Assessment of Polymer Atmospheric Correction Algorithm for Hyperspectral Remote Sensing Imagery over Coastal Waters

Spaceborne imaging spectroscopy, also called hyperspectral remote sensing, has shown huge potential to improve current water colour retrievals and, thereby, the monitoring of inland and coastal water ecosystems. However, the quality of water colour retrievals strongly depends on successful removal of the atmospheric/surface contributions to the radiance measured by satellite sensors. Atmospheric correction (AC) algorithms are specially designed to handle these effects, but are challenged by the hundreds of narrow spectral bands obtained by hyperspectral sensors. In this paper, we investigate the performance of Polymer AC for hyperspectral remote sensing over coastal waters. Polymer is, in nature, a hyperspectral algorithm that has been mostly applied to multispectral satellite data to date. Polymer was applied to data from the Hyperspectral Imager for the Coastal Ocean (HICO), validated against in situ multispectral (AERONET-OC) and hyperspectral radiometric measurements, and its performance was compared against that of the hyperspectral version of NASA’s standard AC algorithm, L2gen. The match-up analysis demonstrated very good performance of Polymer in the green spectral region. The mean absolute percentage difference across all the visible bands varied between 16% (green spectral region) and 66% (red spectral region). Compared with L2gen, Polymer remote sensing reflectances presented lower uncertainties, greater data coverage, and higher spectral similarity to in situ measurements. These results demonstrate the potential of Polymer to perform AC on hyperspectral satellite data over coastal waters, thus supporting its application in current and future hyperspectral satellite missions

Structural enrichment for laboratory mice: exploring the effects of novelty and complexity

Providing structural enrichment is a widespread refinement method for laboratory rodents and other animals in captivity. So far, animal welfare research has mostly focused on the effect of increased complexity either by accumulating or combining different enrichment items. However, increasing complexity is not the only possibility to refine housing conditions. Another refinement option is to increase novelty by regularly exchanging known enrichment items with new ones. In the present study, we used pair-housed non-breeding female C57BL/6J and DBA/2N mice to investigate the effect of novelty when applying structural enrichment. We used a double cage system, in which one cage served as home cage and the other as extra cage. While the home cage was furnished in the same way for all mice, in the extra cage we either provided only space with no additional enrichment items (space), a fixed set of enrichment items (complexity), or a changing set of enrichment items (novelty). Over 5  weeks, we assessed spontaneous behaviors, body weight, and extra cage usage as indicators of welfare and preference. Our main results showed that mice with access to structurally enriched extra cages (complexity and novelty) spent more time in their extra cages and complexity mice had lower latencies to enter their extra cages than mice with access to the extra cages without any structural enrichment (space). This indicates that the mice preferred the structurally enriched extra cages over the structurally non-enriched space cages. We found only one statistically significant difference between the novelty and complexity condition: during week 3, novelty mice spent more time in their extra cages than complexity mice. Although we did not detect any other significant differences between the novelty and complexity condition in the present study, more research is required to further explore the potential benefits of novelty beyond complexity

Unified Topographic and Atmospheric Correction for Remote Imaging Spectroscopy

Models linking surface characteristics within incident solar radiation are inexorably dependent on the topography of the given region. To date, however, most operational surface reflectance retrievals treat this dependence by assuming a flat terrain, leading to significant deviations in the estimated reflectance. Here, we demonstrate that incorporating dynamic topography directly into the joint surface and atmospheric model during retrievals has several advantages. First, it allows for a more complete physical accounting of downwelling illumination, providing more accurate estimates of the absolute magnitude of reflectance. Second, it facilitates a superior resolution of the atmospheric state, most notably due to the confounding influence of atmospheric aerosols and unresolved topographic effects. Our methodology utilizes a practical, high-fidelity, model-driven approach to separate out diffuse and direct irradiation and account for topographic effects during the joint inversion of atmosphere and surface properties. We achieve this by enhancing the atmosphere/surface inversion to account for the radiative transfer effects of surface slope. We further demonstrate how uncertainties in topographic features can be quantified and leveraged within our formulation for a more realistic posterior uncertainty estimates. Our results demonstrate that the inclusion of topographic effects into the retrieval model reduces errors in the reflectance of an only moderately rugged terrain by more than 15%, and that a post hoc accounting of topography cannot achieve these same results

Public Painting - Malerei und Handlung

Das Magazin "Public Painting – Malerei und Handlung" versammelt künstlerischen Projekte, die auf unterschiedliche Weise Verhältnisse von Malerei zum öffentlichen Raum reflektieren, und Verhältnisse thematisieren, die im öffentlichen Raum ausagiert werden. Die Beiträge entstanden als Resultat der Kooperation des kunstwissenschaftlichen Seminars "Malerei als Handlung" von Anne Röhl und des kunstpraktischen Seminars "public painting" von Sebastian Freytag während des Sommersemesters 2021 an der Universität Siegen. Unter dem Titel "public painting" wurden Schnittstellen von malerischer Praxis und öffentlichen Raum diskutiert. Die Studierenden des Seminars "Malerei als Handlung" haben sich wiederum damit beschäftigt, wie die Gattung Malerei im Verlauf des 20. Jahrhunderts durch die Abkehr von traditionellen Entstehungsprozessen und Malhandlungen befragt wurde und skulptural und/oder performativ wird. Daneben widmeten sich die Studierenden des kunsthistorischen Seminars der schriftlichen Auseinandersetzung mit den künstlerischen Resultaten des kunstpraktischen Seminars. Die Auseinandersetzung mit dem öffentlichen Raum stellte im Sommersemester 2021 eine besondere Herausforderung dar, da er pandemiebedingt nur eingeschränkt nutzbar war. Die künstlerischen Ergebnisse dokumentieren somit auch diese Zeit

The EnMAP imaging spectroscopy mission towards operations

EnMAP (Environmental Mapping and Analysis Program) is a high-resolution imaging spectroscopy remote sensing mission that was successfully launched on April 1st, 2022. Equipped with a prism-based dual-spectrometer, EnMAP performs observations in the spectral range between 418.2 nm and 2445.5 nm with 224 bands and a high radiometric and spectral accuracy and stability. EnMAP products, with a ground instantaneous field-of-view of 30 m x 30 m at a swath width of 30 km, allow for the qualitative and quantitative analysis of surface variables from frequently and consistently acquired observations on a global scale. This article presents the EnMAP mission and details the activities and results of the Launch and Early Orbit and Commissioning Phases until November 1st, 2022. The mission capabilities and expected performances for the operational Routine Phase are provided for existing and future EnMAP users

Mechanical Stress Induces Remodeling of Vascular Networks in Growing Leaves

International audienceDifferentiation into well-defined patterns and tissue growth are recognized as key processes in organismal development. However, it is unclear whether patterns are passively, homogeneously dilated by growth or whether they remodel during tissue expansion. Leaf vascu-lar networks are well-fitted to investigate this issue, since leaves are approximately two-dimensional and grow manyfold in size. Here we study experimentally and computationally how vein patterns affect growth. We first model the growing vasculature as a network of viscoelastic rods and consider its response to external mechanical stress. We use the so-called texture tensor to quantify the local network geometry and reveal that growth is heterogeneous , resembling non-affine deformations in composite materials. We then apply mechanical forces to growing leaves after veins have differentiated, which respond by anisotropic growth and reorientation of the network in the direction of external stress. External mechanical stress appears to make growth more homogeneous, in contrast with the model with viscoelastic rods. However, we reconcile the model with experimental data by incorporating randomness in rod thickness and a threshold in the rod growth law, making the rods viscoelastoplastic. Altogether, we show that the higher stiffness of veins leads to their reorientation along external forces, along with a reduction in growth heterogeneity. This process may lead to the reinforcement of leaves against mechanical stress. More generally , our work contributes to a framework whereby growth and patterns are coordinated through the differences in mechanical properties between cell types

Abbildende Spektroskopie der drei Phasen des Wassers - Bewertung von verbundenen Inversionsmethoden

Water is one of the most essential substances on Earth as it occurs in all three thermodynamic phases both in the atmosphere and the surface: solid water in terms of snow and ice grains, liquid water enclosed in-between ice crystals and leaves of vegetation, and gaseous water forming the water vapor in the atmosphere. The different phases of water control large amounts of the environmental energy cycle and a quantitative mapping on a global scale is of particular importance as it provides a valuable input to climate models and helps to understand underlying processes. The three phases of water show subtle differences in absorption shape in the optical range of the solar spectrum, so that a quantitative mapping requires high-resolution measurements of solar radiation reflected from Earth's surface. The technique of imaging spectroscopy provides such measurements, but has been almost entirely applied to small local scales based on airborne sensors. However, a new generation of orbital missions, including the Italian Hyperspectral Precursor of the Application Mission (PRISMA), NASA’s Earth Surface Mineral Dust Source Investigation (EMIT), the German Environmental Mapping and Analysis Program (EnMAP), ESA's Copernicus Hyperspectral Imaging Mission (CHIME), and NASA’s Surface Biology and Geology (SBG) designated observable, is expected to deliver high-resolution data both on a global scale and daily basis. This requests for independently applicable retrieval algorithms including a rigorous quantification of uncertainties. In this context, this thesis presents two new spectroscopic retrieval methods to quantify the three phases of water from space, which are aligned with future instrument characteristics, adapted to an increased atmospheric path as well as to a different ground sampling distance. Both algorithms use the optimal estimation formalism that assumes Gaussian error distribution and leverages prior knowledge as well as measurement noise in an inversion scheme that also produces posterior uncertainty estimates. The first method couples atmospheric radiative transfer simulations from the MODTRAN code to a surface reflectance model based on the Beer-Lambert law. A unique coupling of the 3D Hyperspectral Simulation of Canopy Reflectance (HySimCaR) model and the EnMAP end-to-end Simulation tool (EeteS) is exploited for a sensitivity analysis of estimated vegetation liquid water content. Furthermore, the retrieved values are validated with concurrent field measurements of canopy water content. The second algorithm is based on a simultaneous retrieval of atmosphere and surface state and exploits statistical relationships between reflectance spectra and additional surface parameters to estimate their most probable quantities. Retrieved snow and ice properties are investigated based on a sensitivity analysis and validated with laboratory and field measurements from the Greenland Ice Sheet. Finally, the applicability of the proposed methods to forthcoming spaceborne imaging spectrometers is demonstrated on the example of PRISMA cryosphere observations by providing retrieval maps of surface liquid water and ice grain size as well as associated retrieval uncertainties. The results from this thesis show that spaceborne imaging spectroscopy permits improved atmospheric water vapor estimations, facilitates a prediction of vegetation drought stress and wildfire potential, and contributes to the understanding of biophysical processes on Earth’s Ice Sheets in the context of climate change. Concurrently, three key aspects have been identified to be of particular importance for globally applicable retrieval algorithms: (i) considering topographic characteristics, such as surface slope and aspect as well as sky view factor and shadow fraction, (ii) integrating directional effects depending on illumination and observation conditions, (iii) accounting for mixed pixels by determining influences from background reflectance and fractional cover. Overall, this thesis demonstrates that upcoming launches of several imaging spectroscopy missions open new perspectives in regularly monitoring and mapping atmosphere and surface properties including the three phases of water on a global scale. These maps will provide a valuable input to the modeling of biological and physical processes that help to better understand climate change and to predict and adapt to its socioeconomic consequences.Wasser ist eine der wichtigsten Substanzen auf der Erde, da es in allen drei thermodynamischen Phasen sowohl in der Atmosphäre als auch auf der Oberfläche vorkommt: festes Wasser in Form von Schnee und Eiskörnern, flüssiges Wasser zwischen Eiskristallen und als Bestandteil von Pflanzenblättern sowie gasförmiges Wasser, das den Wasserdampf in der Atmosphäre bildet. Die verschiedenen Wasserphasen steuern große Teile des ökologischen Energiekreislaufes, so dass eine quantitative Kartierung auf globaler Ebene von besonderer Bedeutung ist. Sie leistet außerdem einen wertvollen Beitrag zur Klimamodellierung und hilft, die zugrunde liegenden Prozesse besser zu verstehen. Die drei Phasen des Wassers weisen feine Unterschiede in ihrer Absorptionsform im optischen Bereich des solaren Spektrums auf, so dass eine quantitative Bestimmung hochauflösende Messungen der von der Erdoberfläche reflektierten Sonnenstrahlung erfordert. Die Technik der abbildenden Spektroskopie liefert solche Messungen, wurde aber bisher fast ausschließlich auf der Grundlage von flugzeuggestützten Sensoren auf kleinen lokalen Skalen angewandt. Eine neue Generation von Weltraummissionen, darunter die italienische Hyperspectral Precursor of the Application Mission (PRISMA), die Earth Surface Mineral Dust Source Investigation (EMIT) der NASA, das deutsche Environmental Mapping and Analysis Program (EnMAP), die Copernicus Hyperspectral Imaging Mission (CHIME) der ESA und das NASA Surface Biology and Geology (SBG) Observable, soll jedoch hochauflösende Daten sowohl auf globaler Ebene als auch auf täglicher Basis liefern. Dies erfordert unabhängig anwendbare Kartierungsalgorithmen einschließlich einer präzisen Quantifizierung der Unsicherheiten. In diesem Zusammenhang werden in dieser Arbeit zwei neue spektroskopische Methoden zur Quantifizierung der drei Phasen von Wasser aus dem Weltraum vorgestellt, die auf die zukünftigen Instrumentencharakteristika abgestimmt sind und sowohl an einen längeren Weg der Strahlung durch die Atmosphäre als auch an eine andere räumliche Auflösung auf dem Erdboden angepasst sind. Beide Algorithmen verwenden den Formalismus der Maximum-a-posteriori-Schätzung, der von einer Gauß'schen Fehlerverteilung ausgeht und sowohl Vorwissen als auch Messrauschen in einem Inversionsschema nutzt, das zusätzlich a posteriori Unsicherheitsschätzungen liefert. Bei der ersten Methode werden atmosphärische Strahlungstransfersimulationen aus dem MODTRAN-Code mit einem auf dem Beer-Lambert-Gesetz basierenden Oberflächenreflexionsmodell gekoppelt. Eine einzigartige Kopplung des 3D Hyperspectral Simulation of Canopy Reflectance (HySimCaR) Systems und des EnMAP end-to-end Simulationstools (EeteS) wird für eine Sensitivitätsanalyse des geschätzten Flüssigwassergehalts von Vegetation genutzt. Außerdem werden die ermittelten Werte mit gleichzeitigen Feldmessungen des Wassergehalts von Vegetationskronen validiert. Der zweite Algorithmus basiert auf der simultanen Ermittlung des Zustands von Atmosphäre und Oberfläche und nutzt statistische Beziehungen zwischen Reflexionsspektren und zusätzlichen Oberflächenparametern, um deren wahrscheinlichste Größen zu schätzen. Die ermittelten Schnee- und Eiseigenschaften werden auf der Grundlage einer Sensitivitätsanalyse untersucht und mit Labor- und Feldmessungen vom grönländischen Eisschild validiert. Abschließend wird die Anwendbarkeit der vorgeschlagenen Methoden auf die kommenden weltraumgestützten abbildenden Spektrometer am Beispiel von PRISMA Aufnahmen von Schnee- und Eisflächen demonstriert, indem Karten von Flüssigwasser und Eiskorngröße sowie die damit verbundenen Unsicherheiten dargestellt werden. Die Ergebnisse dieser Arbeit zeigen, dass die weltraumgestützte abbildende Spektroskopie verbesserte Abschätzungen des atmosphärischen Wasserdampfs ermöglicht, die Vorhersage von Pflanzenstress und Waldbrandgefahr erleichtert und zum Verständnis der biophysikalischen Prozesse auf den Eisschilden der Erde im Zusammenhang mit dem Klimawandel beiträgt. Gleichzeitig werden drei Schlüsselaspekte identifiziert, die für global anwendbare Kartierungsalgorithmen von besonderer Bedeutung sind: (i) die Berücksichtigung topographischer Merkmale, wie z.B. Oberflächenneigung und -aspekt sowie Himmelslichtquotient und Schattenanteil, (ii) die Integration von Richtungseffekten in Abhängigkeit von Beleuchtungs- und Beobachtungsbedingungen, (iii) die Berücksichtigung von Mischpixeln durch die Bestimmung von Einflüssen der Hintergrundreflexion und des Bedeckungsgrades. Insgesamt zeigt diese Arbeit, dass die bevorstehenden Starts mehrerer abbildender Spektroskopiemissionen neue Perspektiven für die regelmäßige Überwachung und Kartierung von Atmosphären- und Oberflächeneigenschaften, einschließlich der drei Phasen des Wassers, auf globaler Ebene eröffnen. Diese Karten werden einen wertvollen Beitrag zur Modellierung biologischer und physikalischer Prozesse leisten, die zu einem besseren Verständnis des Klimawandels und zur Vorhersage und Anpassung an seine sozioökonomischen Folgen beiträgt