Estimating forest parameters from top of atmosphere multi-angular radiance data using coupled radiative transfer models

ABSTRACT -Traditionally, the estimation of forest parameters using physically-based canopy radiative transfer models (RT

Automated Directional Measurement System for the Acquisition of Thermal Radiative Measurements of Vegetative Canopies

The potential for directional optical and thermal imagery is very large. Field measurements have been performed with a goniometer on which thermal instruments were attached. In order to reduce dynamical effects the goniometer was adjusted to run in automated mode, for zenith and azimuthal direction. Directional measurements were performed over various crops with increasing heterogeneity. The improvements to the goniometer proved successful. For all the crops, except the vineyard, the acquisition of the directional thermal brightness temperatures of the crops went successfully. The large scale heterogeneity of the vineyard proved to be larger then the goniometer was capable of. The potential of directional thermal brightness temperatures has been proven

A 28-day oral dose toxicity study enhanced to detect endocrine effects of hexabromocyclododecane in wistar rats

A 28-day repeated dose study in rats (OECD407) enhanced for endocrine and immune parameters was performed with hexabromocyclododecane (HBCD). Rats were exposed by daily gavage to HBCD dissolved in corn oil in 8 dose groups with doses ranging between 0 and 200 mg/kg bw per day (mkd). Evaluation consisted of dose-response analysis with calculation of a benchmark dose at the lower 95% one-sided confidence bound (BMDL) at predefined critical effect sizes (CESs) of 10-20%. The most remarkable findings were dose-related effects on the thyroid hormone axis, that is, decreased total thyroxin (TT4, BMDL 55.5 mkd at CES--10%), increased pituitary weight (29 mkd at 10%) and increased immunostaining of TSH in the pituitary, increased thyroid weight (1.6 mkd at 10%), and thyroid follicle cell activation. These effects were restricted to females. Female rats also showed increased absolute liver weights (22.9 mkd at 20%) and induction of T4-glucuronyl transferase (4.1 mkd at 10%), suggesting that aberrant metabolization of T4 triggers feedback activation of the thyroid hormone system. These effects were accompanied by possibly secondary effects, including increased cholesterol (7.4 mkd at 10%), increased tibial bone mineral density (> 49 mkd at 10%), both in females, and decreased splenocyte counts (0.3-6.3 mkd at 20%; only evaluated in males). Overall, female rats appeared to be more sensitive to HBCD than male rats, and an overall BMDL is proposed at 1.6 mkd, based on a 10% increase of the thyroid weight, which was the most sensitive parameter in the sequence of events

FluorMODgui: A Graphic User Interface for the Spectral Simulation of Leaf and Canopy Fluorescence Effects

2nd International Workshop on Remote Sensing of Vegetation Fluorescence, 17-19 Nov. 2004, Montreal, CanadaThis paper reports on the status of the FluorMODgui, a Graphic User Interface (GUI) software package developed within the frame of the FluorMOD project "Development of a Vegetation Fluorescence Canopy Model". The study was launched in 2002 by the European Space Agency to advance the science of vegetation fluorescence simulation through the development and integration of leaf and canopy fluorescence models based on physical methods. The FluorMODgui enables simulation of leaf and canopy reflectance with the effects of chlorophyll fluorescence, running the leaf and canopy models (dubbed FluorMODleaf and FluorSAIL) independently, as well as through a coupling scheme. Inputs for the FluoMODleaf layer are N (number of leaf layers, as in PROSPECT), Cab (chlorophyll a+b content), Cw (water equivalent thickness), Cm (dry matter content), Fi (fluorescence quantum efficiency), T (temperature), S (species type), and Sto (stoichiometry). Inputs for the FluorSAIL canopy layer are: a MODTRAN4 6-parameter spectra, a soil reflectance spectra, leaf reflectance & transmittance spectra, a excitation-fluorescence response matrix (back & forward), 2 PAR-dependent coefficients for the fluorescence response to light level, solar zenith angle, viewing zenith & relative azimuth angles, canopy LAI and LIDF parameters, and a hot spot parameter. Outputs for the linked leaf-canopy fluorescence model are the leaf spectral reflectance, transmittance, and canopy reflectance with and without the fluorescence signal. Current software developments also accommodate multiple runs to simulate diurnal effects under different viewing geometries.The development of the FluorMODgui interface has been carried out in the frame of the ESA-project Development of a Vegetation Fluorescence Canopy Model, ESTEC contract no. 16365/02/NL/FF. Within the same project, the leaf and canopy fluorescence models FluorMODleaf and FluorSAIL were developed and provided by R. Pedrós and S. Jacquemoud of LED, University of Paris, I. Moya, Y. Goulas and J. Louis of LURE, University of Paris-South, and Wout Verhoef, National Aerospace Laboratory NLR.Peer reviewe

PROSPECT+SAIL: 15 Years of Use for Land Surface Characterization

Presented at Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on , vol., no., pp.1992-1995, July 31 2006-Aug. 4 2006The combined PROSPECT leaf optical properties model and SAIL canopy bidirectional reflectance model, i.e. PROSAIL, has been used for about fifteen years to increase our understanding of plant canopy spectral and bidirectional reflectance in the solar domain and to develop new methods of vegetation biophysical properties retrieval. It links the spectral variation of canopy reflectance with its directional variation. This link is the key to simultaneously estimate biophysical/structural canopy variables for applications in agriculture, plant physiology, and forestry at different scales. PROSPECT and SAIL are still evolving: they have undergone recent improvements both at the leaf and the plant levels and became one of the most popular radiative transfer tools in these domains due to their ease of use, their robustness, and because they have been validated by many lab/field/space experiments over the years. This paper is intended to review this subject, which has been extensively researched in optical remote sensingWe are grateful to the space agencies (CNES, ESA, EU, NASA, NLR) and national remote sensing programs (PNTS, CalSpace) for funding provided during the last 15 years.Peer reviewe

Retrieval of maize canopy fluorescence and reflectance by spectral fitting in the O2-A absorption band

Canopy level chlorophyll fluorescence and reflectance of maize were retrieved simultaneously by using spectral fitting (SF) techniques applied to canopy and reference upwelling radiances measured on the ground in the O2-A atmospheric absorption band by means of a ground-measurements-based (GMB) method, using a white reference panel. This method was inspired by the Fluorescence Experiment (FLEX) mission concept, which is expected to provide the user community with a top-of-canopy radiance product, as well as sufficient data on atmospheric conditions to enable the simulation of a white reference panel radiance, after which the ground-based method can also be applied by the users of FLEX data. For the retrieval, a coupled surface-atmosphere radiative transfer model was also used to simulate the canopy radiance in specific atmospheric conditions and to quantify fluorescence and reflectance variables by using a second method based on the canopy radiance simulation (CRS), which uses the canopy radiance measurements only. The CRS method does not require any cross calibration of reference measurements, and is extremely useful when a reliable reference cannot be found. Part of the mathematical functions that modeled reflectance and fluorescence were recently used by the authors to perform simulations of observations from space. Simulations of the retrievals for both methods were performed at two different spectral band widths of 9 nm and 20 nm to evaluate the accuracy limits for a signal to noise ratio equal to 300:1. These simulations demonstrated an enhanced accuracy as compared to previously reported retrievals on the ground, and indicated that the CRS model can indeed be successfully applied for the retrieval of fluorescence. In the retrievals from measurements, the two intervals were compared to better evaluate the combined influence of the atmospheric conditions and forward modeling spectral accuracy on the CRS method. The 20 nm interval was also used to evaluate the possibility of retrieving the bi-directional and hemispherical-directional reflectances in the viewing direction of the canopy and surroundings. Lastly, the narrower 9 nm interval delivered the most accurate simulations and was chosen for comparing the retrievals obtained by means of the two different methods. From this comparison fluorescence retrieved by means of the CRS method resulted higher (about 5%) than that retrieved with the GMB method by means of the same mathematical functions, while the retrieved reflectances were very similar. The methods presented here demonstrate that fluorescence can be retrieved even when atmospheric and surface information is limited.JRC.H.4-Monitoring Agricultural Resource

The SPART model: A soil-plant-atmosphere radiative transfer model for satellite measurements in the solar spectrum

Radiative transfer models (RTMs) of vegetation canopies can be applied for the retrieval of numerical values of vegetation properties from satellite data. For such retrieval, it is necessary first to apply atmospheric correction to translate the top-of-atmosphere (TOA) satellite data into top-of-canopy (TOC) values. This atmospheric correction typically assumes a Lambertian surface reflection, which introduces errors if the real surface is non-Lambertian. Furthermore, atmospheric correction requires atmospheric characterization as input, which is not always available. In this study, we present an RTM for soil-plant-atmosphere systems to model TOC and TOA reflectance as observed by sensors, and to retrieve vegetation properties directly from TOA reflectance skipping the atmosphere correction processes with the inversion mode of the RTM. The model uses three computationally efficient RTMs for soil (BSM), vegetation canopies (PROSAIL) and atmosphere (SMAC), respectively. The sub-models are coupled by using the four-stream theory and the adding method. The resulting ‘Soil-Plant-Atmosphere Radiative Transfer model’ (SPART) simulates directional TOA spectral observations, with all major effects included, such as sun-observer geometries and non-Lambertian reflectance of the land surface. A sensitivity anaylsis of the model shows that neglecting anisotropic reflection of the surface in coupling the surface with atmosphere causes considerable errors in TOA reflectance. The model was validated by comparing TOC and TOA reflectance simulations with those simulated with the atmosphere-included version of the DART RTM model. We show that the differences between DART and SPART are less than 7% for simulating TOC reflectance, and are less than 20% (less than 10% at most bands) for simulating TOA reflectance. The model performance in retrieving key vegetation and atmospheric properties was evaluted by using a synthetic dataset and a satellite dataset. The inversion mode allows estimating vegetation properties along with atmospheric properties and TOC reflectance with reasonable accuracy directly from TOA observations, and remarkable accuracy can be achieved if prior information is used in the model inversion. The model can be used to investigate the sensitivity of surface and atmospheric properties on TOC and TOA reflectance and for the simulation of synthetic data of existing and forthcoming satellite missions. More importantly, it facilitates a quantitative use of remote sensing data from satellites directly without the need for atmospheric correction

A Method to Reconstruct the Solar-Induced Canopy Fluorescence Spectrum from Hyperspectral Measurements

A method for canopy Fluorescence Spectrum Reconstruction (FSR) is proposed in this study, which can be used to retrieve the solar-induced canopy fluorescence spectrum over the whole chlorophyll fluorescence emission region from 640–850 nm. Firstly, the radiance of the solar-induced chlorophyll fluorescence (Fs) at five absorption lines of the solar spectrum was retrieved by a Spectral Fitting Method (SFM). The Singular Vector Decomposition (SVD) technique was then used to extract three basis spectra from a training dataset simulated by the model SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes). Finally, these basis spectra were linearly combined to reconstruct the Fs spectrum, and the coefficients of them were determined by Weighted Linear Least Squares (WLLS) fitting with the five retrieved Fs values. Results for simulated datasets indicate that the FSR method could accurately reconstruct the Fs spectra from hyperspectral measurements acquired by instruments of high Spectral Resolution (SR) and Signal to Noise Ratio (SNR). The FSR method was also applied to an experimental dataset acquired in a diurnal experiment. The diurnal change of the reconstructed Fs spectra shows that the Fs radiance around noon was higher than that in the morning and afternoon, which is consistent with former studies. Finally, the potential and limitations of this method are discussed