«Geological Mapping of Remote Mountainous Regions Using Metric Camera Imagery Initial Experiences with Photogrammetric Space Images *) By Manfred F. ...»
As already mentioned in this paper and in other publications (KONECNY 1981, 1984, KONECNY & SCHRÖDER 1979, KONECNY, SCHUHR & Wu 1982, DOYLE 1984), the possibility of stereoviewing is a tremendous advantage not only for topographic but also for thematic evaluation. According to KONECNY, SCHUHR & Wu 1982, with stereoscopic observation ground pixels can be twice as large as with monoscopic interpretation to obtain an equivalent amount of information. With regard to UltraHigh Altitude Photography (UHAP) GIERLOFF-EMDEN 1983 and GIERLOFF-EMDEN & DiETZ 1983 state the potential of stereopairs for interpretations of higher quality in comparison with monoscopic observation. For mapping of lithological units and geological structures these authors take about 30 m as lower limit for the requirement in ground resolution. These demands are already met by the Landsat Thematic Mapper data, and will be exceeded by far by the European SPOT system. The specified resolution of 39 line pairs/mm of Metric Camera images is equivalent to some 20 m on ground (cf. KONECNY, SCHUHR & Wu 1982). This quality still enables a thematic photo-interpreter to detect (even short, approx. 100-150 m long) linear features of less than 10 m in width in stereoscopic observation, as long as a decent contrast and/or difference in colour exists.
One more word shall be given to the relation in quality with Landsat Multispectral Scanner (MSS) images and space photographs of earlier manned missions (cf. section 3.2). The superiority of Metric Camera images to Landsat MSS with respect to better ground resolution and stereoscopy is evident. Especially for the geologist, who very Geological Mapping of Remote Mountainous Regions Table 4: Comparison between the number of conventional 23 X 23 cm2 aerial photographs of different scales covering the area of a Metric Camera stereomodel. For the airborne photography a forward overlap of 60 or 80% and?asidelap of of 20% were considered. The figure before the x always gives the number of photographs in a flight line, the second one the number of flight lines.
Table 5: Comparison between the time spent on mounting and relative orientation of the aerial photographs needed to cover the area of one Metric Camera stereo model on the Kern DSR-1 analytical plotter (taking a mean of some 15 min for one stereopair) and under a mirror stereoscope (considering a mean of about 5 min per pair). Note that these activities alone would almost take 60 8-hour working days when using 1 : 30 000 imagery on the DSR-1, and still 20 days with a mirror stereoscope.
much relies on third dimension, stereoscopy is an essential tool for the interpretation. On the other hand, sets of digital multispectral data provide the possibility to accomplish improved automated (supervised) classification. In comparison with landuse mapping, for example, computer-aided classification only plays a subordinate role in geological mapping with space data, at least in areas which do not offer bare soil or rock. It shall not be ignored, however, that for the field of previsual geobotanical prospection Landsat MSS data (and TM data the more) represent an excellent means. Their advantage of guaranteed repetition of data acquisition (weather permitting) has been stressed often enough.
Metric Camera photographs are superior to earlier photographs of manned space missions due to their well-defined geometry and consistant stereo-coverage. Comparisons with space sensors as Seasat and SIR-A shall not be given here, as the whole character of active sensing systemes is completely different. However, used together with Metric Camera imagery which could provide data for digital elevation models, space radar should yield interesting additional geological information.
Table 4 shows the numbers of aerial photographs of different image scales needed to cover the area of one Metric Camera stereomodel. The relationship in surface cover between Metric Camera and conventional airborne photographs is illustrated in fig. 11. Table 5 gives a good idea of how great the saving of time is, depending
Fig. 11: Comparison of the surface coverage of a Metric Camera stereopair and stereomodels of conventional aerial photographs with a mean image scale of 1 : 30 000. For both types of imagery an overlap of 60% was considered. For the airborne photographs a sidelap of 20% was taken. Hatched area indicates one stereomodel of air photographs. Compare also table 4 and 5.
Geological Mapping of Remote Mountainous Regions whether you use geometrically relevant interpretation at a photogrammetric stereoplotter or "simply" a mirror stereoscope. The facts given in these tables and fig. 11 are rather self-explanatory.
For most countries of the world neither panchromatic nor infrared aerial colour photographs are available. As the importance of colour in airborne photography is uncontested, this fact is another great advantage besides stereoviewing. Also for the photogeologist, who frequently uses vegetation as an identifaction or at least detection key, infrared colour photography represents an enormous benefit in mapping.
In general, the content of geographic information of Metric Camera imagery is certainly considerable and rich enough in detail to make it an operational tool for scientific studies as well as for applied research, e. g. regional planning (where geology has its influence again). Geographical analyses of the Metric Camera scenes treated in this paper are surely interesting (e. g. the irrigated agricultural areas of Saudi Arabia and Afghanistan), and compare favorably with analyses from Landsat data. Studies of the Hindu Kush and Himalaya scenes concerning landuse and natural vegetation are in progress and will be published in the proceedings of the ESA research project "High Mountain Research in Southern Central Asia".
It would not be realistic and fair to neglect the drawbacks of photogrammetric space images. Thus, to the end of this paper, it seems justified to give some critical aspects on the Metric Camera system (and the planned Large Format Camera, too), in passages following the statements of DOYLE 1984.
Although the technical and economical feasibility to produce topographic and that is the main target of a geologist - thematic maps of 1 : 100 000 and even 1 : 50 000 can be demonstrated, there are many problems remaining, the major one probably being the financial aspect. The primary goal of this type of metric space photographs is the production of topographic maps. To a certain degree thematic mapping is only a "fellow traveller". If there is no financial support for topographic map production using photogrammetric space imagery, the thematic aspect will be the less influential to materialize further projects. NASA has agreed to fly the Large Format Camera (LFC) on two missions (in summer/fall 1984, NASA announced a third flight of the LFC in a 28.5° inclination orbit which would take place in December 1984), but photographs from those missions will be acquired simply where it is convenient for the flight plan rather than where the demand is greatest.
Apparently, plans for future flights, either governmental or commercial, are at the best nebulous.
N o matter, whether the photographs are eventually acquired by governmental, intergovernmental or commercial enterprises, the user will have little control over the circumstances of acquisition. Different users will certainly need images from different seasons, or even multitemporal photo coverage. With the seasonal aspect, degrading features like snow, haze, clouds and shadow due to relief come into the game. The problem of the correct sun angle (30°) has already been treated by GIERLOFF-EMDEN & DIETZ 1983 and KONECNY 1984 (cf. also section 5.1 and 5.2).
Haze, due to the favourable geographical/climatic position, did not degrade the scenes studies within this project too much. Definite statements on the influence of hazy atmosphere, however, would require in-depth meteorological investigations.
10 Mitteilungen der Österr. Geol. Ges., Bd. 77 Manfred F. Buchroithner Lack of experience in handling metric space photography, black-and-white as well as colour-infrared, will hopefully be diminished by the production and first thematic interpretations of Metric Camera images. The present analyses shall help to develop the actual procedures for utilizing photographs acquired by the future Large Format Camera to the best advantage. As already mentioned earlier, one of the major benefits of film systems over electro-optical data transmission systems is, that the photographs are immediately useable in instruments such as analytical plotters, which are rapidly replacing the conventional analog stereoplotters around the world.
Doubtless, some emendments in software will be required for exploitation of photogrammetric space imagery. First steps towards the realization of this objective have been made in developing additional programs for the analytical plotter CRISP software package at the Institute for Image Processing and Computer Graphics in Graz (cf. section 5.2 and tab. 3).
With a resolution of 100 line pairs/mm and original image scales of 1 : 400 000 to 1 : 600 000, depending on flight altitude, the photographs acquired by the Large Format Camera will be more than two times better in resolution than the Metric Camera images (cf. tab. 1 and section 5.2): perspectives that are stimulating for optimistic exspectations in geological mapping by means of metric space photography.
7. AcknowledgementsI am grateful for the kind assistance of or discussion with H. FUCHS, M. GRUBER, K. HAFNER, H. HAUSER, R. HÜTTER and M. RANZINGER all Institute for Image Processing and Computer Graphics of the Graz Research Center, regarding programming, photogrammetric evaluation, digitizing and plotting. My thanks also goto R. KOSTKA, Technical University of Graz, who, years ago, invited me to carry out these studies, and who provided useful topographic and other collateral data.
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