Extraction of Vegetation Biophysical Structure from Small-Footprint Full-Waveform Lidar Signals

The National Ecological Observatory Network (NEON) is a continental scale environmental monitoring initiative tasked with characterizing and understanding ecological phenomenology over a 30-year time frame. To support this mission, NEON collects ground truth measurements, such as organism counts and characterization, carbon flux measurements, etc. To spatially upscale these plot-based measurements, NEON developed an airborne observation platform (AOP), with a high-resolution visible camera, next-generation AVIRIS imaging spectrometer, and a discrete and waveform digitizing light detection and ranging (lidar) system. While visible imaging, imaging spectroscopy, and discrete lidar are relatively mature technologies, our understanding of and associated algorithm development for small-footprint full-waveform lidar are still in early stages of development. This work has as its primary aim to extend small-footprint full-waveform lidar capabilities to assess vegetation biophysical structure. In order to fully exploit waveform lidar capabilities, high fidelity geometric and radio-metric truth data are needed. Forests are structurally and spectrally complex, which makes collecting the necessary truth challenging, if not impossible. We utilize the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model, which provides an environment for radiometric simulations, in order to simulate waveform lidar signals. The first step of this research was to build a virtual forest stand based on Harvard Forest inventory data. This scene was used to assess the level of geometric fidelity necessary for small-footprint waveform lidar simulation in broadleaf forests. It was found that leaves have the largest influence on the backscattered signal and that there is little contribution to the signal from the leaf stems and twigs. From this knowledge, a number of additional realistic and abstract virtual “forest” scenes were created to aid studies assessing the ability of waveform lidar systems to extract biophysical phenomenology. We developed an additive model, based on these scenes, for correcting the attenuation in backscattered signal caused by the canopy. The attenuation-corrected waveform, when coupled with estimates of the leaf-level reflectance, provides a measure of the complex within-canopy forest structure. This work has implications for our improved understanding of complex waveform lidar signals in forest environments and, very importantly, takes the research community a significant step closer to assessing fine-scale horizontally- and vertically-explicit leaf area, a holy grail of forest ecology

Towards an Improved LAI Collection Protocol via Simulated and Field-Based PAR Sensing

In support of NASA’s next-generation spectrometer—the Hyperspectral Infrared Imager (HyspIRI)—we are working towards assessing sub-pixel vegetation structure from imaging spectroscopy data. Of particular interest is Leaf Area Index (LAI), which is an informative, yet notoriously challenging parameter to efficiently measure in situ. While photosynthetically-active radiation (PAR) sensors have been validated for measuring crop LAI, there is limited literature on the efficacy of PAR-based LAI measurement in the forest environment. This study (i) validates PAR-based LAI measurement in forest environments, and (ii) proposes a suitable collection protocol, which balances efficiency with measurement variation, e.g., due to sun flecks and various-sized canopy gaps. A synthetic PAR sensor model was developed in the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model and used to validate LAI measurement based on first-principles and explicitly-known leaf geometry. Simulated collection parameters were adjusted to empirically identify optimal collection protocols. These collection protocols were then validated in the field by correlating PAR-based LAI measurement to the normalized difference vegetation index (NDVI) extracted from the “classic” Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) data ( R 2 was 0.61). The results indicate that our proposed collecting protocol is suitable for measuring the LAI of sparse forest (LAI < 3–5 ( m 2 / m 2 ))

A. ostenfeldii und Salinität: Untersuchung von Toxinprofilen zur Bewertung der Hypothese der Salinitätsabhängigkeit von Toxinprofilen

Alexandrium ostenfeldii ist ein wichtiger Vertreter mariner planktischer Dinoflagellaten. Von dieser Art ist bekannt, dass sie in der Lage ist, drei verschiedene Arten von Algentoxinen zu produzieren. Dabei handelt es sich um Paralytic Shellfish Toxins (PST) (vgl. Kapitel 5.2), Spirolide (vgl. Kapitel 5.3.1) und die strukturell verwandten Gymnodimine (vgl. Kapitel 5.3.2). Die Toxinprofile unterschiedlicher Populationen unterscheiden sich je nach geographischer Region in Zusammensetzung und produzierter Menge der Toxine. PST sind sehr gut untersucht, da sie potente Neurotoxine sind und mehrfach Vergiftungen beim Menschen verursacht haben, von denen einige zu Todesfällen geführt haben. Diese Dinoflagellaten treten normalerweise in geringen Konzentrationen zusammen mit anderen dominanten Spezies auf und haben deswegen bisher eine geringe Bedrohung für Aquakulturen oder Ähnliches dargestellt. In den letzten Jahren wurden vermehrt dichte monospezifische Blüten von A. ostenfeldii beobachtet. Diese treten hauptsächlich in Brackwassersystemen mit geringeren Salinitäten als im offenen Ozean auf. Dies ist ein Grund, warum bisher relativ wenig über die von A. ostenfeldii produzierten Toxine und deren Zusammenhänge untereinander bekannt ist und in den letzten Jahren vermehrt Forschungsinteresse aufgekommen ist. Dabei gibt es erste Hinweise, dass die Toxinvariabilität weit größer ist als bisher bekannt. Die Ursache für das Vorkommen variabler Toxinprofile und ob eine Korrelation zwischen den drei Toxingruppen besteht, ist unklar. Es gibt Stämme, die lediglich eine Toxinart produzieren und wiederum Stämme welche alle drei Arten produzieren. Die dieser Arbeit zugrunde liegende Hypothese besagt, dass A. ostenfeldii Kulturen in Brackwassersystemen mit geringeren Salinitäten als im offenen Ozean ein komplexeres Toxinprofil mit Toxinen aller drei Toxingruppen ausbilden. Kulturen aus marinen Bedingungen produzieren im Vergleich dazu nur Toxine einer Gruppe, der Spirolide. Zusätzlich soll eine weitere Hypothese überprüft werden, wonach ein Zusammenhang zwischen der Produktion von Gymnodiminen und PST besteht. In dieser Arbeit werden dazu die Toxinprofile verschiedener bisher nicht untersuchter Stämme aus Chile, Argentinien, Kanada, dem Limfjord (Dänemark), der Nordsee, dem Kattegat, Norwegen und den Niederlanden mittels Tandem-Massenspektrometrie und HPLC-FLD analysiert. Um weitere Informationen über das Toxinprofil zu erhalten, werden diese Stämme neben den bekannten Toxinen auf bisher unbekannte Toxine untersucht. Darüber hinaus sollen weitere Informationen über den Zusammenhang der unterschiedlichen Toxingruppen gewonnen werden und durch den Vergleich der Ergebnisse eventuelle Zusammenhänge in den Toxinprofilen aufgeklärt werden. Die durchgeführte Analyse ergab zwei bisher unbekannte Gymnodimine, sechs zusätzliche Spirolide sowie zehn weitere Verbindungen, bei denen es sich ebenfalls um Spirolide handelt, für die jedoch keine Struktur mit ausreichender Sicherheit erklärt werden konnte (vgl. Kapitel 8.1)

Polyphenols bind to low density lipoprotein at biologically relevant concentrations that are protective for heart disease

There is ample evidence in the epidemiological literature that polyphenols, the major non-vitamin antioxidants in plant foods and beverages, have a beneficial effect on heart disease. Until recently other mechanisms which polyphenols exhibit such as cell signaling and regulating nitric oxide bioavailability have been investigated. The oxidation theory of atherosclerosis implicates LDL oxidation as the beginning step in this process. Nine polyphenols from eight different classes and several of their O-methylether, O-glucuronide and O-sulfate metabolites have been shown in this study to bind to the lipoproteins and protect them from oxidation at lysosomal/inflammatory pH (5.2), and physiological pH (7.4). Polyphenols bind to the apoprotein at pH 7.4 with K-b > 10(6) M (1) and the number of molecules of polyphenols bound per LDL particle under saturation conditions varied from 0.4 for ferulic acid to 13.1 for quercetin. Competition studies between serum albumin and LDL show that sub-stantial lipoprotein binding occurs even in the presence of a great molar excess of albumin, the major blood protein. These in vitro results are borne out by published human supplementation studies showing that polyphenol metabolites from red wine, olive oil and coffee are found in LDL even after an overnight fast. A single human supplementation with various fruit juices, coffee and tea also produced an ex vivo protection against lipoprotein oxidation under postprandial conditions. This in vivo binding is heart-protective based on published olive oil consumption studies. Relevant to heart disease, we hypothesize that the binding of polyphenols and metabolites to LDL functions as a transport mechanism to carry these antioxidants to the arterial intima, and into endothelial cells and macrophages. Extracellular and intracellular polyphenols and their metabolites are heart-protective by many mechanisms and can also function as potent intraparticle and intracellular antioxidants due to their localized concentrations that can reach as high as the micromolar level. Low plasma concentrations make polyphenols and their metabolites poor plasma antioxidants but their concentration in particles such as lipoproteins and cells is high enough for polyphenols to provide cardiovascular protection by direct antioxidant effects and by other mechanisms such as cell signaling