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911 results on '"Kerr, Yann"'

4. Use of a new Tibetan Plateau network for permafrost to characterize satellite-based products errors: An application to soil moisture and freeze/thaw

Author

Zheng, Jingyao, Zhao, Tianjie, Lü, Haishen, Zou, Defu, Rodriguez-Fernandez, Nemesio, Mialon, Arnaud, Richaume, Philippe, Xiao, Jianshe, Ma, Jun, Fan, Lei, Song, Peilin, Zhu, Yonghua, Li, Rui, Yao, Panpan, Yang, Qingqing, Du, Shaojie, Wang, Zhen, Peng, Zhiqing, Xiong, Yuyang, Xing, Zanpin, Zhao, Lin, Kerr, Yann, and Shi, Jiancheng

Published
2024
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10. Fourier-Correlation Imaging

Author

Braun, Daniel, Monjid, Younes, Rougé, Bernard, and Kerr, Yann

Subjects
Physics - Instrumentation and Detectors, Physics - Data Analysis, Statistics and Probability
Abstract

We investigate to what extent correlating the Fourier components at slightly shifted frequencies of the fluctuations of the electric field measured with a one-dimensional antenna array on board of a satellite flying over a plane, allows one to measure the two-dimensional brilliance temperature as function of position in the plane. We find that the achievable spatial resolution resulting from just two antennas is of the order of $h\chi$, with $\chi=c/(\Delta r \omega_0)$, both in the direction of flight of the satellite and in the direction perpendicular to it, where $\Delta r$ is the distance between the antennas, $\omega_0$ the central frequency, $h$ the height of the satellite over the plane, and $c$ the speed of light. Two antennas separated by a distance of about 100m on a satellite flying with a speed of a few km/s at a height of the order of 1000km and a central frequency of order GHz allow therefore the imaging of the brilliance temperature on the surface of Earth with a resolution of the order of one km. For a single point source, the relative radiometric resolution is of order $\sqrt{\chi}$, but for a uniform temperature field in a half plane left or right of the satellite track it is only of order $1/\chi^{3/2}$, indicating that two antennas do not suffice for a precise reconstruction of the temperature field. Several ideas are discussed how the radiometric resolution could be enhanced. In particular, having $N$ antennas all separated by at least a distance of the order of the wave-length, allows one to increase the signal-to-noise ratio by a factor of order $N$, but requires to average over $N^2$ temperature profiles obtained from as many pairs of antennas., Comment: 39 pages of latex in preprint format, 2 figures

Published
2017
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11. Characterizing the channel dependence of vegetation effects on microwave emissions from soils.

Author

Zhang, Jiaqi, Zhao, Tianjie, Tan, Shurun, Rodriguez-Fernandez, Nemesio, Xue, Huazhu, Yang, Na, Kerr, Yann, and Shi, Jiancheng

Abstract

The two vegetation transfer parameters of $\tau $ τ (Vegetation Optical Depth,VOD) and $\omega $ ω (Omega) could vary significantly across microwave channels in terms of frequencies, polarizations, and incidence angles, and their channel-dependent characteristics have not yet been fully investigated. In this study, we investigate the channel dependence of vegetation effects on microwave emissions from soils using a higher-order vegetation radiative transfer model of Tor Vergata. Corn was selected as the subject of investigation, and a corn growth model was developed utilizing field data collected from the multifrequency and multi-angular ground-based microwave radiation experiment from the Soil Moisture Experiment in the Luan River (SMELR). Upon compilation of the simulation dataset of microwave emissions of the corn field, the effective scattering albedo across different channels were calculated using the Tor Vergata model. Results show that vertical polarization of the vegetation optical depth is more affected by incidence angle changes, while horizontal polarization exhibits lower variations in vegetation optical depth due to incidence angle adjustments. The channel dependence of vegetation optical depth can be described as the polarization dependence parameter (${C_P}$ C P ) and the frequency dependence parameter (${C_f}$ C f ). These two parameters enable the calculation of vegetation optical depth at any channel under three adjacent frequencies (L-band, C-band and X-band). The effective scattering albedo of vegetation does not vary significantly with vegetation height or angle. It primarily depends on frequency and polarization, showing an overall increasing trend with increasing frequency. The effective scattering albedo with vertical polarization is slightly higher than that with horizontal polarization at higher frequencies, while both are lower in the L-band. This investigation is helpful for understanding the vegetation effects on microwave emissions from soils, ultimately advancing the accuracy of large-scale soil moisture retrieval in vegetated areas. [ABSTRACT FROM AUTHOR]

Published
2024
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14. Sentinel-1 soil moisture at 1 km resolution: a validation study

Author

Balenzano, Anna, Mattia, Francesco, Satalino, Giuseppe, Lovergine, Francesco P., Palmisano, Davide, Peng, Jian, Marzahn, Philip, Wegmüller, Urs, Cartus, Oliver, Dąbrowska-Zielińska, Katarzyna, Musial, Jan P., Davidson, Malcolm W.J., Pauwels, Valentijn R.N., Cosh, Michael H., McNairn, Heather, Johnson, Joel T., Walker, Jeffrey P., Yueh, Simon H., Entekhabi, Dara, Kerr, Yann H., and Jackson, Thomas J.

Published
2021
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18. A roadmap for high-resolution satellite soil moisture applications – confronting product characteristics with user requirements

Author

Peng, Jian, Albergel, Clement, Balenzano, Anna, Brocca, Luca, Cartus, Oliver, Cosh, Michael H., Crow, Wade T., Dabrowska-Zielinska, Katarzyna, Dadson, Simon, Davidson, Malcolm W.J., de Rosnay, Patricia, Dorigo, Wouter, Gruber, Alexander, Hagemann, Stefan, Hirschi, Martin, Kerr, Yann H., Lovergine, Francesco, Mahecha, Miguel D., Marzahn, Philip, Mattia, Francesco, Musial, Jan Pawel, Preuschmann, Swantje, Reichle, Rolf H., Satalino, Giuseppe, Silgram, Martyn, van Bodegom, Peter M., Verhoest, Niko E.C., Wagner, Wolfgang, Walker, Jeffrey P., Wegmüller, Urs, and Loew, Alexander

Published
2021
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19. Generalization of the Van Cittert--Zernike theorem: observers moving with respect to sources

Author

Braun, Daniel, Monjid, Younes, Rougé, Bernard, and Kerr, Yann

Subjects
Physics - Data Analysis, Statistics and Probability, Physics - Instrumentation and Detectors, Physics - Optics
Abstract

The use of the Van Cittert--Zernike theorem for the formulation of the visibility function in satellite-based Earth observation with passive radiometers does not take into account the relative motion of the observer (the satellite antenna) with respect to sources of the electro-magnetic fields at the surface of the Earth. The motion of the observer leads on the one hand to a more complex signal due to a pixel-dependent Doppler shift that is neglected in the standard derivation of the Van Cittert--Zernike theorem, but on the other hand one may hope that it could be employed for a temporal aperture synthesis, where virtual baselines are created through the motion of the satellite. Here, we generalize the formulation of the aperture synthesis concept to the case of observers moving with respect to the sources, and to the correlation of fields measured at times that differ by the travel time of the observer along a virtual baseline. Our derivation is based on first principles, starting with the wave propagation in the Earth reference frame of electro-magnetic fields arising from incoherent current sources, and Lorentz transforming the fields into the reference frame of the satellite. Our detailed study leads to the remarkable conclusion that the delay time due to observer motion cancels exactly the Doppler effect. This justifies the neglect of the Doppler effect in existing imaging systems based on the standard Van Cittert--Zernike theorem., Comment: 13 pages in IOP MST format

Published
2015
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22. Satellite-observed pantropical carbon dynamics

Author

Fan, Lei, Wigneron, Jean-Pierre, Ciais, Philippe, Chave, Jérôme, Brandt, Martin, Fensholt, Rasmus, Saatchi, Sassan S., Bastos, Ana, Al-Yaari, Amen, Hufkens, Koen, Qin, Yuanwei, Xiao, Xiangming, Chen, Chi, Myneni, Ranga B., Fernandez-Moran, Roberto, Mialon, Arnaud, Rodriguez-Fernandez, N. J., Kerr, Yann, Tian, Feng, and Peñuelas, Josep

Published
2019
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24. A Comparison of Passive Microwave Emission Models for Estimating Brightness Temperature at L- and P-Bands Under Bare and Vegetated Soil Conditions.

Author

Brakhasi, Foad, Walker, Jeffrey P., Judge, Jasmeet, Liu, Pang-Wei, Shen, Xiaoji, Ye, Nan, Wu, Xiaoling, Yeo, In-Young, Boopathi, Nithyapriya, Kim, Edward, Kerr, Yann H., and Jackson, Thomas J.

Abstract

P-band radiometry has been demonstrated to have a deeper sensing depth than L-band, making the consideration of multilayer microwave interactions necessary. In addition, the scattering and phase interference effects are different at the P-band, requiring a reconsideration of the need for coherent models. However, the impact remains to be clarified, and understanding the validity and limitations of these models at both L- and P-bands is crucial for their refinement and application. Therefore, two general categories of microwave emission models, including two stratified coherent models (Njoku and Wilhite) and four incoherent models (conventional tau-omega model and three multilayer models being zero-order, first-order, and incoherent solution), were intercompared for the first time on the same dataset. This evaluation utilized observations of L- and P-bands radiometry under different land cover conditions from a tower-based experiment in Victoria, Australia. Model estimations of brightness temperature (TB) were consistent with measurements, with the lowest root mean square error (RMSE) at P-band V-polarization under corn (2 K) and the highest RMSE at L-band H-polarization under bare soil (13 K). Coherent models performed slightly better than incoherent models under bare soil (3 K less RMSE), while the opposite was true under vegetated soil conditions (1 K less RMSE). Coherent and incoherent models showed maximum differences (3 K at P-band and 2 K at L-band), correlating strongly with soil moisture variations at 0–10 cm. Findings suggest that coherent and incoherent models performed similarly; thus, incoherent models may be preferable for estimating TB at L- and P-bands due to reduced computational complexity. [ABSTRACT FROM AUTHOR]

Published
2024
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28. Analyzing the reliability of in situ soil moisture measurements for satellite product validation: What makes fiducial reference measurements fiducial?

Author

Himmelbauer, Irene, primary, Gruber, Alexander, additional, Aberer, Daniel, additional, Preimesberger, Wolfgang, additional, Stradiotti, Pietro, additional, Dorigo, Wouter A., additional, Boresch, Alexander, additional, Tercjak, Monika, additional, Gibon, Francois, additional, Mialon, Arnaud, additional, Richaume, Philippe, additional, Kerr, Yann, additional, Diez Garcia, Raul, additional, Crapolicchio, Raffaele, additional, Sabia, Roberto, additional, Scipal, Klaus, additional, and Goryl, Philippe, additional

Published
2023
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30. QA4SM: a service for transparent and reproducible evaluation of satellite soil moisture products

Author

Aberer, Daniel, primary, Preimesberger, Wolfgang, additional, Stradiotti, Pietro, additional, Scherrer, Samuel, additional, Tercjak, Monika, additional, Gruber, Alexander, additional, Dorigo, Wouter, additional, Boresch, Alexander, additional, Himmelbauer, Irene, additional, Gibon, François, additional, Richaume, Philippe, additional, Mialon, Arnaud, additional, Kerr, Yann, additional, Mahmoodia, Ali, additional, Crapolicchio, Raffaele, additional, Sabia, Roberto, additional, Garcia, Raul, additional, Goryl, Philippe, additional, and Scipal, Klaus, additional

Published
2023
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31. Fiducial Reference Measurements for Soil Moisture (FRM4SM): Toward a better understanding of (satellite) soil moisture uncertainties 

Author

Gibon, François, primary, Boresch, Alexander, additional, Himmelbauer, Irene, additional, Aberer, Daniel, additional, Crapolicchio, Raffaele, additional, Díez-García, Raúl, additional, Dorigo, Wouter, additional, Goryl, Philippe, additional, Gruber, Alexander, additional, Kerr, Yann, additional, Mialon, Arnaud, additional, Preimesberger, Wolfgang, additional, Richaume, Philippe, additional, Rodriguez-Fernandez, Nemesio, additional, Sabia, Roberto, additional, Scipal, Klaus, additional, Stradiotti, Pietro, additional, and Tercjak, Monika, additional

Published
2023
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37. Integrated SMAP and SMOS Soil Moisture Observations

Author

Bindlish, Rajat, Chan, Steven, Colliander, Andreas, Kerr, Yann, and Jackson, Thomas J

Subjects
Earth Resources And Remote Sensing
Abstract

Soil Moisture Active Passive (SMAP) mission and the Soil Moisture and Ocean Salinity (SMOS) missions provide brightness temperature and soil moisture estimates every 2-3 days. SMAP brightness temperature observations were compared with SMOS observations at 40o incidence angle. The brightness temperatures from the two missions are close to each other but SMAP observations show a warmer TB bias (about 0.64 K: V pol and 1.14 K: H pol) as compared to SMOS. SMAP and SMOS missions use different retrieval algorithms and ancillary datasets which result in further inconsistencies between their soil moisture products. The reprocessed constant-angle SMOS brightness temperatures (SMOS-SMAP) were used in the SMAP soil moisture retrieval algorithm to develop a consistent multi-satellite product. The integrated product has an increased global revisit frequency (1 day) and period of record that is unattainable by either one of the satellites alone. The SMOS-SMAP soil moisture retrievals compared with in situ observations show a retrieval accuracy of less than 0.04 m3/m3. Results from the development and validation of the integrated soil moisture product will be presented.

Published
2019

38. Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands

Author

Brandt, Martin, Wigneron, Jean-Pierre, Chave, Jerome, Tagesson, Torbern, Penuelas, Josep, Ciais, Philippe, Rasmussen, Kjeld, Tian, Feng, Mbow, Cheikh, Al-Yaari, Amen, Rodriguez-Fernandez, Nemesio, Schurgers, Guy, Zhang, Wenmin, Chang, Jinfeng, Kerr, Yann, Verger, Aleixandre, Tucker, Compton, Mialon, Arnaud, Rasmussen, Laura Vang, Fan, Lei, and Fensholt, Rasmus

Published
2018
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44. Sea Surface Salinity Observations from Space with the SMOS Satellite: A New Means to Monitor the Marine Branch of the Water Cycle

Author

Reul, Nicolas, Fournier, Severine, Boutin, Jaqueline, Hernandez, Olga, Maes, Christophe, Chapron, Bertrand, Alory, Gaël, Quilfen, Yves, Tenerelli, Joseph, Morisset, Simmon, Kerr, Yann, Mecklenburg, Susanne, Delwart, Steven, Bengtsson, Lennart, editor, Bonnet, R.-M., editor, Calisto, M., editor, Destouni, G., editor, Gurney, R., editor, Johannessen, J., editor, Kerr, Y., editor, Lahoz, W.A., editor, and Rast, M., editor

Published
2014
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47. Satellite and In Situ Observations for Advancing Global Earth Surface Modelling: A Review

Author

Balsamo, Gianpaolo, Agusti-Panareda, Anna, Albergel, Clement, Arduini, Gabriele, Beljaars, Anton, Bidlot, Jean, Bousserez, Nicolas, Boussetta, Souhail, Brown, Andy, Buizza, Roberto, Buontempo, Carlo, Chevallier, Frédéric, Choulga, Margarita, Cloke, Hannah, Cronin, Meghan F, Dahoui, Mohamed, De Rosnay, Patricia, Dirmeyer, Paul A, Drusch, Matthias, Dutra, Emanuel, Ek, Michael B, Gentine, Pierre, Hewitt, Helene, Keeley, Sarah P. E, Kerr, Yann, Kumar, Sujay, Lupu, Cristina, Mahfouf, Jean-Francois, McNorton, Joe, Mecklenburg, Susanne, Mogensen, Kristian, Muñoz-Sabater, Joaquín, Orth, Rene, Rabier, Florence, Reichle, Rolf, Ruston, Ben, Pappenberger, Florian, Sandu, Irina, Seneviratne, Sonia I, Tietsche, Steffen, Trigo, Isabel F, Uijlenhoet, Remko, Wedi, Nils, Woolway, R. Iestyn, and Zeng, Xubin

Subjects
Earth Resources And Remote Sensing
Abstract

In this paper we review the use of satellite-based remote sensing in combination with in situ data to inform Earth surface modelling. This involves verification and optimization methods that can handle both random and systematic errors and result in effective model improvement for both surface monitoring and prediction applications. The reasons for diverse remote sensing data and products include (i) their complementary areal and temporal coverage, (ii) their diverse and covariant information content, and (iii) their ability to complement in situ observations, which are often sparse and only locally representative. To improve our understanding of the complex behavior of the Earth system at the surface and sub-surface, we need large volumes of data from high-resolution modelling and remote sensing, since the Earth surface exhibits a high degree of heterogeneity and discontinuities in space and time. The spatial and temporal variability of the biosphere, hydrosphere, cryosphere and anthroposphere calls for an increased use of Earth observation (EO) data attaining volumes previously considered prohibitive. We review data availability and discuss recent examples where satellite remote sensing is used to infer observable surface quantities directly or indirectly, with particular emphasis on key parameters necessary for weather and climate prediction. Coordinated high-resolution remote-sensing and modelling/assimilation capabilities for the Earth surface are required to support an international application-focused effort.

Published
2018
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