The present work aimed at testing the potential of the upcoming Earth Observation satellite Sentinel-2 (European Global Monitoring for Environment and Security (GMES) programme) for the operational estimation of the leaf area index (LAI) of two contrasting agricultural crops (sugar beet and maize). Mapping of LAI was achieved using a look-up table (LUT) based inversion of a physically based radiative transfer model (SAILH + PROSPECT). In addition to the Sentinel-2 spectral sampling, another band set described as “ideal” for vegetation studies has been evaluated in a comparative way. Analyses were mainly carried out using hyperspectral data acquired by the optical airborne instrument Compact Airborne Spectrographic Imager (CASI) during the European Space Agency (ESA) AgriSAR 2006 campaign. Additionally, data from two other experiments were tested to extend the validation database. Alternative inversion methods, i.e., an iterative optimization technique (SQP) and a neural network (NN), have been evaluated f... Dans le cadre de la présente étude nous examinons le potentiel du futur satellite Sentinel-2 (programme européen GMES) pour l’estimation opérationnelle de l’indice de surface foliaire (LAI) de deux cultures différentes (maïs et betterave à sucre). L’inversion du LAI a été effectuée en utilisant des tables pré-calculées par un modèle de transfer radiatif (SAILH + PROSPECT). Les mesures hyper spectrales de l’instrument aéroporté CASI faites dans le cadre de la campagne ESA AgriSAR 2006 ont été utilisées pour cette analyse. Deux configurations de bandes spectrales ont été utilisées l’une correspondante à l’instrument Sentinel-2 et une autre correspondante à une configuration idéale pour l’étude des couverts végétaux. Plusieurs techniques d’inversion ont également été considérées, une technique d’optimisation itérative (SQP) et une autre utilisant les réseaux de neurones. En utilisant des mesures in situ du LAI ainsi que celle de deux expériences supplémentaires nous montrons que il est possible d’obtenir une...

Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece, July 1–13, 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within ±20%. About half of the instruments agreed to within ±5%, while only three fell outside the ±10% agreement limit. As for the accuracy of the wavelength registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy, and in 1993 in Garmisch‐Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

Global warming has already affected European rivers and their aquatic biota, and climate models predict an increase of temperature in central Europe over all seasons. We simulated the influence of expected changes in heat wave intensity during the 21st century on water temperatures of a heavily impacted pre-alpine Austrian river and analysed future mitigating effects of riparian vegetation shade on radiant and turbulent energy fluxes using the deterministic Heat Source model. Modelled stream water temperature increased less than 1.5 ∘C within the first half of the century. Until 2100, a more significant increase of around 3 ∘C in minimum, maximum and mean stream temperatures was predicted for a 20-year return period heat event. The result showed clearly that in a highly altered river system riparian vegetation was not able to fully mitigate the predicted temperature rise caused by climate change but would be able to reduce water temperature by 1 to 2 ∘C. The removal of riparian vegetation amplified stream temperature increases. Maximum stream temperatures could increase by more than 4 ∘C even in annual heat events. Such a dramatic water temperature shift of some degrees, especially in summer, would indicate a total shift of aquatic biodiversity. The results demonstrate that effective river restoration and mitigation require re-establishing riparian vegetation and emphasize the importance of land–water interfaces and their ecological functioning in aquatic environments.

The validity of a radiative transfer model can be checked either by comparing its results with measurements or with solutions for artificial cases. Unfortunately, neither type of comparison can guarantee that the spectral UV surface irradiance is accurately calculated for real atmospheric cases. There is a need therefore for benchmarks, i.e., standard results that can be used as a validation tool for UV radiation models. In this paper we give such benchmarks for six cloud‐free situations. The chosen cases are characterized by different values of solar zenith angle, ozone column, aerosol loading, and surface albedo. Observations are also available for these cases to allow a further comparison between model results and measurements. An intercomparison of 12 numerical models is used to construct the benchmarks. Each model is supplied with identical input data, and a distinction is made between models that assume a planeparallel geometry and those that use a pseudospherical approximation. Differences remain between the model results, because of different treatments of the input data set. Calculations of direct and global transmission and direct and global irradiance are within 3% for wavelengths longer than 320 nm. For the low‐Sun cases the calculations are within 10% for wavelengths longer than 300 nm. On the basis of these calculations, six benchmark UV spectra (295–400 nm) are established with a standard deviation of 2%. Relative standard deviations are higher for the lowest absolute intensities at low Sun (5% at 300 nm). The variation between models is typically less than the variation seen between model and measurement. Differences between the benchmarks and the observed spectra are mainly due to the uncertainty in the input parameters. In four of the six cases the benchmarks agree with the observed spectra within 13% over the whole UV spectral region.