The idea that eventually led to Geomorphology from Space: A Global Overview of Regional Landforms can be traced back to the moment that its predecessor, Mission to Earth: Landsat Views the Earth, was conceived. The senior editor of both books was privileged to be the scientist asked to display the first roll of film on the day the initial images were received from Landsat-1 (then known as ERTS-1 1 ) in late July of 1972. As dozens of managers, scientists, and technicians crowded around a viewing console at NASA's Goddard Space Flight Center (GSFC), the scenes along an orbit across the upper Midwest were quickly scanned until one spectacular cloudfree image captured everyone's attention. This scene was centered on the western end of the Ouachita Mountains in eastern Oklahoma. There, the spectacular landforms carved from open plunging folds and thrust faults in this Appalachian Mountains offshoot stood out sharply against a background of surrounding farmlands and woods (see Plate T-14, this book). After viewing still more superb scenes from the western United States, the present editor was heard to announce to all that, if Landsat images from other parts of the world were like these from the United States, then a picture book documenting these fascinating glimpses of the Earth's surface should be prepared for both the scientific community and the general public. By 1977, Mission to Earth had become a reality. During the same period, a companion volume, ERTS-1: A New Window on Our Planet,2 was published. The two books clearly demonstrated the value of repetitive coverage from spaceborne sensors in conducting regional and global studies of our planet as a new means for monitoring and understanding the natural and cultural (manmade) processes that have shaped, and will continue to shape, the Earth's dynamic surface.

Anyone examining the color Plates in both books would soon realize that many images are replete with geologic themes. In fact, two aspects of geology, both geomorphic in expression, dominate most such scenes: structural patterns associated with tectonic actions and water-, wave-, wind-, and ice-generated landforms. Although this is also true for many aerial photographs, the main advantage of space imagery over the larger scale (and more detailed) aerial views stems from the synoptic or broad-area coverage possible from orbiting sensors. This means that entire mountain systems, large stretches of rivers and their drainage basins, a whole coastal or inland delta, swarms of sand dunes, clusters of volcanoes, and groups of mountain glaciers as well as polar ice caps and ice sheets can be recorded in single images under uniform solar illumination that is nearly impossible in aerial photomosaics. From such synoptic views, the geomorphic character of a complex diverse terrain is easily studied from a regional perspective. This perspective allows one to analyze the impact of multiple geomorphic processes operating over wide areas. Above all, the regional outlook characteristic of space imagery permits effective planimetric portrayal on a global scale of most of the larger landforms that make up the Earth's land surface. With Landsat, for the first time a capability has existed for mapping major geomorphic units over vast areas. One efficient way to accomplish this mapping is to construct a photobase by joining reprocessed Landsat images into mosaics (as, for example, the famed Soil Conservation Service black and white mosaic of the United States, Alaska, and Hawaii).

In the 14 years since the first Landsat launch, more than 150 NASA-funded investigations and many other federal and private studies, both in the United States and worldwide, have defined and evaluated many plausible uses of space remote sensing data (mainly images) for geology. In addition, comparable studies have used data from photography obtained during Gemini, Apollo, Skylab, and Space Transportation System (Shuttle Orbiter) missions and from imaging sensors on Skylab, Seasat, Heat Capacity Mapping Mission (HCMM), and the Shuttle. The principal applications include: (1) reconnaissance-level geologic mapping and editing, (2) rock-type discrimination, (3) stratigraphic facies recognition, (4) detection of hydrothermal alteration zones sometimes associated with mineralization, (5) mapping of fractures and lineaments, (6) regional tectonic analysis, (7) search for surficial indications of subsurface structure, (8) geologic hazards assessment, (9) environmental geology, (10) movements of surging glaciers and sand seas, and (11) geomorphic analysis of land forms.

Surprisingly, the list of studies directly concerned with geomorphic topics is comparatively small. These studies have dealt with glaciation and glacial deposits, volcanism and volcanoes, deltas and coastlines, desertification and sand deposits, and stream systems and fluvial landforms. Most studies were observational and descriptive rather than analytical. A common use of geomorphically rich space images has been to illustrate regional features in introductory geology textbooks. Few investigations have attempted to produce maps of the landforms that are recognizable from space. Indeed, it is ironic to realize that geologic maps of one half to nearly all of four planetary bodies (Venus, Mercury, Moon, and Mars) and parts of 21 moons imaged by camera, radar, and scanners on various planetary probes and spacecraft have now been completed. Yet, only a small fraction of the Earth's surface is comparably mapped from similar photobases produced from Landsat and other sensor data, despite the current availability of worldwide coverage. Small-scale mapping of any planetary surface relies primarily on geomorphological and stratigraphic principles (e.g., on Mars the maps are combinations of landforms and surface units whose relative ages are determined largely from rules of superposition).

The preceding serves as background for the "why" of this book. The purpose of the book is threefold: first, to serve as a stimulant in rekindling interest in descriptive geomorphology and landforms analysis at the regional scale; second, to introduce the community of geologists, geographers, and others who analyze the Earth's surficial forms to the practical value of space-acquired remotely sensed data in carrying out their research and applications; and third, to foster more scientific collaboration between geomorphologists who are studying the Earth's landforms and astrogeologists who analyze landforms on other planets and moons in the solar system, thereby strengthening the growing field of comparative planetology. Additional rationale for the book is developed in the introductory chapter, written to establish the background and status today of the regional approach to geomorphology.

After a decade in which support of active programs connecting research in geomorphology to Earth observations from space remained at a low priority, a new expression of interest from geoscience managers within NASA led to a favorable reception of a proposal to underwrite preparation and publication of Geomorphology from Space. This firm commitment to a revitalized geomorphology program promises to redirect attention to the potential role of space data in supporting both theoretical and applied geomorphology through the combination of pictorial examples of regional scale landforms with astute descriptions of their scientific significance and, when feasible, with examples of their efficacy as analytical devices.