The Application of Remote Sensing
and Geographic Information Systems

The Ythan Estuary Case Study

An outline of some environmental remote sensing research projects from the ERS programme at Aberdeen University.

Table of Contents

Introduction

The integration of remote sensing and Geographical Information Systems (GIS) technology is increasingly finding favour for applications to the marine and coastal zone environment. This includes estuaries.

With growing awareness and concern over the use of the marine environment, estuaries, the focus of many potential conflicts between multiple different user groups, will increasingly require very careful management of the resources. This will require knowledge and understanding based upon the acquisition of 'up-to-date' data and information.

Remotely sensed data, including [aerial photography], [airborne video], and [satellite imagery], offers one way to provide such data. They can be used to monitor and map such environments, whilst GIS provide the tools to help manage and analyse the spatial data.

The following two examples examine the application of remote sensing and GIS to an estuary environment helping to provide some insight into the potential of these two technologies to provide data and to improve our knowledge and understanding about estuary environments and processes. In particular they focus on the Ythan Estuary (JPEG), an area of some considerable scientific interest, just north of Aberdeen.Study Area (GIF)

Overview of Case Study

Objective

The objective of these two studies has been to investigate the potential of integrating GIS and remote sensing technologies to study aspects of this problem.

Study Area

The River Ythan catchment lies some 30 km (10 miles) to the North of Aberdeen covering an area of 690 km. 95% of this area is classified as agricultural.

Problem

In recent years concern has been expressed about the increasing concentration of Nitrogen in the Ythan's tributaries over the period 1980-1992.

The chemicals used by farmers (e.g. pig farming and oil seed rape in the area along the Ythan are considered by some to be responsible for causing an increase in the amount and extent of weed mats (JPEG) in the lower part of the Ythan estuary.

Projects in the Case Study

Project 1

Background

Throughout the 1980s and 1990s the agricultural landscape of the UK has changed markedly with changes in EC (European Community) policy.

One of the most striking changes to the visual landscape has been the marked increase in the production of Winter [Oil Seed Rape] Oilseed Rape(GIF). This has arisen due to the subsidy of Oil Seed processing, and the fact that Winter Oil Seed Rape cropping regimes fit into the crop cycle of more traditional cereal crops.

Remote Sensing

Whilst there are more traditional and well established approaches to agricultural surveys, these can now be perfomed using satellite remote sensing techniques. An operational example is provided by the [National Remote Sensing Centre] (NRSC) in the UK (Albedo, 1993).

The application of satellite remote sensing has several advantages over the more traditional methods:

  • Results are not restricted by national boundaries or administrative and political bias.
  • They can provide information at different scales.
  • Temporal comparisons can easily be made between different years.
  • Data can be processed in near-real-time.

Method

Using the [ERDAS] digital image processing system, multi-temporal [LANDSAT TM] imagery and a series of training sites for each different crop type in the [classification scheme], a supervised classification technique was used to provide crop maps for each of three dates for the Bronie Burn sub-catchment (part of the Ythan watershed (GIF)).

After export of the classifications from the ERDAS system to the [SMALLWORLD GIS], the latter was used to complete the classification process, and to add additional geographic information to improve the visual appearance and interpretability of the imagery.

Summary statistics for total crop areas and the relative proportions of the total sub-catchment under each crop for each year were derived and compared. In addition, simple modelling of the relationship between nitrate inputs and agricultural data derived from the LANDSAT imagery were undertaken.

Examples of Images Produced

Bronie Burn - Classified image and surrounding boundaries of fields (GIF).

Bronie Burn - Outline of watershed (GIF).

Bronie Burn - Boundary of watershed against map background (GIF).

References

Albedo, 1993. Down on the Farm. The Newsletter of the National Remote Sensing Centre Limited.

Rees, Geoffrey, 1994. Modelling the Effects of Changing Cropping Regimes on River Pollution. Unpublished M.Sc. Thesis. M.Sc. in Environmental Remote Sensing. University of Aberdeen. 136p.

Project 2

Background

To date, ground-based survey and the use of conventional aerial photography from light aircraft have not proved practical or cost-effective where long-term multi-temporal monitoring and mapping of weed mats (JPEG) in the Ythan is required.

The combination of a model aircraft, a global positioning system (GPS), desktop scanning technology, Digital Image Processing, and Geographic Information Systems (GIS) provides a powerful tool for environmental monitoring, assessment and analysis.This study establishes a methodology for data acquisition, conversion, input, processing, and enhancement using digital image processing techniques.

Remote Sensing

A large-scale model aircraft (JPEG) has a number of advantages as an airborne remote sensing platform. For example, it is possible to acquire large-scale, low-cost aerial photography, at virtually any time desired for environmental applications

Method

35mm [multi-spectral] [panchromatic] ([Wratten] blue, green and red filters), black and white infrared, colour and colour infrared aerial photography using a [large-scale model aircraft] with a 2m wingspan was acquired for a single date in August 1994.

A grid of 25 Ground Control Points (JPEG) (GCPs), laid out prior to the overflight, and surveyed using a [Trimble Global Positioning System] (GPS) prior to the overflights provided the basis to subsequently correct the distortions present in the photography within the digital image processing system.

The contact prints acquired were scanned using an HP desktop colour [scanner] (picture), saved as [TIFF] (Tagged Image File Format) files and imported into an [ERDAS] system using the [RDTIFF] import option. File compression techniques were used to aid in the handling of the large computer files generated by scanning.

Results

Visual examination of the aerial photography (JPEG) revealed that areas of weed matting, sand and mud flats, and streams could easily and clearly be distinguished and identified. Combinations of the different spectral bands of imagery using the ERDAS system enabled the display of both colour and false colour imagery. Various visual enhancement techniques and tools also allowed improvement in the interpretability of the imagery.

A GIS (e.g. ERDAS or [IDRISI]) was subsequently used to provide the basis for the quantitative analysis of the aerial imagery.

References

Green, D.R., and Morton, D.C., 1994. Acquiring Environmental Remotely Sensed Data from Model Aircraft for Input to Geographic Information Systems. Proceedings of AGI94 Conference. Birmingham, England. pp.15.3.1-15.3.28.

Morton, D.C., 1994. Low-Cost Multi-Band Remote Sensing. Unpublished M.Sc. Thesis. M.Sc. in Environmental Remote Sensing. University of Aberdeen. 152p + Appendices.

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