in coastal regions and in small islands
Coastal management sourcebooks 3
How to Use this Handbook
The Remote Sensing Handbook for Tropical Coastal Management is aimed primarily at practitioners, that is those in government, non-governmental organisations (NGOs), universities, research institutes and consulting who are responsible for or directly involved in managing the coastal resources of tropical nations to ensure sustainable and wise use. It is also a unique compendium of information from diverse sources which will be invaluable to undergraduate and graduate students and research workers studying remote sensing in general and its application to coastal management or marine resource conservation in particular. Remote sensing is a rapidly developing subject and, although every effort has been made to ensure that information is accurate at the time of going to press, readers may wish to check out recent technological advances.
Linked to the Handbook is a computer-based remote sensing distance-learning module on Applications of Satellite and Airborne Image Data to Coastal Management produced for UNESCO which is available on CD-ROM or over the World Wide Web. This consists of image processing software (Bilko for Windows v. 2.0), digital images and training materials which teach practitioners how to carry out a range of key coastal management applications.
The Handbook is not intended to be read from cover to cover but to be dipped into and treated as a reference work. It outlines the ways in which remote sensing instruments carried by satellites and aircraft can practically assist the achievement of coastal management objectives with particular attention to the costs involved and the accuracy of outputs such as habitat maps. Cost and accuracy are two factors crucial to practitioners but factors which are all too often neglected by enthusiastic researchers intent on exploring the theoretical potential (i.e. what could be done given levels of resourcing, technical support and time seldom available to practitioners) of the new and exciting remote sensing technologies continually being developed.
With regard to accuracy, the research worker may be primarily interested in establishing a relationship between remotely sensed image data and, for example, a habitat type or fishery resource. However, such a worker will be less concerned as to whether the strength of the relationship and consequent accuracy of habitat/resource maps are sufficient for decision making, or with the likely economic consequences of decisions on resource management or habitat conservation. With regard to costs, a knowledge of the likely costs of inputs (images, processing, field survey) and the accuracies of outputs achievable for given levels of inputs is essential to practitioners in deciding whether a remote sensing approach is appropriate (i.e. will it accomplish objectives within the available budget), and, if it is, which technologies are most cost-effective. Given the importance of these factors to practitioners, they are emphasised throughout the Handbook.
Technical chapters present information at three levels to cater for readers with different levels of technical expertise and differing needs. At the start of each chapter is a lay-man’s introduction to the techniques or processes being covered. This provides a concise back ground to the topic then gives an intuitive discussion of the concepts, objectives and practical importance of the techniques in non-technical language. These chapter introductions are likely to be all that a decision make r, project manager or funding agency personnel might need to gain a grasp of the key issues. For those with greater technical involvement, they provide a clear overview of the topic and indications of further sections it may be advantageous or necessary to study.
At the next level, the technical reader is guided in a practical step-by-step fashion through the techniques or processes under discussion. Flow diagrams are used extensively to allow the practitioner a clear view of the goals and the often complex route to achieving them. Also practical hints based on our experience are scattered through the text (flagged with the symbol ). So as not to interfere with the process of leading the practitioner through the techniques or processes, the mathematical and theoretical background is kept to a bare minimum in the main text. However, this background information may be included in boxes so those readers wishing to explore the essential mathematical foundation and theory behind techniques can do so. For those wishing to delve even deeper into techniques, each chapter has its own bibliography. Where appropriate, chapters also examine the sensitivity of outputs to increased sophistication of image processing and the costs and effort required, so that practitioners can assess the importance of techniques in the context of their project objectives.
Layout of the Handbook
A synopsis of the Handbook is given in an initial section entitled Guidelines for Busy Decision Makers which provides readers with a one page Executive Summary and a nine page overview of key findings.
The main Handbook is divided into six parts, each comprising a number of chapters. Part 1 forms an introduction to remote sensing for coastal managers. Following a general introduction to the remote sensing of coastal environments in Chapter 1, the precise objectives of coastal managers in using remote sensing are explored in Chapter 2. Objectives of remote sensing campaigns are quite often poorly defined (with a ‘we used the technology because it was there’ type of approach) and we suspect that many past remote sensing studies of tropical coasts would either not have been undertaken or would have been radically redesigned if objectives (and the inputs required to meet them) had been clearly defined. A major aim of the Handbook is that Chapter 2 and later chapters assist users in clear and achievable objective setting to avoid this problem. In Chapter 3 the plethora of sensors on satellites and aircraft which are available to assist in meeting management related objectives are reviewed and the key specifications of the sensors and the platforms carrying them are discussed. Constraints on sensor operation such as cloud cover and suspended sediments in coastal waters, and the effects of these constraints in practice, are outlined.
Chapter 4 deals with the crucial process of building the links between the remotely sensed image and the objects of interest on the Earth's surface with a practical guide to the planning of field surveys on tropical coasts and the assessment of the accuracy of outputs such as habitat maps.
In summary, Part 1 introduces the reader to the coastal management objectives achievable using remote sensing, the remote sensing technologies available to meet these objectives, and the need for concomitant field survey.
Part 2 of the Handbook covers the acquisition, correction and calibration of remotely sensed data. Firstly, the processes involved in acquiring satellite imagery, digital airborne imagery and aerial photographs of the type routinely used for coastal management applications are out-lined in Chapter 5. Digital imagery is seldom directly useable for coastal management applications in the form in which it is supplied; the succeeding three chapters describe how to make it useable. The techniques for correcting the supplied image data are described in Chapters 6–8. These techniques seek to correct: i) spatial distortions of the image (Chapter 6), ii) scattering of radiation and other effects of the atmosphere lying between the sensor and the Earth’s surface (Chapter 7), and for under-water features, iii) the confounding effects of the depth of seawater on the signal recorded from the seabed (Chapter 8). Without these corrections, outputs are not likely to contribute effectively to management objectives. By giving clear guidance as to how to carry out atmospheric and water column correction we hope that these will be more routinely carried out by practitioners and the quality of management information thereby improved.
In summary, Part 2 takes the reader through how to obtain remotely sensed image data then prepare those data so that they are optimised for achieving coastal management objectives.
Part 3 is perhaps the core of the Handbook and describes how the corrected image data can be used for the classification and mapping of coastal habitats. Chapter 9 looks at four approaches to defining and classifying habitats on the ground and their advantages and disadvantages in terms of different project objectives. Chapter 10 then describes how to classify images and match image classes with field survey data to produce habitat maps of known accuracy. The three succeeding chapters focus on three major types of coastal habitats – coral reefs and macro-algal assemblages, seagrass beds, and mangroves – and explore the particular problems and practical solutions of mapping these. In each chapter, the critical question of the accuracy of outputs achievable and the type of field survey required is explored in some detail.
In summary, Part 3 describes how remote sensing is used routinely to support coastal management initiatives and what can be readily accomplished in the way of mapping coastal habitats.
Part 4 describes how image data can be used for the mapping of water quality and bathymetry. Chapter 14 reviews the ways in which remote sensing can be used to monitor coastal water quality, particularly poor water quality resulting from pollution. Uses and limitations of remote sensing for monitoring sediment loadings, oil pollution, sewage discharges, toxic algal blooms, eutrophication, industrial wastes and thermal discharges are reviewed. Chapter 15 describes how the bathymetry of shallow water areas (<25 m deep) can be crudely mapped using passive optical imagery in areas where the water is relatively clear. Alternative approaches to mapping bathymetry using LIDAR and acoustic technologies are outlined briefly.
In summary, Part 4 reviews how remote sensing is used for coastal management applications other than habitat mapping.
Part 5 focuses on the next step in data analysis, which is to move beyond the mapping and classification of habitats to some sort of quantitative measurement of ecological parameters of the ecosystems supporting coastal production (Chapters 16 and 17) and assessment of key marine resources (e.g. fish, seaweeds, conch and Trochus) associated with particular habitats or oceanographic features (Chapter 18). Such studies involve the use of detailed field survey data to construct empirical models which establish relationships between image attributes and ecological parameters such as seagrass standing crop, mangrove canopy structure (e.g. leaf area index or percentage canopy closure), or the abundance of a resource. This type of assessment is relatively novel and requires the deployment of considerable technical and human resources in field survey. It does, however, provide out-puts directly relevant to coastal management and is an area where remote sensing appears to offer great potential to resource managers. Whether this potential is likely to be achievable is discussed in some detail.
In summary, Part 5 takes the practitioner beyond the routine uses to applications where the greatest potential may exist to support management.
Part 6 consists of a single chapter which reviews the crucial question of the cost-effectiveness of remote sensing technologies in helping coastal managers meet resource management objectives. This is divided into two sections. The first of these briefly explores the objectives and yardsticks which can be used to assess ‘cost-effectiveness’ and how in the long term one might expect remote sensing campaign outputs to contribute to sustainable economic development of coastal areas (i.e. what precisely are the benefits). The second section is much more pragmatic and summarises the relative cost-effectiveness of a range of airborne and satellite sensors used to map habitats and assess resources in the Turks and Caicos Islands at meeting each of a number of objectives.
The Handbook ends with a brief look at the future prospects for remote sensing in the context of coastal management. Considerable useful reference information is given in a series of appendices.
Remote sensing technologies are evolving rapidly but we hope that this handbook provides a concise, informative and easily used companion for those involved in coastal management so that they can both use the existing technologies to full advantage and evaluate new ones as they become available.
Associated training module
A computer-based remote sensing distance-learning module on Applications of Satellite and Airborne Image Data to Coastal Management has been written for the UNESCO Coastal Regions and Small Islands (CSI) unit to link with the Handbook. It consists of eight lessons which relate to topics cove red in Handbook chapters as follows:
Visual interpretation of images with the help of colour composites: getting to know the study area (relates to Chapters 4 and 10).
The importance of acquiring images of the appropriate scale and spatial resolution for your objectives (relates to Chapters 11–13).
Radiometric correction of satellite images: when and why radiometric correction is necessary (relates to Chapter 7).
Crude bathymetric mapping using Landsat TM satellite imagery (relates to Chapter 15).
Compensating for variable water depth to improve mapping of underwater habitats: why it is necessary (relates to Chapter 8).
Mapping the major inshore marine habitats of the Caicos Bank by multispectral classification using Landsat TM (relates to Chapters 9–11).
Predicting seagrass standing crop from SPOT XS satellite imagery (relates to Chapters 12 and 16).
Assessing mangrove leaf-area index (LAI) using CASI airborne imagery (relates to Chapters 13 and 17).
The image processing software (Bilko for Windows v. 2.0), digital images and training materials are available on CD-ROM or via the World Wide Web (http://www.unesco.bilko.org/). The training module allows practitioners to develop their image processing and interpretation skills on their desktop PC, guides them t h rough fairly complex procedures such as radiometric and water column correction, and introduces them to exciting new resource assessment techniques such as mapping seagrass standing crop and mangrove leaf area index fro m satellites and digital airborne imagery. Once the techniques have been mastered they can be applied to local image data.
The module has been field tested at a workshop in East Africa under the auspices of the Intergovernmental Oceanographic Commission (IOC) and United Nations Environment Programme (UNEP) and has benefited from feedback from the regional scientists who participated.
We have found two books to be particularly useful and recommend them to practitioners as companion volumes to the Handbook. The first is Computer Processing of Remotely-Sensed Images: An Introduction, by Paul Mather, which provides an excellent and very readable introduction to the principles of remote sensing and techniques of image analysis, enhancement and display. A very useful feature of this book is the provision of a CD-ROM containing software and image data sets. The second is the ERDAS Field Guide produced by ERDAS Inc. † , the company which produces the popular ERDAS Imagine image analysis and GIS software. This guide naturally focuses on how to do image processing tasks using E R DAS Imagine but the wealth of detailed, very clearly explained hands-on advice and information is extremely useful to practitioners whatever software they are using.
Mather, P.J., 1999, Computer Processing of Remotely-Sensed Images: An Introduction. 2nd Edition. (Chichester: John Wiley & Sons). ISBN 0-471-98550-3 (paperback).
Inc., 1994, ERDAS Field Guide. Third Edition. (Atlanta: ERDAS
† Mention of a company name does not constitute endorsement of a particular product by the authors.