to provide high-resolution and high-accuracy global maps of soil moisture and freeze/thaw state every two to three days. In addition, the SMAP project will use these observations with advanced modeling and data assimilation to provide deeper root-zone soil moisture and net ecosystem exchange of carbon. SMAP is scheduled for launch in the 2014-2015 time frame. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
6. L-Band Radar Estimation of Forest Attenuation for Active/Passive Soil Moisture Inversion.
- Author
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Kurum, Mehmet, Lang, Roger H., O'Neill, Peggy E., Joseph, Alicia T., Jackson, Thomas J., and Cosh, Michael H.
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RADAR ,SOIL moisture ,REMOTE sensing ,FOREST canopies ,BACKSCATTERING ,MONTE Carlo method ,RADIOMETERS - Abstract
In the radiometric sensing of soil moisture through a forest canopy, knowledge of canopy attenuation is required. Active sensors have the potential of providing this information since the backscatter signals are more sensitive to forest structure. In this paper, a new radar technique is presented for estimating canopy attenuation. The technique employs details found in a transient solution where the canopy (volume-scattering) and the tree-ground (double-interaction) effects appear at different times in the return signal. The influence that these effects have on the expected time-domain response of a forest stand is characterized through numerical simulations. A coherent forest scattering model, based on a Monte Carlo simulation, is developed to calculate the transient response from distributed scatterers over a rough surface. The forest transient-response model for linear copolarized case is validated with the microwave deciduous tree data acquired the Combined Radar/Radiometer (ComRAD) system. The atteuation algorithm is applicable when the forest height is sufficient to separate the components of the radar backscatter transient response. The frequency correlation functions of double-interaction and volume-scattering returns are normalized after being separated in the time domain. This ratio simply provides a physically based system of equations with reduced parameterizations for the forest canopy. Finally, the technique is used with ComRAD L-band stepped-frequency data to evaluate its performance under various physical conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
7. Soil Moisture Retrieval During a Corn Growth Cycle Using L-Band (1.6 GHz) Radar Observations.
- Author
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Joseph, Alicia T., van der Velde, Rogier, O'Neill, Peggy E., Lang, Roger H., and Gish, Tim
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FUNCTIONAL equations ,SOIL moisture ,SOIL infiltration ,SOIL physics ,GROUNDWATER ,ELECTRONIC pulse techniques ,RADAR ,SURFACE roughness ,DETECTORS - Abstract
This paper reports on the retrieval of soil moisture from dual-polarized L-band (1.6 GHz) radar observations acquired at view angles of 15°, 35°, and 55°, which were collected during a field campaign covering a corn growth cycle in 2002. The applied soil moisture retrieval algorithm includes a surface roughness and vegetation correction and could potentially be implemented as an operational global soil moisture retrieval algorithm. The surface roughness parameterization is obtained through inversion of the Integral Equation Method (IEM) from dual-polarized (HH and VV) radar observations acquired under nearly bare soil conditions. The vegetation correction is based on the relationship found between the ratio of modeled bare soil scattering contribution and observed backscatter coefficient (σ
soil /σobs ) and vegetation water content (W). Validation of the retrieval algorithm against ground measurements shows that the top 5-cm soil moisture can be estimated with an accuracy between 0.033 and 0.064 cm³ · cm-3 , depending on the view angle and polarization. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
8. Passive microwave observation of diurnal surface soil moisture.
- Author
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Jackson, Thomas J. and O'Neill, Peggy E.
- Subjects
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SOIL moisture , *REMOTE sensing - Abstract
Presents a study conducted in 1994 at the United States Department of Agriculture Beltsville Agricultural Research Center, which examined passive microwave observations at low frequencies of diurnal surface soil moisture. Methodology of the study; Results obtained with comparisons of emissivity and volumetric soil metric at four depths; What observations during drying and rainfall demonstrate.
- Published
- 1997
- Full Text
- View/download PDF
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