Observing the Oceans in Real Time

This chapter focuses on recent progress and emerging directions in ocean observations. The importance of sustained observations and status of the global ocean observing network are covered. Emerging trends include many exciting developments, such as Bio-ARGO floats, autonomous or remotely-operated instruments and platforms, and new measurement capabilities focused on fundamental ocean processes. Numerical models that integrate and assimilate multi-scale observations of the atmosphere, land, ice and ocean will lead to new science as well as improved forecasts of great societal value.

The focus of this chapter is on unattended observations of surface meteorology made from surface buoys. Also discussed is the computation of the air-sea fluxes of heat, freshwater, and momentum from the surface meteorological data obtained from surface buoys. The computation of these fluxes requires measurements of wind speed and direction, air temperature and humidity, barometric pressure, incoming shortwave radiation, incoming longwave radiation, sea surface temperature and salinity, and surface currents. Progress has been made in recent years in developing low power, robust, and accurate instrumentation. The present state of the sensors and related hardware is summarized. Typical buoy installations are described, and a summary of where these observations have been made is presented. The accuracies of the observations of surface meteorology are discussed. These accuracies are used together with the bulk formulae and intercomparisons to estimate the uncertainties in the flux observations. In many cases, it is now possible to make measurements of the mean net air–sea heat flux to an accuracy of 8 W m⁻². Challenges remain, and these challenges are also discussed.

The purpose of this chapter is twofold. First, we illustrate the technology used by the Lagrangian drifters deployed by Global Drifter Program (GDP), which is the principal component of the Global Drifter Array; second, we review and summarize the most recent studies on the impact of drifter data for calibration and validation of sea surface temperature (SST) satellite products, Numerical Weather Prediction (NWP) and climate studies, tropical cyclones (TCs)-ocean interaction and ocean circulation studies. Several types of drifters are described, starting from the simplest configuration that measures SST and sea-level atmospheric pressure (SLP), continuing with special drifters designed to measure sea surface salinity (SSS) and sea-level wind (SLW), and ending with air-deployable drifting thermistor chains that measure the temperature of the upper 150 m of the ocean, which are used to study the interaction of the ocean’s mixed layer with TCs. We also discuss the implications of the satellite telecommunication technology on the accuracy of drifter’s geolocation and on the timeliness of the near real-time data stream.

New opportunities for expanding the scope of the GDP are also discussed.

The Wave characteristics play a major role in the upper ocean dynamics, planning port operations, issuing sailing notifications and design of coastal/offshore structures. Waves in open sea exhibit very random and complex behavior with the superposition of many sinusoidal waves, each having its own height, period and direction. The design waves of varied return period based on extreme wave statistics is important for designing the coastal structures. This necessitates the accurate measurement of wave characteristics for various applications. The present chapter explains the state-of-the-art instruments used for measuring waves along with the advantages and disadvantages of each technique. Besides, a case study of estimation of wave climate using measurements and numerical modelling and the general wave characteristics in north Indian Ocean are also presented.

Oceanographic floats have become one of the most widely used oceanographic tools. As part of the international ARGO program, over 3000 floats monitor the temperature and salinity of the global ocean. Specialized floats carrying a broader instrument suite measure the ocean’s biological and chemical properties. Dense arrays of floats make more detailed measurements of regional variations and physical processes. This chapter reviews the physical bases of float operation, the design bases that allow for different float behaviors, and describes an operational float control system that generates these behaviors.

Ocean turbulence (and turbulence in general) tends to be tremendously intermittent, events often dominating average values. Or, put another way, the distribution of turbulence tends to be highly skewed, requiring significant systematic observations to capture the important dynamics that control time and space averages. It is thus imperative to link large-scale processes (macroscale) to turbulence energetics (microscale) to characterize the dynamics of a particular regime and to develop a quantitative understanding of the role of turbulence in ocean momentum and scalar budgets.

This chapter focuses on underwater gliders, placing them in the context of the recent surge in autonomous observing technologies, reviewing the underlying design philosophy and providing a brief history of their development. Gliders resolve scales of kilometers and hours, with the seasonal to annual endurance required to characterize climate variability and capture episodic events – a region of the spatial-temporal sampling spectrum that had previously been challenging to address. Examples of gliders applied to sustained studies of large-scale variability in boundary regions, to physical and biological/biogeochemical process studies, and to studies of polar regions illustrate strategies for efficient use that capitalize on the platform’s strengths. Although gliders are a mature platform with demonstrated scientific output, improvements to reliability, ease of use, and range would have large impacts on platform efficiency, enabling broader adoption and application to a wider range of scientific and operational tasks.

This chapter focuses on recent advances in in-situ ocean measurements. Recent interest in the ocean’s response to and impact on climate change has encouraged the development of improved sensor technologies for measuring oceanic parameters such as conductivity, temperature, dissolved oxygen and pH. It introduces various sensors used for measuring oceanic parameters, the underlying principles of these sensors and their respective calibration parameters. It also discusses what is still needed in the development of sensors to achieve the oceanographic need.

In this chapter, we briefly describe various space-borne sensors which have become the backbone of oceanographic research and applications. Operating in the electromagnetic region (mainly optical to microwave), these sensors provide measurements of various physical oceanographic parameters such as sea surface temperature, height, salinity, wave, winds, sea ice extent, thickness, and concentration on a global scale. This chapter also describes remote sensing techniques, measurement principles, retrieval of geophysical parameters, and their applications.

Passive acoustic monitoring takes advantage of the relative opacity of the ocean to sound. Traditionally, long-term monitoring has employed archival instruments from which data are accessed only when the recording instrument is retrieved. Recent advances in low-power instrumentation and computational speed allow passive acoustic data to be collected, processed and relayed to shore in near real time from fixed and mobile platforms deployed at the sea floor, in the water column or on the ocean’s surface. Measurements of ambient noise provide insight into natural sound sources, such as rainfall, earthquakes or marine animals, as well as anthropogenic sound sources, such as shipping or resource extraction. Near real-time passive acoustic measurements allow scientists and agencies to monitor shipping, observe underwater seismicity and detect the presence of critically endangered large whales. The development and use of real-time passive acoustic monitoring systems will grow in coming decades to help better manage increasing industrialization of the oceans. This chapter reviews the capabilities of real-time passive acoustic monitoring to address civilian scientific needs. The currently available suite of instrumentation and platforms used for passive acoustic monitoring are discussed along with the wide variety of measurements that can be made with this technology. Finally, examples of how real-time passive acoustic monitoring has improved our understanding of the ocean are presented.

Two types of high-frequency (HF) radar systems, long-range CODAR SeaSonde and medium-range WERA, are concurrently operated on the West Florida Coast for the purpose of observing coastal ocean currents and waves. In this chapter, we examine the data return aspect of HF radar performance, using radial currents measured with the CODAR SeaSonde and WERA systems at the same site origin – Venice, Florida. Based on the data collected during February 2 – 5 March, 2014, our analysis revealed that the two HF radar systems exhibited complicated data return variations in both the spatial and temporal domains. Even though data return was generally higher near the site origin rather than in the outer band of the offshore radar footprint, it was unevenly distributed across the bearing angles. The long-range CODAR tended to have more data return in the northern half of its footprint, while the medium-range WERA’s data return was more evenly distributed across the bearing angles. Both radar systems exhibited diurnal and synoptic variations in data return; however, the peak performance hours differed. The 4.90 MHz CODAR system tended to have a higher data return during the daytime hours, while the 12.58 MHz WERA system tended to return more data during nighttime hours. The CODAR system exhibited increased data return performance during the conditions of high sea state, while the WERA system’s performance did not exhibit an obvious sea state relationship with waves measured using an offshore Waverider buoy.

This chapter discusses the optimization of meteorological and oceanographic measurements from ocean surface moorings. First, we give guidelines and procedures for the selection of appropriate instruments and their preparation (calibration, configuration, integration and testing). Then, we present critical steps to evaluate and improve the data quality. We also discuss the limitations and benefits of real-time data, including various data quality control steps. Finally, we briefly compare two commonly used telemetry systems – ARGOS and Iridium. 

The chapter focuses on the basic principles and challenges of transmitting near real-time data from surface and subsurface moorings, and discusses designs and approaches used in the current generation of moorings.

The chapter begins with the requirements for marine meteorological and oceanographic (meteo-ocean) data for WMO applications. The meteo-ocean observations are not only used for scientific research purposes, but also allow realizing socioeconomic benefits and addressing the needs of many activities such as the safety of life and property at sea, operations in the open and coastal ocean areas, the protection and sustainable development of the ocean and marine environment, numerical weather prediction and operational meteorology, the monitoring and prediction of seasonal-to-interannual climate variability and climate change, and the efficient management of marine resources. The chapter provides information on the processes used to assess gaps and to provide guidance and World Meteorological Organization (WMO) Member Countries and Territories to address the gaps and make the observing system evolve. The role of the WMO, collaborating with the Intergovernmental Oceanographic Commission of UNESCO (IOC), in making and collecting observations from and over the oceans is explained. In particular, implementation targets for various types of meteo-ocean observing platforms are detailed. The chapter then provides information on meteoceano data management in the WMO framework, including for the collection of data in real-time and delayed mode, quality control, collection of metadata, and feedback of quality information to the observing platform operators. The existing sources of meteo-ocean data are listed, and relevant data policies explained. Finally, the chapter gives information on how to access data and provides an incentive for sharing the data.

The present status of ocean observation networks, especially in-situ, and their potential applications and societal relevance are summarized here. In-situ ocean observations are imperative to understand dynamics and thermodynamics of the ocean and its near-surface atmosphere, and they enhance our knowledge about weather and climate. Moreover, in-situ observations are directly assimilated into ocean and atmosphere models to support operational forecasts of ocean and atmospheric conditions. They complement the extensive data sets gathered by satellites, and they augment and validate the parameter estimates provided by satellites and other remote sensors through precise, direct measurements of ocean and atmospheric conditions. Global, national, and local ocean observational networks are a key foundation of operational oceanography. They underpin services of broad societal importance and economic value. These include the forecast of weather conditions, including seasonal and subseasonal monsoon forecasts; the provision of warnings of extreme weather and ocean events, such as tropical cyclones, storm surges, high waves and tsunamis; and information services in support of other ocean or coastal activities such as ocean transport and search and rescue operations. These services deliver direct and indirect benefits to a wide spectrum of society.