Climate Monitoring from Orbit to Ocean

Image Source: amgun/Shutterstock.com

By Jeff Shepard for Mouser Electronics

Published January 14, 2021

Fifty-four Essential Climate Variables (ECVs) for worldwide monitoring in the air, on the land, and in the oceans are defined by the Global Climate Observing System, which is managed by the World Metrological Organization, a specialized agency of the United Nations (Figure 1).

It’s a complex and challenging undertaking. Monitoring that many variables requires resources ranging from satellites orbiting the Earth to balloons and aircraft in the atmosphere to land-based observation stations spread around the planet and, increasingly, fleets of robotic platforms roaming the oceans.

Among the earth systems under constant surveillance:

• Biosphere, anthroposphere–The part of the environment made or modified by humans.
• Hydrosphere–All the waters on the Earth's surface, such as lakes and seas, and sometimes including water above the Earth's surface, such as clouds.
• Cryosphere–The frozen water parts of the Earth.

Monitoring the climate can be as simple as personal observations. Or they can be as complex as coordinated sensor arrays on a network of orbiting satellites to measure sea-level rise and instruments carried on balloons and wind profiling radar that provide observations from the surface more than 16 meters high. Some of the data collected include air chemistry, temperature, precipitation, cloud cover, wind speed, and oceans' salinity. A large variety of active and passive sensing technologies is required.

Here, we’ll detail some of the sensors and methods used to continuously monitor climate change worldwide, moving through the various layers of global sensor networks—from orbit, through the atmosphere, onto the land, and finally diving into inner space in the oceans.

Figure 1: The United Nations' Global Climate Observing System has identified 54 Essential Climate Variables that critically contribute to the characterization of Earth’s climate. (Source: GCOS.wmo.int)

Satellites Surveillance of ECVs

ECVs are identified based on the following criteria:

• Relevance–The variable is critical for characterizing the climate system and its changes.
• Feasibility–Observing or deriving the variable globally is technically feasible using proven, scientifically understood methods.
• Cost-effectiveness–Generating and archiving data on the variable is affordable, mainly relying on coordinated observing systems using proven technology, taking advantage where possible of historical data.

Satellites provide detailed observations for over half of the ECVs. The National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Agency (NOAA), and the European Space Agency (ESA) have more than 160 satellites monitoring various aspects of climate change, including atmospheric conditions, temperatures, ocean conditions, and sea-level changes (Figure 2).

For example, instruments on NASA’s Terra and Aqua satellites have provided the first global measurements of aerosols in the atmosphere, from natural sources such as volcanoes, dust storms, and human-made sources such as the burning of fossil fuels. Other instruments onboard the Aura satellite study the processes that regulate the abundance of ozone in the atmosphere. Data from the GRACE and Ice, Cloud and land Elevation Satellite (ICESat) missions and spaceborne radar show unexpectedly rapid changes in the Earth's great ice sheets. In contrast, the Jason-3, OSTM/Jason-2, and Jason-1 missions have recorded a sea-level rise of an average of 3 inches since 1992.

Figure 2: Various Earth science spacecraft/instruments in orbit study all aspects of the Earth system (oceans, land, atmosphere, biosphere, cryosphere), with several more planned for launch in the next few years. (Source: Andrey Armyagov//Shutterstock)

Sea level change, and the rate of this change, is derived from calculations of sea surface height. By averaging the hundreds of thousands of satellite-collected altimetry measurements acquired over the same orbital track, the global mean sea level can be determined with a precision of several millimeters along with its change over time.

Satellite-based remote sensing near 60GHz can determine the temperature in the upper atmosphere by measuring radiation emitted from oxygen molecules that is a function of temperature and pressure. The International Telecommunications Union (ITU) non-exclusive passive frequency allocation at 57GHz to 59.3GHz is used for atmospheric monitoring in meteorological and climate-sensing applications. It is essential for these purposes because of the properties of oxygen absorption and emission in the Earth's atmosphere.

Airborne Atmospheric Monitoring

Satellites remotely monitor from above the atmosphere, from below by ground-based sensor systems and radar, and directly from balloons and aircraft using radiosondes (Figure 3). A radiosonde is a battery-powered telemetry instrument carried into the atmosphere, usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. These parameters include altitude, pressure, temperature, relative humidity, wind speed and direction, cosmic ray readings at high altitude, and geographical position (latitude/longitude).

Figure 3: A balloon is launched at Australia's most remote weather station, the Giles Weather Station in Western Australia near the Northern Territory border. (Source: Edward Haylan//Shutterstock)

Radiosondes measuring ozone concentration are known as ozonesondes. A radiosonde whose position is tracked as it ascends to give wind speed and direction information is called a rawinsonde (radar windsonde). Most radiosondes have radar reflectors and can be used as rawinsondes. A radiosonde dropped from an airplane instead of being carried by a balloon is a dropsonde.

About 1,300 radiosonde launch sites operate worldwide. Most countries share data through a series of international agreements. The majority of radiosonde launches occur 45 minutes before the 0000 Universal Time Coordinated (UTC) and 1200 UTC's official observation times, providing global and instantaneous snapshots of the atmosphere. This is especially important for numerical modeling of atmospheric conditions and climate change.

Radiosondes can also include flasks that gather high-altitude air samples for later analysis in a laboratory. In particular, the relative concentrations of carbon dioxide, methane, nitrous oxide, and ozone affect the atmosphere’s ability to trap solar radiation.

Land-based Monitoring

Land-based sensing is the most established form of climate change monitoring. A global network of thousands of automated surface observing systems (ASOS)—such as those found at airports, military installations, educational facilities, and other locations–monitor surface air conditions. Various climate variables are measured up to 12 times every hour by ASOS installations (Figure 4). Surface air temperature is measured at two meters above the ground. Typical instruments used by ASOS’s to monitor surface-level atmospheric conditions include rain gauges to measure precipitation that falls to the Earth’s surface. Solar pyranometers measure the amount of solar energy that reaches the surface. Barometers are continually monitoring air pressure.

Figure 4: The meteorological garden automated surface observing system (ASOS) is at Ngurah Rai Airport Bali in Kuta, Indonesia (Source: Pande Putu Hadi Wiguna//Shutterstock)

Wind is a vector quantity measured in terms of horizontal speed and direction; anemometers measure the speed while wind vanes and windsocks measure wind direction. Humidity is another multi-dimensional climate variable; hygrometers are used to measure both absolute and relative humidity. Absolute humidity is the actual amount of water vapor in the atmosphere. Relative humidity is the amount of water vapor in the air relative to the amount the air has the potential to hold given current temperature and pressure conditions.

Doppler radar is used to monitor storms. NOAA operates 159 Doppler radar towers across the continental U.S. that can monitor precipitation, rotational speed and direction of thunder clouds, airborne debris in tornados, and overall wind speeds and direction.

Robots Roam the Oceans

The oceans are vast, and monitoring them on a broad and comprehensive basis is challenging. Measuring the surface temperature of the world’s oceans has traditionally been done from ships and networks of buoys. Today satellites remotely monitor the surface temperature of all the oceans. But satellites are limited in what they can effectively monitor. The National Oceanic and Atmospheric Administration (NOAA) operates a fleet of more than 4,000 buoys and floats that monitor ocean chemistry and currents. The international Argo program also has deployed more than 3,800 robot floats, called CTD (conductivity, temperature, and depth) profilers, that monitor the world’s oceans at various depths.

Argo's floats are 1.3-meter robot tubes that sink to depths up to 2,000 meters before resurfacing and transmitting their position and data to satellites. All the data is accessible online. The cost of a robotic float is about the same as two days at sea for a research ship, but the float will operate autonomously for five years, even during storms when ships are held in port.

The newest Argo floats are operated as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project funded by the National Science Foundation. The Southern Ocean is under study because of the unique phenomena within and around it (Figure 5). For example, despite only comprising about 30 percent of the Earth’s ocean area, the Southern Ocean accounts for approximately half of the anthropogenic carbon uptake, as well as the majority of the oceanic anthropogenic heat uptake.

Figure 5: The Southern Ocean consists of the World Ocean's southernmost waters, generally taken to be south of 60° S latitude and encircling Antarctica. (Source: ugljesa//Shutterstock)

In addition to the basic CTD profilers found on most floats, SOCCOM floats are outfitted with additional biogeochemical sensors. They measure:

• Dissolved oxygen in the water represents the amount of primary productivity and respiration of the region, and proportions of oxygen to carbon are related, meaning that with measurements of dissolved oxygen, carbon concentrations can also be determined.
• pH measurements are of interest because this ocean sequesters a large amount of carbon dioxide, which results in the increasing acidification of the ocean as the carbon dioxide reacts with water to form carbonic acid.
• Chlorophyll concentration is easy to measure and is a proxy for phytoplankton abundance; therefore, mapping of chlorophyll results in a greater understanding of how nutrients are cycling in an area.
• Nitrate is an important limiting nutrient for phytoplankton, and nitrate abundance can determine the limits of phytoplankton biomass in the ocean.

Summary

Monitoring dozens of ECVs on a global scale is a complex and challenging undertaking. It requires resources ranging from satellites orbiting the Earth to balloons and aircraft in the atmosphere, automated land-based observation stations spread around the planet, and, increasingly, fleets of robotic monitoring platforms roaming the oceans. It also requires international coordination and cooperation.

Satellites are a crucial part of the effort and provide detailed observations for over half of the ESVs, monitoring various aspects of climate change, including atmospheric conditions, temperatures, ocean conditions, and sea-level changes. Worldwide, 1,300 radiosonde launch sites monitor the upper atmosphere, with most countries sharing the data through a series of international agreements. The majority of radiosonde launches occur 45 minutes before the 0000 UTC and 1200 UTC official observation times, providing global and instantaneous snapshots of the atmosphere that support numerical modeling of atmospheric conditions and climate change.

Land-based sensing of the lower atmosphere is the most established form of climate change monitoring. Surface air conditions are monitored by a global network of thousands of Automated Surface Observing Systems (ASOS) installations. ASOS sites measure various climate variables up to 12 times every hour. Finally, a growing fleet of thousands of increasingly capable robotic buoys and floats use biogeochemical sensors to monitor the world’s oceans, with much of the collected data publicly available on the internet.

Jeff was a co-founder of Jeta Power Systems, a maker of high-wattage switching power supplies acquired by Computer Products. Jeff is also an inventor. His name is on 17 U.S. patents in the fields of thermal energy harvesting and optical metamaterials. He is an industry source and frequent speaker on global trends in power electronics. He has been invited to speak at numerous industry events, including the Plenary Session of the IEEE Applied Power Electronics Conference, Semicon West, Global Semiconductor Alliance Emerging Opportunities Conference, IBM Power and Cooling Symposium, and Delta Electronics Senior Staff Seminar on Global Telecommunications Power. Jeff has a Master's degree in Quantitative Methods and Mathematics from the University of California, Davis. Jeff has been writing about power electronics, electronic components, and other technology topics for over 30 years. He started writing about power electronics as a senior editor at EETimes. He founded Powertechniques, a power electronics design magazine with a monthly circulation of over 30,000. He subsequently founded Darnell Group, a global power electronics research and publishing firm. Among its activities, Darnell Group published PowerPulse.net, which provided daily news for the global power electronics engineering community. He is the author of a switch-mode power supply textbook, titled "Power Supplies," published by the Reston division of Prentice Hall.