Tag Archives: ArcGIS Imagery Book

Imagery has so many uses

Show me my home! The human era of GIS begins          

Little more than a decade ago, seemingly the whole world snapped awake to the power of imagery of the earth from above. We began by exploring a continuous, multiscale image map of the world provided online by Google and other mapping companies. A combination of satellite and aerial photography, these pictures of Earth helped us to experience the power of imagery, and people everywhere began to experience some of what GIS practitioners already knew. We immediately zoomed in on our neighborhoods and saw locational contexts for where we reside in the world. This emerging capability allowed us to see our local communities and neighborhoods through a marvelous new microscope. Eventually, naturally, we focused beyond that first local exploration to see anywhere in the world. What resulted was a whole new way to experience and think about the world.

Initially, we zoomed in on our homes and explored our neighborhoods through this new lens. This experience transformed how people everywhere began to more fully understand their place in the world. We immediately visited other places that we knew about. Today, we continue by traveling to faraway places we want to visit. Aerial photos provide a new context from the sky and have forever changed our human perspective. This map tour visits selected areas in several communities where ultra-high-resolution imagery is available.

These simple pictures captured people’s imagination, providing whole new perspectives, and inspired new possibilities. Today, virtually anyone with Internet access can zero in on their own neighborhood to see their day-to-day world in entirely new ways. In addition, people everywhere truly appreciate the power of combining all kinds of map layers with imagery for a richer, more significant understanding.

Almost overnight, everyone with access to a computer became a GIS user.

A range of applications

By now, it’s apparent that imagery enables whole new perspectives and insights into your world and the issues you want to address. Imagery also has numerous advantages and capabilities.

Almost daily access to new information

Image collection is rapid and increasing. And access to imagery is increasingly becoming more responsive. Many satellites and sensors are already deployed with more coming all the time, collecting new data, adding to a continuous collection effort—a time series of observations about our planet. These image collections are enabling us to map, measure, and monitor virtually everything on or near the earth’s surface. All of us can quite rapidly gather much of the data that we need for our work. Imagery has become our primary method for exploration when we “travel” to other planets and beyond. We send probes into space and receive returns primarily in the form of imagery that provides a continuous time series of information observations. And it enables us to derive new information in many interesting ways.

Looking back in time

The use of aerial imagery is still relatively young. While imagery only began to be used in the twentieth century, it is easy to compare observations for existing points in time that reside in our imagery collections. In addition, we can overlay imagery with historical maps, enabling us to compare the past with the present.

Imagery data collections are becoming richer every day

Imagery is creating an explosion of discovery. Many imagery initiatives are repetitive and growing, expanding and adding to image databases for our areas of interest. ArcGIS is scaling out, enabling the management of increasingly large, dynamically growing earth observations. This points to the immediacy of imagery and its capacity for easy integration, enabling all kinds of new applications and opportunities for use—things like before-and-after views for disaster response, rapid exploitation of newly collected imagery, image interpretation and classification, and the ability to derive intelligence. Over time, many of these techniques will grow in interesting new ways, enabling deeper learning about our communities, the problems and issues we face, and how we can use GIS to address these.

Imagery enables powerful analytic capabilities

Imagery and its general raster format enable rich analysis using ArcGIS. And, in turn, these enable more meaningful insights and perspectives about the problems we want to address.

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This post is excerpted from The ArcGIS Imagery Book: New View, New Vision. Imagery is suddenly a big deal, and those who are adept at finding it, analyzing it, and understanding what it actually means are going to be in demand in the years ahead. The purpose of this book is to help everyone from GIS professionals to app developers, and web designers to virtually anyone how to become smarter, more skillful, and more powerful appliers of image data. The book is available through Amazon.com and other booksellers, and is also available at http://www.TheArcGISImageryBook.com for free.

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Seeing Beyond the Visible

The electromagnetic spectrum

In the early history of powered aircraft, aerial photographs—pictures of the earth from above—began to be found useful for military and scientific applications. Quite quickly, imaging professionals and scientists realized that it was possible to detect beyond what is visible to the unassisted human eye. Deeper and richer information could be revealed by detecting waveforms from beyond the rainbow of visible light, into the invisible. As it turns out, these hard-to-detect realms of the spectrum offered some of the most meaningful insights. Hidden in these signals were previously unknown facts about Earth that have enabled us to understand our world far more effectively than had been possible.

Many of these sensors measure bands across the electromagnetic spectrum and are known as Electro-Optic (EO) sensors. They record energy wavelengths from the sun that are reflected off or emitted from everything on the ground. These electromagnetic signals include visible light, infrared, and other frequency bands across the reflected energy spectrum.

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The Nature of Remote Sensing

Information gathered from a distance

Remote sensing—the acquisition of information from a distance—has had a profound impact on human affairs in modern history. This image of British Beach (the WWII code name for one landing spot of the June 1944 Normandy invasion) taken from a specially equipped US Army F5, reveals rifle troops on the beach coming in from various large and small landing craft. Seven decades later—even as its application has expanded to unimaginable reaches—remote sensing remains the most significant of reconnaissance and earth observation technologies.

Many platforms, many applications

Modern imagery is captured from a broad range of altitudes starting from ground level to over 22,000 miles above earth. The images that come from each altitude offer distinct advantages for each application. While not meant to be an exhaustive inventory, let’s take a look at some of the most commonly used sensor altitudes.

Geosynchronous—22,236 miles

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The View From Above: The Power of Remote Sensing

Humans have always sought the high vantage point above the landscape. Throughout history, whether from a treetop or a mountain peak or a rocky cliff, the view from above allowed our ancestors to answer important questions: Where is there water? Where is the best hunting ground? Where are my enemies? Aerial photography was first practiced by balloonist Gaspard-Félix Tournachon in 1858 over Paris. With the advent of both photography and practical air flight in the early twentieth century, the advantages of having the high ground led to a quantum shift forward and the field of remote sensing was born.

The technology came of age rapidly during World War I as a superior new military capability. From 1914 to 1918, aerial reconnaissance evolved from basically nothing to a rigorous, complex science. Many of the remote sensing procedures, methods, and terminology still in use today had their origins in this period. Throughout World War II the science and accuracy of remote sensing increased.

The use of aerial photography rapidly matured during the First World War, as aircraft used for reconnaissance purposes were outfitted with cameras to record enemy movements and defenses. At the start of the conflict, the usefulness of aerial photography was not fully appreciated, with reconnaissance being accomplished by cartographers sketching out maps from the air.

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Using Satellite Archaeology to Protect Ancient Sites

There may be hundreds of thousands, if not millions, of undiscovered ancient sites across the globe, and Sarah Parcak wants to locate them. As a satellite archaeologist, she analyzes infrared imagery collected from far above the earth’s surface and identify subtle changes that signal a man-made presence hidden from view. Doing so, she and her colleagues aim to make invisible history visible once again—and to offer a new understanding of the past.

Sarah Parcak is a leading expert on space archaeology. She is from Bangor, Maine, and is a National Geographic Society Archaeology Fellow, Fellow of the Society of Antiquaries, and a 2013 TED Senior Fellow. Sarah serves as the founding director of the Laboratory for Global Observation at the University of Alabama at Birmingham, where she is a professor.

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What are mosaic datasets?

Collections of images

The recommended data structure within ArcGIS to manage and process imagery is the mosaic dataset. A mosaic structure enables significant big data capabilities for large, even massive, image collections. Each mosaic is composed of a number of related raster datasets, enabling you to keep your original individual image files on disk and to access them as part of a larger, integrated single collection. Mosaics are used to create a continuous image surface across large areas. For example, among other scenarios, you can use mosaics to handle coverage of very high-resolution image files for an entire continent. Or you can manage an entire historical map series for a nation for every year and every map scale. You can even manage huge multidimensional collections of time series information for earth observations and climate forecast modeling (often referred to as 4D). Creating mosaics is straightforward. You can point to a series of source georeferenced image files and automatically assemble a mosaic in minutes where each image acts as a tile within the collection.

Managing extremely large collections

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A new level of cool

The Arctic Ocean Basemap

Over the past few years, Esri’s Ocean Basemap team has noted the world’s scientific attention shifting north. The receding sea ice and increased vessel traffic within the Arctic Ocean is coming front and center in discussions within the marine and maritime communities. To support the communities, Esri’s Ocean Basemap team developed the Arctic Ocean Basemap.

The Arctic Ocean Basemap (left) uses a special projection that is optimized for study of this region covering the northern latitudes of the globe from 90 to 50 degrees north. This (and the companion imagery version) is designed to be used as a basemap for overlaying other data for the Arctic region, such as this example (right) featuring sea ice extent and oil exploration data on top of the polar basemap.

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Imagery deepens understanding

GIS technology is both intuitive and cognitive. It combines powerful visualization and mapping with strong analytic and modeling tools. Remotely sensed earth observation—generally referred to in GIS circles simply as imagery—is the definitive visual reference at the heart of GIS. It provides the key—the geographic Rosetta stone that unlocks the mysteries of how the planet operates and brings it to life. When we see photos of Earth taken from above, we understand immediately what GIS is all about.

The story of imagery as an earth observation tool begins with photography, and in the early part of the twentieth century, photography underwent extraordinary changes and social adoption. Photos not only offered humanity a new, accessible kind of visual representation—they also offered a change in perspective. The use of color photography grew. Motion pictures and television evolved into what we know today. And humans took to the sky flying in airplanes, which, for the first time, enabled us to take pictures of the earth from above. It was a time of transformation in mapping and observation, providing an entirely new way of seeing the world.

World War II: Reconnaissance and intelligence gathering

During World War II, major advances in the use of imagery for intelligence were developed. The Allied Forces began to use offset photographs of the same area of interest, combining them to generate stereo photo pairs for enhancing their intelligence gathering activities. In one of many intelligence exercises called Operation Crossbow, pilots flying in planes—modified so heavily for photo gathering that there was no room for weapons—captured thousands of photographs over enemy-held territory. These resulting collections required interpretation and analysis of hundreds of thousands of stereo-photographic pairs by intelligence analysts.

Stereoscopic imagery was instrumental in identifying the facilities of Nazi rocket programs. This photo shows stereo glasses used for viewing offset photo pairs.

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The ArcGIS Imagery Book: A Geographic Rosetta Stone

Imagery is Visible Intelligence

By: Dave Grenley

The next generation of imagery intelligence comes alive in The ArcGIS Imagery Book: New View. New Vision., published by Esri Press. It is now available in print, interactive PDF, and interactive companion website.

The new book provides readers with a wealth of gorgeous, inspiring images and links to powerful web apps and maps that weave interesting stories about our planet and the issues we face. Readers will also gain foundational knowledge about how imagery and remote sensing is used for geographic information system (GIS) technology.

The ArcGIS Imagery Book offers a look back at the fascinating history and rapid evolution of earth observation technology. Readers will learn about modern earth imaging technologies and how imagery data can be used in GIS—for real world applications such as asset management, precision agriculture, emergency response, real estate geolocation, urban planning, natural disaster assessment, and climate studies.

Additionally, readers will gain hands-on experience working with powerful imagery and remote-sensing data through the book’s companion lesson plan from the Learn ArcGIS organization.

The book’s editors, Clint Brown, Esri director of software products, and Christian Harder, Esri senior editor and writer, said they hope the book will help turn readers into “GIS and imagery aces.”

The ArcGIS Imagery Book is the second in a series of publications from Esri (following The ArcGIS Book) that provides an online interactive learning experience for readers to take advantage of, at their own pace. “It comes with intelligent information items: maps, web scenes, analytic models, story maps—just amazing rich content,” said Brown. “We get into real-world problem solving and real-world applications.”

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What is orthorectified imagery?

Using elevation to enable accurate image georeferencing

Imagery has an amazing amount of information, but raw aerial or satellite imagery cannot be used in a GIS until it has been processed such that all pixels are in an accurate (x,y) position on the ground. Photogrammetry is a discipline, developed over many decades, for processing imagery to generate accurately georeferenced images, referred to as orthorectified images (or sometimes simply orthoimages). Orthorectified images have been processed to apply corrections for optical distortions from the sensor system, and apparent changes in the position of ground objects caused by the perspective of the sensor view angle and ground terrain.

A view captured from an oblique angle (for example, 25°, left) must be corrected for relief displacement caused by terrain to generate the orthorectified view (looking straight down, right). Orthoimagery is produced by calculating the nadir view for every pixel.

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