KFA-1000 camera

KFA-1000 cameras (focal length 1000 mm, spectral range 570–680 nm and 680–810 nm) have been deployed aboard several Russian Cosmos-series satellites, orbiting at an average height of 270 km. This gives an average scale of 1 : 270 000 for photographs from the KFA-1000. Photographic frame size is 300 × 300 mm and the nominal area of ground coverage is, therefore, 80 × 80 km. Two cameras are mounted in each satellite, photographing a strip to either side of the sub-satellite track. These cameras are inclined outwards at 8° from the nadir direction. An overlap of 60% is present between successive images along track, providing considerable scope for stereoscopic analysis of ice surface topography. The Cosmos-series satellites, on which several KFA-1000 cameras have been deployed, have variable orbits, some of which reach to above 82°N/S, which means that coverage of all northern hemisphere ice masses and much of Antarctica is available in principle. Calibration standards and grey scales are not provided with each image, and so the potential for detailed analysis of radiometric data is limited to relative brightness levels.

To enable KFA-1000 photographic products to be compared in detail with digital data from the other sensors, black and white positives on film (produced directly from the original negative) were digitized using a high resolution Joyce-Loebl scanner at the Royal Aircraft Establishment, Farnborough, U.K. The resolution of the scanner was 25 μm, which gives the equivalent of 6 m resolution for a 300 × 300 mm film positive. This represents a slight undersampling of the full detail on the photographic product. We recommend the use of a 12.5 μm scanner in future work, in order to obtain the full resolution of the photographic imagery in digital form. Once the KFA-1000 data were transformed into computer-compatible tape (CCT) format, they were analyzed using standard image processing techniques on a Sun-based system.

It should be noted that a lower resolution camera, KATE-200, has been deployed on several Cosmos satellites, and its products are also available through Sojuzkarta. This camera has a focal length of 200 mm, and three spectral bands (500–600, 600–700 and 700–850 nm). The orbital height is 270km, giving a scale of 1 : 1 350000. Image frame size is 180 × 180 mm, producing ground coverage of 243 × 243 km per scene. The nominal resolution of these products is given as 15–30 m by Sojuzkarta, with the range in this value resulting from variations in the orbital height of individual satellites. We have obtained imagery of ice masses in Svalbard and Franz Josef Land from this camera, but only data from the higher resolution KFA-1000 are discussed in this paper.

Table 1. Details of digital satellite images of northwest Spitsbergen, Svalbard, examined as part of this study

Landsat and SPOT data

The spatial and radiometric properties of digital KFA-1000 data are compared with digital imagery obtained from the Landsat Multispectral Scanner (MSS), Thematic Mapper (TM) and SPOT High Resolution Visible (HRV) sensors, available from our glaciological investigations of Svalbard ice masses. The specifications of the CCT-format images of northwest Spitsbergen examined in this study are given in Table 1.

Data from these instruments provide a range of spatial resolution against which to compare the utility of KFA-1000 imagery in glaciological studies. The Landsat MSS has a nominal pixel size of 79 × 56 m, the Landsat TM has 28.5 m pixels, and the HRV multispectral scanner carried aboard SPOT has 20 m pixels. Comparison between data from these instruments and digital KFA-1000 imagery was carried out using our in-house image processing system, based on a Sun SPARC station IPC.

Spatial resolution of KFA-1000 imagery

Fig. 2. Map and imagery of the Ny Ȧlesund settlement and surrounding area, northwest Spitsbergen ( see inset in Fig. 1). (a) Map of buildings, roads, jetties and airstrip at Ny Ȧlesund (courtesy of Norsk Polarinstitutt). (b) KFA-1000 image, with the location of the map inset, (c) Landsat TM image, (d) Landsat MSS image. Note the distortion of image (d), due to the 79 × 56 m pixel size of the MSS. The images labelled (c) and (d) cover a similar area to (b). Scale bar is 1 km.

In order to assess the spatial resolution of digitized imagery derived from KFA-1000 photographic products, features of known size and shape were examined before moving on to glaciological phenomena. KFA-1000 data imaging the man-made structures at the settlement of Ny Ålesund in northwest Spitsbergen were compared with 1 : 5000 topographic maps showing individual buildings, roads, air strip and jetties (Fig. 2a). The area of the settlement and its surroundings is also imaged by the KFA-1000 (Fig. 2b) and the Landsat TM and MSS (Fig. 2c–d). The airstrip, a lake and a number of roads and buildings are visible on the KFA-1000 imagery in Figure 2b. Close inspection of the film positives also shows that almost all the individual buildings shown in Figure 2a can be identified. We were able to resolve individual structures only 6 m in width, and spaced about 6 m apart, on the film positives. The pattern of these structures is close to the design of resolution test targets. This enables us to estimate that the resolution of the KFA-1000 products is on the order of 3 m, somewhat better than the nominal value of 5 m claimed by Sojuzkarta. Under favourable atmospheric conditions the spatial resolution can equal 2 m, according to tests by the American Institute of Aeronautics and Astronautics (Reference BaxterBaxter, 1991).

The Landsat TM and MSS images shown in Figure 2c–d can resolve significantly less detail than the KFA-1000 photographic products. The lakes and jetties are visible in the TM scene, but the airstrip, roads and buildings are not resolved (Fig. 2c). In the MSS scene none of the above features is visible, and only the outline of the coast can be seen clearly (Fig. 2d).

It should also be noted that KFA-1000 imagery is suitable for stereoscopic analysis, in that adjacent scenes have an overlap of 60%. We have viewed two overlapping images acquired in 1985 (Table 1) in order to observe topographic effects qualitatively, but have not gone on to produce stereo-models of the terrain. The following simple expression may be used to calculate the heighting accuracy (Δh) of this stereoscopic imagery (Reference ReesRees, 1990):

(1)

where H is camera altitude, Δh′ is the accuracy of measurement of relief displacement on the film, and s is film width. With a nominal camera altitude of 270 km, an estimate of 25 μm for film measurement accuracy, and a film width of 0.3 m, the accuracy of height determination is calculated as 45 m. We define film measurement accuracy by our choice of digitizing interval and take no account of film instability. This suggests that high relative accuracies should be obtained for local areas, but absolute errors will increase over larger regions due to the increasing effects of film distortion. Film distortion errors are likely to dominate over those associated with optical errors in the lens.

Fig. 3. The glacier surface of Kronebreen and Kongsvegen, and adjacent nunatak, northwest Spitsbergen (see inset in Fig. l).(a) KFA-1000 image, (b) SPOT HRV-XS image, (c) Landsat ΤM image, (d) Landsat MSS image. Note the distortion due to the 79 × 56 m pixel size of the MSS. Scale bar is 1 km.

Comparison with glaciers imaged by Landsat and SPOT

The spatial resolution of digitized KFA-1000 imagery was compared with that from Landsat and SPOT sensors by producing sub-scenes of a similar area from each instrument at very much enlarged scales. The area used for comparison was the terminus region of Kongsvegen and Kronebreen, tidewater glaciers in northwest Spits-bergen (Fig. 1). This location was selected for study because it is fast-flowing, highly crevassed and has a number of medial moraines, providing easily recognized glaciological features for intercomparison. We are also familiar with this glacier system through our own field studies (e.g. Reference Dowdeswell, Drewry, Liestøl and OrheimDowdeswell and others, 1984; Reference Hagen and SaetrangHagen and Saetrang, 1991).

Digital enlargements of the tidewater glacier termini imaged by the KFA-1000, Landsat MSS, Landsat TM and SPOT multispectral scanner are shown in Figure 3. The fine resolution of the KFA-1000 means that, at the scale of reproduction used here, individual pixels cannot be seen (Fig. 3a). This allows the straightforward identification of ice surface features such as crevasses and medial moraines. Several icebergs can also be resolved at the bottom left of Figure 3a, in the marine waters beyond the terminal ice cliffs of the tidewater glaciers. By contrast, the 79 × 56 m resolution of the Landsat MSS means that pixels show up clearly, whereas ice surface detail is less apparent (Fig. 3d). Crevasses and mountainside gullies cannot be identified on the MSS image. The SPOT and TM images, with 20 m and 28.5 m pixels, respectively, are intermediate between these two extremes (Fig. 3b–c). Crevasses are, however, noticibly better resolved on the SPOT image (Fig. 3b), whereas the effect of individual pixels is more apparent on the TM sub-scene (Fig. 3c). Visual comparison of the mountain at the top left of each image in Figure 3 also illustrates the decline in resolving ability through the four sensors clearly.

Glacier fluctuations and surges

An important use of satellite imagery is to provide time series of data on glacier marginal positions, which can then be related to climate change or, as in the case of glacier surges, to changes internal to the ice mass itself. The digital superimposition of glacier margins imaged several years apart by the KFA-1000 and the other imagery used in this study allows a ten-year series of ice marginal fluctuations to be recorded (Table 1). The relatively large pixel size of the Landsat MSS, with an error term of approximately 160 m (i.e. ±2 pixels) in the location of the ice margin (cf. Reference DowdeswellDowdeswell, 1986), implies that it is useful only when relatively large shifts in terminus position have taken place. A similar error term of ± 2 pixels for KFA-1000 imagery would yield a value of ± 12 m. The high resolution of KFA-1000 products, by contrast, makes them a particularly appropriate tool for investigating glacier terminus fluctuations. The ability to superimpose digital data from several satellites means that the digitized Sojuzkarta data can be integrated with existing high resolution satellite imagery to enhance time series of ice marginal positions.

Fig. 4. KFA-1000 images of the tidewater terminus region of Blomstrandbreen, northwest Spitsbergen (see inset in Fig. 1). (a) 12 June 1985; (b) 12 June 1988. Fast ice covers the sea in (b) and the righthandpart of (a). Scale bar is 1 km. Note the narrowing of the isthmus of ice attaching the glacier to the peninsula.

Two examples illustrate the utility of KFA-1000 imagery in measuring and monitoring changes in the position of glacier margins. In Figure 4 the terminus region of Blomstrandbreen is shown on the same day in 1985 and 1988. This glacier has been retreating since a surge in 1960, when it advanced some 600 m (Reference LiestolLiestøl, 1988). Retreat since that date has lead to the development of an increasingly narrow isthmus of ice attaching the parent glacier to the peninsula of Blomstrandhalvøya (bottom right in Figure 4). Measurements taken from the June 1985 and 1988 imagery of the area (Fig. 4) show that the isthmus of ice has narrowed by 230 m over this period. If the same rate of change, about 80 m a⁻¹, were to continue, the remaining ice isthmus (200 m wide in 1988) would be predicted to disappear in a little less than three years. The ice was in fact breached by the sea early in 1991.

Fig. 5. KFA-1000 images of the lower parts of Conwaybreen and Kongsbreen, northwest Spitsbergen (see inset in Fig. 1). (a) 12 June 1985; (b) 12 June 1988. Note the icebergs embedded in fast ice in (b). Scale bar is 1 km.

A second example of the utility of KFA-1000 imagery concerns two other tidewater glaciers entering Kongs-fjorden, Conwaybreen and Kongsbreen (Fig. 1). Comparison of the ice marginal positions of these two glaciers in 1985 and 1988 imagery (Fig. 5) indicates that Conwaybreen retreated by up to 190 m over the period, whereas Kongsbreen advanced by up to 100 m. The differing sign and magnitude of ice marginal fluctuations on these adjacent glaciers is a significant finding. However, changes of this order are certainly beyond the spatial resolution of the Landsat MSS and would be detected only with a significantly lower accuracy through the analysis of Landsat TM and SPOT multispectral data.

The active phase of the surge cycle on surge-type glaciers can also be identified from KFA-1000 data. The high resolution of the KFA-1000 allows the identification of individual crevasses and, hence, both the initiation of the active phase of the surge cycle and the propagation of the surge front. The KFA-1000 imagery from 1985 and 1988 which we have obtained (Table 1) includes the tidewater glacier Osbornebreen, which began to surge during the 1986–87 winter (Reference Dowdeswell, Hamilton and HagenDowdeswell and others, 1991). The change from a relatively smooth to a highly crevassed ice surface between 1985 and 1988 can be seen clearly on KFA-1000 images from these dates, along with changes in the glacier terminus position.

Several studies have also used Landsat imagery in order to obtain ice surface velocities (e.g. Reference Lucchitta and FergusonLucchitta and Ferguson, 1986; Reference Bindschadler and ScambosBindschadler and Scambos, 1991). However, due to the lower resolution of the Landsat MSS and TM in particular, the method has been restricted largely to the parts of major ice sheets flowing at hundreds of metres per year. The significantly higher resolution of KFA-1000 imagery means that it can be used successfully in the measurement of velocities on smaller ice masses, and those with rates of flow of tens of metres per year. The technique is thus suitable for analyzing glacier velocities within the Svalbard archipelago, for example, where previously velocity measurements have been restricted to field surveys and the detailed study of sequential aerial photographs.