Estimation of Mean Radiant Temperature in Urban Canyons Using Google Street View: A Case Study on Seoul

Extreme heat exposure has severe negative impacts on humans, and the issue is exacerbated by climate change. Estimating spatial heat stress such as mean radiant temperature (MRT) is currently difficult to apply at city scale. This study constructed a method for estimating the MRT of street canyons using Google Street View (GSV) images and investigated its large-scale spatial patterns at street level. We used image segmentation using deep learning to calculate the view factor (VF) and project panorama into fisheye images. We calculated sun paths to estimate MRT using panorama images from Google Street View. This paper shows that regression analysis can be used to validate between estimated short-wave, long-wave radiation and the measurement data at seven field measurements in the clear-sky (0.97 and 0.77, respectively). Additionally, we compared the calculated MRT and land surface temperature (LST) from Landsat 8 on a city scale. As a result of investigating spatial patterns of MRT in Seoul, South Korea, we found that a high MRT of street canyons (>59.4 °C) is mainly distributed in open space areas and compact low-rise density buildings where the sky view factor is 0.6–1.0 and the building view factor (BVF) is 0.35–0.5, or west-east oriented street canyons with an SVF of 0.3–0.55. However, high-density buildings (BVF: 0.4–0.6) or high-density tree areas (Tree View Factor, TVF: 0.6–0.99) showed low MRT (<47.6). The mapped MRT results had a similar spatial distribution to the LST; however, the MRT was lower than the LST in low tree density or low-rise high-density building areas. The method proposed in this study is suitable for a complex urban environment consisting of buildings, trees, and streets. This will help decision makers understand spatial patterns of heat stress at the street level.

Wie hängen lokale Wärmeinseln von der Horizontüberhöhung ab? – Analyse von Modellsimulationen In Stadtquartieren von Dresden und Erfurt

&lt;p&gt;Thermische Belastungen der Stadtbewohner in Hitzeperioden sind mit den Besonderheiten des Stadtklimas verbunden und spielen f&amp;#252;r die Stadt- und Umweltplanung eine zunehmende Rolle im Rahmen des Klimawandels. Um die tageszeitlich variable Auspr&amp;#228;gung lokaler W&amp;#228;rmeinseln zu erfassen, stehen verschiedene Messmethoden sowie Stadtklimamodelle unterschiedlicher Komplexit&amp;#228;t zur Verf&amp;#252;gung. Mit der Anwendung solcher Verfahren ist der Einsatz von Ressourcen verbunden, der in der planerischen Praxis nicht einfach umsetzbar ist. Um W&amp;#228;rmeinseln zu identifizieren und wirksame Anpassungsma&amp;#223;nahmen an sommerliche Hitze f&amp;#252;r die Freiraum- und Geb&amp;#228;udegestaltung abzuleiten, wurden in dieser Studie funktionale Zusammenh&amp;#228;nge zwischen stadtmorphologischen Parametern und meteorologischen Daten betrachtet. Die abgeleiteten Beziehungen erm&amp;#246;glichen eine praxistaugliche Anwendung.&lt;/p&gt; &lt;p&gt;Dazu wurden Modellsimulationen mit SOLWEIG und ENVI-met f&amp;#252;r zwei Stadtquartiere in Dresden und Erfurt durchgef&amp;#252;hrt und ausgewertet. Basierend darauf wurden Beziehungen zwischen Parametern aus manuell erstellten bzw. digitalen Objektmodellen (DOM) und Gr&amp;#246;&amp;#223;en der W&amp;#228;rmebelastung (u.&amp;#160;a. mittlere Strahlungstemperatur Tmrt, Universeller Thermischer Klimaindex UTCI) bestimmt. Die Arbeiten fanden im Rahmen des BMBF-Projektes HeatResilientCity statt.&lt;/p&gt; &lt;p&gt;F&amp;#252;r den lokalen W&amp;#228;rmeinseleffekt und seine raumzeitlichen Variationen spielt der Sky View Factor (SVF) eine Schl&amp;#252;sselrolle. Dieser Parameter beschreibt den Anteil des sichtbaren Himmels an einem Ort und gibt Aufschluss &amp;#252;ber die Stra&amp;#223;engeometrie und Bebauungsdichte sowie zur Verteilung von B&amp;#228;umen und Str&amp;#228;uchern. Der SVF ist wichtig, um die Strahlungsbilanz in Modellen zu bestimmen und damit die mittlere Strahlungstemperatur (Tmrt) an einem Ort. Die Gr&amp;#246;&amp;#223;e Tmrt ist ein zuverl&amp;#228;ssiger Pr&amp;#228;diktor f&amp;#252;r die Hitzebelastung tags&amp;#252;ber bei hoher solarer Einstrahlung, aber auch nachts in Bezug auf eine verminderte langwellige Ausstrahlung bzw. die W&amp;#228;rmestrahlung von Bauk&amp;#246;rpern. Um den Einfluss des SVF auf Tmrt darzustellen, ist die m&amp;#246;glichst detaillierte und aktuelle Beschreibung der urbanen Morphologie und Vegetation mit Hilfe hochaufl&amp;#246;sender DOMs essentiell. Je h&amp;#246;her der SVF desto mehr Einstrahlung erfolgt tags&amp;#252;ber. Gleichzeitig sorgt ein h&amp;#246;herer SVF nachts auch f&amp;#252;r eine gr&amp;#246;&amp;#223;ere Abstrahlung und kann damit f&amp;#252;r eine Verringerung von Tmrt und W&amp;#228;rmestress sorgen. Die &amp;#252;ber die strahlungsreichen Tageszeiten gemittelte Tmrt weist die h&amp;#246;chsten Werte an unbeschatteten (hoher SVF) oder nach S&amp;#252;den exponierten Orten auf. Dazu z&amp;#228;hlen offene Pl&amp;#228;tze und Innenh&amp;#246;fe oder Stra&amp;#223;enz&amp;#252;ge in West-Ost-Ausrichtung. Hier ist die thermische Belastung, ausgedr&amp;#252;ckt mit dem UTCI, tags&amp;#252;ber ebenfalls maximal. Orte mit geringer Tmrt findet man tags&amp;#252;ber dort, wo der SVF sehr gering ist, z. B. im Baumschatten.&lt;/p&gt; &lt;p&gt;Die Einfl&amp;#252;sse der richtungsabh&amp;#228;ngigen Strahlungsexposition lassen sich mit dem integralen SVF, der einen gesamten Halbraum beschreibt, nicht darstellen. Deshalb wurden auch Wirkungsunterschiede des SVF in Abh&amp;#228;ngigkeit von den Charakteristiken der horizonteinschr&amp;#228;nkenden Elemente (Geb&amp;#228;ude vs. Vegetation) quantifiziert, um belastbare Beziehungen zwischen SVF und W&amp;#228;rmeinseleffekt aufzustellen.&lt;/p&gt;

Visibility analysis of Phobos to support a science and exploration platform

The surfaces of the Martian moons, Phobos and Deimos may offer a stable environment for long-term operation of platforms. We present a broad assessment of potential scientific investigations, as well as strategic and operational opportunities offered by long-term operation of an instrumented lander. Studies using observations of Mars’ moons, and the detailed new findings expected from the JAXA Martian Moons eXploration (MMX) mission, International Mars Sample Return (MSR) Campaign and other upcoming Mars missions, provide a driver for feasibility and trade studies for follow-on missions that would build on the knowledge gain from those missions. We discuss the scientific questions and operational objectives that may be pertinent for landed platforms on the martian moons, including (1) monitoring and scientific investigations of Mars’ surface and atmosphere, (2) scientific investigations of the martian moons, (3) monitoring and scientific investigations of the space environment, (4) data relay for Mars surface assets or interplanetary missions and 5) use in a Mars navigation/positioning system. We present results from visibility calculations performed using the SPICE observation geometry system for space science missions, and a Phobos shape model. We compute as a function of location on Phobos, visibility quantities that are most relevant to science and operational objectives. These include visibility from Phobos of the Sun, Earth, Mars surface and atmosphere, Deimos, and Jupiter. We also consider occultation events by the Mars atmosphere of Earth and Deimos that may provide opportunities for radio science. Calculations are performed for a study period spanning one Mars year in a hypothetical future operational scenario (1 Jan 2030–18 Nov 2031). We combine visibility metrics to identify locations on Phobos most suitable for long-term operation of a platform. We find the Mars-facing side of Phobos, and limited areas on the leading and trailing sides, satisfy the most requirements defined for Mars and Phobos science, space environment monitoring, and data relay/navigation. We demonstrate that compliance with requirements related to visibility of Mars and its atmosphere are not mutually exclusive with those that are better satisfied on Phobos’ anti-Mars side, such as those aided by maximizing their cumulative view factor to the ecliptic plane (i.e. visibility to the Sun, Earth or outer solar system). Finally, our methodology allows to assess the extent to which combined visibility metrics can meet mission requirements. The process we describe can be used to support landing site identification and selection on planets, moons and small bodies. Graphical Abstract

Self-AdaptIve LOcal Relief Enhancer (SAILORE): A New Filter to Improve Local Relief Model Performances According to Local Topography

The use of Light Detection and Ranging (LiDAR) is becoming more and more common in different landscape exploration domains such as archaeology or geomorphology. In order to allow the detection of features of interest, visualization filters have to be applied to the raw Digital Elevation Model (DEM), to enhance small relief variations. Several filters have been proposed for this purpose, such as Sky View Factor, Slope, negative and positive Openness, or Local Relief Model (LRM). The efficiency of each of these methods is strongly dependent on the input parameters chosen in regard of the topography of the investigated area. The LRM has proved to be one of the most efficient, but it has to be parameterized in order to be adapted to the natural slopes characterizing the investigated area. Generally, this setting has a single value, chosen as the best compromise between optimal values for each relief configuration. As LiDAR is mainly used in wide areas, a large distribution of natural slopes is often encountered. The aim of this paper is to propose a Self AdaptIve LOcal Relief Enhancer (SAILORE) based on the Local Relief Model approach. The filtering effect is adapted to the local slope, allowing the detection at the same time of low-frequency relief variation on flat areas, as well as the identification of high-frequency relief variation in the presence of steep slopes. First, the interest of this self-adaptive approach is presented, and the principle of the method, compared to the classical LRM method, is described. This new tool is then applied to a LiDAR dataset characterized by various terrain configurations in order to test its performance and compare it with the classical LRM. The results of this test show that SAILORE significantly increases the detection capability while simplifying it.

Ellipsoidal Optical Cavities for Enhanced Thermophotovoltaics

Herein we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor between the PV cell and the emitter, and to minimize the emission losses. Numerical analysis shows the ellipsoidal optical cavity can be designed to achieve an effective view factor of 88.7% between the emitter and PV cell within a STPV system. Results show an efficiency of 5.62% in a STPV system with a GaSb PV cell and a black-body emitter under solar radiation at a concentration factor of 350X. Further, assuming the surface of the ellipsoidal optical cavity is capable of reflecting 99% of the radiation incident onto its surface, efficiencies of 15.54% can be attained when the solar concentration factor is 1400X. These results are attained for STPV systems without using selective absorbers, emitters or filters. The ellipsoidal optical cavity can be integrated into the design of advanced TPV systems and bring them closer to the high theoretical efficiencies TPV systems are capable of.

Ellipsoidal Optical Cavities for Enhanced Thermophotovoltaics

Herein we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor between the PV cell and the emitter, and to minimize the emission losses. Numerical analysis shows the ellipsoidal optical cavity can be designed to achieve an effective view factor of 88.7% between the emitter and PV cell within a STPV system. Results show an efficiency of 5.62% in a STPV system with a GaSb PV cell and a black-body emitter under solar radiation at a concentration factor of 350X. Further, assuming the surface of the ellipsoidal optical cavity is capable of reflecting 99% of the radiation incident onto its surface, efficiencies of 15.54% can be attained when the solar concentration factor is 1400X. These results are attained for STPV systems without using selective absorbers, emitters or filters. The ellipsoidal optical cavity can be integrated into the design of advanced TPV systems and bring them closer to the high theoretical efficiencies TPV systems are capable of.