Towards a long-term dataset of ELBARA-II measurements assisting SMOS level-3 land product and algorithm validation at the Valencia Anchor Station
Keywords:brightness temperature, ELBARA-II, L-MEB, SMOS, SMOS level 3 data, soil moisture, soil roughness, Valencia Anchor Station, vegetation optical depth
AbstractThe Soil Moisture and Ocean Salinity (SMOS) mission was launched on 2nd November 2009 with the objective of providing global estimations of soil moisture and sea salinity. The main activity of the Valencia Anchor Station (VAS) is currently to assist in a long-term validation of SMOS land products. This study focus on a level 3 SMOS data validation with in situ measurements carried out in the period 2010-2012 over the VAS. ELBARA-II radiometer is placed in the VAS area, observing a vineyard field considered as representative of a major proportion of an area of 50×50 km, enough to cover a SMOS footprint. Brightness temperatures (TB) acquired by ELBARA-II have been compared to those observed by SMOS at the same dates and time. They were also used for the L-MEB model inversion to retrieve soil moisture (SM), which later on have been compared to those provided by SMOS as level 3 data. A good correlation between both TB datasets was found, improving year by year, mainly due to the decrease of precipitations in the analyzed period and the mitigation of radio frequency interferences at L-band. The larger homogeneity of the radiometer footprint as compared to SMOS explains the higher variability of its TB. Periods of more intense precipitation (spring and autumn) also presented higher SM, which corroborates the consistency of SM retrieved from ELBARA-II’s observations. However, the results show that SMOS level 3 data underestimate SM as compared to ELBARA-II’s, probably due to the influence of the small soil fraction which is not cultivated in vineyards. SMOS estimations in descending orbit (6 pm) had better quality (higher correlation, lower RMSE and bias) than the ones in ascending orbit (6 am, when there is a higher soil moisture).
Cano, A., Saleh, K., Wigneron, J. P., Antolín, C., Balling, J. E., Kerr, Y. H., Kruszewski, A., MillánScheiding, C., Schmidl Søbjærg, S., Skou, N., López-Baeza, E. 2010. The SMOS Mediterranean Ecosystem L-Band characterisation EXperiment (MELBEX-I) over natural shrubs. Remote Sensing of Environment, 114(4): 844-853. http://dx.doi.org/10.1016/j.rse.2009.11.019
Cognard, A. L., Loumagne, C., Normand, M., Olivier, P., Ottlé, C., Vidal-Madjar, D., Louahala, S., Vidal, A. 1995. Evaluation of the ERS 1/Synthetic Aperture Radar Capacity to Estimate Surface Soil Moisture: Two-Year Results Over the Naizin Watershed. Water Resources Research, 31(4): 975- 982. http://dx.doi.org/10.1029/94WR03390
Kerr, Y. H., Waldteufel, P., Richaume, P., Wigneron, J. P., Ferrazzoli, P., Mahmoodi, A., Al Bitar, A., Cabot, F., Gruhier, C., Juglea, S. E., Leroux, D., Mialon, A., Delwart, S. 2012. The SMOS soil moisture retrieval algorithm. IEEE Transactions on Geoscience and Remote Sensing, 50(5): 1384-1403. http://dx.doi.org/10.1109/TGRS.2012.2184548
Kerr, Y. H, Waldteufel, P., Wigneron, J. P., Delwart, S., Cabot, F., Boutin, J., Escorihuela, M. J., Font, J., Reul, N., Gruhier, C., Juglea, S. E., Drinkwater, M. R., Hahne, A., Martin-Neira, M., Mecklenburg, S. 2010. The SMOS mission: new tool for monitoring key elements of the global water cycle. Proceedings of the IEEE, 98(5): 666-687. http://dx.doi. org/10.1109/JPROC.2010.2043032
Lawrence, H., Wigneron, J. P., Demontoux, F., Mialon, A., Kerr, Y. H. 2013. Evaluating the Semiempirical H - Q Model Used to Calculate the L-Band Emissivity of a Rough Bare Soil. IEEE Transactions on Geoscience and Remote Sensing, 51(7): 4075-4084. http://dx.doi.org/10.1109/TGRS.2012.2226995
Schwank, M., Wigneron, J. P., Lopez-Baeza, E., Völksch, I., Mätzler, C., Kerr, Y. H. 2012. L-Band Radiative Properties of Vine Vegetation at the MELBEX III SMOS Cal/Val Site. IEEE Transactions on Geoscience and Remote Sensing, 50(5): 1587-1601.
Völksch, I., Wiesmann, A. and Schwank, M., 2011. Calibration Algorithms and Documentation (D2). GAMMA, Gümligen.
Wigneron, J. P., Kerr, Y., Waldteufel, P., Saleh, K., Escorihuela, M. J.,
Richaume, P., Ferrazzoli, P., de Rosnay, P., Gurney, R., Calvet, J.C., Grant, J. P., Guglielmetti, M., Hornbuckle, B., Mätzler, C., Pellarin, T., Schwank, M. 2007. L-band Microwave Emission of the Biosphere (L-MEB) Model: description and calibration against experimental data sets over crop fields. Remote Sensing of Environment, 107(4): 639-655. http://dx.doi. org/10.1016/j.rse.2006.10.014
Wigneron, J. P., Schwank, M., López-Baeza, E., Kerr, Y., Novello, N., Millan, C., Moisy, C., Richaume, P., Mialon, A., Al Bitar, A., Cabot, F., Lawrence, H., Guyon, D., Calvet, J. C., Grant, J. P., Casal, T., de Rosnay, P., Saleh, K., Mahmoodi, A., Delwart, S., Mecklenburg, S. 2012. First Evaluation of the simultaneous SMOS and ELBARA-II observations in the Mediterranean region. Remote Sensing of Environment, 124, 26-37. http://dx.doi. org/10.1016/j.rse.2012.04.014
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