Dr. Juan Manuel Sánchez Tomás

Assistant Professor and Researcher with the
Department of Applied Physics, University of Castilla-La Mancha

Monitoring Earth Surface Energy Balance From Remote Sensing as a Key Actor in Climate Change

Anomalies in the surface energy balance play an important role in the Global Climate Change (IPCC, 2001, 2007). In particular, a good knowledge of the water cycle is essential to help the scientist community at this point. Also, as stressed in the guidelines of the WMO programmes, as the world enters the 21st Century, sustainable development demands sustainable management of the world limited resources of freshwater. Since 70% of the global freshwater consumption goes to agriculture irrigation, control on this sector and particularly on the irrigation management is imperative. Water waste in irrigation tasks can be avoided by knowing the plant water necessities, which can be easily estimated from evapotranspiration (ET) information. In this framework, my main research line deals with the accurate monitoring of the surface energy balance in general, and ET in particular, at local to global scales via satellite, and its applications in monitoring drought and consumptive water use, predicting local and regional water demand, providing important boundary conditions to hydrological and weather forecast models, and improving our understanding of the role that surface flux patterns play in Climate Change.

The basis for the characterization of the surface energy balance is the accurate determination of the surface temperature. For this reason, thermal remote sensing techniques need to be applied to already orbiting satellites (MSG-SEVIRI, EOS-ASTER, EOS-MODIS,..), and adapted to cover the necessities of those upcoming new sensors (Sentinel-3, HyspIRI,..). Also, characterization of natural surface radiative properties, such as emissivity, and dependences with factors such as moisture, observation angle, etc. must be improved.

Data registered in field experimental campaigns using radiometric and meteorological instrumentation provide crucial information for calibrating, improving and validating the algorithms developed, contributing to a better understanding of the overall exchange processes between the surface and the atmosphere. My professional experience in this field was acquired in Spain (University of Valencia and University of Castilla-La Mancha), and USA (HydroLab and ALARC research centres).

My competence in this research line is endorsed by 13 papers in SCI journals, 11 works in non-SCI journals, 3 book chapters and more than 40 conference proceedings, in direct relation to this topic

Implementation of experimental campaigns. Data Processing. Data fusion

Experimental campaigns concurrent with flights and overpasses of sensors aboard space platforms are vital to the test of new instruments precursor of future sensors, the calibration in flight of operational instruments, and the validation of algorithms. In this sense, I have 5 SCI publications (see CV for details), result of this work since 2003 in the validation of the products of temperature and emissivity provided by AATSR on board the ENVISAT satellite (Coll et al., 2006 Journal of Geophysical Research (JGR)), of the instruments ASTER (Coll et al., 2007 Remote Sensing of Environment (RSE)) and MODIS (Coll et al., 2005 RSE) on board of EOS Terra/Aqua, and the Landsat5-TM and Landsat7_ETM+ (Coll et al., 2009 IEEE Transactions on Geosciences and Remote Sensing (IEEE TGRS)) through experimental campaigns (CAL/VAL) every summer in a pilot calibration area located in rice fields of the Albufera in Valencia. I have also collaborated with the University of Castilla-La Mancha in experimental campaigns for the measurement of energy and CO2 fluxes on natural vegetation (Sánchez et al. 2011, Evapotranspiration). In addition, the development of methodologies to estimate water pollution from remote sensing also required of experimental campaigns in which parameters showing the trophic state of the water were measured (Doña et al. 2011 International Journal of Remote Sensing (IJRS)).

Developing atmospheric correction methods in the thermal infrared

Atmospheric correction of the radiances measured from satellite is critical to obtain accurate values of land surface temperature. I collaborated in the development of a database (Galve et al. 2008 IEEE TGRS) to obtain simulated measurements of any instrument, using as entry information global datasets of radiosoundings, data of reanalysis models (NCEP for example), and atmosphere sounding instruments present at the same platform (such as AVHRR and TOVS, or MODIS and AIRS). Also, a database of ground measures was created to compare the results obtained by the different information sources mentioned (Coll et al. 2005 RSE).

The optimal coefficients were obtained to dispose of global split-window and dual-angle algorithms (Coll et al., 2006 JGR), multichannel algorithms (Coll et al., 2007 RSE) and monochannel algorithms (Coll et al., 2009 IEEE TGRS) adapted to different sensors by regression on the database of simulated measures for these sensors from the database of atmospheric data. In addition to the above-mentioned SCI publications, I have 13 additional works about this topic with include non-SCI papers and conference proceedings

Emissivity correction of the values measured from satellite is also essential to obtain accurate values of land surface temperature. I have experience in measuring emissivity spectra of different types of surfaces taken in both laboratory and field conditions, and also in obtaining emissivity maps of the surface from land use classification maps and geometric models. For example, Niclòs et al. 2005 RSE and Niclòs et al. 2009 IJRS showed measurements of sea surface emissivity and characterized this emissivity as a function of observation angle, foam coverage and wind speed. In Mira et al. 2010 IEEE TGRS, I studied the effect of the soil moisture on the thermal emissivity values in the laboratory. I also analyzed this effect under field conditions in Sánchez et al. 2011 RSE TGRS using data from a field campaign carried out during my stay in Arizona,USA.

The idea is to use these relations with estimates of soil moisture from satellite to improve the emissivity calculations in the infrared and, thus, the surface temperature. There is also the possibility of obtaining the soil moisture degree from emissivity measures inverting the equations obtained. A current agreement between ESA and the Thermal Remote Sensing Unit of the Universtiy of Valencia, which I collaborate with, will permit me to have images of the SMOS-MIRAS sensor that estimates soil moisture from satellite. In addition to the above-mentioned SCI publications, I have published 6 works as conference proceedings and non-SCI papers.

Multispectral Methods

There are now various multispectral sensors in the space that operate in the thermal infrared, as for example ASTER and MODIS (5 and 15 channels, respectively), and a few more in project, as the HyspIRI (8 channels). In addition, there are available some hyperspectral instruments, for example SEBASS, HyMap or TASI, which provide higher radiometric, spatial and spectral resolution. The use of these instruments require the development of multispectral algorithms capable to extract useful information, particularly the surface emissivity spectra, in addition to their temperature. I have experience in the analysis of different multispectral emissivity-temperature separation methods (Coll et al., 2007 RSE). Within the partnership with the USDA-ARS Arid-Land Research Center, and in the framework of a project funded by NASA, I am using MASTER data to simulate HyspIRI images and propose suitable algorithms for future estimate of the surface temperature through this new multispectral sensor

Evaluation of the carbon and water vapour fluxes balance

As mentioned above in the description of the main research line, I have experience in the measure and modeling of fluxes over different types of crops and forests. Recently, I have also been looking into the relationship between the H2O and CO2 cycles at ecosystem level (López et al. 2010 Foresta) by analyzing daily cycles of both fluxes and trying to explain and model this interrelationship in agreement with the functional connections that are known. The study of the vegetation and soil components will be done simultaneously to the continuous measurements of fluxes at the ecosystem level which will enable us to investigate how the flux partition is produced and to estimate the soil contribution in the H2O and CO2 total net flux. A micrometeorological tower placed in a Mediterranean forest area is providing the data required for this aim. Also, these data are being used to study the effect of forest fires on the CO2 and H2O fluxes (Sánchez et al. 2011 Evapotranspiration), which may have a significant impact on the global change. I have published 6 works related to this matter.

Micrometeorology and energy balance closure

I show competence also in the field of micrometeorology. The physical models I developed to estimate surface energy fluxes are based on the energy exchange in the atmosphere boundary-layer (Sánchez et al. 2008 RSE, 2008 Journal of Hydrology (JH)). I have experience in the use of Eddy-Covariance and Bowen Ratio stations under different conditions: boreal forest (Sánchez et al. 2009 Agricultural and Forest Meteorology (AFM); Niclòs et al. 2005 IJRS), Mediterranean forest (Sánchez et al. 2009 Revista de Teledetección (RT)), variety of crops (Sánchez et al. 2008 RSE, 2008 Journal of Hydrology (JH)). The lack of closure in the energy balance is still an unresolved problem we have to deal with when working with eddy-covariance instrumentation. I identified and quantified some of the main sources responsible of this imbalance in his recent publication Sánchez et al. 2010 Hydrology and Earth Systems Science (HESS). Besides the 6 aforementioned SCI papers, I have also published 32 works, involving micrometeorological aspects and dealing with the surface energy imbalance, in non-SCI journals, book chapters, and conference proceedings.

Prediction of forest fire risk using satellite data

In the framework of a project carried out in collaboration with the Universities of Santiago, La Coruña, and Vigo, I worked on the use of remote sensing information to help in the prediction of forest fires risk. I developed a risk index that allows us to determine what areas are more prone to suffer a fire on the basis to certain characteristics of the surface observable from satellite. This tool can be very useful for the stakeholders responsible for the prediction and extinction of fires. This was done by using images of the sensor MODIS-Terra with a spatial resolution of 250 m, without ruling out other with higher spatial resolution such as Landsat-TM/ETM+ or ASTER, and a robust database to obtain relations between the variations suffered in the surface conditions and fires occurred. In this way a relation that allows us to calculate the fire occurrence probability in a particular area was obtained and validated in two Spanish regions (Bisquert et al. 2011 International Journal of Wildland Fires (IJWF); Bisquert et al. 2011 International Journal of Applied Earth Observation and Geoinformation (IJAEOG)). I have supervised a doctoral thesis in this field, and I have published 5 works related to this matter in non-SCI journals and conference proceedings, in addition to the 2 aforementioned SCI papers.

Monitoring the contamination level of water masses using satellite data

I have also experience on the use of remote sensing information for the assessment of water quality from lakes, reservoirs and rivers. Water reflectivity in different ranges of the visible spectrum can be used as an indicator of Chlorophyll concentration, seston content, transparency, etc. I took part in several experimental campaigns carried out in the Albufera Lake. Water samples were collected concurrent to Landsat5-TM overpasses. Using these data a model was developed that enables us to determine the trophic state of the water using satellite imagery (Doña et al. 2011, IJRS).

A recent contract with the company Deimos Imaging will permit me to use Deimos-1 images to test these models.

In addition, these techniques were used in a study of flood areas in ephemeral fluvial systems (Conesa et al. 2010 Remote Sensing (RS)). I am supervising another doctoral thesis in this field.