Land Remote Sensing and Global Environmental Change

NASA’s Earth Observing System and the Science of ASTER and MODIS

Prologue

Global environmental change fundamentally transforms the physical, chemical,and biological aspects of ecosystems with corresponding socioeconomic repercussions across planet Earth. These changes are largely driven by human as well as natural causes. Global warming and climate change, two near-universal terms in our everyday lexicon, increasingly symbolize environmental change globally. A

closer examination reveals that land use change is perhaps the most immediate and visible type of environmental change occurring globally.

A number of natural phenomena display the effects of climate change. Examples include modified growing season phenologies, melting alpine glaciers, sea ice, permafrost, and increasing frequency of extreme weather events. Perhaps, one of the more dramatic examples is Shishmaref, a village on Sarichef Island in the Chukchi Sea, north of the Bering

Strait in Alaska. Rising temperatures have led to permafrost thawing that affects the very foundation of the village, which plans to relocate further to the south. This thawing renders its shoreline more vulnerable to further erosion, and the loss of protective sea ice leaves Shishmaref exposed to storm surges. 

Environmental change remains one of the most serious long-term global issues since human sustainability depends on how well our physico-ecological and socioeconomic systems function together. Earth and environmental scientists constantly seek to better understand the processes, impacts, and projections of global change that provides the input to inform appropriate policies and management strategies. A system’s approach to Earth science enables scientists to investigate and analyze complex interactions of the biophysical, geophysical, and human components germane to understanding global environmental change. The dynamics of the Earth system fosters complex spatiotemporal variations that highlight the significance of, and the need to monitor the

Earth as a unified whole. Accurate, timely, and reliable data are a precursor to analyze and study several aspects of the integrated Earth system. The Earth observing satellites have helped generate unprecedented volumes of remotely sensed data that are vital to an array of Earth science investigations. Remote sensing observations have catalyzed several aspects of Earth system science by providing panoptic views and time-series measurements of the study environment in ways nearly impossible to replicate by traditional ground-based methods.

Earth observations and measurements are a vital part of the US Global Change Research Program, which provides the basis for Earth system science. NASA’s Earth Observing System mission is a 15-year effort to collect and analyze a multi-sensor, multitemporal data stream across all elements of the Earth’s life-support systems. NASA’s EOS is a remarkably successful accomplishment in engineering

a global science enterprise dedicated to advancing our understanding of global environmental change. This volume specifically focuses on the terrestrial components of change based on the scientific knowledge derived from data produced by two EOS instruments, ASTER and MODIS, which are part of the Terra and Aqua satellite missions. This volume is divided into six sections. The first three sections provide insights into the history, philosophy, and evolution of the EOS, ASTER and MODIS instrument designs and calibration mechanisms, and the data systems components used to manage and provide the science data and derived products. The latter three sections exclusively deal with ASTER and MODIS data products and their applications, and the future of these two classes of remotely sensed observations.

ASTER and MODIS instruments serve different science and application communities, though important synergies exist between the two. The ASTER mission crystallized as a synthesis of two independent efforts in the USA and Japan. JPL’s Thermal Infrared Multispectral Scanner, an early EOS strawman instrument, was later refined and proposed as the Thermal Infrared Ground Emission Radiometer (TIGER) in 1988. Around the same time, Japan’s Ministry of International Trade and Industry (MITI) offered to provide the Intermediate Thermal Infrared Radiometer (ITIR). NASA accepted MITI’s design and called upon the TIGER team to integrate its design with that of the Japanese ITIR. This synthesis produced the ASTER instrument, a triad of sensor systems spanning from the visible to the thermal wavelengths of the electromagnetic spectrum, which produce data at

Landsat-class spatial resolutions. ASTER’s claim to fame derives from a number of its features. They include a VNIR stereo mapping capability and eleven spectral bands in the SWIR and TIR channels. The SWIR band selection helps map surface soil and mineral lithologies to target the phyllosilicate and carbonate absorption features. The TIR-derived emissivities not only facilitate estimating the silica content, but they help accurately determine the variable spectral emissivity of the land surface and its temperature. ASTER science applications include land surface change, geology, hydrology, soils, volcanology, glaciology, vegetation and ecosystems, and digital elevation models. Unfortunately, the SWIR sensor suffered a setback due to its anomalously high detector temperatures, which have rendered its data unusable since April 2008.

In contrast to ASTER’s Landsat-class spatial resolutions, limited duty cycle, and user request-based tasking and scheduling, the MODIS instruments were designed to generate daily, continuous, global, multitemporal data that help build a holistic record of our Earth’s parameters, including land, oceans, and the atmosphere. The MODIS instrument’s design heritage includes the Advanced Very High Resolution Radiometer, Coastal Zone Color Scanner, High Resolution Infrared Radiation Sounder, and Landsat Thematic Mapper. The MODIS-related chapters in this volume deal exclusively with the land component. MODIS land science primarily revolves around its three product families: (1) Radiation budget variables: land surface reflectance is the most fundamental processed surface parameter for the solar reflective channels, which is used to generate the higher-level products including surface albedo; (2) Ecosystem variables: 

MODIS-derived data enable direct global observations of ecosystem phenology and photosynthesis, which help characterize and monitor terrestrial primary productivity essential for climate models; and (3) Land cover characteristics: human-induced land use and land cover change remain clear transformers of the land surface. MODIS products examine different aspects of these changes through its global land cover, phenology, thermal anomalies and fires, and vegetation continuous fields products. 

The MODIS land science mission is a clear demonstration of how satellite observations of Earth’s biophysical dynamics, processes, and parameters contribute to a better understanding of our global ecosystem and their response to, and effects on global environmental change.The first half of this volume contains chapters that articulate the data systems components embodied by the EOS Data and Information System (EOSDIS) to support both the ASTER and MODIS missions.
The EOSDIS evolved considerably from its initial design. The EOS science enterprise owes its success to a large extent on the present structural components of the EOSDIS architecture. Just as the larger science community relies on advances in algorithms, analyses, and new knowledge itself, EOSDIS relies on leveraging advances in software and hardware engineering and information technologies to provide an advanced data management system infrastructure. Conceived just as the software industry was emerging from its crisis in the mid-1980s, 

EOSDIS provides a number of services for the larger EOS. They range from data acquisition, spacecraft command, control, and telemetry processing to data production, archival, and dissemination. EOSDIS remains one of the single largest distributed Earth science data and information management systems in the world, designed to support the larger EOS science mission to observe, analyze, and interpret global environmental change. Technology remains an integral part of virtually every aspect of the EOS mission playing key roles from building and launching the instruments, performing satellite command, control, and telemetry, and all data management aspects related to EOSDIS. Future missions stand to benefit further through advances in information technology. The Internet and the Web remain primary catalysts for information and data exchange, which facilitates data brokers and end-users to benefit from the larger science missions. Service oriented architecture holds much promise to provide packaged functionality as interoperable Web services across different organizations.The end of 2009 marks the 10th anniversary of the Terra platform’s launch. 

The ASTER- and MODIS-derived land data and product suites have contributed to several biophysical, geological, and geophysical applications. These data also play a critical role as intellectual bridges connecting the pre-EOS era data and knowledge with future missions still taking shape. The next decade and beyond will witness the launch of a number of missions crucial to furthering terrestrial science.They include the Landsat Data Continuity Mission, the National Polar-orbiting Operational Environmental Satellite System mission and its preparatory precursor, and the NASA Decadal Survey missions, namely the Hyperspectral Infrared Imager, and the Deformation Ecosystem Structure and Dynamics of Ice missions.The overall lessons learned from the EOS ASTER and MODIS missions are critical for these future missions. Emerging frameworks for coordination like the Global Earth Observing System of Systems provide additional credence and context for these future missions as well.

As global environmental change in the Anthropocene age becomes more ubiquitous, the papers presented in this volume demonstrate the value of EOS for studying the Earth’s surface. The future may reflect upon the EOS era as the golden age of land remote sensing, which engendered multiple new instruments specifically designed to meet Earth science data needs. This era also saw the development of distributed data systems to generate unprecedented volumes of science quality data

and an entirely new array of validated geophysical products at multiple resolutions to address major land science questions. EOS demonstrates the rich synergistic confluence of science, engineering, and technology, which can help us decipher how our terrestrial systems both contribute and respond to global environmental change.

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Land Remote Sensing and Global Environmental Change