Taking the Temperature of the Earth: Steps towards Integrated Understanding of Variability and Change

Taking the Temperature of the Earth: Steps towards Integrated Understanding of Variability and Change presents an integrated, collaborative approach to observing and understanding various surface temperatures from a whole-Earth perspective. The book describes the progress in improving the quality of surface temperatures across different domains of the Earth’s surface (air, land, sea, lakes and ice), assessing variability and long-term trends, and providing applications of surface temperature data to detect and better understand Earth system behavior.

As cooperation is essential between scientific communities, whose focus on particular domains of Earth’s surface and on different components of the observing system help to accelerate scientific understanding and multiply the benefits for society, this book bridges the gap between domains.

• Includes sections on data validation and uncertainty, data availability and applications
• Integrates remote sensing and in situ data sources
• Presents a whole earth perspective on surface temperature datasets, delving into all domains to build and understand relationships between the datasets

• Language: English
• Publisher: Elsevier Science
• Release date: Jun 15, 2019
• ISBN: 9780128144596

Book preview

Taking the Temperature of the Earth

Steps towards Integrated Understanding of Variability and Change

First Edition

Glynn C. Hulley

Darren Ghent

Table of Contents

Cover image

Title page

Copyright

Contributors

1: Introduction to the Remote Sensing of Earth-Surface Temperatures

Abstract

2: Global Sea Surface Temperature

Abstract

2.1 Introduction

2.2 Retrieval and Measurement Methodology

2.3 Validation

2.4 Satellite Data Availability

2.5 Science Applications

3: Land Surface Temperature

Abstract

3.1 Introduction

3.2 Thermal Infrared Theory

3.3 LST Retrieval Algorithms

3.4 Validation

3.5 Satellite Data and Availability

3.6 Science and User Applications

4: Lake Surface Temperature

Abstract

4.1 Introduction

4.2 Validation of Lake Surface Water Temperature

4.3 Satellite Data and Availability

4.4 Use of Lake Surface Water Temperature for Trend Studies

5: Ice Surface Temperatures in the Arctic Region

Abstract

5.1 Introduction

5.2 Satellite Data and Availability

5.3 Retrievals and Measurement Methodology

5.4 Validation

5.5 Science and User Application

5.6 Summary and Conclusions

6: Surface Temperature Interrelationships

Abstract

6.1 Introduction

6.2 A Brief History of Air Temperature Measurements and Development of a Global Temperature Monitoring System

6.3 Air Temperature Measurement Standards

6.4 Challenges of a Point-Based In Situ Temperature Network

6.5 Relationship Between Air Temperature and Land Surface Temperature

6.6 Estimation of Air Temperature With Remotely Sensed Land Surface Temperature

6.7 Relationship of Surface Temperature With the Cryosphere

6.8 Conclusions

7: Surface Temperatures in the Urban Environment

Abstract

7.1 The Urban Heat Island (UHI)

7.2 Satellite Thermal Monitoring of Urban Heat Waves

8: A Look to the Future: Thermal-Infrared Missions and Measurements

Abstract

8.1 ECOSTRESS

8.2 HyspIRI Surface Biology and Geology

8.3 Landsat 9

8.4 Joint Polar Satellite System (JPSS)

8.5 Meteosat Third Generation (MTG)

8.6 Polar System (EPS-SG)

8.7 Copernicus Sentinel-3 (C and D Modules)

Index

Copyright

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Contributors

Helen Beggs     Bureau of Meteorology, Melbourne, VIC, Australia

César Coll     Department of Earth Physics and Thermodynamics, Faculty of Physics, University of Valencia, Burjassot, Valencia, Spain

Josefino C. Comiso     NASA Goddard Space Flight Center, Greenbelt, MD, United States

Gary K. Corlett     EUMETSAT, Darmstadt, Germany

Bénédicte Dousset     University of Hawai‘i at Mānoa, Hawai‘i Institute of Geophysics and Planetology, Honolulu, HI, United States

Chelle Gentemann     Earth and Space Research, Seattle, WA, United States

Darren Ghent     National Centre for Earth Observation, Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom

Frank M. Göttsche     Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research (IMK-ASF), Eggenstein-Leopoldshafen, Germany

Pierre C. Guillevic     Department of Geographical Sciences, University of Maryland, College Park, MD, United States

Dorothy K. Hall     Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, United States

Andrew R. Harris     University of Maryland, College Park, MD, United States

Nathan C. Healey     Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States

Simon J. Hook     Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States

Jacob Hoyer     Danish Meteorological Institute, Copenhagen, Denmark

Glynn C. Hulley     Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States

Jeffrey C. Luvall     NASA Marshall Space Flight Center, Huntsville, AL, United States

Eileen Maturi     NOAA Center for Weather and Climate Prediction, College Park, MD, United States

Christopher J. Merchant     University of Reading and National Centre for Earth Observation, Reading, United Kingdom

David J. Mildrexler     Department of Forest Ecosystems and Society, College of Forestry, Oregon State University, Corvallis, OR, United States

Peter J. Minnett     University of Miami, Coral Gables, FL, United States

Jared W. Oyler     BASF Corporation, Bellefonte, PA, United States

Ignatius Rigor     Polar Science Center, Univ. Washington, Seattle, WA, United States

Philipp Schneider     NILU—Norwegian Institute for Air Research, Kjeller, Norway

1

Introduction to the Remote Sensing of Earth-Surface Temperatures

Glynn C. Hulley⁎; Darren Ghent†; Christopher J. Merchant‡    ⁎ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States

† National Centre for Earth Observation,Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom

‡ University of Reading and National Centre for Earth Observation, Reading, United Kingdom

Abstract

This is an introduction to Earth surface temperatures, and the role of the EarthTemp Network in establishing an international collaborative group dedicated to a better understanding of surface temperatures in various domains of the Earth.

Keywords

EarthTemp; Surface temperature; LST; Thermal; Remote sensing

The various surface temperatures of Earth are fundamental and critical observables that are strongly linked to climate and weather patterns. Surface temperatures determine habitats of animal and plant species, affect human health and comfort, and are critical for agricultural and water-resource management practices. The surface temperatures of Earth encompass several distinct, well-defined regimes, including surface air, sea, land, lakes, and ice domains. All these temperatures play interconnected roles in the Earth surface-atmosphere system, vary and co-vary at different scales in space and time, and are measured with complementary techniques.

The EarthTemp Network, initially funded by the UK's Natural Environment Research Council, was established in 2012 to bring together a global alliance of scientists with expertise in a variety of Earth-surface temperature domains. The inaugural meeting, held in Edinburgh, UK, in June 2012, focused on the concept of viewing surface temperatures from a whole-Earth perspective, i.e., including all domains of air, sea, land, lakes, and ice. This resulted in a set of 10 overarching recommendations and societal needs for better understanding surface temperatures and related applications. Some examples include improving understanding of relationships between surface temperatures in different domains, demonstrating novel surface-temperature applications, and making surface-temperature datasets easier to obtain and utilize by the scientific community for fundamental research. These needs were broadly expressed in a community white paper and published manuscript (Merchant et al., 2013). Subsequent meetings consisted of annual themes such as characterizing surface temperatures in data sparse regions in high latitude domains (2013), in key land regions such as Africa (2014), and better understanding the complexity of temperatures in urban areas (2015). Members of the EarthTemp Network have also successfully organized and chaired sessions dedicated to these topics at the annual European Geophysical Union (EGU) and American Geophysical Union (AGU) meetings since 2013.

Surface temperatures on a global scale are primarily measured using thermal infrared (TIR) remote-sensing observations acquired by ground, airborne, and spaceborne instruments sensitive to the infrared wavelength domain (3–15 μm). All objects with a temperature above absolute zero (0 K, − 273°C) emit electromagnetic radiation, and this radiation can be measured by TIR sensors and translated into a kinetic temperature of the object or region being measured at the scale of the imagery. For sea, land, ice, and lake temperatures, this constitutes the temperature you would feel if you placed your hand on the surface of an object. The physical basis for TIR spectroscopy will be discussed in more detail within the chapters of this book for each surface domain, including the intricacies involved with correcting for geometrical and atmospheric effects.

The chapters in this book were written and led in large part by founding members of the EarthTemp Network but also by an international team of scientists that are active in the remote-sensing field of surface temperatures. The material consists of a comprehensive overview of each surface-temperature regime, including background and theory, retrieval and measurement methodology, validation and uncertainty, data availability, and science applications. Also included are chapters focused on surface temperature interrelationships (e.g., skin and air), and a prospective overview of observing systems that will measure surface temperatures of our planet.

Future TIR missions include NASA's Ecosystem Thermal Radiometer Experiment on Space Station (ECOSTRESS, launched in June 2018), HyspIRI-SBG, and Landsat-9/10, NOAA's Joint Polar Satellite System (JPSS) program including current Suomi NPP and JPSS-1 (NOAA-20) satellites and future JPSS 1-4, continuity of the Copernicus Sentinel-3 series (C and D units) developed by ESA, and EUMETSAT's Meteosat Third Generation (MTG-I 1-4), and Polar System (EPS-SG 1-3). Other relevant candidate missions include the Copernicus High Spatio-Temporal Resolution Land Surface Temperature Mission and, in the microwave domain, the Copernicus Imaging Microwave Radiometer. TIR and microwave measurements from these sensors will ensure the long-term and consistent monitoring of surface temperatures and will extend the multidecadal satellite record of the temperatures of our planet.

As such, the TIR community continues to grow and play an active role in planning of future missions, advancing the fundamental understanding of the Earth system, providing knowledge that can be provided for societal use, and to monitor climate. The requirements and recommendations for a functional and robust Global Climate Observing System (GCOS) are enshrined in the GCOS Implementation Plan (GCOS-202, 2016). All surface-temperature domains are addressed with the newest addition to the list of Essential Climate Variables (ECVs) being land surface temperature in 2016. ESA's Climate Change Initiative (CCI) confronts the strict GCOS requirements, exploiting the full potential of long-term satellite data to deliver the significant improvements demanded for climate science. Surface temperature is represented across the domains in the Sea Surface Temperature (SST) CCI, Land Surface Temperature (LST) CCI, and Lakes CCI projects. Similarly, NASA has identified land surface temperature data as an important Earth System Data Record (ESDR), and efforts are currently underway to produce long time series of these data with well-characterized uncertainties through NASA's Making Earth System Data Records for Use in Research Environments (MEaSUREs) project. MEaSUREs was developed to synergistically link together data sources from multiple satellites to form consistent and coherent long time series of data with estimates of uncertainty.

It is our hope that this book will provide a valuable resource of information for both students and professionals in this field and for experts in related fields. For this reason, the book includes not only the fundamental physics of surface temperatures and TIR theory, but also aims to provide a set of common and standard practices for the use and validation of surface-temperature data, and gives a broad overview on the current state-of-the-art in the field of TIR remote sensing, including future missions.

We are optimistic that information in this book will be a flagship for future research and measurements related to Earth surface temperatures and their interrelationships, and that the spirit of the EarthTemp Network will live on through active international collaboration and participation in the surface temperature and TIR remote sensing fields.

Reference

Merchant C.J., Matthiesen S., Rayner N.A., Remedios J.J., Jones P.D., Olesen F., Trewin B., Thorne P.W., Auchmann R., Corlett G.K., Guillevic P.C., Hulley G.C. The surface temperatures of Earth: steps towards integrated understanding of variability and change. Geosci. Instrum. Methods Data Syst. 2013;2(2):305–321.

2

Global Sea Surface Temperature

Christopher J. Merchant⁎; Peter J. Minnett†; Helen Beggs‡; Gary K. Corlett§; Chelle Gentemann¶; Andrew R. Harris‖; Jacob Hoyer#; Eileen Maturi⁎⁎    ⁎ University of Reading and National Centre for Earth Observation, Reading, United Kingdom

† University of Miami, Coral Gables, FL, United States

‡ Bureau of Meteorology, Melbourne, VIC, Australia

§ EUMETSAT, Darmstadt, Germany

¶ Earth and Space Research, Seattle, WA, United States

‖ University of Maryland, College Park, MD, United States

# Danish Meteorological Institute, Copenhagen, Denmark

⁎⁎ NOAA Center for Weather and Climate Prediction, College Park, MD, United States

Abstract

Two-thirds of Earth's surface is liquid water, the upper boundary of the global oceans. This vast surface is in constant interaction with the atmosphere. In these interactions, the sea surface temperature (SST) plays a central role. Knowing the distribution of SST is essential for numerical weather prediction (i.e., modern weather forecasting) and operational oceanography (such as forecasts for shipping and resource exploitation). Estimates of the large-scale changes in SST over the last 150 years are a sufficient constraint to drive simulations of a large proportion of the climatic variability and change seen during the period, because SST has a pivotal role in the climate system. As well as being a contributing factor to air-sea interactions and the large-scale climate, SST is a signature of many processes of scientific and practical interest, including impacts on highly prized ecosystems such as fisheries and coral reefs. Satellite observations are crucial to taking the temperature of the oceans in the modern era, and the state of the art is reviewed.

Keywords

Sea surface temperature; Coral reefs; Global ocean; Satellite sensors; Validation; Climate system

Chapter Outline

2.1Introduction

2.1.1Importance of Global Sea Surface Temperature

2.1.2Definitions of Sea Surface Temperature

2.1.3Global and Seasonal Distributions of SST

2.1.4Large-Scale SST-Atmosphere Interactions

2.1.5Sea Surface Temperature and Climate

2.2Retrieval and Measurement Methodology

2.2.1Relationship of SST to Top-of-Atmosphere Radiances

2.2.2Satellite Infrared Retrievals of SST

2.2.3Satellite Microwave Retrievals of SST

2.3Validation

2.3.1Types of In Situ Measurements of Sea Surface Temperature

2.3.2Factors Causing Alternative Sea Surface Temperature Measurements to Differ

2.3.3Practical Validation Approaches

2.3.4Sea Surface Temperature Validation and Uncertainty Budgets

2.4Satellite Data Availability

2.4.1Selected Missions Past and Present

2.4.2International Collaboration on Data Sharing

2.4.3Future Developments in Satellite SST

2.5Science Applications

2.5.1Operational Forecasting

2.5.2Climate Monitoring and Research

2.5.3Marine Biology

2.5.4Concluding Remarks

References

Further Reading

2.1 Introduction

2.1.1 Importance of Global Sea Surface Temperature

Two-thirds of Earth's surface is liquid water, the upper boundary of the global oceans. This vast surface is in constant interaction with the atmosphere. In these interactions, the sea surface temperature (SST) plays a central role. Knowing the distribution of SST is essential for numerical weather prediction (i.e., modern weather forecasting) and operational oceanography (such as forecasts for shipping and resource exploitation). Estimates of the large-scale changes in SST over the last 150 years are a sufficient constraint to drive simulations of a large proportion of the climatic variability and change seen during the period, because SST has a pivotal role in the climate system. As well as being a contributing factor to air-sea interactions and the large-scale climate, SST is a signature of many processes of scientific and practical interest, including impacts on highly prized ecosystems such as fisheries and coral reefs.

Global sea surface temperatures are therefore important to measure. For the measurements to be relevant to a wide range of processes and applications (see Table 2.1), SST needs to be quantified on a wide range of scales of space and time. The only practicable means of obtaining data across the global oceans with sufficient frequency is from satellite-based Earth observation, also known as remote sensing. In situ measurements are crucial to the success of the overall SST observing system, even though their coverage is inevitably spotty. In situ measurements are needed to link satellite SSTs to the vertical variations of temperature below the surface and to correct errors, reduce uncertainties, and validate satellite SST observations. (In situ measurements of SST are also generally made together with other important variables.)

Table 2.1

Extracted and updated from Robinson (2004), which provides further examples.

Sea surface temperature has been an important application of remote sensing from space for nearly four decades, during which time user requirements have become more demanding, even as the resolution and uncertainty of SST products have improved. Improvements have been driven by technological developments in satellite sensors, by increased understanding of the physics relating SST to top-of-atmosphere radiance measurements, and by applying that physics to the inverse problem of inferring SST from radiance using more sophisticated mathematical approaches. Using satellite and a variety of in situ data together has been essential to the progress made.

The remainder of this introduction will elaborate on the general importance and context of SST observation, addressing:

•the definitions of sea surface temperature

•the spatial distribution and variability of SST across the globe and ocean basins

•examples of the large-scale interactions of the atmosphere and ocean

•the roles SST plays in air-sea heat and momentum fluxes at local scales

•the relevance of SST to the climate system

2.1.2 Definitions of Sea Surface Temperature

2.1.2.1 Foundation Temperature

The concept of sea surface temperature sounds rather obvious: it is the temperature of sea water close to the ocean surface. In the context of thinking about different processes, spatio-temporal scales, and measurement technologies, it is helpful to define SST more precisely. Vertical variations in temperature are often present within the surface waters of the ocean (let's say, within the upper 10 m), and so the key to a refined definition is to distinguish the sea surface temperatures at different depths. An internationally agreed set of definitions based on SST depths has been developed (Donlon et al., 2007) and will be described below. But before doing so, it is worth reflecting on the limitations of any depth-based classification of SSTs in the face of real-world variability. Depth-based definitions may be clear enough for relatively calm conditions, but what is the meaning of 1 m depth during a violent storm, where wave heights may be an order of magnitude > 1 m and the air-sea interface is characterized by prevalent foam and spray? Depth in the near-surface zone is clearly problematic in such conditions, although in this scenario mechanical mixing efficiently equalizes the water temperature near the surface; depth-based distinctions are then less relevant, and we can concentrate on definitions that work for less extreme situations. Nonetheless, we bear in mind that these definitions are ideas imposed on nature and not fully descriptive of nature's possibilities.

At 10 m depth, between 50% and 90% of sunlight impinging on the surface has typically been absorbed above that depth level. The light that does penetrate further is essentially blue-green. The vertical rate of change of the flux of light at 10 m on a clear-sky day around noon at the equator gives an estimate of the maximum rate at which the sea water temperature is directly heated by sunshine at this depth and turns out to be of order 0.02 K h− 1. A globally representative daily-averaged rate would be 3 mK h− 1 which is < 0.1 K/day. The temperature at 10 m is therefore relatively stable with respect to the direct heating by the daily cycle of solar heating. For this reason, the SST around this depth is conceptualized as a foundation temperature above which larger subdaily variability is superimposed, particularly under conditions of low to moderate wind speeds and high insolation (Soloviev and Lukas, 1997; Ward, 2006). This means that the depth of the foundation temperature at a given location changes from day to day, but not within the day. The diurnal variability will be described further below. The 10 m SST is measured by in situ profilers, with such measurements being made globally and routinely since about 2005 within the context of the Argo program (Roemmich et al., 2009). Prior to Argo, and continuing now, vertical profiles of temperature have been measured from ships, such as the current GO-SHIP program (Talley et al., 2016), and by single use eXpendable BathyThermographs (XBTs, Abraham et al., 2013). The 10 m SST is not directly measurable from remote sensing, although a satellite-derived SST observed around local dawn can be used to estimate the foundation SST. Near-surface temperature stratification that develops during daytime is usually eroded by dawn by surface heat loss, causing density-driven mixing and wind-driven turbulent mixing (e.g., Sutherland et al., 2014). Satellite SSTs observed under well-mixed moderate (e.g., 7–12 m/s) wind conditions are also considered to be reasonable estimates of foundation temperature.

2.1.2.2 Near-Surface Depth Temperatures

Between the foundation temperature and the ocean skin (see below), the solar heating cycle in interaction with low wind-driven mixing may drive near-surface stratification, which may be quantified by the difference in temperature just below the skin (at a depth of order 1 cm) to that at a foundation depth. (Stratification refers to the concept that strata of water at different depths are distinct in their density because of differences in temperature; in reality, the temperature profile is continuously varying.) Since vertical stratification may form and dissipate on subdaily timescales driven by the solar cycle, the effect is referred to as diurnal warming.

Over the majority of the ocean at a given time, the diurnal warming signal is zero or small (< 0.1 K difference), but in areas of adequate insolation and persistent slow wind speeds, diurnal warming of order 1 K is readily observed (Fig. 2.1A–C). In satellite data, amplitudes of 5 K or more have been demonstrated (Gentemann et al., 2008; Merchant et al., 2008a,b). Fig. 2.1D illustrates a calculation of the maximum diurnal warming during a 24-h period using a 1-d ocean model. It illustrates the patchy and streaky nature of significant diurnal warming events, which are also seen in analyses of SST from geostationary satellites that resolve this cycle with regular observations (at intervals of 10 min to 1 h). The patterns reflect areas with low winds during the period of high sunshine.

Fig. 2.1 (A–C) Near-surface profile of temperature from mooring data in the Indian Ocean. Each panel shows a depth profile of temperature: a sun whose area is relative to the daily maximum at noon and a scale showing wind speed. (A) Typical profile shortly after dawn, temperature is close to isothermal. (B) Mid-day profile under low wind (< 3 m/s) conditions, showing a warm shallow layer. (C) Mid-day profile from the following day with moderate (> 4 m/s) conditions, showing heat is mixed down more evenly over the water column by the greater wind mixing energy. (D) Model calculations of the daily maximum diurnal warming on May 24, 2014. The significant events are mainly in the summer hemisphere and tropics, and reflect areas of predominantly low wind conditions between dawn and mid-afternoon. (A–C) Data courtesy of Bob Weller, Woods Hole Oceanographic Institute.

Large diurnal warming in terms of 1 cm to 10 m difference corresponds to strong stratification over a relatively shallow layer (< 1 m), whereas events with lesser amplitude at the surface have the warmer temperatures over a deeper range (several meters). This reflects that roughly the same net-energy gain is involved, but it is differently distributed by wind-driven mixing. This is illustrated in Fig. 2.1A–C.

2.1.2.3 The Thermal Skin of the Ocean

The processes that influence the sea temperature in the uppermost few millimeters and less of the ocean are complex and very difficult to measure, both in the field and the laboratory. They are also difficult to address theoretically. Yet, the sea-water properties on these small vertical scales have profound influences on the way the ocean and atmosphere are coupled, how we