0000000000034697
AUTHOR
Maria Mira
Comparison of Split-Window and Single-Channel Methods for Land Surface Temperature Retrieval from MODIS and AATSR Data
In this study, two different methods for retrieving the Land Surface Temperature (LST) from Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) and Envisat/Advanced Along Track Scanning Radiometer (AATSR) data are compared against a database of ground measured LSTs. These are the split-window (SW) and the single-channel (SC) methods. The SW method expresses LST as a combination of the brightness temperatures in the 11 iquestm and 12 iquestm channels with coefficients that can have local or global validity, depending on the way they are obtained. SC methods are based on the atmospheric radiative transfer equation. To solve this equation, convenient atmospheric temperature and water v…
Analysis of ASTER Emissivity Product Over an Arid Area in Southern New Mexico, USA
The accuracy of thermal infrared emissivities derived from Advanced Spaceborne Thermal Emission and Reflectance radiometer (ASTER) was assessed in an arid area in southern New Mexico, which includes the White Sands National Monument (WSNM) during 2006-2008. ASTER emissivities retrieved by the temperature and emissivity separation (TES) algorithm were directly compared with laboratory measurements of samples from WSNM. Good agreement was found for the high spectral contrast of gypsum and for the low spectral contrast of water bodies. Furthermore, the day/night consistency of ASTER emissivities was checked, and day/night emissivity differences lower than ±0.013 were observed. However, unexpec…
EVASPA (EVapotranspiration Assessment from SPAce) tool: an overview
International audience; Evapotranspiration (ET) is a fundamental variable of the hydrological cycle and its estimation is required for irrigation management, water resources planning and environmental studies. Remote sensing provides spatially distributed cost-effective information for ET maps production at regional scale. We have developed EVASPA too for mapping ET from remote sensing data at spatial and temporal scales relevant to hydrological or agronomica studies. EVASPA includes several algorithms for estimating evapotranspiration and various equations for estimating the required input information (net radiation, ground heat flux, evaporative fraction…), which provides a way to assess …
Temperature and emissivity separation from ASTER data for low spectral contrast surfaces
Abstract The performance of Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) thermal infrared (TIR) data product algorithms was evaluated for low spectral contrast surfaces (such as vegetation and water) in a test site close to Valencia, Spain. Concurrent ground measurements of surface temperature, emissivity, and atmospheric radiosonde profiles were collected at the test site, which is a thermally homogeneous area of rice crops with nearly full vegetation cover in summer. Using the ground data and the local radiosonde profiles, at-sensor radiances were simulated for the ASTER TIR channels and compared with L1B data (calibrated at-sensor radiances) showing discrepancies up…
Influence of soil water content on the thermal infrared emissivity of bare soils. Implication for land surface temperature determination.
[1] The influence of soil water content in thermal infrared emissivity is a known fact but has been poorly studied in the past. A laboratory study for quantifying the dependence of emissivity on soil moisture was carried out. Six samples of surface horizons of different soil types were selected for the experiment. The gravimetric method was chosen for determining the soil moisture, whereas the emissivity was measured at different soil water contents using the two-lid variant of the box method. As a result, the study showed that emissivity increases from 1.7% to 16% when water content becomes higher, especially in sandy soils in the 8.2–9.2 μm range. Accordingly, a set of equations was deriv…
Combining a Two-Source Patch Model with Satellite Data to Monitor Daily Evapotranspiration at a Regional Scale
In this work, we present a micro-meteorological approach for estimating surface energy fluxes that can be operationally used together with satellite images to monitor surface energy fluxes at a regional scale. In particular we will focus on the retrieval of daily evapotranspiration. The feasibility of the model is explored at a local scale using data collected over a maize crop in Beltsville, Maryland, USA, and a boreal forest in Sodankyla, Finland. Comparison of the results with ground measurements shows errors between plusmn15 and plusmn50 W m-2 for the retrieval of net radiation, soil heat flux, and sensible and latent heat fluxes in both sites. A methodology to apply the model to Landsa…
Comparison of Thermal Infrared Emissivities Retrieved With the Two-Lid Box and the TES Methods With Laboratory Spectra
Knowledge of surface emissivity in the thermal infrared (TIR) region is critical for determining the land surface temperature (LST) from remote-sensing measurements. If emissivity is not well determined, it can cause a significant systematic error in obtaining the LST. The main aim of this paper is to compare different methods for measuring accurate land surface emissivity in the field, namely, the box method and the temperature and emissivity separation (TES) algorithm. Field emissivities were compared with soil spectra from laboratory measurements. Emissivities were measured for the bands of a multispectral radiometer CE312-2 with effective wavelengths at 8.4, 8.7, 9.1, 10.6, and 11.3 mum…
A Cloudless land atmosphere radiosounding database for generating land surface temperature retrieval algorithms
A database of global, cloud-free, atmospheric radiosounding profiles was compiled with the aim of simulating radiometric measurements from satellite-borne sensors in the thermal infrared. The objective of the simulation is to generate split-window (SW) and dual-angle (DA) algorithms for the retrieval of land surface temperature (LST) from Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) and Envisat/advanced along track scanning radiometer (AATSR) data. The database contains 382 radiosonde profiles acquired over land, with nearly-uniform distribution of precipitable water between 0 and 5.5 cm. Radiative transfer calculations were performed with the MODTRAN 4 code. Different viewin…
Evaluation of different methods to retrieve the hemispherical downwelling irradiance in the thermal infrared region for field measurements
International audience; The thermal infrared hemispherical downwelling irradiance (HDI) emitted by the atmosphere and surrounding elements contributes through reflection to the signal measured over an observed surface by remote sensing. This irradiance must be estimated in order to obtain accurate values of land-surface temperature (LST). There are some fast methods to measure the HDI with a single measurement pointing to the sky at a specified viewing direction, but these methods require completely cloud-free or cloudy skies, and they do not account for the radiative contribution of surrounding elements. Another method is the use of a diffuse reflectance panel (usually, a rough gold-coated…
Thermal Infrared Emissivity Dependence on Soil Moisture in Field Conditions
An accurate estimate of land surface temperature, which is a key parameter in surface energy balance models, requires knowledge of surface emissivity. Emissivity dependence on soil water content has been already reported and modeled under controlled conditions at the laboratory. This paper completes and extends that previous work by providing emissivity measurements under field conditions without elimination of impurities, local heterogeneities, or soil cracks appearing in the drying process. The multispectral radiometer CE312-2, with five narrow bands and a broad band in the 8-13-μm range, was used, and surface emissivity values were determined through a temperature-emissivity separation a…
Soil Moisture Effect on Thermal Infrared (8–13-μm) Emissivity
Thermal infrared (TIR) emissivities of soils with different textures were measured for several soil moisture (SM) contents under controlled conditions using the Box method and a high-precision multichannel TIR radiometer. The results showed a common increase of emissivity with SM at water contents lower than the field capacity. However, this dependence is negligible for higher water contents. The highest emissivity variations were observed in sandy soils, particularly in the 8-9-μm range due to water adhering to soil grains and decreasing the reflectance in the 8-9-μm quartz doublet region. Thus, in order to model the emissivity dependence on soil water content, different approaches were st…
Evaluation of Surface Temperature and Emissivity Derived from ASTER Data: A Case Study Using Ground-Based Measurements at a Volcanic Site
Abstract The land surface temperature (LST) and emissivity (LSE) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were evaluated in a low spectral contrast volcanic site at an altitude of 2000 m on the island of Tenerife, Spain. The test site is almost flat, thermally homogeneous, and without vegetation cover or variation in its surface composition. ASTER data correspond to six scenes, under both day- and nighttime conditions during 2008. This case study analyzes the impacts of the sources of inaccuracies using the temperature–emissivity separation (TES) algorithm. Uncertainties associated with inaccurate atmospheric correction were minimized by means…
Comparison of field emissivities with laboratory measurements and ASTER data
Surface emissivity in the thermal infrared (TIR) region is an important parameter for determining the land surface temperature from remote sensing measurements. This work compares the emissivities measured by different field methods (the Box method and the Temperature and Emissivity Separation, TES, algorithm) as well as emissivity data from ASTER scenes and the spectra obtained from the ASTER Spectral Library. The study was performed with a field radiometer having TIR bands with central wavelengths at 11.3 μm, 10.6 μm, 9.1 μm, 8.7 μm and 8.4 μm, similar to the ASTER TIR bands. The measurements were made at two sites in southern New Mexico. The first was in the White Sands National Monument…
Long-term accuracy assessment of land surface temperatures derived from the Advanced Along-Track Scanning Radiometer
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…
Angular dependence of the emissivity of bare soils in the thermal infrared
Emissivity is one of the main factors to take into account when studying processes that take place in the Earth surface by using radiance measurements in the thermal infrared, such as surface energy balance, land surface temperature (LST) retrieval, classification of different types of surface, etc. For this reason it is necessary to study the factors that can influence the emissivity. The present work evaluates one of these factors: the variation of the emissivity with the zenithal observation angle over bare soils, specifically the variation of the relative emissivity calculated from measurements of radiances, almost simultaneous, at nadir (0o) and at a certain angle (Θ). The measurements…