A remote sensing surface energy balance algorithm for land (SEBAL). 1. Formulation

Braga

Rev. bras. eng. agríc. ambient.

et al. 2016

A B S T R A C TThe surface albedo plays an important role in the exchanges of energy and mass in the planetary boundary layer. Therefore, changes in albedo affect the balance of radiation and energy at the surface, which can be detected with its monitoring. Albedo determination has been performed through various sensors, but there is not yet any publication dealing with albedo calculation procedures using OLI (Operational Land Imager) -Landsat 8 images. The objective of the study is to present the procedures for computing the albedo with OLI images and map it in irrigated areas of the São Gonçalo Irrigated District, PB, Brazil. Images of the year 2013, path 215 and row 65, were selected. The data necessary for calculating the albedo were extracted from each image metadata: additive and multiplicative terms of radiance and reflectance, and sun elevation angle. There were large differences between the albedo values of irrigated plots, water bodies and native vegetation. The albedo obtained with OLI images provides a higher degree of differentiation of the various types of land use, due to the substantial increase in the radiometric resolution of this new sensor.Procedimentos para cômputo do albedo com imagens OLI-Landsat 8: Aplicação ao semiárido brasileiro R E S U M O O albedo da superfície desempenha papel importante nas trocas de energia e massa na camada limite planetária. Neste sentido, alterações no albedo modificam os balanços de radiação e energia à superfície, que podem ser detectadas com seu monitoramento. A determinação do albedo tem sido feita através de diversos sensores mas ainda não foram publicados procedimentos de cálculo do mesmo com imagens do OLI (Operational Land Images) do Landsat 8. O objetivo do estudo é apresentar, em detalhes, procedimentos de cômputo do albedo com imagens OLI e mapear o mesmo em áreas do perímetro irrigado São Gonçalo, PB. Foram selecionadas imagens do ano 2013, órbita e ponto 215 e 65, respectivamente. Os dados necessários ao cômputo do albedo foram extraídos do meta dados de cada imagem, quais sejam: termos aditivo e multiplicativo da radiância e reflectância das bandas de 2 a 7 e ângulo de elevação do Sol. Verificaram-se grandes diferenças entre os valores do albedo das parcelas irrigadas, corpos d'água e de vegetação nativa. Concluise que o albedo obtido com as imagens OLI apresenta maior grau de diferenciação dos diversos tipos de uso da terra, resultado do aumento substancial da resolução radiométrica deste novo sensor.

“…4) with the mean weights represented in Table 5. As can be seen in this Table, (Bastiaanssen et al, 1998;Allen et al, 2007;Tasumi et al, 2008).…”

Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Procedures for calculation of the albedo with OLI-Landsat 8 images: Application to the Brazilian semi-arid

Braga

Rev. bras. eng. agríc. ambient.

et al. 2016

“…These include measurements from the ERS-scatterometer of microwave backscatter with a spatial resolution of 50 by 50 km [59], and inference from the surface energy balance with algorithms that combine various satellite products, e.g., SEBAL [60]. Some other large scale measurement missions have recently started, with the SMOS (Soil Moisture and Ocean Salinity) satellite of the ESA, in orbit since 2009, that measures soil moisture with a spatial resolution of 35-50 km, with an accuracy of 4%, and a revisit time of one to three days.…”

Section: Satellite Productsmentioning

confidence: 99%

Soil Moisture & Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

et al. 2013

Moisture content in the soil and snow in the alpine environment is an important factor, not only for environmentally oriented research, but also for decision making in agriculture and hazard management. Current observation techniques quantifying soil moisture or characterizing a snow pack often require dedicated instrumentation that measures either at point scale or at very large (satellite pixel) scale. Given the heterogeneity of both snow cover and soil moisture in alpine terrain, observations of the spatial distribution of moisture and snow-cover are lacking at spatial scales relevant for alpine hydrometeorology. This paper provides an overview of the challenges and status of the determination of soil moisture and snow properties in alpine environments. Current measurement techniques and newly proposed ones, based on the reception of reflected Global Navigation Satellite Signals (i.e., GNSS Reflectometry or GNSS-R), or the use of laser scanning are reviewed, and the perspectives offered by these new techniques to fill the current gap in the instrumentation level are discussed. Some key enabling technologies OPEN ACCESSRemote Sens. 2013, 5 3517 including the availability of modernized GNSS signals and GNSS array beamforming techniques are also considered and discussed.

Encyclopedia of Hydrological Sciences

Evaporation Modeling: Potential

Allen

2005

Potential evaporation ( E p ) has had a relatively broad range of definition over the past century. It is defined here as the quantity of water evaporated per unit area per unit time from an idealized extensive free‐water surface under existing atmospheric conditions. Three primary, common means to estimate E p have been used during the past century. These are (i) pan evaporation measurement, (ii) an estimate of potential evapotranspiration based on weather data, and (iii) a reference evapotranspiration. Of these three, reference evapotranspiration ( ET ref ) has the more practical application. “Potential evapotranspiration” ( ET p ) had widespread usage from the 1940s through the 1970s, when the term was used to represent a maximum evaporative index from which to derive estimates of actual ET from vegetation. However, there are several major, contrasting definitions for ET p and several challenges associated with its usage. One of the primary definitions used for ET p is the rate of evaporation and transpiration from a saturated (free‐water) vegetated surface so that the evaporation process occurs at the potential level. Challenges in sustaining a saturated surface and in measuring weather data that are coincident with such a surface make this definition for ET p theoretically attractive, but practically difficult. Standardized parameterizations of the Penman–Monteith equation are described for calculating ET for grass and alfalfa references. The reference evapotranspiration, despite some shortcomings, can be a consistent and reproducible index for a weather‐based potential evaporation.