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.
Two field experiments named WISE (WInd and Salinity Experiment) were sponsored by the European Space Agency (ESA) to better understand the wind and sea state effects on the L-band brightness temperatures. They took place at the Casablanca oil rig located in the North Mediterranean Sea, 40 km off shore the Ebro river delta: WISE 2000 from November 25 to December 18, 2000, and continued during the January 9 to 16, 2001, and WISE 2001 from October 23 to November 22, 2001. During the spring of 2003, under Spanish National funds, a third field experiment named FROG (Foam, Rain, Oil slicks and GPS reflectometry) took place at the Ebro river delta, to measure the phenomena that were not completely understood during the WISE field experiments, mainly the effect of foam and rain. In order to achieve the objectives of the WISE field experiments the LAURA L-band fully polarimetric radiometer from the Technical University of Catalonia (UPC) was mounted on the Casablanca oil-rig at the 32 meters deck above the sea surface, pointing to the North and North-West, in the direction of the dominant winds. In this paper we present the results of the first study to determine the relationship between the brightness temperature and the sea state.
The current request of a minimum precision of ± 0.3 K in the sea surface temperature for climate studies and the use of high observation angles in the present space missions require a thorough analysis of sea surface emissivity (SSE) and its angular dependence. In this paper, we present SSE experimental values determined from thermal infrared radiometric measurements carried out from an oilrig under open Mediterranean conditions during the WInd and Salinity Experiment 2000 campaign (WISE 2000) founded by ESA. The methodology consists of quasi-simultaneous measurements of the radiance coming from the sea surface and the downwelling sky radiance, in addition to the corresponding sea temperature as reference. Radiometric data were taken by a CE 312 radiometer, with 4 channels placed in the 8-14 μm interval. Sea temperature was measured with high-precision thermal probes located on oceanographic buoys. SSE was obtained under several observation angles and surface wind speed conditions, allowing us to study both angular and sea surface roughness dependence. SSE decreases 2% - 3% for 55°. Finally, we compare our results with several theoretical models, showing the validity of the Masuda et al. (1988) model for observation angles up to 50°. For higher angles, the effect of possible double or multiple reflections on the sea surface produces discrepancies between measured and theoretical SSEs, such as Wu and Smith (1997) advised.