Search results for "ALBEDO"
showing 10 items of 110 documents
Comparing Airborne and Satellite Retrievals of Optical and Microphysical Properties of Cirrus and Deep Convective Clouds using a Radiance Ratio Techn…
2017
Abstract. Solar radiation reflected by cirrus and deep convective clouds (DCCs) was measured by the Spectral Modular Airborne Radiation Measurement System (SMART) installed on the German HALO (High Altitude and Long Range Research Aircraft) during the ML-CIRRUS and the ACRIDICON-CHUVA campaigns. In particular flights, HALO performed closely collocated measurements with overpasses of the Moderate Resolution Imaging Spectroradiometer (MODIS) on board of Aqua satellite. Based on the nadir upward radiance, the optical thickness τ and bulk particle effective radius reff of cirrus and DCC are retrieved using a radiance ratio algorithm which considers the cloud thermodynamic phase, the cloud verti…
Spectral optical layer properties of cirrus from collocated airborne measurements and simulations
2016
Abstract. Spectral upward and downward solar irradiances from vertically collocated measurements above and below a cirrus layer are used to derive cirrus optical layer properties such as spectral transmissivity, absorptivity, reflectivity, and cloud top albedo. The radiation measurements are complemented by in situ cirrus crystal size distribution measurements and radiative transfer simulations based on the microphysical data. The close collocation of the radiative and microphysical measurements, above, beneath, and inside the cirrus, is accomplished by using a research aircraft (Learjet 35A) in tandem with the towed sensor platform AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be re…
Mapping evapotranspiration on vineyards: A comparison between Penman-Monteith and energy balance approaches for operational purposes
2012
Estimation of evapotranspiration (ET) in Sicilian vineyard is an emerging issue since these agricultural systems are more and more converted from rainfed to irrigated conditions, with significant impacts on the management of the scarce water resources of the region. The choice of the most appropriate methodology for assessing water use in these systems is still an issue of debating, due to the complexity of canopy and root systems and for their high spatial fragmentation. In vineyards, quality and quantity of the final product are dependent on the controlled stress conditions to be set trough irrigation. This paper reports an application of the well-known Penman-Monteith approach, applied i…
Assessment of inputs to land surface processes models derived from hyperspectral multiangular data
2002
Global Models of the Earth - Atmosphere System describe the role of the terrestrial biosphere using increasingly complex Land Surface Models (LSM). These models mimic the exchange of energy, water and carbon between the land and the atmosphere, with emphasis on the role of terrestrial vegetation. Literature shows a clear trend towards fully interactive LSM-s, i.e. accounting for the dynamic response of vegetation to weather and climate. The latter may not be limited to biomass accumulation and address slower changes in vegetation type and composition. Improving the performance of such models require addressing two broad questions: Can we measure vegetation properties with the accuracy requi…
Crop and irrigation water management using high resolution remote sensing and agrohydrological models
2006
A combined agrohydrological and remote sensing approach, called SIMODIS (Simulation and Management of On‐Demand Irrigation Systems) (D’Urso, 2001), has been used in a Sicilian test area to simulate the operation of on‐demand irrigation system. In SIMODIS the spatial distribution of crop factor, Kc, is directly calculated from canopy variables r (albedo), LAI (Leaf Area Index) and hc (crop height) derived from satellite‐based canopy spectral reflectance. Coupling these canopy variables with a specific data set of soil properties, the SIMODIS procedure was setup to simulate, in a distributed way, the water balance and, therefore, the irrigation deliveries for a set of 136 grape fields. For th…
Estimation of Evapotranspiration by Hargreaves Formula and Remotely Sensed Data in Semi-arid Mediterranean Areas
1997
Abstract A methodology is proposed for estimating evapotranspiration by Hargreaves formula and image analysis of remotely sensed data. At first, for a large sicilian basin (Belice basin), theactualevapotranspiration values are estimated by the energy balance equation, spectral data of two Landsat TM images and ground agrometereological measurements. Then theseactualevapotranspiration estimates and thereferenceevapotranspiration values obtained by a slightly modified Hargreaves formula, which incorporates the outgoing short-wave radiation and an albedo coefficient equal to 0·23, are used for calculating suitable crop coefficients. Finally, the minimum area of each land-use map unit, obtained…
Evaluation of the maximum evapotranspiration over the La Mancha region, Spain, using NO A A AVHRR data
1992
Abstract Actual evapotranspiration is an important parameter in crop yield models, soil moisture determination and crop stress detection. As actual evapotranspiration is not routinely available, maximum evapotranspiration (ETJ is normally used in agronomic models to calculate watering needs over irrigated areas. For this reason an empirical method has been developed to obtain ETra from albedo and temperature data suplied by the Advanced Very High Resolution Radiometer (AVHRR) sensor on board NOAA satellites. This model has been applied to the La Mancha region, Spain, where barley, vine and maize are the main crops, and ETM was obtained with an acceptable error of ± 1-4 mm of water per day.
Critical analysis of empirical ground heat flux equations on a cereal field using micrometeorological data
2009
The rate at which the net radiation is transferred to the soil as ground heat flux varies with surface characteristics. Surface energy balance algorithms use empirical relationships taking into account the effects of the canopy cover to insulate the soil through vegetation indexes, the soil capacity to absorb incoming net radiation via the albedo, and the surface temperature promoting the energy transfer. However empirical relationships are often dependent on local conditions, such as the soil humidity and vegetation type. Ground heat flux assumes a minimum value in case of full canopy cover and a maximum value for dry bare soil. Aim of the present research is the critical analysis of some …
Calibrating the effective scattering albedo in the SMOS algorithm: some first results
2016
International audience; This study focuses on the calibration of the effective scattering albedo (ω) of vegetation in the soil moisture (SM) retrieval at L-Band. Currently, in the SMOS Level 2 and 3 algorithms, the value of ω is set to 0 for low vegetation and ∼ 0.06 – 0.08 for forests. Different parameterizations of vegetation (in terms of ω values) were tested in this study. The possibility of combining soil roughness and vegetation contributions as a single parameter (“combined” method) leads to an important simplification in the algorithm and was also evaluated here. Following these assumptions, retrieved values of SMOS SM were compared with SM data measured over many in situ sites worl…
Incidence Angle Diversity on L-Band Microwave Radiometry and Its Impact on Consistent Soil Moisture Retrievals
2021
Incidence angle diversity of space-borne L-band radiometers needs to be taken into account for a consistent estimation of surface soil moisture (SM). In this study, the Land Parameter Retrieval Model (LPRM) is applied to SMOS brightness temperatures to calibrate the effective scattering albedo (w) and the soil roughness (h 1 ) parameter against ERA5-land SM. The analysis is carried out for SMOS data at three different incidence angles ( 32.5±5∘, 42.5±5∘ and 52.5±5∘ ) focusing in 2016 on the three main land cover types of the Iberian Peninsula according to the Climate Change Initiative (agricultural, forest and grassland). The parameterization shows an increasing trend of w and h 1 with rise…