projections for coastal States. Most zones within a single State are based on the same projection, but Alaska, Florida, and New York have zones on both projections. Alaska has 10 zones: zone 1 in southeast Alaska is on an oblique Mercator projection; zone 2 through 9 are on the transverse Mercator projection; and zone 10 in the Aleutian Islands is on the Lambert projection.

Universal Transverse Mercator Grid

The Universal Transverse Mercator (UTM) grid is designed for world use between 84° N. and 80° S. The area bounded by these latitudes is divided into 60 zones running north-south, each 6° wide and bounded by meridians that are multiples of 6°. Each zone is projected on the transverse Mercator projection and has a central meridian that is an odd multiple of 3°. The zones are numbered consecutively, starting with zone 1 between 180° and 174° W. and increasing eastward to zone 60 between 174° and 180° E.

Using the intersection of a central meridian and the Equator as an origin or starting point, a location can be given by stating its linear distance north or south of the Equator and east or west of the central meridian of the zone. However, this would require the use of north or south and east or west or the use of plus and minus values to identify the location relative to the origin. This inconvenience has been diminished by assigning to the origin numerical values that keep the coordinate values positive for all points within a zone.

The value of 500,000 m east is assigned to the central meridian to avoid negative numbers at the

observe conditions on the surface of the Earth, in the atmosphere, and on other planets. Remote sensing is used principally to detect and record energy (emitted or reflected radiation) in a selected portion of the electromagnetic spectrum (fig. 9).

Remote sensors operating in the electromagnetic spectrum are either passive or active. Passive systems record the natural level of radiation; active systems utilize artificial energy sources such as radar pulses and laser beams.

Photographic cameras operate in the visible, infrared, and ultraviolet portion of the spectrum. Black-and-white panchromatic film is the most economical and most commonly used. Color film increases the value of photography for the identification of features such as rocks and soils, vegetation, surface water conditions, and building materials in houses, roads, and other structures. Infrared films respond to wavelengths up to about 900 nm. Exposure is made through a yellow filter that blocks the passage of blue light and admits green, red, and infrared light. One kind of infrared film produces a black-and-white image. A second type, color infrared, records in colors that are not true to nature but are designed to make it easier to distinguish conditions of vegetation. Originally developed for camouflage detection, color infrared film records infrared energy representative of live vegetation, enhancing the contrast between it and dead vegetation. Leaves of healthy plants generally have high reflectance in the infrared; the amount of reflectance varies with leaf structure and geometry and with plant vitality and chlorophyll level. Thus, variations of red on color infrared

as false eastings and increase numerically from west to east. For north-south values in the Northern Hemisphere the Equator is designated zero m north and northings increase numerically toward the North Pole. In the Southern Hemisphere the Equator is designated 10,000,000 m north and the northings decrease toward the South Pole. These are known as false northings. (For more information on the UTM grid see Raisz, 1962, and Robinson and Sale, 1969.)

REMOTE SENSING

Remote sensing is the science of gathering information from a distance. In practice, remote sensing uses cameras and other information-gathering devices carried by aircraft and spacecraft to

and the diminuation or absence of red in certain members of a single planting is likely to indicate diseased or dead plants.

Optical-mechanical scanning radiometers, or scanners, operate in the ultraviolet, visible, infrared, and microwave energy regions. Unlike cameras that record all parts of a scene simultaneously, scanners sense one spot at a time, covering the surface by sweeping their view from side to side as the aircraft proceeds. This is accomplished with a rotating or oscillating mirror. The incoming radiation is focused on a detector, which translates its intensity into a corresponding electrical signal. The signal may be used to activate a cathode-ray tube that reconstructs the scene line by line in the manner of a television set, and the resulting picture can then be photographed. Alternatively, the signal may be used to energize a glow tube that ex

poses film directly, or it may be recorded on magnetic tape for later processing.

Measuring temperatures and mapping their distributions are valuable in resource and environment studies. Infrared scanner imagery can reveal surface temperatures that indicate volcanic activity, burning in abandoned coal mines, diseased plants, animals obscured by darkness, and heated buildings. It can reveal surface temperature distributions in water which aids in discovering sources of water or oil discharge into lakes, rivers, and oceans. Temperature differences also reveal currents and show the surface boundaries between fresh and salt water in bays and estuaries. Infrared scanners are useful in mapping the distribution of soil moisture near the surface because variations of soil temperature are related to variations of moisture.

Landsat-1 and -2 each carry two sensor systems, the return beam vidicon (RBV) cameras and the multispectral scanner (MSS). Each Landsat image represents a synoptic view of 34,253 km2 (13,225 mi2) that permits recognition of some large features

not previously recognized on the ground or on lowaltitude photographs. Landsat repeats each orbit every 18 days. The repetitive coverage provides information for land use planning and makes it possible to monitor crop production, rangeland conditions, snow cover, floods, and many other dynamic phenomena. The Landsat imagery is obtained in spectral bands (RBV, three bands; MSS, four bands) from which the data may be used alone or in combination. Color infrared imagery (app. 7, fig. 1) enhances the identification of special features such as vegetation in vigorous growth, water, and certain kinds of pollution.

PHOTOGRAMMETRIC MAPPING

TECHNIQUES

Photogrammetry is the science or art of making accurate measurements by means of photography. Today maps are produced largely from aerial photographs with a minimum of fieldwork.

Modern mapping procedures rely almost ex

clusively on photogrammetry for preparation and processing of basic data. Instruments and operational phases vary among agencies and with applications, but basic procedures do not differ significantly. Costs increase rapidly when extensive fieldwork is required. Recent developments in instruments, materials, and methods have eliminated or rescheduled fieldwork, saving much time and money.

The basic operational phases are:

Project planning.

Ground control.

Aerial photography.

Aerotriangulation.
Compilation.

Field completion.

• Final drafting and review.

Reproduction.

The order of phases may be altered, or two or more may be combined. Each phase is discussed. briefly below. Consult references in the bibliography for technical details.

PROJECT PLANNING

The first step in planning a mapping project is to define the boundaries. The entire coastal zone of a State may be too large to cover in one project. As a general rule mapping projects should be kept to a managable size. Senior managers may define the area, or it may be dictated by legislation. In either case, qualified mapping personnel should assist in the decisionmaking.

Detailed technical planning can begin after mapping limits have been determined. The planning should be assigned to qualified personnel within the organization, or arrangements should be made to obtain their services from outside.

Whether a mapping project is done in-house or under contract, managers will be faced with many of the same problems. Managers without a mapping department will have the most difficult decisions. Some of the decisions will concern (1) publication scale, map size, and paper size, (2) method of aerotriangulation, (3) method and scale of compilation, (4) contour interval (if relief is to be compiled), (5) evaluation of established control, (6) photography (camera, filter, emulsion, and scale of photographs), and (7) operational schedules.

A project diagram is prepared, showing map limits and horizontal and vertical control stations. After photographs are acquired, the center of each is marked on the diagram. Specific instructions for

both field and office operations are prepared either as a part of planning or immediately before assignment of each operation.

GROUND CONTROL

Photogrammetric mapping requires adequate ground control to show map features in the correct relationship to each other and to the Earth's surface. Both horizontal and vertical control are needed, horizontal to establish correct scale, position, and orientation, and vertical to establish the level datum.

It is frequently difficult to evaluate established control because adequate and current information is lacking. However, extra effort in using established control may result in significant cost reduction and improved scheduling by reducing or avoiding fieldwork for supplemental control. In addition to providing published control data, NGS may be able to supply advance information about data being prepared for publication.

Adequate horizontal control is essential in preparing coastal maps that meet established accuracy standards. In most areas, the established network with the addition of a minimum of supplemental control will be adequate for modern techniques. The network meets all requirements in a few areas, but in others attrition of monuments from the network (from destruction or obliteration) may be serious enough to require extensive supplemental control.

To prevent excessive costs, qualified personnel should analyze and monitor requirements for horizontal control. The aerotriangulation method significantly affects the amount of required control and mapping costs.

Horizontal control points are often paneled or targeted in the field before mapping photographs are taken. Paneling consists in fastening three or four strips of cloth or plastic to the ground to form a pattern identifying the exact location of the control monument (or some other precisely surveyed nearby point that is visible from the air). The color of the marking material should provide good contrast with the ground.

The spacing of horizontal control points depends on the required accuracy and limitations of the photogrammetric method. For example, in 7.5-min topographic quadrangle mapping, horizontal control stations are established at 7.5-min spacing on the perimeter of the project. Horizontal control within the project area is established by aerotriangulation.

Similarly, vertical control is needed for correct plotting of contours. Therefore, the elevations of

selected points must be determined in the field. As a rule, more vertical stations are required than horizontal stations. Vertical control is a major expense in topographic mapping because of the amount needed. A minimum of four vertical control points, which need not be (and seldom are) monumented control stations are needed for each stereomodel. Many are image points whose positions and elevations have been determined by photogrammetric methods: the important requirement is photoidentifiability-examples are road intersections and fence corners. Therefore, one of the major field operations is establishing elevations (often by planetable and alidade).

Vertical control for routine preparation of base maps, excluding mapping of most features below. the chart datum, usually can be obtained from tidal data and from available topographic maps.

AERIAL PHOTOGRAPHY

Acquisition of aerial photographs for coastal mapping is perhaps the easiest and least expensive phase of mapping. Mapping quality, that is, clarity, accuracy, and stability sufficient for distance measurement, is the chief requisite of aerial photographs intended for aerotriangulation and basic compilation. Information such as thermal infrared data can be obtained only from instruments that do not have the necessary metric quality. Thermal information can, if needed, be added to manuscripts after proper processing despite the lack of metric quality. Optical systems of most modern mapping cameras, with appropriate filters and films, can yield photographs of the required quality provided that the exposed film and subsequent photographic products are processed properly.

Aerial photographs already available are often unsuitable for actual mapping for various reasons. For example, they may be outdated, at the wrong scale, or unsuitably spaced or oriented. Also, the photographs may have been taken with the tide at the wrong stage.

Planning for aerial photography is based on the project specifications plus the following considerations:

• Season of the year, affecting:

a. Sun angle (shadows, reflections, glare).
b. Ground cover (snow, leaves, crops, floods).
c. Local weather conditions.

Type of photography (orientation, focal length,

format, emulsion).

Direction of flights (for most efficient coverage).

Flight height:

a. Capabilities of stereoplotter; relation to stereomodel scale.

b. Contour interval; C-factor of the stereoscopic instrument system.

c. Visibility and interpretability of planimetric detail.

• Number and spacing of flight lines; width-height ratio.

Spacing of photographs along flight lines; baseheight ratio.

. Federal Aviation Administration regulations governing flight operations in Federally controlled and special-use airspace.

A flight plan is plotted on the best available map of the area, showing the centerline of each flight. Photographs are taken with modern mapping cameras (fig. 10), on panchromatic, black-and-white infrared, natural color, and color infrared films.

Panchromatic emulsions are the original and most popular emulsions because they are lowest in cost and easy to use. Disadvantages result from the rendition of all images in shades of gray. Fieldwork is needed to resolve discrepancies.

Natural color aerial film was not readily available until the 1960's. Natural color emulsions record images of objects in fairly natural hues, tints, and tones insofar as these qualities are not altered by atmospheric filtering. Reliability and speed of photointerpretation essential to photogrammetric mapping can be greatly improved by using color emulsions. However, at higher flight altitudes, which vary with location, color contrast is reduced to a monotone tint because of atmospheric effects.

Black-and-white infrared film has a special panchromatic emulsion with response into the near infrared. The film is normally exposed through a filter that blocks visible light. Spectral response is thus rather narrow, about 740-900 nm in the near infrared region. The film is valuable in mapping because it records the land-water relationship accurately and sharply. It is not sensitive to long infrared waves and therefore does not record thermal or heat energy.

Color infrared film (sometimes called "false color") is a relative newcomer to aerial photography. The three sensitized layers of the emulsion respond to green, red, and near-infrared wavelengths. The film must be exposed through a filter such as the Wratten 12 to stop the blue light to which all three layers are sensitive. When the emulsion is properly exposed and processed, infrared-reflective objects, such as healthy trees, appear bright red, hence the use of the term "false color." The sharp contrasts between various types of features make color infrared film of special value in coastal mapping.

Photographs are taken within a specified time, with weather largely determining the actual flight times. The exposed film is developed preferably in a modern automatic processor (fig. 11), which permits exact quality control. After processing, proof prints are made and stapled together in relative position, and the composite is examined to determine whether coverage is complete and has the required overlap. If the negatives are acceptable, contact prints are made and each is marked with the date of photography, frame number, and project code. An index photomosaic is prepared to aid subsequent operations. Sometimes duplicate negatives are made to preserve the originals as archival material, and transparent positives are made for checking and editing.

AEROTRIANGULATION

Aerotriangulation photogrammetrically extends established control to meet the requirements of a

mapping project. Either horizontal or horizontal and vertical control can be extended, thereby reducing or eliminating costly field surveys.

Various aerotriangulation methods have been devised since the advent of photogrammetry. Development has been successfully directed toward increased accuracy and economy (mainly by reduction of field control) and capability to extend vertical control that meets accuracy standards for mapping and charting. Also, general efficiency increased as stereoscopic plotting instruments and related systems were developed and improved. The aerotriangulation methods in use today can be broadly classed as graphic, analog, and analytical. In actual practice, methods are combined and modified as needed to produce results conforming to accuracy requirements and available resources.

Graphical aerotriangulation, such as radial line plotting and using various types of templets, is seldom used now except in emergencies because of inefficiency and relatively poor accuracy. A hybrid type, stereotemplets, can be used effectively because the unit of measurement is a stereomodel rather than the single photograph, so that errors due to the perspective nature of photographs are virtually eliminated before adjustment in the templet laydown. Another advantage of stereotemplets is the use of simple, relatively inexpensive plotting instruments to prepare the templets (fig. 12). However, none of the graphical methods can be used to extend vertical control.

Analog aerotriangulation requires use of some form of stereoplotting instrument. The simplest form, now obsolete, is called long-bar bridging because as many as 20 projectors are successively oriented to stimulate the flight strip in miniature. Adjustment of closure errors along the strip and between strips is by graphical or other approximation methods. A similar procedure can be used with a single large and expensive stereoplotter, such as the Wild Autograph and Zeiss Stereoplanigraph plotters. In these so-called bridging instruments, the left and right projectors can be interchanged by optical switches. The principle is the same as with long-bar bridging, but the photographs are placed alternately left and right in the projectors of the instrument as aerotriangulation proceeds along the strip.

The results of analog aerotriangulation can be adjusted by several methods, including mathematical computation by automatic data processing, which effectively produces another hybrid system, semianalytical aerotriangulation. In this context, proce