W. G. Rees

Mapping land cover change in a reindeer herding area of the Russian Arctic using Landsat TM and ETM+ imagery and indigenous knowledge

Much of Russia north of the treeline is grazed by reindeer, and this grazing has materially altered the vegetation cover in many places. Monitoring vegetation change in these remote but ecologically sensitive regions is an important task for which satellite remote sensing is well suited. Further difficulties are imposed by the highly dynamic nature of arctic phenology, and by the difficulty of obtaining accurate official data on land cover in arctic Russia even where such data exist. We have approached the problem in a novel fashion by combining a conventional multispectral analysis of satellite imagery with data on current and historical land use gathered by the techniques of social anthropology, using a study site in the Nenets Autonomous Okrug (NAO). A Landsat-7 ETM+ image from the year 2000 was used to generate a current land cover classification. A Landsat-5 TM image was used to generate a land-cover classification for 1988, taking due account of phenological differences and between the two dates. A cautious comparison of these two classifications, again taking account of possible effects of phenological differences, shows that much of the study area has already undergone a notable transformation to grass-dominated tundra, almost certainly as a result of heavy grazing by reindeer. The grazing pattern is quite heterogeneous, and may have reached unsustainable levels in some areas. Finally, we suggest that this situation is unlikely to be unique to our study area and may well be widespread throughout the Eurasian tundra zone, particularly in the west.

Evaluating the potential of high‐resolution airborne LiDAR data in glaciology

We present the results of an investigation into the capabilities of high‐resolution airborne Light Detection And Ranging (LiDAR) for the study of a small glacier in Svalbard. The data are shown to be capable of producing a digital elevation model (DEM) with a horizontal resolution of 1–2 m and a vertical resolution of 5–15 cm. This degree of resolution is suitable for mass‐balance estimation using repeat data on an annual or semi‐annual basis, but it is also reveals linear surface features such as meltwater channels and crevasses. These have potential for tracking in repeat imagery to deduce the surface flow of the glacier. The intensity of the returned LiDAR pulse can also be used to discriminate snow‐covered parts of the glacier from bare ice.

Angular variation of the infrared emissivity of ice and water surfaces

Abstract An experimental investigation of the emissivity of water and ice surfaces in ihe thermal infrared (8-14 μm) band is described. The experimental technique is a particularly simple one, suited for rapid determination of emissivity in the laboratory, yet it yields an accuracy of ±001 for relative emissivity over a wide range of viewing angles. The results show that the emissivity of an ice surface is significantly lower than that of a water surface for angles up to at least 65° from the surface normal and thai both are in approximate agreement with the Fresnel formula for a plane interface between homogeneous media. The implications of the numerical results for airborne and spaceborne remote sensing of freezing water are discussed.

Monitoring changes in land cover induced by atmospheric pollution in the Kola Peninsula, Russia, using Landsat-MSS data

Abstract We present the results of hybrid unsupervised-supervised classification of a series of Landsat-MSS images, spanning the period from 1978 to 1992, to study the impact of SO2 emissions from the nickel smelter at Monchegorsk (67 55 N, 32 50 E) in the Kola Peninsula, Russia, on adjacent boreal forest and upland (lichen-dominated) tundra vegetation. Ground truth data were collected from a 2500 km2 area during airborne and surface field campaigns in 1994 and 1995, and used to classify the 1992 image into 56 different surface types, including a characterisation of the level of vegetation damage. The pre-1992 images could not be classified by transferring the spectral signatures from the 1992 image, mainly as a result of phenological differences. Instead, they were classified using spatial context and a set of observationally-derived botanical rules governing the types of allowable land-cover change. A comparison of the classified images was performed by further combining the land-cover classes into grou...

Remote sensing of industrial impact on Arctic vegetation around Noril'sk, northern Siberia: Preliminary results

This study applies remote sensing techniques for monitoring non-ferrous metal smelting impacts in the extreme environment of northern Siberia. Ground and at-satellite reflectance and normalized difference vegetation index (NDVI) values for different vegetation types have been compared and a hybrid supervised-unsupervised classification of Landsat TM data performed, based on field and ancillary data. This has allowed us to distinguish several degrees of vegetation damage in tundra and forests. However, it was difficult to differentiate between some significant classes, such as damaged grass tundra and sparse dead larch forests with a grass understorey. We suggest possible refinement of our results, including the combination of images taken at different phenological stages and from different sensors. However, it should be noted that the north-Siberian environment presents unusually severe limitations of optical-infrared satellite observation possibilities and problems in imagery interpretation. Standard ind...

Scale-dependent roughness of a glacier surface : implications for radar backscatter and aerodynamic roughness modelling

The roughness of the snow-free surface of the glacier midre Lovenbreen, Svalbard, has been investigated on scales between 1 mm and 300 m. It is shown that the roughness is reasonably well described by scale-free (fractal) models for scales longer than a few metres and shorter than about 100 mm. However, there is a break in the behaviour between these scales which can be characterized by a definite scale length of 70-500 mm and a root-mean-square height variation between around 6 and 70 mm. The aerodynamic roughness length contributed by these features is estimated to be 0.3-1.5 mm. Features on this scale are consistent with the observed microwave backscattering properties of the glacier.

Mass balance and dynamics of a valley glacier measured by high-resolution LiDAR

The changing surface geometry of the glacier Midre Lovenbreen on Svalbard was investigated using LiDAR data acquired on 9 August 2003 and again on 5 July 2005. The data were processed to generate Digital Elevation Models (DEMs) of unprecedentedly high spatial resolution (2 m) and accuracy (better than 0.15 m). Comparison of the two DEMs allowed the mass balance of the glacier to be determined as more negative than −0.62 m yr −1 water equivalent, about twice as negative as the value estimated from in situ measurements. Comparison of the DEMs also showed that the area of the glacier decreased by around 0.3%, and the position of its margin retreated by around 14 m, from 2003 to 2005. It was also possible to track the motion of fine-scale features in the surface geometry such as meltwater channels, and hence to determine the glaciers surface velocity, in some areas. Typical average speeds were around 1–2 cm per day.

Characterisation of Arctic treelines by LiDAR and multispectral imagery

The Arctic treeline, or more precisely the tundra-taiga interface (TTI) region, is poorly defined and characterised despite its high climatological significance. The international coordinated research programme ‘ PPS Arctic ’, under the auspices of the International Polar Year, represents one response to this gap in our knowledge. This paper presents preliminary work within one of the four principal research areas of PPS Arctic , the characterisation of spatial variations in vegetation, land cover and land use in the TTI using remote sensing methods. Airborne remote sensing data were collected from a 120 km 2 TTI study site near Porsangmoen, Finnmark, Norway in 2004 and 2005. Three datasets were acquired: two sets of multispectral visible-infrared imagery with spatial resolutions of around 3 m, and airborne scanning LiDAR data with a horizontal resolution of 2 m and a vertical precision of around 0.2 m. While some difficulties were experienced in processing and analysing the imagery, the LiDAR data proved exceptionally well suited to the task of characterising the structure of the forest edge. Preliminary analyses were strongly suggestive of fractal characteristics, with corresponding consequences for the scale-dependence of descriptors such as canopy density and the location of the forest edge.

Segmentation of synthetic-aperture Radar imagery of sea ice

Abstract This paper describes a ‘segmentation’ algorithm, which has been designed for Synthetic-Aperture Radar (SAR) sea-ice images as part of the U.K. Earth Observation Data Centre (EODC) Science Team activity. The segmented sea-ice product consists of distinct, statistically-homogeneous regions of ice and water from which various atttributes can be determined, such as area, centroid position, mean intensity and standard deviation, shape, orientation and texture. Such attributes are important in providing a template from which it is possible to derive information such as ice type, concentration and dynamics, the position of the ice edge, and the characteristics of leads and polynyas. Although the method has been developed for processing ERS-1 data, it is demonstrated in this work using both simulations and SAR sea-ice data obtained from the Seasat campaign of 1978, as ERS-1 data were not yet available at the t ime of implementation.

Infrared emissivities of Arctic land cover types

Abstract This letter describes a field investigation of the thermal infrared (8-14/on) emissivities at normal incidence of a number of land cover types typical of the Arctic during summer. The types studied include water, various forms of ice and snow, fine shale particles from moraines, and sandstone. The results should assist the interpretation of thermal infrared imagery (e.g. from the infrared channels of the ERS-1 along-track scanning radiometer (ATSR) ) of Arctic areas.