- Email: [email protected]
Introduction to the Remote Sensing of Earth-Surface Temperatures
INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
1
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
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 Taking the Temperature of the Earth. https://doi.org/10.1016/B978-0-12-814458-9.00001-0 # 2019 Elsevier Inc. All rights reserved.
1
2
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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 remotesensing 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
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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.
3
4
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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., 2013. The surface temperatures of Earth: steps towards integrated understanding of variability and change. Geosci. Instrum. Methods Data Syst. 2 (2), 305–321.
1
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
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 Taking the Temperature of the Earth. https://doi.org/10.1016/B978-0-12-814458-9.00001-0 # 2019 Elsevier Inc. All rights reserved.
1
2
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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 remotesensing 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
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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.
3
4
Chapter 1 INTRODUCTION TO THE REMOTE SENSING OF EARTH-SURFACE TEMPERATURES
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., 2013. The surface temperatures of Earth: steps towards integrated understanding of variability and change. Geosci. Instrum. Methods Data Syst. 2 (2), 305–321.