49 research outputs found

    BDS GNSS for Earth Observation

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    For millennia, human communities have wondered about the possibility of observing phenomena in their surroundings, and in particular those affecting the Earth on which they live. More generally, it can be conceptually defined as Earth observation (EO) and is the collection of information about the biological, chemical and physical systems of planet Earth. It can be undertaken through sensors in direct contact with the ground or airborne platforms (such as weather balloons and stations) or remote-sensing technologies. However, the definition of EO has only become significant in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit. Referring strictly to civil applications, satellites of this type were initially designed to provide satellite images; later, their purpose expanded to include the study of information on land characteristics, growing vegetation, crops, and environmental pollution. The data collected are used for several purposes, including the identification of natural resources and the production of accurate cartography. Satellite observations can cover the land, the atmosphere, and the oceans. Remote-sensing satellites may be equipped with passive instrumentation such as infrared or cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly called ’temporal resolution’), i.e., in a certain number of orbits around the Earth. The first remote-sensing satellites were the American NASA/USGS Landsat Program; subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the Chinese BuFeng-1 and Fengyun-3 series. Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers worldwide for a multitude of Earth monitoring and exploration applications. On the other hand, over the past 40 years, GNSSs have become an essential part of many human activities. As is widely noted, there are currently four fully operational GNSSs; two of these were developed for military purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation Satellite System (IRNSS/NavIC), will become available in the next few years, which will have enormous potential for scientific applications and geomatics professionals. In addition to their traditional role of providing global positioning, navigation, and timing (PNT) information, GNSS navigation signals are now being used in new and innovative ways. Across the globe, new fields of scientific study are opening up to examine how signals can provide information about the characteristics of the atmosphere and even the surfaces from which they are reflected before being collected by a receiver. EO researchers monitor global environmental systems using in situ and remote monitoring tools. Their findings provide tools to support decision makers in various areas of interest, from security to the natural environment. GNSS signals are considered an important new source of information because they are a free, real-time, and globally available resource for the EO community

    An improved global pressure and zenith wet delay model with optimized vertical correction considering the spatiotemporal variability in multiple height-scale factors

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    Atmospheric pressure and zenith wet delay (ZWD) are essential for global navigation satellite system (GNSS) tropospheric correction and precipitable water vapor (PWV) retrieval. As the development progresses of real-time GNSS kinematic technology, moving platforms, such as airborne and shipborne, require high-quality tropospheric delay information to pre-correct errors. Most existing tropospheric models are only applicable to the Earth's surface and exhibit poor accuracies in high-altitude areas due to simple vertical fitting functions and limited temporal resolution of the underlying parameters. Hence, an improved global empirical pressure and ZWD model is developed using 5-year ERA5 hourly reanalysis data, called IGPZWD, which takes seasonal and intraday variations into consideration. The vertical accuracy and applicability of IGPZWD model are further optimized by introducing the annual and semi-annual harmonics for pressure and ZWD height-scale factors of exponential function with three orders. Taking the ERA5 and radiosonde profile data in 2020 as reference, the pressure and ZWD of IGPZWD model show superior performance compared to those of three state-of-the-art models, i.e., GPT3, IGPT, and GTrop. Furthermore, IGPZWD-predicted zenith tropospheric delay (ZTD) yields improvements of up to 65.7 %, 2.4 %, and 7.8 % over that of GPT3, RGPT3, and GTrop models on a global scale, respectively. The proposed vertical correction algorithm effectively weakens the impact of accumulation error caused by excessive height difference, achieving optimal accuracy and feasibility in the high-altitude area. The IGPZWD model can be extensively applied in GNSS kinematic precision positioning, as well as atmospheric water vapor sounding.</p

    Amélioration de la capabilité de modélisation et de mitigation du gel radiatif au milieu agricole

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    Le gel radiatif est une des conditions météorologiques sévère affect la production agricole dans de nombreuses région du monde. Les objectives de cette étude inclut deux innovations scientifiques liées aux dégâts causés par le gel radiatif : (1) l'amélioration de la capacité de prédiction du gel local (température nocturne minimale à une résolution de 30 mètres) grâce à un modèle d’échange énergétique entre la végétation et l’atmosphère, et (2) une nouvelle méthode de diminution des risques et de protection des cultures agricoles pendant les périodes de gel. La première innovation a été réalisée en suivant plusieurs objectifs spécifiques visant à améliorer les capacités d'un modèle de répartition spatiale météorologique (Micro-Met) via quatre sous-modèles : (i) estimation journalière du gradient thermique adiabatique de l'air, (ii) modification de l’équation de rayonnement des grandes longueurs d'onde en l’absence de nuage dans l’atmosphère, (iii) quantification des effets de l’écoulement de l’air froid sur la température de l’air, et (iv) quantifier l’effet de haies brise–vent sur la vitesse du vent. La deuxième innovation a été réalisée en mettant en œuvre et en testant une nouvelle méthode active basée sur le cycle thermodynamique. Le site d'étude se localise dans la région de Vallée de Coaticook de l’Estrie (Québec) subit les conséquences désastreuses du gel. Le premier sous-modèle utilise une combinaison de profils de température provenant du satellite AIRS et de stations météorologiques afin d’estimer quotidiennement et régionalement le gradient thermique de l’air. L'utilisation de valeurs journalières, au lieu de valeurs fixes, permet d’estimer plus précisément les conditions atmosphériques. Les résultats ont démontré l’utilité de l’utilisation de la température de l'air obtenue par AIRS (850 hPa et 700 hPa) pour l’estimation du gradient thermique. Le second sous-modèle utilise les données associées aux conditions synoptiques du gel radiatif pour obtenir une équation du rayonnement descendant localement ajustée. Alors que l’erreur aux moindres carrés (RMSE) de Micro-Met était de 176.95 Wm-2 avec une erreur absolue (MAE) moyenne de 176.40 Wm-2, la nouvelle équation génère une RMSE de 4.90 Wm-2 et une MAE de 4.00 Wm-2. Le troisième sous-modèle contient trois parties :la détection des vallées fermées, l’estimation de la rapidité de drainage de l’air, et l’intégration de la perte de chaleur sensible ainsi que le refroidissement radiatif en vallée durant la nuit. La comparaison entre les simulations Micro-Met et les mesures de la température de l’air montrent une MAE de 1.11 (°C) et une RMSE de 1.66 (°C). La comparaison avec le modèle amélioré indique un gain avec une MAE de 0.68 (°C) et une RMSE de 1.08 (°C). Le quatrième sous-modèle était construit sur des résultats expérimentaux de vitesse du vent générés en laboratoire par des simulations. Trois équations ont été proposées pour estimer la vitesse du vent. Les résultats indiquent un coefficient de corrélation (R2) de 71% pour une vitesse de vent en dessous de 6 ms-1. La version améliorée de Micro-Net fournit une nouvelle plateforme pour des modèles d’énergie végétation-atmosphère et permet de prévoir la température minimale nocturne. Les résultats des tests de prédiction de cette température minimum concordent avec les mesures in-situ. Ces mesures ont été prises dans 5 secteurs topographiques différents afin d’améliorer les modèles de prédiction et engendrent des erreurs pour des vallées fermées (RMSE = 1.34, MAE = 1.03), pour différentes pentes (RMAE = 0.93, MAE = 0.73), crêtes (RMSE = 1.02, MAE = 0.88), plaines (RMSE = 0.44, MAE = 0.40), et aux orées des forêts (RMSE = 0.58, MAE = 0.53). En plus des objectifs spécifiques précédents, cette étude a proposé une nouvelle méthode d'atténuation du gel basée sur la thermodynamique du transport de la vapeur d'eau d'une source humide à un puits sec. Nous avons ajouté au Selective Inverse System (SIS) déjà utilisé dans le milieu, un contenant d'eau chaude à sa base pour diffuser la vapeur d'eau dans l'air ambiant. Cette opération a augmenté l’humidité de l'air ambiant et augmenté l'entropie humide. Cet essai a été réalisé dans un verger. La méthode d'atténuation la plus courante se concentre sur la température de l'air. La méthode proposée repose plutôt sur les principes physiques de l'entropie humide, qui combinait à la fois la température et l'humidité de l'air et le contenu thermique représenté. Dans l'ensemble, pour ce projet de recherche, un modèle couplé a été conçu pour prévision la température minimale nocturne de l'air dans des terrains agricoles vallonnés. En particulier, en améliorant la précision des prévisions, nous avons élaboré et ajouté des sous-modèles pour estimer les baisses de température dues à la stagnation du drainage de l'air froid et à l'effet des brise-vent forestiers sur la vitesse du vent. Pour réduire l'effet de gel, une nouvelle méthode de mitigation active respectueuse de l'environnement a été présentée. Cette étude a le potentiel d’aider les agriculteurs à réduire les dommages causés par le gel. De plus, elle peut être utile pour les services agricoles en termes de prise de décision, réduisant ainsi les dommages économiques.Abstract: The main objective of this study was related to radiation frost damage: (1) improving the forecasting capability of local frost, which was adapted to forecast nocturnal minimum temperature at a 30-meter resolution, using a vegetation atmosphere energy exchange framework, and (2) proposing a new mitigation approach to protect agricultural crops during frost periods. The first advance was achieved through several specific objectives to enhance the capabilities of a meteorological spatial distribution model (Micro-Met) on four sub-models: (i) estimating local air temperature lapse rate on a daily basis (ii) modifying downward longwave equation under clear sky condition, (iii) quantifying the effects of cold air drainage on air temperature, and (iv) quantifying the forest shelter effect on wind speed. The second advance advancement was accomplished by implementing and testing a new active method based on steam cycle thermodynamic. The first sub-model used AIRS (Atmosphere infrared sounder) air temperature profile and surface station data to estimate air temperature lapse rate on the daily and regional scale. The use of daily basis lapse rate, instead of the fixed value, allowed to present more accurate atmospheric condition. The results showed the potential of the AIRS air temperature profiles (850 hPa and 700 hPa) to estimate the temperature lapse rate. The second sub-model used observational data associated with synoptic conditions of radiation frost to present a locally adjusted downward longwave equation. The reported root means square error (RMSE) and mean absolute error (MAE) for the current version of Micro-Met were 176.95 (Wm-2) and 176.40 (Wm-2) respectively, while the results of the new equation led to an RMSE and MAE of 4.90 (Wm-2) and 4.00 (Wm-2) respectively. The third sub–model constituted three components: detected closed valley, estimated cold air drainage velocity, and integrated sensible heat loss and radiative cooling during the night on detected valleys. Comparison between the current Micro-Met simulation and the measured air temperature shows MAE of 1.11°C and RMSE of 1.66°C, while the comparison with the enhanced Micro-Met simulation indicated an improvement with MAE of 0.68 °C and RMSE of 1.08 °C. The fourth sub-model was based on experimental results of wind velocity produced in a laboratory with wind-tunnel models. Three separate equations were formulated for wind velocity estimation over the windward, through the shelterbelt, and leeward areas. The results indicated a coefficient of determination (R2) of 71% under the wind's velocity lower than 6ms-1. The Enhanced Micro-Met version provided a new platform to power vegetation-atmosphere energy model to forecast minimum nocturnal temperature. The performance test for forecasting minimum air temperatures indicated agreement with in-situ measurements. Measurements were taken on five topographic sectors in order to assess the improved modeled prediction and led to error assessment on closed valleys (RMSE=1.34, MAE = 1.03), different parts of slopes (RMAE = 0.93, MAE = 0.73), ridges (RMSE = 1.02, MAE = 0.88), flat areas (RMSE = 0.44, MAE = 0.40), and areas close to the forest (RMSE = 0.58, MAE = 0.53). In addition to previous specific objectives, this study proposed a new frost mitigation method based on the thermodynamics of water vapor transport from a moist source to dry sink. A vessel of warm water equipped with a Selective Inverted Sink (SIS) system was used to transport water vapor into the air, which ended up decreasing the air dryness and increasing moist entropy. This test was carried out in an orchard. The most common mitigation method focuses on air temperature. Instead, the proposed method was based on the physical principles of moist entropy, which combined both air temperature and humidity and depicted heat content. Overall, for this research project, a coupled model was designed to predict nocturnal minimum air temperature over hilly agricultural terrain. In particular, through improving prediction accuracy, we developed and added sub-models to estimate drops in temperature due to pooling and stagnation of cold air drainage and the effect of forest shelterbelt on wind velocity. To reduce frost effect, a new environmentally friendly active method was presented. This study served to help farmers reduce frost damages. Moreover, it can be useful for agricultural services in terms of decision-making, thereby, reducing economic damages

    Modern Climatology - Full Text

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    Climatology, the study of climate, is no longer regarded as a single discipline that treats climate as something that fluctuates only within the unchanging boundaries described by historical statistics. The field has recognized that climate is something that changes continually under the influence of physical and biological forces and so, cannot be understood in isolation but rather, is one that includes diverse scientific disciplines that play their role in understanding a highly complex coupled “whole system” that is the Earth’s climate. The modern era of climatology is echoed in this book. On the one hand it offers a broad synoptic perspective but also considers the regional standpoint as it is this that affects what people need from climatology, albeit water resource managers or engineers etc. Aspects on the topic of climate change – what is often considered a contradiction in terms – is also addressed. It is all too evident these days that what recent work in climatology has revealed carries profound implications for economic and social policy; it is with these in mind that the final chapters consider acumens as to the application of what has been learned to date. This book is divided into four sections that cover sub-disciplines in climatology. The first section contains four chapters that pertain to synoptic climatology, i.e., the study of weather disturbances including hurricanes, monsoon depressions, synoptic waves, and severe thunderstorms; these weather systems directly impact humanity. The second section on regional climatology has four chapters that describe the climate features within physiographically defined areas. The third section is on climate change which involves both past (paleoclimate) and future climate: The first two chapters cover certain facets of paleoclimate while the third is centered towards the signals (observed or otherwise) of climate change. The fourth and final section broaches the sub-discipline that is often referred to as applied climatology; this represents the important goal of all studies in climatology–one that affects modes of living. Here, three chapters are devoted towards the application of climatological research that might have useful application for operational purposes in industrial, manufacturing, agricultural, technological and environmental affairs. Please click here to explore the components of this work.https://digitalcommons.usu.edu/modern_climatology/1014/thumbnail.jp

    Remote Sensing Monitoring of Land Surface Temperature (LST)

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    This book is a collection of recent developments, methodologies, calibration and validation techniques, and applications of thermal remote sensing data and derived products from UAV-based, aerial, and satellite remote sensing. A set of 15 papers written by a total of 70 authors was selected for this book. The published papers cover a wide range of topics, which can be classified in five groups: algorithms, calibration and validation techniques, improvements in long-term consistency in satellite LST, downscaling of LST, and LST applications and land surface emissivity research

    CIRA annual report FY 2017/2018

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    Reporting period April 1, 2017-March 31, 2018

    CIRA annual report FY 2016/2017

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    Reporting period April 1, 2016-March 31, 2017

    Energy and Water Cycles in the Third Pole

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    As the most prominent and complicated terrain on the globe, the Tibetan Plateau (TP) is often called the “Roof of the World”, “Third Pole” or “Asian Water Tower”. The energy and water cycles in the Third Pole have great impacts on the atmospheric circulation, Asian monsoon system and global climate change. On the other hand, the TP and the surrounding higher elevation area are also experiencing evident and rapid environmental changes under the background of global warming. As the headwater area of major rivers in Asia, the TP’s environmental changes—such as glacial retreat, snow melting, lake expanding and permafrost degradation—pose potential long-term threats to water resources of the local and surrounding regions. To promote quantitative understanding of energy and water cycles of the TP, several field campaigns, including GAME/Tibet, CAMP/Tibet and TORP, have been carried out. A large amount of data have been collected to gain a better understanding of the atmospheric boundary layer structure, turbulent heat fluxes and their coupling with atmospheric circulation and hydrological processes. The focus of this reprint is to present recent advances in quantifying land–atmosphere interactions, the water cycle and its components, energy balance components, climate change and hydrological feedbacks by in situ measurements, remote sensing or numerical modelling approaches in the “Third Pole” region

    A systematic review of climate change science relevant to Australian design flood estimation

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    In response to flood risk, design flood estimation is a cornerstone of planning, infrastructure design, setting of insurance premiums, and emergency response planning. Under stationary assumptions, flood guidance and the methods used in design flood estimation are firmly established in practice and mature in their theoretical foundations, but under climate change, guidance is still in its infancy. Human-caused climate change is influencing factors that contribute to flood risk such as rainfall extremes and soil moisture, and there is a need for updated flood guidance. However, a barrier to updating flood guidance is the translation of the science into practical application. For example, most science pertaining to historical changes to flood risk focuses on examining trends in annual maximum flood events or the application of non-stationary flood frequency analysis. Although this science is valuable, in practice, design flood estimation focuses on exceedance probabilities much rarer than annual maximum events, such as the 1 % annual exceedance probability event or even rarer, using rainfall-based procedures, at locations where there are few to no observations of streamflow. Here, we perform a systematic review to summarize the state-of-the-art understanding of the impact of climate change on design flood estimation in the Australian context, while also drawing on international literature. In addition, a meta-analysis, whereby results from multiple studies are combined, is conducted for extreme rainfall to provide quantitative estimates of possible future changes. This information is described in the context of contemporary design flood estimation practice to facilitate the inclusion of climate science into design flood estimation practice.</p
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