Daniel N.M. Donoghue

Measuring forest structure with terrestrial laser scanning

This paper investigates the application of a ground‐based laser scanning system for providing quantitative tree measurements in densely stocked plantation forests. A methodology is tested in Kielder Forest, northern England using stands of mature Sitka spruce (Picea sitchensis) and a structured mixture of Sitka spruce and lodgepole pine (Pinus contorta), standing at tree densities of 600 and 2800 stems ha−1 respectively. Three laser scans, two in the Sitka spruce and one in structured mixture, were collected using a Reigl Inc. LPM‐300VHS high‐speed laser scanner. Field measurements were recorded at the same time and included tree diameter at breast height (dbh) and tree height. These measurements were then compared with those derived from the scanner. The results demonstrate that accurate measurements of tree diameter can be derived directly from the laser scan point cloud return in instances where the sensors view of the tree is not obstructed. Measurements of upper stem diameters, branch internodal distance and canopy dimensions can also be measured from the laser scan data. However, at the scanning spatial resolution selected, it was not possible to measure branch size. The level of detail that can be obtained from the scan data is dependent on the number and location of scans within the plot as well as the scanning resolution. Essentially, as the shadowing caused by tree density or branching frequency increases, the amount of useful information contained in the scan decreases.

Evaluation of Corona and Ikonos high resolution satellite imagery for archaeological prospection in western Syria

Satellite surveys in Syria have made use of imagery recorded some 30 years apart. By comparing the earlier pictures (Corona) with the later (Ikonos), sites captured on the former can be accurately located by the latter. The comparison also reveals the stark implications for archaeology as large parts of west Asian landscape change from a state of ‘benign neglect’ to active redevelopment. Based on their experience in the Homs survey, the authors have important advice to offer in the design and costing of surveys using satellite imagery.

Using LIDAR to compare forest height estimates from IKONOS and Landsat ETM+ data in Sitka spruce plantation forests.

This paper compares and contrasts predictions of forest height in Sitka spruce (Picea sitchensis) plantations based on medium‐resolution Landsat Enhanced Thematic Mapper Plus (ETM+), high‐resolution IKONOS satellite imagery and airborne Light Detection and Ranging (LiDAR) data. The relationship between field‐measured height and LiDAR height is linear and highly significant (R2 0.98). Despite the difference in spatial resolution and radiometry between Landsat ETM+ and IKONOS multi‐spectral data, the strength of the relationship between field height and predicted height using the green spectral band was very similar, with R2 values of 0.84 and 0.85, respectively. The inclusion of additional observations taken from the LiDAR data improved the strength of the relationship slightly for the Landsat ETM+ data (R2 = 0.87), but did not change the relationship for the IKONOS data (R2 = 0.84). Comparison of the height models derived from the satellite and LiDAR data shows that the optical models provide accurate predictions up to the point of forest canopy closure (10 m) in densely stocked plantations (>2000 stems ha−1); beyond this point, only the LiDAR model is able to provide a reliable estimate of forest height. The results demonstrate that the retrieval of forest structure information over the lifetime of a plantation forest is best achieved by the integration of satellite, airborne and ground‐based measurements. It is possible to use optical satellite data to identify forest stands that display unexpected growth characteristics, such as areas of high natural regeneration, poor or incomplete stocking.

Remote sensing of upland conifer plantations using Landsat TM data: A case study from Galloway, south-west Scotland

The relationship between reflectance and forest structure is investigated for 52 forest stands in Galloway. Height and basal area are most strongly correlated with reflectance in TM bands 3, 5 and 7 (R2 >= 0.77, P < 0.01). The strength of these relationships decreases substantially after canopy closure has occurred. Stem density cannot be predicted from canopy reflectance. Tree age can only be reliably predicted for areas where growth is uniform, which is rare in upland environments. Analysis of TM imagery provides a cost effective method of mapping certain canopy parameters provided that limited detail is required for older mature plantations with a closed canopy.

Development of an integrated geographical information system prototype for coastal habitat monitoring

This paper describes a prototype Integrated Geographical Information System (IGIS) developed for coastal habitat monitoring. It outlines the advantages and technical difficulties involved in combining specialist image processing functionality within the LaserScan IGIS software so that it could be used routinely by ecologists. The Coastal Habitat Information Monitoring System prototype set out to demonstrate the feasibility of using remotely sensed imagery for the routine mapping of important coastal habitats in the European Union. The prototype aims to provide an integrated software system to transform Earth Observation data into specialist map products. Normally such processing requires input from remote sensing scientists using specialist software and is not easily accessible to end-users. In principle, the methodology allows different satellite and airborne multi-spectral image data to be used to produce specialist coastal habitat maps. In this paper Landsat TM and IRS 1C LISS 3 data are evaluated and shown to be suitable for mapping the inter-tidal habitats of the Wash estuary on the East Coast of England. A strategic objective of study was to test the feasibility of incorporating all the processing functionality into a single integrated geographical information system. The project concluded satellite data from existing sensor systems can provide habitat data at a good level of detail but that to develop a fully operational processing capability would require considerable development of even the most advanced of the existing commercially available IGIS software package.

A preliminary assessment of Landsat TM imagery for mapping vegetation and sediment distribution in the Wash estuary

Abstract Analysis of Landsat Thematic Mapper (TM) image of 14 May 1984 has shown that such data can be used to survey vegetation and sediment distributions in the intertidal zone of the Wash estuary at a spatial detail comparable with current methods practised by the.Nature Conservancy Council. Multispectral classification of this TM image showed good separation of salt-marsh vegetation communities which had recently been surveyed by the Nature Conservancy Council and for which reliable training data could be taken. The sensitivity of classification performance, using both parametric and non-parametric algorithms, to apparently minor differences in phenology at training site locations demonstrates two requirements for improved salt-marsh classification. They are the need for strict definition of training data and that TM wave bands 2, 3, 4 and 5 provide suitable spectral vectors for classifying intertidal environments.

Forest land cover continues to exacerbate freshwater acidification despite decline in sulphate emissions

Evidence from a multi-date regional-scale analysis of both high-flow and annual-average water quality data from Galloway, south-west Scotland, demonstrates that forest land cover continues to exacerbate freshwater acidification. This is in spite of significant reductions in airborne pollutants. The relationship between freshwater sulphate and forest cover has decreased from 1996 to 2006 indicating a decrease in pollutant scavenging. The relationship between forest cover and freshwater acidity (pH) is, however, still present over the same period, and does not show conclusive signs of having declined. Furthermore, evidence for forest cover contributing to a chlorine bias in marine ion capture suggests that forest scavenging of sea-salts may mean that the forest acidification effect may continue in the absence of anthropogenic pollutant inputs, particularly in coastal areas.

Remote sensing: environmental change

Among the advantages of satellite imagery for geographical research is the ability tocapture in an instant a synoptic view of a large part of the Earth’s surface and to acquirerepeated measurements of the same area on a regular basis. It is precisely theseproperties that make satellite remote sensing such an important source of data forstudies of the dynamics of the Earth’s surface and atmosphere. International researchprogrammes such as the Intergovernmental Panel on Climate Change (IPCC), theInternational Geosphere– Biosphere Programme (IGBP), the World Climate ResearchProgram and the International Human Dimensions Programme on GlobalEnvironmental Change (IHDP) make extensive use of satellite observations because itis possible to derive quantitative measurements of the dynamics of many atmospheric,oceanographic and land surface characteristics. Humans are changing the natural rateof carbon exchange between the Earth’s atmosphere and the terrestrial biospherethrough land use change. Remote sensing can provide an effective tool to examinecarbon stocks and their response to human interference through deforestation, refor-estation, afforestation and other forms of land use change. These data are helping toinform the IPCC to formulate policy responses to climate change (for example theKyoto Protocol) and to monitor policies introduced to mitigate the increased levels ofCO

Regional patterns of streamwater acidity and catchment afforestation in Galloway, SW Scotland.

This paper investigates the regional relationships between highflow water chemistry and conifer forest cover in 95 streamsspread over an area of approximately 2000 km2 in Galloway,south-west Scotland, paying particular attention to the use ofdetailed catchment area data. Catchment forest data areextracted from a 30 m resolution tree height map derived fromsatellite imagery; geology data from a digital geology map; andaltitude and slope data from a 50 m resolution Digital TerrainModel (DTM). The results show that over the entire region pHlevels are lower with increasing catchment afforestation whilstaluminium concentrations are higher. Concentrations of sulphate arealso higher with increasing afforestation, which suggests thatconifers play a primary role in increasing the acidity levels ofstreams by exacerbating aerial acid deposition in the entireregion.

Remote sensing: sensors and applications:

This past year has seen considerable progress in remote-sensing science with the launch of several important new sensors. During 1999 there have been many publications that describe the technical details of satellites and their sensors, including articles that address issues such as data quality and processing techniques. Although important, these studies are not reviewed in detail here. Instead, emphasis is given to the developments in the application of remote-sensing data for physical geography.