Raquel Niclòs

The Adjusted Normalized Emissivity Method (ANEM) for land surface temperature and emissivity recovery

In this work we propose a methodology for the retrieval of land surface temperatures and emissivities from thermal infrared data. It is based on the combination of the Vegetation Cover Method (VCM) and the Normalized Emissivity Method (NEM). NEM uses a first guess for emissivity, /spl epsiv//sub NEM/, which is constant for all channels and pixels. The method provides accurate relative emissivity variations, but the accuracy of absolute emissivity depends on the closeness of /spl epsiv//sub NEM/ to the actual maximum emissivity value. The concept in the new methodology is to adjust /spl epsiv//sub NEM/ initially by estimating channel emissivities in a pixel-by-pixel basis accounting for the spatial variation of emissivity with vegetation cover. This estimation can be done with the VCM, using coefficients adapted to each band. /spl epsiv//sub NEM/ is taken as the maximum emissivity value obtained for each pixel, which is then introduced into the NEM algorithm, ANEM was applied to a series of scenes recorded by the Digital Airborne Imaging Spectrometer (DAIS), which was flown over the test site of Barrax, Spain, during the DAISEX campaigns in 1998-2000. Retrieved temperatures and emissivities were validated with ground measurements carried out coincidentally to the DAIS flights. The results showed good agreement between retrieved and measured values, and demonstrated the capability of the method to achieve nearly unbiased temperatures with uncertainties within /spl plusmn/0.8 K, and emissivities with errors mostly within /spl plusmn/0.01.

Single band atmospheric correction tool for thermal infrared data: application to Landsat 7 ETM+

Atmospheric correction of Thermal Infrared (TIR) remote sensing data is a key process in order to obtain accurate land surface temperatures (LST). Single band atmospheric correction methods are used for sensors provided with a single TIR band. Which employs a radiative transfer model using atmospheric profiles over the study area as inputs to estimate the atmospheric transmittances and emitted radiances. Currently, TIR data from Landsat 5-TM, Landsat 7-ETM+ and Landsat 8-TIRS can be atmospherically corrected using the on-line Atmospheric Correction Parameter Calculator (ACPC, http://atmcorr.gsfc.nasa.gov). For specific geographical coordinates and observation time, the ACPC provides the atmospheric transmittance, and both upwelling and downwelling radiances, which are calculated from MODTRAN4 radiative transfer simulations with NCEP atmospheric profiles as inputs. Since the ACPC provides the atmospheric parameters for a single location, it does not account for their eventual variability within the full Landsat scene. The new Single Band Atmospheric Correction (SBAC) tool provides the geolocated atmospheric parameters for every pixel taking into account their altitude. SBAC defines a three-dimensional grid with 1°×1° latitude/longitude spatial resolution, corresponding to the location of NCEP profiles, and 13 altitudes from sea level to 5000 meters. These profiles are entered in MODTRAN5 to calculate the atmospheric parameters corresponding to a given pixel are obtained by weighted spatial interpolation in the horizontal dimensions and linear interpolation in the vertical dimension. In order to compare both SBAC and ACPC tools, we have compared with ground measurements the Landsat-7/ETM+ LST obtained using both tools over the Valencia ground validation site.

An angular-dependent split-window equation for SST retrieval from off-nadir observations

An angular-dependent split-window equation is proposed for determining the Sea Surface Temperature (SST) at any observation angle, including large viewing angles at the image edges of satellite sensors with wide swaths. The proposed equation takes into account the angular dependences of the atmospheric correction and also the emissivity correction. An explicit dependence on the SSE is considered in an independent term. The inclusion of such a term is not common in the current operational SST algorithms but we consider it appropriate taking into account the non-blackness of the sea surface emission for large angles and also the dependence on wind speed. The equation has been adapted to the Moderate Resolution Imaging Spectrometer (MODIS) on board EOS-Terra and EOS- Aqua, with at surface observation angles up to 65deg, and to the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board MSG, with even larger observation angles. Angular- dependent coefficients were estimated for the atmospheric and emissivity terms using synthetic data generated from a series of cloud-free, latitude-equally distributed radio sounding profiles. The use of the proposed expression requires as input data: at- sensor brightness temperatures for the split-window bands, the observation angle at each pixel, an estimate of the water vapor content and accurate SSE values for both channels. A comparison of the results of the equation for MODIS with in-situ measurements gathered from different NOAA ships and buoys placed around the world showed an accuracy of about plusmn 0.3 K for any observation angle, including off-nadir viewings, while the MODIS operational algorithm leaded to an error of plusmn 0.7 K at large angles. The proposed technique is mainly recommended to retrieve SST from observations at large viewing angles, since similar values are obtained by the current operational algorithms for nadir viewings.

Air-canopy temperature difference for fluorescence emission models

Precise canopy temperature (CT) determination of a boreal forest region was needed within SIFLEX-2002 to improve the understanding of fluorescence processes. Taking into account sky radiance effects and emissivity correction, CT was measured with an accuracy of /spl plusmn/0.4 K using the CE 312 radiometer. An inverse correlation between Photochemical Reflectance Index (PRI) and CT, solar illumination and sensible heat flux has been detected in the comparative analysis of these physical quantities.

High-accuracy sea surface temperature retrieval

A sea surface temperature (SST) retrieval methodology based on thermal infrared radiometric measurements from an oil-rig is proposed in order to achieve a precision better than /spl plusmn/ 0.3 K. This precision was required for accurate sea surface salinity determination within the WISE campaigns. Possible error sources in the radiative transfer equation are identified to determine the best possible measurement conditions and radiative data corrections. This method permits us to obtain the SST with a precision of /spl plusmn/ 0.18 K and an accuracy of 0.0 /spl plusmn/ 0.2 K.