Satellite remote sensing of surface winds, waves, and currents: Where are we now?

This review paper reports on the state-of-the-art concerning observations of surface winds, waves, and currents from space and their use for scientific research and subsequent applications. The development of observations of sea state parameters from space dates back to the 1970s, with a significant increase in the number and diversity of space missions since the 1990s. Sensors used to monitor the sea-state parameters from space are mainly based on microwave techniques. They are either specifically designed to monitor surface parameters or are used for their abilities to provide opportunistic measurements complementary to their primary purpose. The principles on which is based on the estimation of the sea surface parameters are first described, including the performance and limitations of each method. Numerous examples and references on the use of these observations for scientific and operational applications are then given. The richness and diversity of these applications are linked to the importance of knowledge of the sea state in many fields. Firstly, surface wind, waves, and currents are significant factors influencing exchanges at the air/sea interface, impacting oceanic and atmospheric boundary layers, contributing to sea level rise at the coasts, and interacting with the sea-ice formation or destruction in the polar zones. Secondly, ocean surface currents combined with wind- and wave- induced drift contribute to the transport of heat, salt, and pollutants. Waves and surface currents also impact sediment transport and erosion in coastal areas. For operational applications, observations of surface parameters are necessary on the one hand to constrain the numerical solutions of predictive models (numerical wave, oceanic, or atmospheric models), and on the other hand to validate their results. In turn, these predictive models are used to guarantee safe, efficient, and successful offshore operations, including the commercial shipping and energy sector, as well as tourism and coastal activities. Long-time series of global sea-state observations are also becoming increasingly important to analyze the impact of climate change on our environment. All these aspects are recalled in the article, relating to both historical and contemporary activities in these fields

In situ airborne measurements of atmospheric and sea surface parameters related to offshore wind parks in the German Bight

Between 6 September 2016 and 15 October 2017, meteorological measurement flights were conducted above the German Bight in the framework of the project WIPAFF (Wind Park Far Field). The scope of the measurements was to study long-range wakes with an extent larger than 10 km behind entire wind parks, and to investigate the interaction of wind parks and the marine atmospheric boundary layer. The research aircraft Dornier 128 of the Technische Universität (TU) Braunschweig performed in total 41 measurement flights during different seasons and different stability conditions. The instrumentation consisted of a nose boom with sensors for measuring the wind vector, temperature and humidity, and additionally sensors for characterizing the water surface, a surface temperature sensor, a laser scanner and two cameras in the visible and infrared wavelength range. A detailed overview of the aircraft, sensors, data post-processing and flight patterns is provided here. Further, averaged profiles of atmospheric parameters illustrate the range of conditions. The potential use of the data set has been shown already by first publications. The data are publicly available in the world data centre PANGAEA (https://doi.org/10.1594/PANGAEA.902845; Bärfuss et al., 2019a)

Sea ice remote sensing using spaceborne global navigation satellite system reflectometry

In this research, the application of spaceborne Global Navigation Satellite System- Reflectometry (GNSS-R) delay-Doppler maps (DDMs) for sea ice remote sensing is investigated. Firstly, a scheme is presented for detecting sea ice from TechDemoSat-1 (TDS-1) DDMs. Less spreading along delay and Doppler axes is observed in the DDMs of sea ice relative to those of seawater. This enables us to distinguish sea ice from seawater through studying the values of various DDM observables, which describe the extent of DDM spreading. Secondly, three machine learning-based methods, specifically neural networks (NNs), convolutional neural networks (CNNs) and support vector machine (SVM), are developed for detecting sea ice and retrieving sea ice concentration (SIC) from TDS-1 data. For these three methods, the architectures with different outputs (i.e. category labels and SIC values) are separately devised for sea ice detection (classification problem) and SIC retrieval (regression problem) purposes. In the training phase, different designs of input that include the cropped DDM (40-by-20), the full-size DDM (128-by-20), and the feature selection (FS) (1-by-20) are tested. The SIC data obtained by Nimbus-7 SMMR and DMSP SSM/I-SSMIS sensors are used as the target data, which are also regarded as ground-truth data in this work. In the experimental stage, CNN output resulted from inputting full-size DDM data shows better accuracy than that of the NN-based method. Besides, performance of both CNNs and NNs is enhanced with the cropped DDMs. It is found that when DDM data are adequately preprocessed CNNs and NNs share similar accuracy. Further comparison is made between NN and SVM with FS. The SVM algorithm demonstrates improved accuracy compared with the NN method. In addition, the designed FS is proven to be effective for both SVM- and NN-based approaches. Lastly, a reflectivity

Application de la réflectométrie GNSS à l'étude des redistributions des masses d'eau à la surface de la Terre

GNSS reflectometry (or GNSS-R) is an original and opportunistic remote sensing technique based on the analysis of the electromagnetic waves continuously emitted by GNSS positioning systems satellites (GPS, GLONASS, etc.) that are captured by an antenna after reflection on the Earth’s surface. These signals interact with the reflective surface and hence contain information about its properties. When they reach the antenna, the reflected waves interfere with those coming directly from the satellites. This interference is particularly visible in the signal-to-noise ratio (SNR) parameter recorded by conventional GNSS stations. It is thus possible to reverse the SNR time series to estimate the reflective surface characteristics. If the feasibility and usefulness of thismethod are well established, the implementation of this technique poses a number of issues. Namely the spatio-temporal accuracies and resolutions that can be achieved and thus what geophysical observables are accessible.The aim of my PhD research work is to provide some answers on this point, focusing on the methodological development and geophysical exploitation of the SNR measurements performed by conventional GNSS stations. I focused on the estimation of variations in the antenna height relative to the reflecting surface (altimetry) and on the soil moisture in continental areas. The SNR data inversion method that I propose has been successfully applied to determine local variations of: (1) the sea level near the Cordouan lighthouse (not far from Bordeaux, France) from March 3 to May 31, 2013, where the main tidal periods and waves have been clearly identified ; and (2) the soil moisture in an agricultural plot near Toulouse, France, from February 5 to March 15, 2014. My method eliminates some restrictions imposed in earlier work, where the velocity of the vertical variation of the reflective surface was assumed to be negligible. Furthermore, I developed a simulator that allowed me to assess the influence of several parameters (troposphere, satellite elevation angle, antenna height, local relief, etc.) on the path of the reflected waves and hence on the position of the reflection points. My work shows that GNSS-R is a powerful alternative and a significant complement to the current measurement techniques, establishing a link between the different temporal and spatial resolutions currently achieved by conventional tools (sensors, radar, scatterometer, etc.). This technique offers the major advantage of being based on already-developed and sustainable satellites networks, and can be applied to any GNSS geodetic station, including permanent networks (e.g., the French RGP). Therefore, by installing a processing chain of these SNR acquisitions, data from hundreds of pre-existing stations could be used to make local altimetry measurements in coastal areas or to estimate soil moisture for inland antennas.La réflectométrie GNSS (ou GNSS-R) est une technique de télédétection originale et pportuniste qui consiste à analyser les ondes électromagnétiques émises en continu par la soixantaine de satellites des systèmes de positionnement GNSS (GPS, GLONASS, etc.), qui sont captées par une antenne après réflexion sur la surface terrestre. Ces signaux interagissent avec la surface réfléchissante et contiennent donc des informations sur ses propriétés. Au niveau de l’antenne, les ondes réfléchies interfèrent avec celles arrivant directement des satellites. Ces interférences sont particulièrement visibles dans le rapport signal-sur-bruit (SNR, i.e., Signal-to-Noise Ratio), paramètre enregistré par une station GNSS classique. Il est ainsi possible d’inverser les séries temporelles du SNR pour estimer des caractéristiques du milieu réfléchissant. Si la faisabilité et l’intérêt de cette méthode ne sont plus à démontrer, la mise en oeuvre de cette technique pose un certain nombre de problèmes, à savoir quelles précisions et résolutions spatio-temporelles peuvent être atteintes, et par conséquent, quels sont les observables géophysiques accessibles.Mon travail de thèse a pour objectif d’apporter des éléments de réponse sur ce point, et est axé sur le développement méthodologique et l’exploitation géophysique des mesures de SNR réalisées par des stations GNSS classiques.Je me suis focalisé sur l’estimation des variations de hauteur de l’antenne par rapport à la surfaceréfléchissante (altimétrie) et de l’humidité du sol en domaine continental. La méthode d’inversion des mesures SNR que je propose a été appliquée avec succès pour déterminer les variations locales de : (1) la hauteur de la mer au voisinage du phare de Cordouan du 3 mars au 31 mai 2013 où les ondes de marées et la houle ont pu être parfaitement identifiées ; et (2) l’humidité du sol dans un champ agricole à proximité de Toulouse, du 5 février au 15 mars 2014. Ma méthode permet de s’affranchir de certaines restrictions imposées jusqu’à présent dans les travaux antérieurs, où la vitesse de variation verticale de la surface de réflexion était supposée négligeable. De plus, j’ai développé un simulateur qui m’a permis de tester l’influence de nombreux paramètres (troposphère, angle d’élévation du satellite, hauteur d’antenne, relief local, etc.) sur la trajectoire des ondes réfléchies et donc sur la position des points de réflexion. Mon travail de thèse montre que le GNSS-R est une alternative performante et un complément non négligeable aux techniques de mesure actuelles, en faisant le lien entre les différentes résolutions temporelles et spatiales actuellement atteintes par les outils classiques (sondes, radar, diffusiomètres, etc.). Cette technique offre l’avantage majeur d’être basé sur un réseau de satellites déjà en place et pérenne, et est applicable à n’importe quelle station GNSS géodésique, notamment celles des réseaux permanents (e.g., le RGP français). Ainsi, en installant une chaîne de traitement de ces acquisitions de SNR en domaine côtier, il serait possible d’utiliser les mesures continues des centaines de stations pré-existantes, et d’envisager de réaliser des mesures altimétriques à l’échelle locale, ou de mesurer l’humidité du sol pour les antennes situées à l’intérieur des terres

NASA oceanic processes program: Status report, fiscal year 1980

Goals, philosophy, and objectives of NASA's Oceanic Processes Program are presented as well as detailed information on flight projects, sensor developments, future prospects, individual investigator tasks, and recent publications. A special feature is a group of brief descriptions prepared by leaders in the oceanographic community of how remote sensing might impact various areas of oceanography during the coming decade

Research and Technology Objectives and Plans Summary (RTOPS)

This publication represents the NASA research and technology program for FY89. It is a compilation of the Summary portions of each of the RTOPs (Research and Technology Objectives and Plans) used for management review and control of research currently in progress throughout NASA. The RTOP Summary is designed to facilitate communication and coordination among concerned technical personnel in government, in industry, and in universities. The first section containing citations and abstracts of the RTOPs is followed by four indexes: Subject, Technical Monitor, Responsible NASA Organization, and RTOP Number

Copernicus Marine Service ocean state report, issue 4

This is the final version. Available from Taylor & Francis via the DOI in this record. FCT/MCTE

Küstennähe numerische Modellierung von windgenerierten Wellen in halgeschlossenen Meeresgebieten: Kalibrierung und Anwendung

A central question in this study is the evaluation and the improvement of the accuracy of wind-wave predictions in semi-enclosed seas. It was investigated how the parametrization of the wave models can be modified to provide accurate predictions in these specific areas. Furthermore, this work outlines how the physical inputs of the wave model such as the wind forcing and the bathymetry can affect wave predictions. An additional objective of this work is to assess the accuracy of the in-situ and remote field observations used in the calibration and validation processes of the numerical wave model. To examine these questions, wind-waves were simulated with the spectral wave model Simulating WAves Nearshore (SWAN) included in the Delft3D modelling package (Deltares, the Netherlands). Extensive calibration and validation of the wave model and its wind forcing were achieved by means of large datasets of in-situ and remote measurement technologies. Numerical predictions of wind-generated waves in two semi-enclosed seas, the Red Sea and the Bohai Sea were improved by means of modifications of the source term responsible of the generation of wave energy by wind in the action balance equation of the wave model. The findings provide support to the scientific community in the field of the operational oceanography. The outputs of the wave model for the Red Sea and the coastal waters of Jeddah were integrated into a coastal monitoring system. The wave model set up for the Bohai Sea is part of a Decision Support System for the Shandong peninsula. The two information systems provide hindcasts and forecasts of hydrodynamic parameters.Eine zentrale Frage in dieser Arbeit ist die Beurteilung und die Verbesserung der Genauigkeit von Vorhersagen für Windseen in halb geschlossenen Meeresgebieten. Es wurde untersucht wie die Parametrisierung des Wellenmodels modifiziert werden kann, um genaue Vorhersagen für die untersuchten Gebiete bereitzustellen. Außerdem umreißt diese Arbeit, wie die physikalischen Eingangsgrößen des Wellenmodells, der Windantrieb und die Bathymetrie die Vorhersage von Wellen beeinflussen können. Ein weiteres Ziel dieser Arbeit besteht darin, die Genauigkeit der In-Situ- und Fernerkundungsdaten einzuschätzen, die im Kalibrierungs- und Validierungsprozess des numerischen Modells benutzt wurden. Um diese Fragen zu untersuchen, wurden Windseen mit dem spektralen Wellenmodel Simulating WAves Nearshore (SWAN) simuliert, dass in der Modellierungssoftware Delft3D (Deltares, Holland) enthalten ist. Eine umfassende Kalibrierung und Validierung des Wellenmodells und seines Antriebs durch Wind wurde mit Hilfe großer Datensätze aus In-Situ- und Fernerkundungs-Meßtechniken erreicht. Numerische Vorhersagen von windgenerierten Wellen in zwei halb geschlossenen Meeresgebieten, dem Roten Meer und der Bohai See, wurden mit Hilfe von Modifikationen des Quellterms verbessert, der für die Erzeugung von Wellenenergie durch Wind in der Gleichung der spektrale Wirkungsdichte des Wellenmodels verantwortlich ist. Die Befunde liefern Unterstützung für die Wissenschaftler auf dem Gebiet der operativen Ozeanographie. Die Ergebnisse aus dem Wellenmodell für das Rote Meer und die Küstengewässer von Jeddah wurden in ein Küsten-Monitoring-System integriert. Das Wellenmodell, dass für die Bohai See aufgestellt wurde, ist ein Bestandteil eines Entscheidungshilfesystems (DSS) für die Shandong Halbinsel. Die beiden Informationssysteme stellen Hindcasts und Vorhersagen hydrodynamischer Parameter bereit

Copernicus Marine Service Ocean State Report, Issue 4

peer reviewe

Earth Resources: A continuing bibliography with indexes, issue 17

This bibliography lists 775 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1 and March 31, 1978. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis