Vegetation height products between 60° S and 60° N from ICESat GLAS data.

We present new coarse resolution (0.5� ×0.5�)vegetation height and vegetation-cover fraction data sets between 60� S and 60� N for use in climate models and ecological models. The data sets are derived from 2003–2009 measurements collected by the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud and land Elevation Satellite (ICESat), the only LiDAR instrument that provides close to global coverage. Initial vegetation height is calculated from GLAS data using a development of the model of Rosette et al. (2008) with further calibration on desert sites. Filters are developed to identify and eliminate spurious observations in the GLAS data, e.g. data that are affected by clouds, atmosphere and terrain and as such result in erroneous estimates of vegetation height or vegetation cover. Filtered GLAS vegetation height estimates are aggregated in histograms from 0 to 70m in 0.5m intervals for each 0.5�×0.5�. The GLAS vegetation height product is evaluated in four ways. Firstly, the Vegetation height data and data filters are evaluated using aircraft LiDAR measurements of the same for ten sites in the Americas, Europe, and Australia. Application of filters to the GLAS vegetation height estimates increases the correlation with aircraft data from r =0.33 to r =0.78, decreases the root-mean-square error by a factor 3 to about 6m (RMSE) or 4.5m (68% error distribution) and decreases the bias from 5.7m to −1.3 m. Secondly, the global aggregated GLAS vegetation height product is tested for sensitivity towards the choice of data quality filters; areas with frequent cloud cover and areas with steep terrain are the most sensitive to the choice of thresholds for the filters. The changes in height estimates by applying different filters are, for the main part, smaller than the overall uncertainty of 4.5–6m established from the site measurements. Thirdly, the GLAS global vegetation height product is compared with a global vegetation height product typically used in a climate model, a recent global tree height product, and a vegetation greenness product and is shown to produce realistic estimates of vegetation height. Finally, the GLAS bare soil cover fraction is compared globally with the MODIS bare soil fraction (r = 0.65) and with bare soil cover fraction estimates derived from AVHRR NDVI data (r =0.67); the GLAS treecover fraction is compared with the MODIS tree-cover fraction (r =0.79). The evaluation indicates that filters applied to the GLAS data are conservative and eliminate a large proportion of spurious data, while only in a minority of cases at the cost of removing reliable data as well. The new GLAS vegetation height product appears more realistic than previous data sets used in climate models and ecological models and hence should significantly improve simulations that involve the land surface

Assessing the effects of forest health on sun-induced chlorophyll fluorescence using the FluorFLIGHT 3-D radiative transfer model to account for forest structure

Sun-induced fluorescence (SIF) has been proven to serve as a proxy of photosynthesis activity and therefore, as an early indicator of physiological alterations for global monitoring of vegetation. However, the interpretation of SIF over different spatial resolutions is critical to bridge the existing gap between local and global scales. This study provides insight into the influence of scene components, and forest structure and composition on the quantification of the red and far-red fluorescence signal as an early indicator of forest decline. The experiments were conducted over an oak forest (Quercus ilex) affected by water stress and Phytophthora infection in the southwest of Spain. SIF retrievals through the Fraunhofer Line Depth (FLD) principle with three spectral bands F (FLD3) was assessed using high resolution (60 cm) hyperspectral imagery extracting sunlit crown, full crown and aggregated pixels. Results showed the link between F (FLD3) extracted from sunlit crown pixels and the tree physiological condition in this context of disease infection, yielding significant relationships (r2=0.57, p0.05). These results demonstrate the need for methods to accurately retrieve crown SIF from aggregated pixels in heterogeneous forest canopies with large physiological variability among individual trees. This aspect is critical where structural canopy variations and the direct influence of background and shadows affect the SIF amplitude masking the natural variations caused by physiological condition. FluorFLIGHT, a modified version of the three dimensional (3-D) radiative transfer model FLIGHT was developed for this work, enabling the simulation of canopy radiance and reflectance including fluorescence effects from different spatial resolutions and percentage cover levels. The 3-D modelling approach proposed here significantly improved the relationship between Fs and F (FLD3) extracted from aggregated pixels (r2=0.70, p<0.001), performing better than when aggregation effects were not considered (r2=0.42, p<0.01). The FluorFLIGHT model used in this study improved the retrieval of SIF from aggregated pixels as a function of fractional cover, leaf area index and chlorophyll content yielding significant relationships between Fs ground-data measurements and fluorescence quantum yield estimated with FluorFLIGHT at p<0.01 (r2=0.79). The methodology presented here using FluorFLIGHT also demonstrated its capabilities for mapping SIF at the tree level for single tree assessment of forest physiological condition in the context of early disease detection.JRC.D.1-Bio-econom

Avances en teledetección para la prevención y detección temprana de Xylella fastidiosa en el marco de los proyectos H2020 POnTE y XF-ACTORS.

Informational article of the tasks carried out in WP6 of POnTE and WP3 of XF-ACTORS in a professional Spanish magazin

Forest ecosystem chlorophyll, content: implications for remotely sensed estimates of net primary productivity, 2003

Current methods for estimating photosynthesis and hence net primary productivity (NPP) of forest ecosystems from remote sensing are based on the relationship between (i) the fraction of incident photosynthetically-active radiation absorbed by the canopy (fPAR) and (ii) spectral indices (e.g. NDVI). However, ground-based estimates of fPAR used to quantify this relationship for a specific vegetation type are derived from measurements of canopy structure only (e.g. using light interception methods such as hemispherical photography). Using a coupled leaf-canopy model of radiative transfer, we demonstrated that NDVI is highly sensitive to both canopy foliar and understorey chlorophyll content, which could account for significant errors in remotely sensed estimates of fPAR and hence NP

Earth observation for land-atmosphere interaction science

The European Space Agency (ESA), iLEAPS (Inte-grated Land Ecosystem-Atmosphere Processes Study, i.e. the land-atmosphere core project of the International Geosphere-Biosphere Programme), and the European Geosciences Union (EGU) jointly organized the “Earth Observation for Land-Atmosphere Interaction Science” Conference, which took place from 3rd to 5th November 2010 at the Italian premises of ESA in Frascati (Rome). The event represented an attempt to effectively draw together Earth-observation (EO) and Earth-system scientists investigating land-atmosphere processes in order to better understand the current gaps in science and derive recommendations to advance in the use of EO technology in the context of this important topic. Around 200 people from more than 30 countries worldwide met and discussed for three intensive days. This paper reports keypoints and the main recommendations of the Symposium for each of the key Themes addressed during the Conference

The inter-comparison of AATSR dual-view aerosol optical thickness retrievals with results from various algorithms and instruments

The Advanced Along-Track Scanning Radiometer (AATSR) dual-view (ATSRDV) aerosol retrieval algorithm is evaluated for a single scene over Germany (49-53° N, 7-12° E) on 13 October 2005 by comparison of the aerosol optical thickness (AOT) at 550 nm with products from Multiangle Imaging SpectroRadiometer (MISR), Moderate Resolution Imaging Spectroradiometer (MODIS) and Medium Resolution Imaging Spectrometer (MERIS), in addition to the Atmospheric Aerosol Retrieval using Dual-View Angle Reflectance Channels (AARDVARC) algorithm developed at Swansea University. The AOT was retrieved from the AATSR using the ATSR-DV algorithm, for the pixel size of 1 km × 1 km (at nadir). Then these values were meshed to be consistent with the sampling of the products from the other satellite instruments. The ATSR-DV results compare favourably with the products from orbiting optical instruments dedicated to aerosol retrieval, such as MODIS and MISR, which leads to the conclusion that AATSR is well suited for aerosol retrieval over land when the dual view is used with the ATSR-DV algorithm. © 2009 Taylor & Francis

Multiangle Imaging of the Earth: Present and Future

The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard the Terra spacecraft is pioneering a new paradigm in remote sensing of the Earth&apos;s environment and climate system. MISR acquires radiometrically and geometrically calibrated imagery at moderately high spatial resolution (275 m) over a widely-spaced array of along-tracking viewing angles (up to 70&quot; from local vertical). New algorithms developed especially for use with these data are demonstrating the ability to retrieve quantitative characteristics of aerosols over a wide variety of land surfaces, generate automated global stereoscopic cloud heights and height-resolved winds, retrieve cloud and surface albedos, distinguish polar clouds from snow and ice, and obtain textural information to distinguish different surface types. Successor mission concepts inspired by MISR seek to incorporate advances in optical, electronic, detector, and computational technologies to reduce the instrument size and mass, broaden the spectral coverage, obtain fine

Aerosol remote sensing over land: A comparison of satellite retrievals using different algorithms and instruments

International audienc