Search results for "Remote Sensing"
showing 10 items of 1262 documents
Canopy directional emissivity: Comparison between models
2005
Land surface temperature plays an important role in many environmental studies, as for example the estimation of heat fluxes and evapotranspiration. In order to obtain accurate values of land surface temperature, atmospheric, emissivity and angular effects should be corrected. This paper focuses on the analysis of the angular variation of canopy emissivity, which is an important variable that has to be known to correct surface radiances and obtain surface temperatures. Emissivity is also involved in the atmospheric corrections since it appears in the reflected downwelling atmospheric term. For this purpose, five different methods for simulating directional canopy emissivity have been analyz…
Recovering Surface Temperature and Emissivity from Thermal Infrared Multispectral Data
1998
Abstract In 1992 Thermal Infrared Multispectral Scanner (TIMS) data were acquired from the NASA C-130 aircraft over the Sahelian region of West Africa as part of the Hydrological and Atmospheric Pilot Experiment in the Sahel (HAPEX). TIMS measures the radiation from the surface modified by the atmosphere in six channels located between 8 mm and 12.5 μm in the thermal infrared. By using a variety of techniques it is possible to extract both the surface temperature and surface emissivity from the areas over which TIMS data were acquired. One such technique was tested with the data acquired during this experiment. Several TIMS images of both the east and west central sites on 2 and 4 September…
Long-term accuracy assessment of land surface temperatures derived from the Advanced Along-Track Scanning Radiometer
2012
Abstract The accuracy of land surface temperatures (LSTs) derived from the Advanced Along-Track Scanning Radiometer (AATSR) was assessed in a test site in Valencia, Spain from 2002 to 2008. AATSR LSTs were directly compared with concurrent ground measurements over homogeneous, full-vegetated rice fields in the conventional temperature-based (T-based) method. We also applied the new radiance-based (R-based) method over bare soil and water surfaces, where ground LST measurements were not available. In the R-based method, ground LSTs are simulated from AATSR brightness temperatures in the 11 μm band and radiative transfer simulations using surface emissivity data and atmospheric water vapor an…
Daytime aerosol extinction profiles from the combination of CALIOP profiles and AERONET products
2018
Abstract. The solar background illumination has a strong effect on CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) measurements, leading to a decrease in the signal-to-noise ratio of the lidar signal. Because of this, CALIOP level 2 data algorithms might be limited in the retrieval of the properties of the aerosols in the atmosphere. In this work, we present a methodology that combines CALIOP level 1 data with AERONET (Aerosol RObotic NETwork) measurements to retrieve aerosol extinction profiles and lidar ratios in daytime conditions. In this way, we fulfill a two-fold objective: first, we obtain more accurate daytime aerosol information; second, we supplement column integrated me…
Estimation of atmospheric water vapour content from direct measurements of radiance in the thermal infrared region
2012
Atmospheric water vapour content is a required parameter in thermal infrared (TIR) to carry out processes such as atmospheric correction or retrieving atmospheric factors (downwelling or upwelling irradiance, transmittance of the atmosphere and so on). This study proposes an alternative method to the ones already in use to measure water vapour content from direct measurements of downwelling atmospheric radiance in the TIR range. It was possible to estimate a linear relationship between atmospheric water vapour and downwelling atmospheric radiance using a simulated study, based on data from a radiosounding database. A subsequent validation concludes that it is possible to obtain water vapour…
Thermal remote sensing of land surface temperature from satellites: Current status and future prospects
1995
Abstract In this paper we review the current status for deriving land surface temperatures (LSTs) by remote sensing from satellites in the thermal infrared. Because of its widespread use and global applicability, we concentrate on the Advanced Very High Resolution Radiometer (AVHRR). The theoretical framework and methodologies used to derive LSTs are reviewed and amplified. Practical algorithms are described and their accuracy and application critically evaluated through sensitivity studies and by inter‐comparison. The important effects of the atmosphere, surface emissivity and instrument noise are considered and the current practice for removing these effects is specified. The accuracy cur…
On the atmospheric dependence of the split-window equation for land surface temperature
1994
Abstract A split-window equation is derived for land surface temperature, yielding T = T4 + A(T4 − T5) + B(e), where T is the true surface temperature, T4 and T5 are the brightness temperatures measured in AVHRR channels 4 and 5, A is a coefficient related to the atmospheric transmittances in AVHRR channels 4 and 5, being dependent on the atmosphere type and independent on surface emissivity, and B(e) takes into account the emissivity effect, which depends on both the channel surface emissivities (e4 and e5) and the atmosphere type. The atmospheric dependence of split-window coefficients, A and B(e), is discussed by means of satellite measurements simulations and in situ data. It is shown t…
Atmospheric water vapour content retrieval from visible and thermal data in the framework of the DAISEX campaigns
2005
In this paper three methods are presented that retrieve the atmospheric water vapour from DAIS (digital airborne imaging spectrometer) data in the framework of the DAISEX (DAIS Experiment) campaigns carried out by ESA (European Space Agency). The three methodologies analysed in the paper are: (i) the ratio technique, in which the water vapour is obtained from visible and near‐infrared bands; (ii) the split‐window technique; and (iii) the split‐window covariance‐variance ratio technique, in which the water vapour content is retrieved from thermal infrared bands. A comparison between the atmospheric water vapour content extracted from the DAIS images using these techniques and that obtained f…
Comparison of top of the atmosphere GERB measured radiances with independent radiative transfer simulations obtained at the Valencia Anchor Station a…
2005
The purpose of this work is to compare top of the atmosphere (TOA) radiances as measured by the Geostationary Earth Radiation Budget (GERB) instrument on board the METEOSAT-8 (METEOSAT Second Generation) satellite to equivalent independent radiances obtained from radiative transfer simulations performed using surface and atmospheric measured parameters gathered during the GERB Surface Ground Validation Campaign at the Valencia Anchor Station (VAS) reference area in February 2004. In this paper we try to extend the methodology previously developed and tested for the NASA Clouds and the Earth's Radiant Energy System (CERES) instrument in the framework of the SEVIRI and GERB Cal/val Area for L…
Narrow-band to broad-band conversion for Meteosat-visiible channel and broad-band albedo using both AVHRR-1 and -2 channels
1995
Abstract Satellite-derived broad-band albedo offers a useful tool for monitoring surface conditions. Given the limited wavelength window of most satellite radiometers, satellite albedo studies need to define narrow-band to a broad-band transformations. Signals from the AVHRR channels on board the NOAA-11 satellite, the Meteosat visible channel and a rectangular spectral band from 0-3 to 2.5 μm were simulated for a set of 20 representative land surfaces. The radiative transfer code described in Tanre et al. (1990) was used to obtain top of the atmosphere radiances. The derived signals were then correlated to predict broadband albedo and the Meteosal response via the two AVHRR signals. The re…